Fix incorrect URL rendering in documentation texts

This commit addresses incorrect URL rendering within documentation text
by improving auto-linkified URL labels, handling `+` symbols as spaces,
enhancing readability of encoded path segments and manually updating
some of the documetation.

Key improvements:

- Parse `+` as whitespace in URLs for accurate script labeling.
- Interpret multiple whitespaces as single for robustness.
- Decode path segments for clearer links.
- Refactor markdown renderer.
- Expand unit tests for comprehensive coverage.

Documentation has been updated to fix inline URL references and improve
linkification across several scripts, ensuring more readable and
user-friendly content.

Affected files and documentation sections have been adjusted
accordingly, including script and category names for consistency and
clarity.

Some of the script/category documentation changing fixing URL rendering
includes:

- 'Disable sending information to Customer Experience Improvement
  Program':
  - Fix reference URLs being inlined.
- 'Disable "Secure boot" button in "Windows Security"':
  - Fix rendering issue due to auto-linkification of `markdown-it`.
- 'Clear Internet Explorer DOMStore':
  - Fix rendering issue due to auto-linkification of `markdown-it`.
- 'Disable "Windows Defender Firewall" service':
  - Fix rendering issue due to auto-linkification of `markdown-it`.
  - Convert YAML comments to markdown comments visible by users.
  - Add breaking behavior to script name, changing script name to.
- 'Disable Microsoft Defender Firewall services and drivers':
  - Remove information about breaking behavior to avoid duplication and
    be consistent with the documentation of the rest of the collections.
- Use consistent styling for warning texts starting with `Caution:`.
- Rename 'Remove extensions' category to 'Remove extension apps' for
  consistency with names of its sibling categories.

.eslintrc.cjs

@@ -10,7 +10,7 @@ module.exports = {
   },
   extends: [
     // Vue specific rules, eslint-plugin-vue
-    'plugin:vue/essential',
+    'plugin:vue/vue3-recommended',
 
     // Extends eslint-config-airbnb
     '@vue/eslint-config-airbnb-with-typescript',

.github/workflows/tests.e2e.yaml

@@ -24,3 +24,41 @@ jobs:
       -
         name: Run e2e tests
         run: npm run test:cy:run
+      -
+        name: Output artifact directories
+        id: artifacts
+        if: always() # Run even if previous steps fail because test run video is always captured
+        shell: bash
+        run: |-
+          declare -r dirs_json_file='cypress-dirs.json'
+          if [ ! -f "${dirs_json_file}" ]; then
+            echo "${dirs_json_file} does not exist"
+            exit 1
+          fi
+
+          SCREENSHOTS_DIR=$(jq -r '.screenshots' "${dirs_json_file}")
+          VIDEOS_DIR=$(jq -r '.videos' "${dirs_json_file}")
+
+          for dir in "${SCREENSHOTS_DIR}" "${VIDEOS_DIR}"; do
+            if [ "${dir}" = 'null' ] || [ -z "${dir}" ]; then
+              echo "One or more directories are null or not specified in cypress-dirs.json"
+              exit 1
+            fi
+          done
+
+          echo "SCREENSHOTS_DIR=${SCREENSHOTS_DIR}" >> "${GITHUB_OUTPUT}"
+          echo "VIDEOS_DIR=${VIDEOS_DIR}" >> "${GITHUB_OUTPUT}"
+      -
+        name: Upload screenshots
+        if: failure() # Run only if previous steps fail because screenshots will be generated only if E2E test failed
+        uses: actions/upload-artifact@v3
+        with:
+          name: e2e-screenshots-${{ matrix.os }}
+          path: ${{ steps.artifacts.outputs.SCREENSHOTS_DIR }}
+      -
+        name: Upload videos
+        if: always() # Run even if previous steps fail because test run video is always captured
+        uses: actions/upload-artifact@v3
+        with:
+          name: e2e-videos-${{ matrix.os }}
+          path: ${{ steps.artifacts.outputs.VIDEOS_DIR }}

.gitignore

@@ -1,5 +1,13 @@
-node_modules
+# Application build artifacts
 /dist-*/
-.vs
+
+# npm
+node_modules
+
+# Visual Studio Code
 .vscode/**/*
-!.vscode/extensions.json
+!.vscode/extensions.json
+
+# draw.io
+*.bkp
+*.dtmp

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 0.12.7 (2023-11-07)
+
+* Add winget download instructions | [b2ffc90](https://github.com/undergroundwires/privacy.sexy/commit/b2ffc90da70367b9e65c82556e8f440f865ceb98)
+* Fix unresponsive copy button on instructions modal | [8ccaec7](https://github.com/undergroundwires/privacy.sexy/commit/8ccaec7af6ea3ecfd46bab5c13b90f71d55e32c1)
+* Fix tree node check states not being updated | [af7219f](https://github.com/undergroundwires/privacy.sexy/commit/af7219f6e12ab4a65ce07190f691cf3234e87e35)
+
+[compare](https://github.com/undergroundwires/privacy.sexy/compare/0.12.6...0.12.7)
+
 ## 0.12.6 (2023-11-03)
 
 * Bump dependencies to latest | [25d7f7b](https://github.com/undergroundwires/privacy.sexy/commit/25d7f7b2a479e51e092881cc2751e67a7d3f179f)

README.md

@@ -122,7 +122,7 @@
 ## Get started
 
 - 🌍️ **Online**: [https://privacy.sexy](https://privacy.sexy).
-- 🖥️ **Offline**: Download directly for: [Windows](https://github.com/undergroundwires/privacy.sexy/releases/download/0.12.6/privacy.sexy-Setup-0.12.6.exe), [macOS](https://github.com/undergroundwires/privacy.sexy/releases/download/0.12.6/privacy.sexy-0.12.6.dmg), [Linux](https://github.com/undergroundwires/privacy.sexy/releases/download/0.12.6/privacy.sexy-0.12.6.AppImage). For more options, see [here](#additional-install-options).
+- 🖥️ **Offline**: Download directly for: [Windows](https://github.com/undergroundwires/privacy.sexy/releases/download/0.12.7/privacy.sexy-Setup-0.12.7.exe), [macOS](https://github.com/undergroundwires/privacy.sexy/releases/download/0.12.7/privacy.sexy-0.12.7.dmg), [Linux](https://github.com/undergroundwires/privacy.sexy/releases/download/0.12.7/privacy.sexy-0.12.7.AppImage). For more options, see [here](#additional-install-options).
 
 Online version does not require to run any software on your computer. Offline version has more functions such as running the scripts directly.
 

cypress-dirs.json

@@ -0,0 +1,5 @@
+{
+  "base": "tests/e2e",
+  "videos": "tests/e2e/videos",
+  "screenshots": "tests/e2e/videos"
+}

cypress.config.ts

@@ -1,18 +1,31 @@
 import { defineConfig } from 'cypress';
 import ViteConfig from './vite.config';
-
-const CYPRESS_BASE_DIR = 'tests/e2e/';
+import cypressDirs from './cypress-dirs.json' assert { type: 'json' };
 
 export default defineConfig({
-  fixturesFolder: `${CYPRESS_BASE_DIR}/fixtures`,
-  screenshotsFolder: `${CYPRESS_BASE_DIR}/screenshots`,
+  fixturesFolder: `${cypressDirs.base}/fixtures`,
+  screenshotsFolder: cypressDirs.screenshots,
 
   video: true,
-  videosFolder: `${CYPRESS_BASE_DIR}/videos`,
+  videosFolder: cypressDirs.videos,
 
   e2e: {
-    baseUrl: `http://localhost:${ViteConfig.server.port}/`,
-    specPattern: `${CYPRESS_BASE_DIR}/**/*.cy.{js,jsx,ts,tsx}`, // Default: cypress/e2e/**/*.cy.{js,jsx,ts,tsx}
-    supportFile: `${CYPRESS_BASE_DIR}/support/e2e.ts`,
+    baseUrl: `http://localhost:${getApplicationPort()}/`,
+    specPattern: `${cypressDirs.base}/**/*.cy.{js,jsx,ts,tsx}`, // Default: cypress/e2e/**/*.cy.{js,jsx,ts,tsx}
+    supportFile: `${cypressDirs.base}/support/e2e.ts`,
   },
+
+  /*
+    Disabling Chrome's web security to allow for faster DOM queries to access DOM earlier than
+    `cy.get()`. It bypasses the usual same-origin policy constraints
+  */
+  chromeWebSecurity: false,
 });
+
+function getApplicationPort(): number {
+  const port = ViteConfig.server?.port;
+  if (port === undefined) {
+    throw new Error('Unknown application port');
+  }
+  return port;
+}

docs/presentation.md

@@ -11,6 +11,8 @@ The presentation layer uses an event-driven architecture for bidirectional react
 ## Structure
 
 - [`/src/` **`presentation/`**](./../src/presentation/): Contains Vue and Electron code.
+  - [**`main.ts`**](./../src/presentation/main.ts): Starts Vue app.
+  - [**`index.html`**](./../src/presentation/index.html): The `index.html` entry file, located at the root of the project as required by Vite
   - [**`bootstrapping/`**](./../src/presentation/bootstrapping/): Registers Vue components and plugins.
   - [**`components/`**](./../src/presentation/components/): Contains Vue components and helpers.
     - [**`Shared/`**](./../src/presentation/components/Shared): Contains shared Vue components and helpers.
@@ -20,8 +22,7 @@ The presentation layer uses an event-driven architecture for bidirectional react
     - [**`fonts/`**](./../src/presentation/assets/fonts/): Contains fonts.
     - [**`styles/`**](./../src/presentation/assets/styles/): Contains shared styles.
       - [**`components/`**](./../src/presentation/assets/styles/components): Contains styles coupled to Vue components.
-      - [**`main.scss`**](./../src/presentation/assets/styles/main.scss): Main Sass file, imported by other components as single entrypoint.
-  - [**`main.ts`**](./../src/presentation/main.ts): Starts Vue app.
+      - [**`main.scss`**](./../src/presentation/assets/styles/main.scss): Main Sass file, imported by other components as single entrypoint..
   - [**`electron/`**](./../src/presentation/electron/): Contains Electron code.
     - [`/main/` **`index.ts`**](./../src/presentation/main.ts): Main entry for Electron, managing application windows and lifecycle events.
     - [`/preload/` **`index.ts`**](./../src/presentation/main.ts): Script executed before the renderer, securing Node.js features for renderer use.
@@ -70,10 +71,11 @@ To add a new dependency:
 1. **Define its symbol**: Define an associated symbol for every dependency in [`injectionSymbols.ts`](./../src/presentation/injectionSymbols.ts). Symbols are grouped into:
    - **Singletons**: Shared across components, instantiated once.
    - **Transients**: Factories yielding a new instance on every access.
-2. **Provide the dependency**: Modify the [`provideDependencies`](./../src/presentation/bootstrapping/DependencyProvider.ts) function to include the new dependency. [`App.vue`](./../src/presentation/components/App.vue) calls this function within its `setup()` hook to register the dependencies.
-3. **Inject the dependency**: Use Vue's `inject` method alongside the defined symbol to incorporate the dependency into components.
-   - For singletons, invoke the factory method: `inject(symbolKey)()`.
-   - For transients, directly inject: `inject(symbolKey)`.
+2. **Provide the dependency**:
+  Modify the [`provideDependencies`](./../src/presentation/bootstrapping/DependencyProvider.ts) function to include the new dependency.
+  [`App.vue`](./../src/presentation/components/App.vue) calls this function within its `setup()` hook to register the dependencies.
+3. **Inject the dependency**: Use `injectKey` to inject a dependency. Pass a selector function to `injectKey` that retrieves the appropriate symbol from the provided dependencies.
+   - Example usage: `injectKey((keys) => keys.useCollectionState)`;
 
 ## Shared UI components
 

docs/tests.md

@@ -68,21 +68,23 @@ These checks validate various qualities like runtime execution, building process
 - [`./src/`](./../src/): Contains the code subject to testing.
 - [`./tests/shared/`](./../tests/shared/): Contains code shared by different test categories.
   - [`bootstrap/setup.ts`](./../tests/shared/bootstrap/setup.ts): Initializes unit and integration tests.
+  - [`Assertions/`](./../tests/shared/Assertions/): Contains common assertion functions, prefixed with `expect`.
 - [`./tests/unit/`](./../tests/unit/)
   - Stores unit test code.
   - The directory structure mirrors [`./src/`](./../src).
     - E.g., tests for [`./src/application/ApplicationFactory.ts`](./../src/application/ApplicationFactory.ts) reside in [`./tests/unit/application/ApplicationFactory.spec.ts`](./../tests/unit/application/ApplicationFactory.spec.ts).
   - [`shared/`](./../tests/unit/shared/)
     - Contains shared unit test functionalities.
-    - [`Assertions/`](./../tests/unit/shared/Assertions): Contains common assertion functions, prefixed with `expect`.
     - [`TestCases/`](./../tests/unit/shared/TestCases/)
       - Shared test cases.
       - Functions that calls `it()` from [Vitest](https://vitest.dev/) should have `it` prefix.
     - [`Stubs/`](./../tests/unit/shared/Stubs): Maintains stubs for component isolation, equipped with basic functionalities and, when necessary, spying or mocking capabilities.
 - [`./tests/integration/`](./../tests/integration/): Contains integration test files.
 - [`cypress.config.ts`](./../cypress.config.ts): Cypress (E2E tests) configuration file.
+- [`cypress-dirs.json`](./../cypress-dirs.json): A central definition of directories used by Cypress, designed for reuse across different configurations.
 - [`./tests/e2e/`](./../tests/e2e/): Base Cypress folder, includes tests with `.cy.ts` extension.
-  - [`/support/e2e.ts`](./../tests/e2e/support/e2e.ts): Support file, runs before every single spec file.
   - [`/tsconfig.json`]: TypeScript configuration for file Cypress code, improves IDE support, recommended to have by official documentation.
   - *(git ignored)* `/videos`: Asset folder for videos taken during tests.
   - *(git ignored)* `/screenshots`: Asset folder for Screenshots taken during tests.
+  - [`/support/e2e.ts`](./../tests/e2e/support/e2e.ts): Support file, runs before every single test file.
+  - [`/support/interactions/`](./../tests/e2e/support/interactions/): Contains reusable functions for simulating user interactions, enhancing test readability and maintainability.

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "privacy.sexy",
-  "version": "0.12.6",
+  "version": "0.12.7",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "privacy.sexy",
-      "version": "0.12.5",
+      "version": "0.12.7",
       "hasInstallScript": true,
       "dependencies": {
         "@floating-ui/vue": "^1.0.2",

package.json

@@ -1,6 +1,6 @@
 {
   "name": "privacy.sexy",
-  "version": "0.12.6",
+  "version": "0.12.7",
   "private": true,
   "slogan": "Now you have the choice",
   "description": "Enforce privacy & security best-practices on Windows, macOS and Linux, because privacy is sexy 🍑🍆",
@@ -24,7 +24,7 @@
     "electron:preview": "electron-vite preview",
     "electron:prebuild": "electron-vite build",
     "electron:build": "electron-builder",
-    "lint:eslint": "eslint . --ignore-path .gitignore",
+    "lint:eslint": "eslint . --max-warnings=0 --ignore-path .gitignore",
     "lint:md": "markdownlint **/*.md --ignore node_modules",
     "lint:md:consistency": "remark . --frail --use remark-preset-lint-consistent",
     "lint:md:relative-urls": "remark . --frail --use remark-validate-links",

src/application/ApplicationFactory.ts

@@ -12,9 +12,6 @@ export class ApplicationFactory implements IApplicationFactory {
   private readonly getter: AsyncLazy<IApplication>;
 
   protected constructor(costlyGetter: ApplicationGetterType) {
-    if (!costlyGetter) {
-      throw new Error('missing getter');
-    }
     this.getter = new AsyncLazy<IApplication>(() => Promise.resolve(costlyGetter()));
   }
 

src/application/Common/Array.ts

@@ -1,7 +1,5 @@
 // Compares to Array<T> objects for equality, ignoring order
 export function scrambledEqual<T>(array1: readonly T[], array2: readonly T[]) {
-  if (!array1) { throw new Error('missing first array'); }
-  if (!array2) { throw new Error('missing second array'); }
   const sortedArray1 = sort(array1);
   const sortedArray2 = sort(array2);
   return sequenceEqual(sortedArray1, sortedArray2);
@@ -12,8 +10,6 @@ export function scrambledEqual<T>(array1: readonly T[], array2: readonly T[]) {
 
 // Compares to Array<T> objects for equality in same order
 export function sequenceEqual<T>(array1: readonly T[], array2: readonly T[]) {
-  if (!array1) { throw new Error('missing first array'); }
-  if (!array2) { throw new Error('missing second array'); }
   if (array1.length !== array2.length) {
     return false;
   }

src/application/Common/CustomError.ts

@@ -20,23 +20,30 @@ export abstract class CustomError extends Error {
   }
 }
 
-export const Environment = {
+interface ErrorPrototypeManipulation {
+  getSetPrototypeOf: () => (typeof Object.setPrototypeOf | undefined);
+  getCaptureStackTrace: () => (typeof Error.captureStackTrace | undefined);
+}
+
+export const PlatformErrorPrototypeManipulation: ErrorPrototypeManipulation = {
   getSetPrototypeOf: () => Object.setPrototypeOf,
   getCaptureStackTrace: () => Error.captureStackTrace,
 };
 
 function fixPrototype(target: Error, prototype: CustomError) {
-  // https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-2.html#support-for-newtarget
-  const setPrototypeOf = Environment.getSetPrototypeOf();
-  if (!functionExists(setPrototypeOf)) {
+  // This is recommended by TypeScript guidelines.
+  //  Source: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-2.html#support-for-newtarget
+  //  Snapshots: https://web.archive.org/web/20231111234849/https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-2.html#support-for-newtarget, https://archive.ph/tr7cX#support-for-newtarget
+  const setPrototypeOf = PlatformErrorPrototypeManipulation.getSetPrototypeOf();
+  if (!isFunction(setPrototypeOf)) {
     return;
   }
   setPrototypeOf(target, prototype);
 }
 
 function ensureStackTrace(target: Error) {
-  const captureStackTrace = Environment.getCaptureStackTrace();
-  if (!functionExists(captureStackTrace)) {
+  const captureStackTrace = PlatformErrorPrototypeManipulation.getCaptureStackTrace();
+  if (!isFunction(captureStackTrace)) {
     // captureStackTrace is only available on V8, if it's not available
     // modern JS engines will usually generate a stack trace on error objects when they're thrown.
     return;
@@ -44,7 +51,7 @@ function ensureStackTrace(target: Error) {
   captureStackTrace(target, target.constructor);
 }
 
-function functionExists(func: unknown): boolean {
-  // Not doing truthy/falsy check i.e. if(func) as most values are truthy in JS for robustness
+// eslint-disable-next-line @typescript-eslint/ban-types
+function isFunction(func: unknown): func is Function {
   return typeof func === 'function';
 }

src/application/Common/Enum.ts

@@ -54,9 +54,6 @@ export function assertInRange<T extends EnumType, TEnumValue extends EnumType>(
   value: TEnumValue,
   enumVariable: EnumVariable<T, TEnumValue>,
 ) {
-  if (value === undefined || value === null) {
-    throw new Error('absent enum value');
-  }
   if (!(value in enumVariable)) {
     throw new RangeError(`enum value "${value}" is out of range`);
   }

src/application/Common/ScriptingLanguage/ScriptingLanguageFactory.ts

@@ -9,19 +9,16 @@ export abstract class ScriptingLanguageFactory<T> implements IScriptingLanguageF
 
   public create(language: ScriptingLanguage): T {
     assertInRange(language, ScriptingLanguage);
-    if (!this.getters.has(language)) {
+    const getter = this.getters.get(language);
+    if (!getter) {
       throw new RangeError(`unknown language: "${ScriptingLanguage[language]}"`);
     }
-    const getter = this.getters.get(language);
     const instance = getter();
     return instance;
   }
 
   protected registerGetter(language: ScriptingLanguage, getter: Getter<T>) {
     assertInRange(language, ScriptingLanguage);
-    if (!getter) {
-      throw new Error('missing getter');
-    }
     if (this.getters.has(language)) {
       throw new Error(`${ScriptingLanguage[language]} is already registered`);
     }

src/application/Common/Timing/BatchedDebounce.ts

@@ -0,0 +1,27 @@
+import { PlatformTimer } from './PlatformTimer';
+import { TimeoutType, Timer } from './Timer';
+
+export function batchedDebounce<T>(
+  callback: (batches: readonly T[]) => void,
+  waitInMs: number,
+  timer: Timer = PlatformTimer,
+): (arg: T) => void {
+  let lastTimeoutId: TimeoutType | undefined;
+  let batches: Array<T> = [];
+
+  return (arg: T) => {
+    batches.push(arg);
+
+    const later = () => {
+      callback(batches);
+      batches = [];
+      lastTimeoutId = undefined;
+    };
+
+    if (lastTimeoutId !== undefined) {
+      timer.clearTimeout(lastTimeoutId);
+    }
+
+    lastTimeoutId = timer.setTimeout(later, waitInMs);
+  };
+}

src/application/Common/Timing/PlatformTimer.ts

@@ -0,0 +1,7 @@
+import { Timer } from './Timer';
+
+export const PlatformTimer: Timer = {
+  setTimeout: (callback, ms) => setTimeout(callback, ms),
+  clearTimeout: (timeoutId) => clearTimeout(timeoutId),
+  dateNow: () => Date.now(),
+};

src/application/Common/Timing/Throttle.ts

@@ -1,47 +1,29 @@
+import { Timer, TimeoutType } from './Timer';
+import { PlatformTimer } from './PlatformTimer';
+
 export type CallbackType = (..._: unknown[]) => void;
 
 export function throttle(
   callback: CallbackType,
   waitInMs: number,
-  timer: ITimer = NodeTimer,
+  timer: Timer = PlatformTimer,
 ): CallbackType {
   const throttler = new Throttler(timer, waitInMs, callback);
   return (...args: unknown[]) => throttler.invoke(...args);
 }
 
-// Allows aligning with both NodeJs (NodeJs.Timeout) and Window type (number)
-export type TimeoutType = ReturnType<typeof setTimeout>;
-
-export interface ITimer {
-  setTimeout: (callback: () => void, ms: number) => TimeoutType;
-  clearTimeout: (timeoutId: TimeoutType) => void;
-  dateNow(): number;
-}
-
-const NodeTimer: ITimer = {
-  setTimeout: (callback, ms) => setTimeout(callback, ms),
-  clearTimeout: (timeoutId) => clearTimeout(timeoutId),
-  dateNow: () => Date.now(),
-};
-
-interface IThrottler {
-  invoke: CallbackType;
-}
-
-class Throttler implements IThrottler {
-  private queuedExecutionId: TimeoutType;
+class Throttler {
+  private queuedExecutionId: TimeoutType | undefined;
 
   private previouslyRun: number;
 
   constructor(
-    private readonly timer: ITimer,
+    private readonly timer: Timer,
     private readonly waitInMs: number,
     private readonly callback: CallbackType,
   ) {
-    if (!timer) { throw new Error('missing timer'); }
     if (!waitInMs) { throw new Error('missing delay'); }
     if (waitInMs < 0) { throw new Error('negative delay'); }
-    if (!callback) { throw new Error('missing callback'); }
   }
 
   public invoke(...args: unknown[]): void {

src/application/Common/Timing/Timer.ts

@@ -0,0 +1,8 @@
+// Allows aligning with both NodeJs (NodeJs.Timeout) and Window type (number)
+export type TimeoutType = ReturnType<typeof setTimeout>;
+
+export interface Timer {
+  setTimeout: (callback: () => void, ms: number) => TimeoutType;
+  clearTimeout: (timeoutId: TimeoutType) => void;
+  dateNow(): number;
+}

src/application/Context/ApplicationContext.ts

@@ -26,7 +26,6 @@ export class ApplicationContext implements IApplicationContext {
     public readonly app: IApplication,
     initialContext: OperatingSystem,
   ) {
-    validateApp(app);
     this.states = initializeStates(app);
     this.changeContext(initialContext);
   }
@@ -36,10 +35,8 @@ export class ApplicationContext implements IApplicationContext {
     if (this.currentOs === os) {
       return;
     }
-    this.collection = this.app.getCollection(os);
-    if (!this.collection) {
-      throw new Error(`os "${OperatingSystem[os]}" is not defined in application`);
-    }
+    const collection = this.app.getCollection(os);
+    this.collection = collection;
     const event: IApplicationContextChangedEvent = {
       newState: this.states[os],
       oldState: this.states[this.currentOs],
@@ -49,12 +46,6 @@ export class ApplicationContext implements IApplicationContext {
   }
 }
 
-function validateApp(app: IApplication) {
-  if (!app) {
-    throw new Error('missing app');
-  }
-}
-
 function initializeStates(app: IApplication): StateMachine {
   const machine = new Map<OperatingSystem, ICategoryCollectionState>();
   for (const collection of app.collections) {

src/application/Context/ApplicationContextFactory.ts

@@ -10,18 +10,23 @@ export async function buildContext(
   factory: IApplicationFactory = ApplicationFactory.Current,
   environment = RuntimeEnvironment.CurrentEnvironment,
 ): Promise<IApplicationContext> {
-  if (!factory) { throw new Error('missing factory'); }
-  if (!environment) { throw new Error('missing environment'); }
   const app = await factory.getApp();
   const os = getInitialOs(app, environment.os);
   return new ApplicationContext(app, os);
 }
 
-function getInitialOs(app: IApplication, currentOs: OperatingSystem): OperatingSystem {
+function getInitialOs(
+  app: IApplication,
+  currentOs: OperatingSystem | undefined,
+): OperatingSystem {
   const supportedOsList = app.getSupportedOsList();
-  if (supportedOsList.includes(currentOs)) {
+  if (currentOs !== undefined && supportedOsList.includes(currentOs)) {
     return currentOs;
   }
+  return getMostSupportedOs(supportedOsList, app);
+}
+
+function getMostSupportedOs(supportedOsList: OperatingSystem[], app: IApplication) {
   supportedOsList.sort((os1, os2) => {
     const getPriority = (os: OperatingSystem) => app.getCollection(os).totalScripts;
     return getPriority(os2) - getPriority(os1);

src/application/Context/State/CategoryCollectionState.ts

@@ -4,23 +4,48 @@ import { UserFilter } from './Filter/UserFilter';
 import { IUserFilter } from './Filter/IUserFilter';
 import { ApplicationCode } from './Code/ApplicationCode';
 import { UserSelection } from './Selection/UserSelection';
-import { IUserSelection } from './Selection/IUserSelection';
 import { ICategoryCollectionState } from './ICategoryCollectionState';
 import { IApplicationCode } from './Code/IApplicationCode';
+import { UserSelectionFacade } from './Selection/UserSelectionFacade';
 
 export class CategoryCollectionState implements ICategoryCollectionState {
   public readonly os: OperatingSystem;
 
   public readonly code: IApplicationCode;
 
-  public readonly selection: IUserSelection;
+  public readonly selection: UserSelection;
 
   public readonly filter: IUserFilter;
 
-  public constructor(readonly collection: ICategoryCollection) {
-    this.selection = new UserSelection(collection, []);
-    this.code = new ApplicationCode(this.selection, collection.scripting);
-    this.filter = new UserFilter(collection);
+  public constructor(
+    public readonly collection: ICategoryCollection,
+    selectionFactory = DefaultSelectionFactory,
+    codeFactory = DefaultCodeFactory,
+    filterFactory = DefaultFilterFactory,
+  ) {
+    this.selection = selectionFactory(collection, []);
+    this.code = codeFactory(this.selection.scripts, collection.scripting);
+    this.filter = filterFactory(collection);
     this.os = collection.os;
   }
 }
+
+export type CodeFactory = (
+  ...params: ConstructorParameters<typeof ApplicationCode>
+) => IApplicationCode;
+
+const DefaultCodeFactory: CodeFactory = (...params) => new ApplicationCode(...params);
+
+export type SelectionFactory = (
+  ...params: ConstructorParameters<typeof UserSelectionFacade>
+) => UserSelection;
+
+const DefaultSelectionFactory: SelectionFactory = (
+  ...params
+) => new UserSelectionFacade(...params);
+
+export type FilterFactory = (
+  ...params: ConstructorParameters<typeof UserFilter>
+) => IUserFilter;
+
+const DefaultFilterFactory: FilterFactory = (...params) => new UserFilter(...params);

src/application/Context/State/Code/ApplicationCode.ts

@@ -1,7 +1,7 @@
-import { SelectedScript } from '@/application/Context/State/Selection/SelectedScript';
-import { IReadOnlyUserSelection } from '@/application/Context/State/Selection/IUserSelection';
 import { EventSource } from '@/infrastructure/Events/EventSource';
 import { IScriptingDefinition } from '@/domain/IScriptingDefinition';
+import { SelectedScript } from '@/application/Context/State/Selection/Script/SelectedScript';
+import { ReadonlyScriptSelection } from '@/application/Context/State/Selection/Script/ScriptSelection';
 import { CodeChangedEvent } from './Event/CodeChangedEvent';
 import { CodePosition } from './Position/CodePosition';
 import { ICodeChangedEvent } from './Event/ICodeChangedEvent';
@@ -17,15 +17,12 @@ export class ApplicationCode implements IApplicationCode {
   private scriptPositions = new Map<SelectedScript, CodePosition>();
 
   constructor(
-    userSelection: IReadOnlyUserSelection,
+    selection: ReadonlyScriptSelection,
     private readonly scriptingDefinition: IScriptingDefinition,
     private readonly generator: IUserScriptGenerator = new UserScriptGenerator(),
   ) {
-    if (!userSelection) { throw new Error('missing userSelection'); }
-    if (!scriptingDefinition) { throw new Error('missing scriptingDefinition'); }
-    if (!generator) { throw new Error('missing generator'); }
-    this.setCode(userSelection.selectedScripts);
-    userSelection.changed.on((scripts) => {
+    this.setCode(selection.selectedScripts);
+    selection.changed.on((scripts) => {
       this.setCode(scripts);
     });
   }

src/application/Context/State/Code/Event/CodeChangedEvent.ts

@@ -1,6 +1,6 @@
 import { IScript } from '@/domain/IScript';
 import { ICodePosition } from '@/application/Context/State/Code/Position/ICodePosition';
-import { SelectedScript } from '../../Selection/SelectedScript';
+import { SelectedScript } from '@/application/Context/State/Selection/Script/SelectedScript';
 import { ICodeChangedEvent } from './ICodeChangedEvent';
 
 export class CodeChangedEvent implements ICodeChangedEvent {
@@ -36,7 +36,18 @@ export class CodeChangedEvent implements ICodeChangedEvent {
   }
 
   public getScriptPositionInCode(script: IScript): ICodePosition {
-    return this.scripts.get(script);
+    return this.getPositionById(script.id);
+  }
+
+  private getPositionById(scriptId: string): ICodePosition {
+    const position = [...this.scripts.entries()]
+      .filter(([s]) => s.id === scriptId)
+      .map(([, pos]) => pos)
+      .at(0);
+    if (!position) {
+      throw new Error('Unknown script: Position could not be found for the script');
+    }
+    return position;
   }
 }
 

src/application/Context/State/Code/Event/ICodeChangedEvent.ts

@@ -3,9 +3,9 @@ import { ICodePosition } from '@/application/Context/State/Code/Position/ICodePo
 
 export interface ICodeChangedEvent {
   readonly code: string;
-  addedScripts: ReadonlyArray<IScript>;
-  removedScripts: ReadonlyArray<IScript>;
-  changedScripts: ReadonlyArray<IScript>;
+  readonly addedScripts: ReadonlyArray<IScript>;
+  readonly removedScripts: ReadonlyArray<IScript>;
+  readonly changedScripts: ReadonlyArray<IScript>;
   isEmpty(): boolean;
   getScriptPositionInCode(script: IScript): ICodePosition;
 }

src/application/Context/State/Code/Generation/CodeBuilder.ts

@@ -16,7 +16,9 @@ export abstract class CodeBuilder implements ICodeBuilder {
       return this;
     }
     const lines = code.match(/[^\r\n]+/g);
-    this.lines.push(...lines);
+    if (lines) {
+      this.lines.push(...lines);
+    }
     return this;
   }
 

src/application/Context/State/Code/Generation/IUserScript.ts

@@ -1,7 +1,7 @@
-import { SelectedScript } from '@/application/Context/State/Selection/SelectedScript';
 import { ICodePosition } from '@/application/Context/State/Code/Position/ICodePosition';
+import { SelectedScript } from '@/application/Context/State/Selection/Script/SelectedScript';
 
 export interface IUserScript {
-  code: string;
-  scriptPositions: Map<SelectedScript, ICodePosition>;
+  readonly code: string;
+  readonly scriptPositions: Map<SelectedScript, ICodePosition>;
 }

src/application/Context/State/Code/Generation/IUserScriptGenerator.ts

@@ -1,9 +1,10 @@
-import { SelectedScript } from '@/application/Context/State/Selection/SelectedScript';
 import { IScriptingDefinition } from '@/domain/IScriptingDefinition';
+import { SelectedScript } from '@/application/Context/State/Selection/Script/SelectedScript';
 import { IUserScript } from './IUserScript';
 
 export interface IUserScriptGenerator {
   buildCode(
     selectedScripts: ReadonlyArray<SelectedScript>,
-    scriptingDefinition: IScriptingDefinition): IUserScript;
+    scriptingDefinition: IScriptingDefinition,
+  ): IUserScript;
 }

src/application/Context/State/Code/Generation/UserScriptGenerator.ts

@@ -1,6 +1,6 @@
-import { SelectedScript } from '@/application/Context/State/Selection/SelectedScript';
 import { ICodePosition } from '@/application/Context/State/Code/Position/ICodePosition';
 import { IScriptingDefinition } from '@/domain/IScriptingDefinition';
+import { SelectedScript } from '@/application/Context/State/Selection/Script/SelectedScript';
 import { CodePosition } from '../Position/CodePosition';
 import { IUserScriptGenerator } from './IUserScriptGenerator';
 import { IUserScript } from './IUserScript';
@@ -17,8 +17,6 @@ export class UserScriptGenerator implements IUserScriptGenerator {
     selectedScripts: ReadonlyArray<SelectedScript>,
     scriptingDefinition: IScriptingDefinition,
   ): IUserScript {
-    if (!selectedScripts) { throw new Error('missing scripts'); }
-    if (!scriptingDefinition) { throw new Error('missing definition'); }
     if (!selectedScripts.length) {
       return { code: '', scriptPositions: new Map<SelectedScript, ICodePosition>() };
     }
@@ -68,8 +66,19 @@ function appendSelection(
 function appendCode(selection: SelectedScript, builder: ICodeBuilder): ICodeBuilder {
   const { script } = selection;
   const name = selection.revert ? `${script.name} (revert)` : script.name;
-  const scriptCode = selection.revert ? script.code.revert : script.code.execute;
+  const scriptCode = getSelectedCode(selection);
   return builder
     .appendLine()
     .appendFunction(name, scriptCode);
 }
+
+function getSelectedCode(selection: SelectedScript): string {
+  const { code } = selection.script;
+  if (!selection.revert) {
+    return code.execute;
+  }
+  if (!code.revert) {
+    throw new Error('Reverted script lacks revert code.');
+  }
+  return code.revert;
+}

src/application/Context/State/Filter/Event/FilterChange.ts

@@ -1,37 +1,37 @@
 import { IFilterResult } from '@/application/Context/State/Filter/IFilterResult';
 import { FilterActionType } from './FilterActionType';
-import { IFilterChangeDetails, IFilterChangeDetailsVisitor } from './IFilterChangeDetails';
+import {
+  IFilterChangeDetails, IFilterChangeDetailsVisitor,
+  ApplyFilterAction, ClearFilterAction,
+} from './IFilterChangeDetails';
 
 export class FilterChange implements IFilterChangeDetails {
-  public static forApply(filter: IFilterResult) {
-    if (!filter) {
-      throw new Error('missing filter');
-    }
-    return new FilterChange(FilterActionType.Apply, filter);
+  public static forApply(
+    filter: IFilterResult,
+  ): IFilterChangeDetails {
+    return new FilterChange({ type: FilterActionType.Apply, filter });
   }
 
-  public static forClear() {
-    return new FilterChange(FilterActionType.Clear);
+  public static forClear(): IFilterChangeDetails {
+    return new FilterChange({ type: FilterActionType.Clear });
   }
 
-  private constructor(
-    public readonly actionType: FilterActionType,
-    public readonly filter?: IFilterResult,
-  ) { }
+  private constructor(public readonly action: ApplyFilterAction | ClearFilterAction) { }
 
   public visit(visitor: IFilterChangeDetailsVisitor): void {
-    if (!visitor) {
-      throw new Error('missing visitor');
-    }
-    switch (this.actionType) {
+    switch (this.action.type) {
       case FilterActionType.Apply:
-        visitor.onApply(this.filter);
+        if (visitor.onApply) {
+          visitor.onApply(this.action.filter);
+        }
         break;
       case FilterActionType.Clear:
-        visitor.onClear();
+        if (visitor.onClear) {
+          visitor.onClear();
+        }
         break;
       default:
-        throw new Error(`Unknown action type: ${this.actionType}`);
+        throw new Error(`Unknown action: ${this.action}`);
     }
   }
 }

src/application/Context/State/Filter/Event/IFilterChangeDetails.ts

@@ -2,13 +2,22 @@ import { IFilterResult } from '@/application/Context/State/Filter/IFilterResult'
 import { FilterActionType } from './FilterActionType';
 
 export interface IFilterChangeDetails {
-  readonly actionType: FilterActionType;
-  readonly filter?: IFilterResult;
-
+  readonly action: FilterAction;
   visit(visitor: IFilterChangeDetailsVisitor): void;
 }
 
 export interface IFilterChangeDetailsVisitor {
-  onClear(): void;
-  onApply(filter: IFilterResult): void;
+  readonly onClear?: () => void;
+  readonly onApply?: (filter: IFilterResult) => void;
 }
+
+export type ApplyFilterAction = {
+  readonly type: FilterActionType.Apply,
+  readonly filter: IFilterResult;
+};
+
+export type ClearFilterAction = {
+  readonly type: FilterActionType.Clear,
+};
+
+export type FilterAction = ApplyFilterAction | ClearFilterAction;

src/application/Context/State/Filter/FilterResult.ts

@@ -9,8 +9,6 @@ export class FilterResult implements IFilterResult {
     public readonly query: string,
   ) {
     if (!query) { throw new Error('Query is empty or undefined'); }
-    if (!scriptMatches) { throw new Error('Script matches is undefined'); }
-    if (!categoryMatches) { throw new Error('Category matches is undefined'); }
   }
 
   public hasAnyMatches(): boolean {

src/application/Context/State/ICategoryCollectionState.ts

@@ -1,18 +1,18 @@
 import { ICategoryCollection } from '@/domain/ICategoryCollection';
 import { OperatingSystem } from '@/domain/OperatingSystem';
 import { IReadOnlyUserFilter, IUserFilter } from './Filter/IUserFilter';
-import { IReadOnlyUserSelection, IUserSelection } from './Selection/IUserSelection';
+import { ReadonlyUserSelection, UserSelection } from './Selection/UserSelection';
 import { IApplicationCode } from './Code/IApplicationCode';
 
 export interface IReadOnlyCategoryCollectionState {
   readonly code: IApplicationCode;
   readonly os: OperatingSystem;
   readonly filter: IReadOnlyUserFilter;
-  readonly selection: IReadOnlyUserSelection;
+  readonly selection: ReadonlyUserSelection;
   readonly collection: ICategoryCollection;
 }
 
 export interface ICategoryCollectionState extends IReadOnlyCategoryCollectionState {
   readonly filter: IUserFilter;
-  readonly selection: IUserSelection;
+  readonly selection: UserSelection;
 }

src/application/Context/State/Selection/Category/CategorySelection.ts

@@ -0,0 +1,11 @@
+import { ICategory } from '@/domain/ICategory';
+import { CategorySelectionChangeCommand } from './CategorySelectionChange';
+
+export interface ReadonlyCategorySelection {
+  areAllScriptsSelected(category: ICategory): boolean;
+  isAnyScriptSelected(category: ICategory): boolean;
+}
+
+export interface CategorySelection extends ReadonlyCategorySelection {
+  processChanges(action: CategorySelectionChangeCommand): void;
+}

src/application/Context/State/Selection/Category/CategorySelectionChange.ts

@@ -0,0 +1,15 @@
+type CategorySelectionStatus = {
+  readonly isSelected: true;
+  readonly isReverted: boolean;
+} | {
+  readonly isSelected: false;
+};
+
+export interface CategorySelectionChange {
+  readonly categoryId: number;
+  readonly newStatus: CategorySelectionStatus;
+}
+
+export interface CategorySelectionChangeCommand {
+  readonly changes: readonly CategorySelectionChange[];
+}

src/application/Context/State/Selection/Category/ScriptToCategorySelectionMapper.ts

@@ -0,0 +1,60 @@
+import { ICategory } from '@/domain/ICategory';
+import { ICategoryCollection } from '@/domain/ICategoryCollection';
+import { ScriptSelection } from '../Script/ScriptSelection';
+import { ScriptSelectionChange } from '../Script/ScriptSelectionChange';
+import { CategorySelection } from './CategorySelection';
+import { CategorySelectionChange, CategorySelectionChangeCommand } from './CategorySelectionChange';
+
+export class ScriptToCategorySelectionMapper implements CategorySelection {
+  constructor(
+    private readonly scriptSelection: ScriptSelection,
+    private readonly collection: ICategoryCollection,
+  ) {
+
+  }
+
+  public areAllScriptsSelected(category: ICategory): boolean {
+    const { selectedScripts } = this.scriptSelection;
+    if (selectedScripts.length === 0) {
+      return false;
+    }
+    const scripts = category.getAllScriptsRecursively();
+    if (selectedScripts.length < scripts.length) {
+      return false;
+    }
+    return scripts.every(
+      (script) => selectedScripts.some((selected) => selected.id === script.id),
+    );
+  }
+
+  public isAnyScriptSelected(category: ICategory): boolean {
+    const { selectedScripts } = this.scriptSelection;
+    if (selectedScripts.length === 0) {
+      return false;
+    }
+    return selectedScripts.some((s) => category.includes(s.script));
+  }
+
+  public processChanges(action: CategorySelectionChangeCommand): void {
+    const scriptChanges = action.changes.reduce((changes, change) => {
+      changes.push(...this.collectScriptChanges(change));
+      return changes;
+    }, new Array<ScriptSelectionChange>());
+    this.scriptSelection.processChanges({
+      changes: scriptChanges,
+    });
+  }
+
+  private collectScriptChanges(change: CategorySelectionChange): ScriptSelectionChange[] {
+    const category = this.collection.getCategory(change.categoryId);
+    const scripts = category.getAllScriptsRecursively();
+    const scriptsChangesInCategory = scripts
+      .map((script): ScriptSelectionChange => ({
+        scriptId: script.id,
+        newStatus: {
+          ...change.newStatus,
+        },
+      }));
+    return scriptsChangesInCategory;
+  }
+}

src/application/Context/State/Selection/IUserSelection.ts

@@ -1,23 +0,0 @@
-import { IScript } from '@/domain/IScript';
-import { ICategory } from '@/domain/ICategory';
-import { IEventSource } from '@/infrastructure/Events/IEventSource';
-import { SelectedScript } from './SelectedScript';
-
-export interface IReadOnlyUserSelection {
-  readonly changed: IEventSource<ReadonlyArray<SelectedScript>>;
-  readonly selectedScripts: ReadonlyArray<SelectedScript>;
-  isSelected(scriptId: string): boolean;
-  areAllSelected(category: ICategory): boolean;
-  isAnySelected(category: ICategory): boolean;
-}
-
-export interface IUserSelection extends IReadOnlyUserSelection {
-  removeAllInCategory(categoryId: number): void;
-  addOrUpdateAllInCategory(categoryId: number, revert: boolean): void;
-  addSelectedScript(scriptId: string, revert: boolean): void;
-  addOrUpdateSelectedScript(scriptId: string, revert: boolean): void;
-  removeSelectedScript(scriptId: string): void;
-  selectOnly(scripts: ReadonlyArray<IScript>): void;
-  selectAll(): void;
-  deselectAll(): void;
-}

src/application/Context/State/Selection/Script/DebouncedScriptSelection.ts

@@ -0,0 +1,171 @@
+import { InMemoryRepository } from '@/infrastructure/Repository/InMemoryRepository';
+import { IScript } from '@/domain/IScript';
+import { EventSource } from '@/infrastructure/Events/EventSource';
+import { ReadonlyRepository, Repository } from '@/application/Repository/Repository';
+import { ICategoryCollection } from '@/domain/ICategoryCollection';
+import { batchedDebounce } from '@/application/Common/Timing/BatchedDebounce';
+import { ScriptSelection } from './ScriptSelection';
+import { ScriptSelectionChange, ScriptSelectionChangeCommand } from './ScriptSelectionChange';
+import { SelectedScript } from './SelectedScript';
+import { UserSelectedScript } from './UserSelectedScript';
+
+const DEBOUNCE_DELAY_IN_MS = 100;
+
+export type DebounceFunction = typeof batchedDebounce<ScriptSelectionChangeCommand>;
+
+export class DebouncedScriptSelection implements ScriptSelection {
+  public readonly changed = new EventSource<ReadonlyArray<SelectedScript>>();
+
+  private readonly scripts: Repository<string, SelectedScript>;
+
+  public readonly processChanges: ScriptSelection['processChanges'];
+
+  constructor(
+    private readonly collection: ICategoryCollection,
+    selectedScripts: ReadonlyArray<SelectedScript>,
+    debounce: DebounceFunction = batchedDebounce,
+  ) {
+    this.scripts = new InMemoryRepository<string, SelectedScript>();
+    for (const script of selectedScripts) {
+      this.scripts.addItem(script);
+    }
+    this.processChanges = debounce(
+      (batchedRequests: readonly ScriptSelectionChangeCommand[]) => {
+        const consolidatedChanges = batchedRequests.flatMap((request) => request.changes);
+        this.processScriptChanges(consolidatedChanges);
+      },
+      DEBOUNCE_DELAY_IN_MS,
+    );
+  }
+
+  public isSelected(scriptId: string): boolean {
+    return this.scripts.exists(scriptId);
+  }
+
+  public get selectedScripts(): readonly SelectedScript[] {
+    return this.scripts.getItems();
+  }
+
+  public selectAll(): void {
+    const scriptsToSelect = this.collection
+      .getAllScripts()
+      .filter((script) => !this.scripts.exists(script.id))
+      .map((script) => new UserSelectedScript(script, false));
+    if (scriptsToSelect.length === 0) {
+      return;
+    }
+    this.processChanges({
+      changes: scriptsToSelect.map((script): ScriptSelectionChange => ({
+        scriptId: script.id,
+        newStatus: {
+          isSelected: true,
+          isReverted: false,
+        },
+      })),
+    });
+  }
+
+  public deselectAll(): void {
+    if (this.scripts.length === 0) {
+      return;
+    }
+    const selectedScriptIds = this.scripts.getItems().map((script) => script.id);
+    this.processChanges({
+      changes: selectedScriptIds.map((scriptId): ScriptSelectionChange => ({
+        scriptId,
+        newStatus: {
+          isSelected: false,
+        },
+      })),
+    });
+  }
+
+  public selectOnly(scripts: readonly IScript[]): void {
+    if (scripts.length === 0) {
+      throw new Error('Provided script array is empty. To deselect all scripts, please use the deselectAll() method instead.');
+    }
+    this.processChanges({
+      changes: [
+        ...getScriptIdsToBeDeselected(this.scripts, scripts)
+          .map((scriptId): ScriptSelectionChange => ({
+            scriptId,
+            newStatus: {
+              isSelected: false,
+            },
+          })),
+        ...getScriptIdsToBeSelected(this.scripts, scripts)
+          .map((scriptId): ScriptSelectionChange => ({
+            scriptId,
+            newStatus: {
+              isSelected: true,
+              isReverted: false,
+            },
+          })),
+      ],
+    });
+  }
+
+  private processScriptChanges(changes: readonly ScriptSelectionChange[]): void {
+    let totalChanged = 0;
+    for (const change of changes) {
+      totalChanged += this.applyChange(change);
+    }
+    if (totalChanged > 0) {
+      this.changed.notify(this.scripts.getItems());
+    }
+  }
+
+  private applyChange(change: ScriptSelectionChange): number {
+    const script = this.collection.getScript(change.scriptId);
+    if (change.newStatus.isSelected) {
+      return this.addOrUpdateScript(script.id, change.newStatus.isReverted);
+    }
+    return this.removeScript(script.id);
+  }
+
+  private addOrUpdateScript(scriptId: string, revert: boolean): number {
+    const script = this.collection.getScript(scriptId);
+    const selectedScript = new UserSelectedScript(script, revert);
+    if (!this.scripts.exists(selectedScript.id)) {
+      this.scripts.addItem(selectedScript);
+      return 1;
+    }
+    const existingSelectedScript = this.scripts.getById(selectedScript.id);
+    if (equals(selectedScript, existingSelectedScript)) {
+      return 0;
+    }
+    this.scripts.addOrUpdateItem(selectedScript);
+    return 1;
+  }
+
+  private removeScript(scriptId: string): number {
+    if (!this.scripts.exists(scriptId)) {
+      return 0;
+    }
+    this.scripts.removeItem(scriptId);
+    return 1;
+  }
+}
+
+function getScriptIdsToBeSelected(
+  existingItems: ReadonlyRepository<string, SelectedScript>,
+  desiredScripts: readonly IScript[],
+): string[] {
+  return desiredScripts
+    .filter((script) => !existingItems.exists(script.id))
+    .map((script) => script.id);
+}
+
+function getScriptIdsToBeDeselected(
+  existingItems: ReadonlyRepository<string, SelectedScript>,
+  desiredScripts: readonly IScript[],
+): string[] {
+  return existingItems
+    .getItems()
+    .filter((existing) => !desiredScripts.some((script) => existing.id === script.id))
+    .map((script) => script.id);
+}
+
+function equals(a: SelectedScript, b: SelectedScript): boolean {
+  return a.script.equals(b.script.id) && a.revert === b.revert;
+}

src/application/Context/State/Selection/Script/ScriptSelection.ts

@@ -0,0 +1,17 @@
+import { IEventSource } from '@/infrastructure/Events/IEventSource';
+import { IScript } from '@/domain/IScript';
+import { SelectedScript } from './SelectedScript';
+import { ScriptSelectionChangeCommand } from './ScriptSelectionChange';
+
+export interface ReadonlyScriptSelection {
+  readonly changed: IEventSource<readonly SelectedScript[]>;
+  readonly selectedScripts: readonly SelectedScript[];
+  isSelected(scriptId: string): boolean;
+}
+
+export interface ScriptSelection extends ReadonlyScriptSelection {
+  selectOnly(scripts: readonly IScript[]): void;
+  selectAll(): void;
+  deselectAll(): void;
+  processChanges(action: ScriptSelectionChangeCommand): void;
+}

src/application/Context/State/Selection/Script/ScriptSelectionChange.ts

@@ -0,0 +1,15 @@
+export type ScriptSelectionStatus = {
+  readonly isSelected: true;
+  readonly isReverted: boolean;
+} | {
+  readonly isSelected: false;
+};
+
+export interface ScriptSelectionChange {
+  readonly scriptId: string;
+  readonly newStatus: ScriptSelectionStatus;
+}
+
+export interface ScriptSelectionChangeCommand {
+  readonly changes: ReadonlyArray<ScriptSelectionChange>;
+}

src/application/Context/State/Selection/Script/SelectedScript.ts

@@ -0,0 +1,9 @@
+import { IEntity } from '@/infrastructure/Entity/IEntity';
+import { IScript } from '@/domain/IScript';
+
+type ScriptId = IScript['id'];
+
+export interface SelectedScript extends IEntity<ScriptId> {
+  readonly script: IScript;
+  readonly revert: boolean;
+}

src/application/Context/State/Selection/Script/UserSelectedScript.ts

@@ -1,14 +1,17 @@
 import { BaseEntity } from '@/infrastructure/Entity/BaseEntity';
 import { IScript } from '@/domain/IScript';
+import { SelectedScript } from './SelectedScript';
 
-export class SelectedScript extends BaseEntity<string> {
+type SelectedScriptId = SelectedScript['id'];
+
+export class UserSelectedScript extends BaseEntity<SelectedScriptId> {
   constructor(
     public readonly script: IScript,
     public readonly revert: boolean,
   ) {
     super(script.id);
     if (revert && !script.canRevert()) {
-      throw new Error('cannot revert an irreversible script');
+      throw new Error(`The script with ID '${script.id}' is not reversible and cannot be reverted.`);
     }
   }
 }

src/application/Context/State/Selection/UserSelection.ts

@@ -1,167 +1,12 @@
-import { InMemoryRepository } from '@/infrastructure/Repository/InMemoryRepository';
-import { IScript } from '@/domain/IScript';
-import { EventSource } from '@/infrastructure/Events/EventSource';
-import { IRepository } from '@/infrastructure/Repository/IRepository';
-import { ICategory } from '@/domain/ICategory';
-import { ICategoryCollection } from '@/domain/ICategoryCollection';
-import { IUserSelection } from './IUserSelection';
-import { SelectedScript } from './SelectedScript';
+import { CategorySelection, ReadonlyCategorySelection } from './Category/CategorySelection';
+import { ReadonlyScriptSelection, ScriptSelection } from './Script/ScriptSelection';
 
-export class UserSelection implements IUserSelection {
-  public readonly changed = new EventSource<ReadonlyArray<SelectedScript>>();
-
-  private readonly scripts: IRepository<string, SelectedScript>;
-
-  constructor(
-    private readonly collection: ICategoryCollection,
-    selectedScripts: ReadonlyArray<SelectedScript>,
-  ) {
-    this.scripts = new InMemoryRepository<string, SelectedScript>();
-    for (const script of selectedScripts) {
-      this.scripts.addItem(script);
-    }
-  }
-
-  public areAllSelected(category: ICategory): boolean {
-    if (this.selectedScripts.length === 0) {
-      return false;
-    }
-    const scripts = category.getAllScriptsRecursively();
-    if (this.selectedScripts.length < scripts.length) {
-      return false;
-    }
-    return scripts.every(
-      (script) => this.selectedScripts.some((selected) => selected.id === script.id),
-    );
-  }
-
-  public isAnySelected(category: ICategory): boolean {
-    if (this.selectedScripts.length === 0) {
-      return false;
-    }
-    return this.selectedScripts.some((s) => category.includes(s.script));
-  }
-
-  public removeAllInCategory(categoryId: number): void {
-    const category = this.collection.findCategory(categoryId);
-    const scriptsToRemove = category.getAllScriptsRecursively()
-      .filter((script) => this.scripts.exists(script.id));
-    if (!scriptsToRemove.length) {
-      return;
-    }
-    for (const script of scriptsToRemove) {
-      this.scripts.removeItem(script.id);
-    }
-    this.changed.notify(this.scripts.getItems());
-  }
-
-  public addOrUpdateAllInCategory(categoryId: number, revert = false): void {
-    const scriptsToAddOrUpdate = this.collection
-      .findCategory(categoryId)
-      .getAllScriptsRecursively()
-      .filter(
-        (script) => !this.scripts.exists(script.id)
-          || this.scripts.getById(script.id).revert !== revert,
-      )
-      .map((script) => new SelectedScript(script, revert));
-    if (!scriptsToAddOrUpdate.length) {
-      return;
-    }
-    for (const script of scriptsToAddOrUpdate) {
-      this.scripts.addOrUpdateItem(script);
-    }
-    this.changed.notify(this.scripts.getItems());
-  }
-
-  public addSelectedScript(scriptId: string, revert: boolean): void {
-    const script = this.collection.findScript(scriptId);
-    if (!script) {
-      throw new Error(`Cannot add (id: ${scriptId}) as it is unknown`);
-    }
-    const selectedScript = new SelectedScript(script, revert);
-    this.scripts.addItem(selectedScript);
-    this.changed.notify(this.scripts.getItems());
-  }
-
-  public addOrUpdateSelectedScript(scriptId: string, revert: boolean): void {
-    const script = this.collection.findScript(scriptId);
-    const selectedScript = new SelectedScript(script, revert);
-    this.scripts.addOrUpdateItem(selectedScript);
-    this.changed.notify(this.scripts.getItems());
-  }
-
-  public removeSelectedScript(scriptId: string): void {
-    this.scripts.removeItem(scriptId);
-    this.changed.notify(this.scripts.getItems());
-  }
-
-  public isSelected(scriptId: string): boolean {
-    return this.scripts.exists(scriptId);
-  }
-
-  /** Get users scripts based on his/her selections */
-  public get selectedScripts(): ReadonlyArray<SelectedScript> {
-    return this.scripts.getItems();
-  }
-
-  public selectAll(): void {
-    const scriptsToSelect = this.collection
-      .getAllScripts()
-      .filter((script) => !this.scripts.exists(script.id))
-      .map((script) => new SelectedScript(script, false));
-    if (scriptsToSelect.length === 0) {
-      return;
-    }
-    for (const script of scriptsToSelect) {
-      this.scripts.addItem(script);
-    }
-    this.changed.notify(this.scripts.getItems());
-  }
-
-  public deselectAll(): void {
-    if (this.scripts.length === 0) {
-      return;
-    }
-    const selectedScriptIds = this.scripts.getItems().map((script) => script.id);
-    for (const scriptId of selectedScriptIds) {
-      this.scripts.removeItem(scriptId);
-    }
-    this.changed.notify([]);
-  }
-
-  public selectOnly(scripts: readonly IScript[]): void {
-    if (!scripts || scripts.length === 0) {
-      throw new Error('Scripts are empty. Use deselectAll() if you want to deselect everything');
-    }
-    let totalChanged = 0;
-    totalChanged += this.unselectMissingWithoutNotifying(scripts);
-    totalChanged += this.selectNewWithoutNotifying(scripts);
-    if (totalChanged > 0) {
-      this.changed.notify(this.scripts.getItems());
-    }
-  }
-
-  private unselectMissingWithoutNotifying(scripts: readonly IScript[]): number {
-    if (this.scripts.length === 0 || scripts.length === 0) {
-      return 0;
-    }
-    const existingItems = this.scripts.getItems();
-    const missingIds = existingItems
-      .filter((existing) => !scripts.some((script) => existing.id === script.id))
-      .map((script) => script.id);
-    for (const id of missingIds) {
-      this.scripts.removeItem(id);
-    }
-    return missingIds.length;
-  }
-
-  private selectNewWithoutNotifying(scripts: readonly IScript[]): number {
-    const unselectedScripts = scripts
-      .filter((script) => !this.scripts.exists(script.id))
-      .map((script) => new SelectedScript(script, false));
-    for (const newScript of unselectedScripts) {
-      this.scripts.addItem(newScript);
-    }
-    return unselectedScripts.length;
-  }
+export interface ReadonlyUserSelection {
+  readonly categories: ReadonlyCategorySelection;
+  readonly scripts: ReadonlyScriptSelection;
+}
+
+export interface UserSelection extends ReadonlyUserSelection {
+  readonly categories: CategorySelection;
+  readonly scripts: ScriptSelection;
 }

src/application/Context/State/Selection/UserSelectionFacade.ts

@@ -0,0 +1,39 @@
+import { ICategoryCollection } from '@/domain/ICategoryCollection';
+import { CategorySelection } from './Category/CategorySelection';
+import { ScriptToCategorySelectionMapper } from './Category/ScriptToCategorySelectionMapper';
+import { DebouncedScriptSelection } from './Script/DebouncedScriptSelection';
+import { ScriptSelection } from './Script/ScriptSelection';
+import { UserSelection } from './UserSelection';
+import { SelectedScript } from './Script/SelectedScript';
+
+export class UserSelectionFacade implements UserSelection {
+  public readonly categories: CategorySelection;
+
+  public readonly scripts: ScriptSelection;
+
+  constructor(
+    collection: ICategoryCollection,
+    selectedScripts: readonly SelectedScript[],
+    scriptsFactory = DefaultScriptsFactory,
+    categoriesFactory = DefaultCategoriesFactory,
+  ) {
+    this.scripts = scriptsFactory(collection, selectedScripts);
+    this.categories = categoriesFactory(this.scripts, collection);
+  }
+}
+
+export type ScriptsFactory = (
+  ...params: ConstructorParameters<typeof DebouncedScriptSelection>
+) => ScriptSelection;
+
+const DefaultScriptsFactory: ScriptsFactory = (
+  ...params
+) => new DebouncedScriptSelection(...params);
+
+export type CategoriesFactory = (
+  ...params: ConstructorParameters<typeof ScriptToCategorySelectionMapper>
+) => CategorySelection;
+
+const DefaultCategoriesFactory: CategoriesFactory = (
+  ...params
+) => new ScriptToCategorySelectionMapper(...params);

src/application/Parser/ApplicationParser.ts

@@ -32,10 +32,7 @@ const PreParsedCollections: readonly CollectionData [] = [
 ];
 
 function validateCollectionsData(collections: readonly CollectionData[]) {
-  if (!collections?.length) {
+  if (!collections.length) {
     throw new Error('missing collections');
   }
-  if (collections.some((collection) => !collection)) {
-    throw new Error('missing collection provided');
-  }
 }

src/application/Parser/CategoryCollectionParser.ts

@@ -28,10 +28,7 @@ export function parseCategoryCollection(
 }
 
 function validate(content: CollectionData): void {
-  if (!content) {
-    throw new Error('missing content');
-  }
-  if (!content.actions || content.actions.length <= 0) {
+  if (!content.actions.length) {
     throw new Error('content does not define any action');
   }
 }

src/application/Parser/CategoryParser.ts

@@ -1,5 +1,5 @@
 import type {
-  CategoryData, ScriptData, CategoryOrScriptData, InstructionHolder,
+  CategoryData, ScriptData, CategoryOrScriptData,
 } from '@/application/collections/';
 import { Script } from '@/domain/Script';
 import { Category } from '@/domain/Category';
@@ -16,7 +16,6 @@ export function parseCategory(
   context: ICategoryCollectionParseContext,
   factory: CategoryFactoryType = CategoryFactory,
 ): Category {
-  if (!context) { throw new Error('missing context'); }
   return parseCategoryRecursively({
     categoryData: category,
     context,
@@ -30,8 +29,8 @@ interface ICategoryParseContext {
   readonly factory: CategoryFactoryType,
   readonly parentCategory?: CategoryData,
 }
-// eslint-disable-next-line consistent-return
-function parseCategoryRecursively(context: ICategoryParseContext): Category {
+
+function parseCategoryRecursively(context: ICategoryParseContext): Category | never {
   ensureValidCategory(context.categoryData, context.parentCategory);
   const children: ICategoryChildren = {
     subCategories: new Array<Category>(),
@@ -55,7 +54,7 @@ function parseCategoryRecursively(context: ICategoryParseContext): Category {
       /* scripts: */ children.subScripts,
     );
   } catch (err) {
-    new NodeValidator({
+    return new NodeValidator({
       type: NodeType.Category,
       selfNode: context.categoryData,
       parentNode: context.parentCategory,
@@ -72,7 +71,7 @@ function ensureValidCategory(category: CategoryData, parentCategory?: CategoryDa
     .assertDefined(category)
     .assertValidName(category.category)
     .assert(
-      () => category.children && category.children.length > 0,
+      () => category.children.length > 0,
       `"${category.category}" has no children.`,
     );
 }
@@ -94,14 +93,14 @@ function parseNode(context: INodeParseContext) {
   validator.assertDefined(context.nodeData);
   if (isCategory(context.nodeData)) {
     const subCategory = parseCategoryRecursively({
-      categoryData: context.nodeData as CategoryData,
+      categoryData: context.nodeData,
       context: context.context,
       factory: context.factory,
       parentCategory: context.parent,
     });
     context.children.subCategories.push(subCategory);
   } else if (isScript(context.nodeData)) {
-    const script = parseScript(context.nodeData as ScriptData, context.context);
+    const script = parseScript(context.nodeData, context.context);
     context.children.subScripts.push(script);
   } else {
     validator.throw('Node is neither a category or a script.');
@@ -109,19 +108,18 @@ function parseNode(context: INodeParseContext) {
 }
 
 function isScript(data: CategoryOrScriptData): data is ScriptData {
-  const holder = (data as InstructionHolder);
-  return hasCode(holder) || hasCall(holder);
+  return hasCode(data) || hasCall(data);
 }
 
 function isCategory(data: CategoryOrScriptData): data is CategoryData {
   return hasProperty(data, 'category');
 }
 
-function hasCode(data: InstructionHolder): boolean {
+function hasCode(data: unknown): boolean {
   return hasProperty(data, 'code');
 }
 
-function hasCall(data: InstructionHolder) {
+function hasCall(data: unknown) {
   return hasProperty(data, 'call');
 }
 

src/application/Parser/DocumentationParser.ts

@@ -1,9 +1,6 @@
 import type { DocumentableData, DocumentationData } from '@/application/collections/';
 
 export function parseDocs(documentable: DocumentableData): readonly string[] {
-  if (!documentable) {
-    throw new Error('missing documentable');
-  }
   const { docs } = documentable;
   if (!docs) {
     return [];

src/application/Parser/NodeValidation/NodeValidator.ts

@@ -32,7 +32,7 @@ export class NodeValidator {
     return this;
   }
 
-  public throw(errorMessage: string) {
+  public throw(errorMessage: string): never {
     throw new NodeDataError(errorMessage, this.context);
   }
 }

src/application/Parser/Script/CategoryCollectionParseContext.ts

@@ -17,8 +17,7 @@ export class CategoryCollectionParseContext implements ICategoryCollectionParseC
     scripting: IScriptingDefinition,
     syntaxFactory: ISyntaxFactory = new SyntaxFactory(),
   ) {
-    if (!scripting) { throw new Error('missing scripting'); }
     this.syntax = syntaxFactory.create(scripting.language);
-    this.compiler = new ScriptCompiler(functionsData, this.syntax);
+    this.compiler = new ScriptCompiler(functionsData ?? [], this.syntax);
   }
 }

src/application/Parser/Script/Compiler/Expressions/Expression/Expression.ts

@@ -15,19 +15,10 @@ export class Expression implements IExpression {
     public readonly evaluator: ExpressionEvaluator,
     parameters?: IReadOnlyFunctionParameterCollection,
   ) {
-    if (!position) {
-      throw new Error('missing position');
-    }
-    if (!evaluator) {
-      throw new Error('missing evaluator');
-    }
     this.parameters = parameters ?? new FunctionParameterCollection();
   }
 
   public evaluate(context: IExpressionEvaluationContext): string {
-    if (!context) {
-      throw new Error('missing context');
-    }
     validateThatAllRequiredParametersAreSatisfied(this.parameters, context.args);
     const args = filterUnusedArguments(this.parameters, context.args);
     const filteredContext = new ExpressionEvaluationContext(args, context.pipelineCompiler);

src/application/Parser/Script/Compiler/Expressions/Expression/ExpressionEvaluationContext.ts

@@ -12,8 +12,5 @@ export class ExpressionEvaluationContext implements IExpressionEvaluationContext
     public readonly args: IReadOnlyFunctionCallArgumentCollection,
     public readonly pipelineCompiler: IPipelineCompiler = new PipelineCompiler(),
   ) {
-    if (!args) {
-      throw new Error('missing args, send empty collection instead.');
-    }
   }
 }

src/application/Parser/Script/Compiler/Expressions/Expression/ExpressionPositionFactory.ts

@@ -0,0 +1,16 @@
+import { ExpressionPosition } from './ExpressionPosition';
+
+export function createPositionFromRegexFullMatch(
+  match: RegExpMatchArray,
+): ExpressionPosition {
+  const startPos = match.index;
+  if (startPos === undefined) {
+    throw new Error(`Regex match did not yield any results: ${JSON.stringify(match)}`);
+  }
+  const fullMatch = match[0];
+  if (!fullMatch.length) {
+    throw new Error(`Regex match is empty: ${JSON.stringify(match)}`);
+  }
+  const endPos = startPos + fullMatch.length;
+  return new ExpressionPosition(startPos, endPos);
+}

src/application/Parser/Script/Compiler/Expressions/ExpressionsCompiler.ts

@@ -11,14 +11,11 @@ export class ExpressionsCompiler implements IExpressionsCompiler {
   ) { }
 
   public compileExpressions(
-    code: string | undefined,
+    code: string,
     args: IReadOnlyFunctionCallArgumentCollection,
   ): string {
-    if (!args) {
-      throw new Error('missing args, send empty collection instead.');
-    }
     if (!code) {
-      return code;
+      return '';
     }
     const context = new ExpressionEvaluationContext(args);
     const compiledCode = compileRecursively(code, context, this.extractor);
@@ -145,7 +142,7 @@ function ensureParamsUsedInCodeHasArgsProvided(
   providedArgs: IReadOnlyFunctionCallArgumentCollection,
 ): void {
   const usedParameterNames = extractRequiredParameterNames(expressions);
-  if (!usedParameterNames?.length) {
+  if (!usedParameterNames.length) {
     return;
   }
   const notProvidedParameters = usedParameterNames

src/application/Parser/Script/Compiler/Expressions/IExpressionsCompiler.ts

@@ -2,6 +2,7 @@ import { IReadOnlyFunctionCallArgumentCollection } from '../Function/Call/Argume
 
 export interface IExpressionsCompiler {
   compileExpressions(
-    code: string | undefined,
-    args: IReadOnlyFunctionCallArgumentCollection): string;
+    code: string,
+    args: IReadOnlyFunctionCallArgumentCollection,
+  ): string;
 }

src/application/Parser/Script/Compiler/Expressions/Parser/CompositeExpressionParser.ts

@@ -10,12 +10,9 @@ const Parsers = [
 
 export class CompositeExpressionParser implements IExpressionParser {
   public constructor(private readonly leafs: readonly IExpressionParser[] = Parsers) {
-    if (!leafs) {
+    if (!leafs.length) {
       throw new Error('missing leafs');
     }
-    if (leafs.some((leaf) => !leaf)) {
-      throw new Error('missing leaf');
-    }
   }
 
   public findExpressions(code: string): IExpression[] {

src/application/Parser/Script/Compiler/Expressions/Parser/Regex/RegexParser.ts

@@ -1,9 +1,9 @@
 import { IExpressionParser } from '../IExpressionParser';
-import { ExpressionPosition } from '../../Expression/ExpressionPosition';
 import { IExpression } from '../../Expression/IExpression';
 import { Expression, ExpressionEvaluator } from '../../Expression/Expression';
 import { IFunctionParameter } from '../../../Function/Parameter/IFunctionParameter';
 import { FunctionParameterCollection } from '../../../Function/Parameter/FunctionParameterCollection';
+import { createPositionFromRegexFullMatch } from '../../Expression/ExpressionPositionFactory';
 
 export abstract class RegexParser implements IExpressionParser {
   protected abstract readonly regex: RegExp;
@@ -21,7 +21,7 @@ export abstract class RegexParser implements IExpressionParser {
     const matches = code.matchAll(this.regex);
     for (const match of matches) {
       const primitiveExpression = this.buildExpression(match);
-      const position = this.doOrRethrow(() => createPosition(match), 'invalid script position', code);
+      const position = this.doOrRethrow(() => createPositionFromRegexFullMatch(match), 'invalid script position', code);
       const parameters = createParameters(primitiveExpression);
       const expression = new Expression(position, primitiveExpression.evaluator, parameters);
       yield expression;
@@ -37,12 +37,6 @@ export abstract class RegexParser implements IExpressionParser {
   }
 }
 
-function createPosition(match: RegExpMatchArray): ExpressionPosition {
-  const startPos = match.index;
-  const endPos = startPos + match[0].length;
-  return new ExpressionPosition(startPos, endPos);
-}
-
 function createParameters(
   expression: IPrimitiveExpression,
 ): FunctionParameterCollection {

src/application/Parser/Script/Compiler/Expressions/Pipes/PipeDefinitions/InlinePowerShell.ts

@@ -28,7 +28,7 @@ function hasLines(text: string) {
 */
 function inlineComments(code: string): string {
   const makeInlineComment = (comment: string) => {
-    const value = comment?.trim();
+    const value = comment.trim();
     if (!value) {
       return '<##>';
     }

src/application/Parser/Script/Compiler/Expressions/Pipes/PipeFactory.ts

@@ -15,12 +15,6 @@ export class PipeFactory implements IPipeFactory {
   private readonly pipes = new Map<string, IPipe>();
 
   constructor(pipes: readonly IPipe[] = RegisteredPipes) {
-    if (!pipes) {
-      throw new Error('missing pipes');
-    }
-    if (pipes.some((pipe) => !pipe)) {
-      throw new Error('missing pipe in list');
-    }
     for (const pipe of pipes) {
       this.registerPipe(pipe);
     }
@@ -28,10 +22,11 @@ export class PipeFactory implements IPipeFactory {
 
   public get(pipeName: string): IPipe {
     validatePipeName(pipeName);
-    if (!this.pipes.has(pipeName)) {
+    const pipe = this.pipes.get(pipeName);
+    if (!pipe) {
       throw new Error(`Unknown pipe: "${pipeName}"`);
     }
-    return this.pipes.get(pipeName);
+    return pipe;
   }
 
   private registerPipe(pipe: IPipe): void {

src/application/Parser/Script/Compiler/Expressions/SyntaxParsers/WithParser.ts

@@ -5,6 +5,7 @@ import { FunctionParameter } from '@/application/Parser/Script/Compiler/Function
 import { IExpression } from '../Expression/IExpression';
 import { ExpressionPosition } from '../Expression/ExpressionPosition';
 import { ExpressionRegexBuilder } from '../Parser/Regex/ExpressionRegexBuilder';
+import { createPositionFromRegexFullMatch } from '../Expression/ExpressionPositionFactory';
 
 export class WithParser implements IExpressionParser {
   public findExpressions(code: string): IExpression[] {
@@ -42,31 +43,25 @@ function parseAllWithExpressions(
     expressions.push({
       type: WithStatementType.Start,
       parameterName: match[1],
-      position: createPosition(match),
+      position: createPositionFromRegexFullMatch(match),
     });
   }
   for (const match of input.matchAll(WithStatementEndRegEx)) {
     expressions.push({
       type: WithStatementType.End,
-      position: createPosition(match),
+      position: createPositionFromRegexFullMatch(match),
     });
   }
   for (const match of input.matchAll(ContextVariableWithPipelineRegEx)) {
     expressions.push({
       type: WithStatementType.ContextVariable,
-      position: createPosition(match),
+      position: createPositionFromRegexFullMatch(match),
       pipeline: match[1],
     });
   }
   return expressions;
 }
 
-function createPosition(match: RegExpMatchArray): ExpressionPosition {
-  const startPos = match.index;
-  const endPos = startPos + match[0].length;
-  return new ExpressionPosition(startPos, endPos);
-}
-
 class WithStatementBuilder {
   private readonly contextVariables = new Array<{
     readonly positionInScope: ExpressionPosition;
@@ -125,7 +120,7 @@ class WithStatementBuilder {
 
   private substituteContextVariables(
     scope: string,
-    substituter: (pipeline: string) => string,
+    substituter: (pipeline?: string) => string,
   ): string {
     if (!this.contextVariables.length) {
       return scope;
@@ -157,7 +152,7 @@ function parseWithExpressions(input: string): IExpression[] {
     .sort((a, b) => b.position.start - a.position.start);
   const expressions = new Array<IExpression>();
   const builders = new Array<WithStatementBuilder>();
-  const throwWithContext = (message: string) => {
+  const throwWithContext = (message: string): never => {
     throw new Error(`${message}\n${buildErrorContext(input, allStatements)}}`);
   };
   while (sortedStatements.length > 0) {
@@ -178,12 +173,15 @@ function parseWithExpressions(input: string): IExpression[] {
         }
         builders[builders.length - 1].addContextVariable(statement.position, statement.pipeline);
         break;
-      case WithStatementType.End:
-        if (builders.length === 0) {
+      case WithStatementType.End: {
+        const builder = builders.pop();
+        if (!builder) {
           throwWithContext('Redundant `end` statement, missing `with`?');
+          break;
         }
-        expressions.push(builders.pop().buildExpression(statement.position, input));
+        expressions.push(builder.buildExpression(statement.position, input));
         break;
+      }
     }
   }
   if (builders.length > 0) {

src/application/Parser/Script/Compiler/Function/Call/Argument/FunctionCallArgumentCollection.ts

@@ -5,9 +5,6 @@ export class FunctionCallArgumentCollection implements IFunctionCallArgumentColl
   private readonly arguments = new Map<string, IFunctionCallArgument>();
 
   public addArgument(argument: IFunctionCallArgument): void {
-    if (!argument) {
-      throw new Error('missing argument');
-    }
     if (this.hasArgument(argument.parameterName)) {
       throw new Error(`argument value for parameter ${argument.parameterName} is already provided`);
     }

src/application/Parser/Script/Compiler/Function/Call/Compiler/CodeSegmentJoin/NewlineCodeSegmentMerger.ts

@@ -3,18 +3,22 @@ import { CodeSegmentMerger } from './CodeSegmentMerger';
 
 export class NewlineCodeSegmentMerger implements CodeSegmentMerger {
   public mergeCodeParts(codeSegments: readonly CompiledCode[]): CompiledCode {
-    if (!codeSegments?.length) {
+    if (!codeSegments.length) {
       throw new Error('missing segments');
     }
     return {
       code: joinCodeParts(codeSegments.map((f) => f.code)),
-      revertCode: joinCodeParts(codeSegments.map((f) => f.revertCode)),
+      revertCode: joinCodeParts(
+        codeSegments
+          .map((f) => f.revertCode)
+          .filter((code): code is string => Boolean(code)),
+      ),
     };
   }
 }
 
 function joinCodeParts(codeSegments: readonly string[]): string {
   return codeSegments
-    .filter((segment) => segment?.length > 0)
+    .filter((segment) => segment.length > 0)
     .join('\n');
 }

src/application/Parser/Script/Compiler/Function/Call/Compiler/FunctionCallSequenceCompiler.ts

@@ -21,9 +21,7 @@ export class FunctionCallSequenceCompiler implements FunctionCallCompiler {
     calls: readonly FunctionCall[],
     functions: ISharedFunctionCollection,
   ): CompiledCode {
-    if (!functions) { throw new Error('missing functions'); }
-    if (!calls?.length) { throw new Error('missing calls'); }
-    if (calls.some((f) => !f)) { throw new Error('missing function call'); }
+    if (!calls.length) { throw new Error('missing calls'); }
     const context: FunctionCallCompilationContext = {
       allFunctions: functions,
       rootCallSequence: calls,

src/application/Parser/Script/Compiler/Function/Call/Compiler/SingleCall/Strategies/InlineFunctionCallCompiler.ts

@@ -1,6 +1,6 @@
 import { ExpressionsCompiler } from '@/application/Parser/Script/Compiler/Expressions/ExpressionsCompiler';
 import { IExpressionsCompiler } from '@/application/Parser/Script/Compiler/Expressions/IExpressionsCompiler';
-import { ISharedFunction } from '@/application/Parser/Script/Compiler/Function/ISharedFunction';
+import { FunctionBodyType, ISharedFunction } from '@/application/Parser/Script/Compiler/Function/ISharedFunction';
 import { FunctionCall } from '@/application/Parser/Script/Compiler/Function/Call/FunctionCall';
 import { CompiledCode } from '@/application/Parser/Script/Compiler/Function/Call/Compiler/CompiledCode';
 import { SingleCallCompilerStrategy } from '../SingleCallCompilerStrategy';
@@ -12,19 +12,33 @@ export class InlineFunctionCallCompiler implements SingleCallCompilerStrategy {
   }
 
   public canCompile(func: ISharedFunction): boolean {
-    return func.body.code !== undefined;
+    return func.body.type === FunctionBodyType.Code;
   }
 
   public compileFunction(
     calledFunction: ISharedFunction,
     callToFunction: FunctionCall,
   ): CompiledCode[] {
+    if (calledFunction.body.type !== FunctionBodyType.Code) {
+      throw new Error([
+        'Unexpected function body type.',
+        `\tExpected: "${FunctionBodyType[FunctionBodyType.Code]}"`,
+        `\tActual: "${FunctionBodyType[calledFunction.body.type]}"`,
+        'Function:',
+        `\t${JSON.stringify(callToFunction)}`,
+      ].join('\n'));
+    }
     const { code } = calledFunction.body;
     const { args } = callToFunction;
     return [
       {
         code: this.expressionsCompiler.compileExpressions(code.execute, args),
-        revertCode: this.expressionsCompiler.compileExpressions(code.revert, args),
+        revertCode: (() => {
+          if (!code.revert) {
+            return undefined;
+          }
+          return this.expressionsCompiler.compileExpressions(code.revert, args);
+        })(),
       },
     ];
   }

src/application/Parser/Script/Compiler/Function/Call/Compiler/SingleCall/Strategies/NestedFunctionCallCompiler.ts

@@ -1,4 +1,4 @@
-import { ISharedFunction } from '@/application/Parser/Script/Compiler/Function/ISharedFunction';
+import { CallFunctionBody, FunctionBodyType, ISharedFunction } from '@/application/Parser/Script/Compiler/Function/ISharedFunction';
 import { FunctionCall } from '@/application/Parser/Script/Compiler/Function/Call/FunctionCall';
 import { FunctionCallCompilationContext } from '@/application/Parser/Script/Compiler/Function/Call/Compiler/FunctionCallCompilationContext';
 import { CompiledCode } from '@/application/Parser/Script/Compiler/Function/Call/Compiler/CompiledCode';
@@ -13,7 +13,7 @@ export class NestedFunctionCallCompiler implements SingleCallCompilerStrategy {
   }
 
   public canCompile(func: ISharedFunction): boolean {
-    return func.body.calls !== undefined;
+    return func.body.type === FunctionBodyType.Calls;
   }
 
   public compileFunction(
@@ -21,7 +21,7 @@ export class NestedFunctionCallCompiler implements SingleCallCompilerStrategy {
     callToFunction: FunctionCall,
     context: FunctionCallCompilationContext,
   ): CompiledCode[] {
-    const nestedCalls = calledFunction.body.calls;
+    const nestedCalls = (calledFunction.body as CallFunctionBody).calls;
     return nestedCalls.map((nestedCall) => {
       try {
         const compiledParentCall = this.argumentCompiler

src/application/Parser/Script/Compiler/Function/Call/FunctionCallParser.ts

@@ -5,9 +5,6 @@ import { FunctionCallArgument } from './Argument/FunctionCallArgument';
 import { ParsedFunctionCall } from './ParsedFunctionCall';
 
 export function parseFunctionCalls(calls: FunctionCallsData): FunctionCall[] {
-  if (calls === undefined) {
-    throw new Error('missing call data');
-  }
   const sequence = getCallSequence(calls);
   return sequence.map((call) => parseFunctionCall(call));
 }
@@ -19,22 +16,21 @@ function getCallSequence(calls: FunctionCallsData): FunctionCallData[] {
   if (calls instanceof Array) {
     return calls as FunctionCallData[];
   }
-  return [calls as FunctionCallData];
+  const singleCall = calls;
+  return [singleCall];
 }
 
 function parseFunctionCall(call: FunctionCallData): FunctionCall {
-  if (!call) {
-    throw new Error('missing call data');
-  }
   const callArgs = parseArgs(call.parameters);
   return new ParsedFunctionCall(call.function, callArgs);
 }
 
 function parseArgs(
-  parameters: FunctionCallParametersData,
+  parameters: FunctionCallParametersData | undefined,
 ): FunctionCallArgumentCollection {
-  return Object.keys(parameters || {})
-    .map((parameterName) => new FunctionCallArgument(parameterName, parameters[parameterName]))
+  const parametersMap = parameters ?? {};
+  return Object.keys(parametersMap)
+    .map((parameterName) => new FunctionCallArgument(parameterName, parametersMap[parameterName]))
     .reduce((args, arg) => {
       args.addArgument(arg);
       return args;

src/application/Parser/Script/Compiler/Function/Call/ParsedFunctionCall.ts

@@ -9,8 +9,5 @@ export class ParsedFunctionCall implements FunctionCall {
     if (!functionName) {
       throw new Error('missing function name in function call');
     }
-    if (!args) {
-      throw new Error('missing args');
-    }
   }
 }

src/application/Parser/Script/Compiler/Function/ISharedFunction.ts

@@ -4,15 +4,21 @@ import { FunctionCall } from './Call/FunctionCall';
 export interface ISharedFunction {
   readonly name: string;
   readonly parameters: IReadOnlyFunctionParameterCollection;
-  readonly body: ISharedFunctionBody;
+  readonly body: SharedFunctionBody;
 }
 
-export interface ISharedFunctionBody {
-  readonly type: FunctionBodyType;
-  readonly code: IFunctionCode | undefined;
-  readonly calls: readonly FunctionCall[] | undefined;
+export interface CallFunctionBody {
+  readonly type: FunctionBodyType.Calls,
+  readonly calls: readonly FunctionCall[],
 }
 
+export interface CodeFunctionBody {
+  readonly type: FunctionBodyType.Code;
+  readonly code: IFunctionCode,
+}
+
+export type SharedFunctionBody = CallFunctionBody | CodeFunctionBody;
+
 export enum FunctionBodyType {
   Code,
   Calls,

src/application/Parser/Script/Compiler/Function/Parameter/FunctionParameterCollection.ts

@@ -18,9 +18,6 @@ export class FunctionParameterCollection implements IFunctionParameterCollection
   }
 
   private ensureValidParameter(parameter: IFunctionParameter) {
-    if (!parameter) {
-      throw new Error('missing parameter');
-    }
     if (this.includesName(parameter.name)) {
       throw new Error(`duplicate parameter name: "${parameter.name}"`);
     }

src/application/Parser/Script/Compiler/Function/SharedFunction.ts

@@ -1,7 +1,7 @@
 import { FunctionCall } from './Call/FunctionCall';
 
 import {
-  FunctionBodyType, IFunctionCode, ISharedFunction, ISharedFunctionBody,
+  FunctionBodyType, IFunctionCode, ISharedFunction, SharedFunctionBody,
 } from './ISharedFunction';
 import { IReadOnlyFunctionParameterCollection } from './Parameter/IFunctionParameterCollection';
 
@@ -10,7 +10,7 @@ export function createCallerFunction(
   parameters: IReadOnlyFunctionParameterCollection,
   callSequence: readonly FunctionCall[],
 ): ISharedFunction {
-  if (!callSequence || !callSequence.length) {
+  if (!callSequence.length) {
     throw new Error(`missing call sequence in function "${name}"`);
   }
   return new SharedFunction(name, parameters, callSequence, FunctionBodyType.Calls);
@@ -33,7 +33,7 @@ export function createFunctionWithInlineCode(
 }
 
 class SharedFunction implements ISharedFunction {
-  public readonly body: ISharedFunctionBody;
+  public readonly body: SharedFunctionBody;
 
   constructor(
     public readonly name: string,
@@ -42,11 +42,22 @@ class SharedFunction implements ISharedFunction {
     bodyType: FunctionBodyType,
   ) {
     if (!name) { throw new Error('missing function name'); }
-    if (!parameters) { throw new Error('missing parameters'); }
-    this.body = {
-      type: bodyType,
-      code: bodyType === FunctionBodyType.Code ? content as IFunctionCode : undefined,
-      calls: bodyType === FunctionBodyType.Calls ? content as readonly FunctionCall[] : undefined,
-    };
+
+    switch (bodyType) {
+      case FunctionBodyType.Code:
+        this.body = {
+          type: FunctionBodyType.Code,
+          code: content as IFunctionCode,
+        };
+        break;
+      case FunctionBodyType.Calls:
+        this.body = {
+          type: FunctionBodyType.Calls,
+          calls: content as readonly FunctionCall[],
+        };
+        break;
+      default:
+        throw new Error(`unknown body type: ${FunctionBodyType[bodyType]}`);
+    }
   }
 }

src/application/Parser/Script/Compiler/Function/SharedFunctionCollection.ts

@@ -5,7 +5,6 @@ export class SharedFunctionCollection implements ISharedFunctionCollection {
   private readonly functionsByName = new Map<string, ISharedFunction>();
 
   public addFunction(func: ISharedFunction): void {
-    if (!func) { throw new Error('missing function'); }
     if (this.has(func.name)) {
       throw new Error(`function with name ${func.name} already exists`);
     }

src/application/Parser/Script/Compiler/Function/SharedFunctionsParser.ts

@@ -1,4 +1,6 @@
-import type { FunctionData, InstructionHolder } from '@/application/collections/';
+import type {
+  FunctionData, CodeInstruction, CodeFunctionData, CallFunctionData, CallInstruction,
+} from '@/application/collections/';
 import { ILanguageSyntax } from '@/application/Parser/Script/Validation/Syntax/ILanguageSyntax';
 import { CodeValidator } from '@/application/Parser/Script/Validation/CodeValidator';
 import { NoEmptyLines } from '@/application/Parser/Script/Validation/Rules/NoEmptyLines';
@@ -23,9 +25,8 @@ export class SharedFunctionsParser implements ISharedFunctionsParser {
     functions: readonly FunctionData[],
     syntax: ILanguageSyntax,
   ): ISharedFunctionCollection {
-    if (!syntax) { throw new Error('missing syntax'); }
     const collection = new SharedFunctionCollection();
-    if (!functions || !functions.length) {
+    if (!functions.length) {
       return collection;
     }
     ensureValidFunctions(functions);
@@ -55,16 +56,18 @@ function parseFunction(
 }
 
 function validateCode(
-  data: FunctionData,
+  data: CodeFunctionData,
   syntax: ILanguageSyntax,
   validator: ICodeValidator,
 ): void {
-  [data.code, data.revertCode].forEach(
-    (code) => validator.throwIfInvalid(
-      code,
-      [new NoEmptyLines(), new NoDuplicatedLines(syntax)],
-    ),
-  );
+  [data.code, data.revertCode]
+    .filter((code): code is string => Boolean(code))
+    .forEach(
+      (code) => validator.throwIfInvalid(
+        code,
+        [new NoEmptyLines(), new NoDuplicatedLines(syntax)],
+      ),
+    );
 }
 
 function parseParameters(data: FunctionData): IReadOnlyFunctionParameterCollection {
@@ -85,19 +88,18 @@ function parseParameters(data: FunctionData): IReadOnlyFunctionParameterCollecti
     }, new FunctionParameterCollection());
 }
 
-function hasCode(data: FunctionData): boolean {
-  return Boolean(data.code);
+function hasCode(data: FunctionData): data is CodeFunctionData {
+  return (data as CodeInstruction).code !== undefined;
 }
 
-function hasCall(data: FunctionData): boolean {
-  return Boolean(data.call);
+function hasCall(data: FunctionData): data is CallFunctionData {
+  return (data as CallInstruction).call !== undefined;
 }
 
 function ensureValidFunctions(functions: readonly FunctionData[]) {
-  ensureNoUndefinedItem(functions);
   ensureNoDuplicatesInFunctionNames(functions);
-  ensureNoDuplicateCode(functions);
   ensureEitherCallOrCodeIsDefined(functions);
+  ensureNoDuplicateCode(functions);
   ensureExpectedParametersType(functions);
 }
 
@@ -105,7 +107,7 @@ function printList(list: readonly string[]): string {
   return `"${list.join('","')}"`;
 }
 
-function ensureEitherCallOrCodeIsDefined(holders: readonly InstructionHolder[]) {
+function ensureEitherCallOrCodeIsDefined(holders: readonly FunctionData[]) {
   // Ensure functions do not define both call and code
   const withBothCallAndCode = holders.filter((holder) => hasCode(holder) && hasCall(holder));
   if (withBothCallAndCode.length) {
@@ -132,7 +134,7 @@ function isArrayOfObjects(value: unknown): boolean {
     && value.every((item) => typeof item === 'object');
 }
 
-function printNames(holders: readonly InstructionHolder[]) {
+function printNames(holders: readonly FunctionData[]) {
   return printList(holders.map((holder) => holder.name));
 }
 
@@ -144,22 +146,19 @@ function ensureNoDuplicatesInFunctionNames(functions: readonly FunctionData[]) {
   }
 }
 
-function ensureNoUndefinedItem(functions: readonly FunctionData[]) {
-  if (functions.some((func) => !func)) {
-    throw new Error('some functions are undefined');
-  }
-}
-
 function ensureNoDuplicateCode(functions: readonly FunctionData[]) {
-  const duplicateCodes = getDuplicates(functions
+  const callFunctions = functions
+    .filter((func) => hasCode(func))
+    .map((func) => func as CodeFunctionData);
+  const duplicateCodes = getDuplicates(callFunctions
     .map((func) => func.code)
     .filter((code) => code));
   if (duplicateCodes.length > 0) {
     throw new Error(`duplicate "code" in functions: ${printList(duplicateCodes)}`);
   }
-  const duplicateRevertCodes = getDuplicates(functions
-    .filter((func) => func.revertCode)
-    .map((func) => func.revertCode));
+  const duplicateRevertCodes = getDuplicates(callFunctions
+    .map((func) => func.revertCode)
+    .filter((code): code is string => Boolean(code)));
   if (duplicateRevertCodes.length > 0) {
     throw new Error(`duplicate "revertCode" in functions: ${printList(duplicateRevertCodes)}`);
   }

src/application/Parser/Script/Compiler/ScriptCompiler.ts

@@ -1,4 +1,4 @@
-import type { FunctionData, ScriptData } from '@/application/collections/';
+import type { FunctionData, ScriptData, CallInstruction } from '@/application/collections/';
 import { IScriptCode } from '@/domain/IScriptCode';
 import { ScriptCode } from '@/domain/ScriptCode';
 import { ILanguageSyntax } from '@/application/Parser/Script/Validation/Syntax/ILanguageSyntax';
@@ -18,27 +18,24 @@ export class ScriptCompiler implements IScriptCompiler {
   private readonly functions: ISharedFunctionCollection;
 
   constructor(
-    functions: readonly FunctionData[] | undefined,
+    functions: readonly FunctionData[],
     syntax: ILanguageSyntax,
     sharedFunctionsParser: ISharedFunctionsParser = SharedFunctionsParser.instance,
     private readonly callCompiler: FunctionCallCompiler = FunctionCallSequenceCompiler.instance,
     private readonly codeValidator: ICodeValidator = CodeValidator.instance,
   ) {
-    if (!syntax) { throw new Error('missing syntax'); }
     this.functions = sharedFunctionsParser.parseFunctions(functions, syntax);
   }
 
   public canCompile(script: ScriptData): boolean {
-    if (!script) { throw new Error('missing script'); }
-    if (!script.call) {
-      return false;
-    }
-    return true;
+    return hasCall(script);
   }
 
   public compile(script: ScriptData): IScriptCode {
-    if (!script) { throw new Error('missing script'); }
     try {
+      if (!hasCall(script)) {
+        throw new Error('Script does include any calls.');
+      }
       const calls = parseFunctionCalls(script.call);
       const compiledCode = this.callCompiler.compileFunctionCalls(calls, this.functions);
       validateCompiledCode(compiledCode, this.codeValidator);
@@ -53,7 +50,17 @@ export class ScriptCompiler implements IScriptCompiler {
 }
 
 function validateCompiledCode(compiledCode: CompiledCode, validator: ICodeValidator): void {
-  [compiledCode.code, compiledCode.revertCode].forEach(
-    (code) => validator.throwIfInvalid(code, [new NoEmptyLines()]),
-  );
+  [compiledCode.code, compiledCode.revertCode]
+    .filter((code): code is string => Boolean(code))
+    .map((code) => code as string)
+    .forEach(
+      (code) => validator.throwIfInvalid(
+        code,
+        [new NoEmptyLines()],
+      ),
+    );
+}
+
+function hasCall(data: ScriptData): data is ScriptData & CallInstruction {
+  return (data as CallInstruction).call !== undefined;
 }

src/application/Parser/Script/ScriptParser.ts

@@ -1,4 +1,4 @@
-import type { ScriptData } from '@/application/collections/';
+import type { ScriptData, CodeScriptData, CallScriptData } from '@/application/collections/';
 import { NoEmptyLines } from '@/application/Parser/Script/Validation/Rules/NoEmptyLines';
 import { ILanguageSyntax } from '@/application/Parser/Script/Validation/Syntax/ILanguageSyntax';
 import { Script } from '@/domain/Script';
@@ -14,7 +14,6 @@ import { ICategoryCollectionParseContext } from './ICategoryCollectionParseConte
 import { CodeValidator } from './Validation/CodeValidator';
 import { NoDuplicatedLines } from './Validation/Rules/NoDuplicatedLines';
 
-// eslint-disable-next-line consistent-return
 export function parseScript(
   data: ScriptData,
   context: ICategoryCollectionParseContext,
@@ -24,7 +23,6 @@ export function parseScript(
 ): Script {
   const validator = new NodeValidator({ type: NodeType.Script, selfNode: data });
   validateScript(data, validator);
-  if (!context) { throw new Error('missing context'); }
   try {
     const script = scriptFactory(
       /* name: */ data.name,
@@ -34,12 +32,12 @@ export function parseScript(
     );
     return script;
   } catch (err) {
-    validator.throw(err.message);
+    return validator.throw(err.message);
   }
 }
 
 function parseLevel(
-  level: string,
+  level: string | undefined,
   parser: IEnumParser<RecommendationLevel>,
 ): RecommendationLevel | undefined {
   if (!level) {
@@ -56,39 +54,45 @@ function parseCode(
   if (context.compiler.canCompile(script)) {
     return context.compiler.compile(script);
   }
-  const code = new ScriptCode(script.code, script.revertCode);
+  const codeScript = script as CodeScriptData; // Must be inline code if it cannot be compiled
+  const code = new ScriptCode(codeScript.code, codeScript.revertCode);
   validateHardcodedCodeWithoutCalls(code, codeValidator, context.syntax);
   return code;
 }
 
 function validateHardcodedCodeWithoutCalls(
   scriptCode: ScriptCode,
-  codeValidator: ICodeValidator,
+  validator: ICodeValidator,
   syntax: ILanguageSyntax,
 ) {
-  [scriptCode.execute, scriptCode.revert].forEach(
-    (code) => codeValidator.throwIfInvalid(
-      code,
-      [new NoEmptyLines(), new NoDuplicatedLines(syntax)],
-    ),
-  );
+  [scriptCode.execute, scriptCode.revert]
+    .filter((code): code is string => Boolean(code))
+    .forEach(
+      (code) => validator.throwIfInvalid(
+        code,
+        [new NoEmptyLines(), new NoDuplicatedLines(syntax)],
+      ),
+    );
 }
 
-function validateScript(script: ScriptData, validator: NodeValidator) {
+function validateScript(
+  script: ScriptData,
+  validator: NodeValidator,
+): asserts script is NonNullable<ScriptData> {
   validator
     .assertDefined(script)
     .assertValidName(script.name)
     .assert(
-      () => Boolean(script.code || script.call),
-      'Must define either "call" or "code".',
+      () => Boolean((script as CodeScriptData).code || (script as CallScriptData).call),
+      'Neither "call" or "code" is defined.',
     )
     .assert(
-      () => !(script.code && script.call),
-      'Cannot define both "call" and "code".',
+      () => !((script as CodeScriptData).code && (script as CallScriptData).call),
+      'Both "call" and "code" are defined.',
     )
     .assert(
-      () => !(script.revertCode && script.call),
-      'Cannot define "revertCode" if "call" is defined.',
+      () => !((script as CodeScriptData).revertCode && (script as CallScriptData).call),
+      'Both "call" and "revertCode" are defined.',
     );
 }
 

src/application/Parser/Script/Validation/CodeValidator.ts

@@ -9,7 +9,7 @@ export class CodeValidator implements ICodeValidator {
     code: string,
     rules: readonly ICodeValidationRule[],
   ): void {
-    if (!rules || rules.length === 0) { throw new Error('missing rules'); }
+    if (rules.length === 0) { throw new Error('missing rules'); }
     if (!code) {
       return;
     }

src/application/Parser/Script/Validation/Rules/NoDuplicatedLines.ts

@@ -3,9 +3,7 @@ import { ICodeLine } from '../ICodeLine';
 import { ICodeValidationRule, IInvalidCodeLine } from '../ICodeValidationRule';
 
 export class NoDuplicatedLines implements ICodeValidationRule {
-  constructor(private readonly syntax: ILanguageSyntax) {
-    if (!syntax) { throw new Error('missing syntax'); }
-  }
+  constructor(private readonly syntax: ILanguageSyntax) { }
 
   public analyze(lines: readonly ICodeLine[]): IInvalidCodeLine[] {
     return lines

src/application/Parser/ScriptingDefinition/CodeSubstituter.ts

@@ -17,7 +17,6 @@ export class CodeSubstituter implements ICodeSubstituter {
 
   public substitute(code: string, info: IProjectInformation): string {
     if (!code) { throw new Error('missing code'); }
-    if (!info) { throw new Error('missing info'); }
     const args = new FunctionCallArgumentCollection();
     const substitute = (name: string, value: string) => args
       .addArgument(new FunctionCallArgument(name, value));

src/application/Parser/ScriptingDefinition/ScriptingDefinitionParser.ts

@@ -18,8 +18,6 @@ export class ScriptingDefinitionParser {
     definition: ScriptingDefinitionData,
     info: IProjectInformation,
   ): IScriptingDefinition {
-    if (!info) { throw new Error('missing info'); }
-    if (!definition) { throw new Error('missing definition'); }
     const language = this.languageParser.parseEnum(definition.language, 'language');
     const startCode = this.codeSubstituter.substitute(definition.startCode, info);
     const endCode = this.codeSubstituter.substitute(definition.endCode, info);

src/application/Repository/Repository.ts

@@ -0,0 +1,17 @@
+import { IEntity } from '@/infrastructure/Entity/IEntity';
+
+export interface ReadonlyRepository<TKey, TEntity extends IEntity<TKey>> {
+  readonly length: number;
+  getItems(predicate?: (entity: TEntity) => boolean): readonly TEntity[];
+  getById(id: TKey): TEntity;
+  exists(id: TKey): boolean;
+}
+
+export interface MutableRepository<TKey, TEntity extends IEntity<TKey>> {
+  addItem(item: TEntity): void;
+  addOrUpdateItem(item: TEntity): void;
+  removeItem(id: TKey): void;
+}
+
+export interface Repository<TKey, TEntity extends IEntity<TKey>>
+  extends ReadonlyRepository<TKey, TEntity>, MutableRepository<TKey, TEntity> { }

src/application/collections/collection.yaml.d.ts

@@ -12,29 +12,38 @@ declare module '@/application/collections/*' {
   }
 
   export type CategoryOrScriptData = CategoryData | ScriptData;
-  export type DocumentationData = ReadonlyArray<string> | string;
+  export type DocumentationData = ReadonlyArray<string> | string | undefined;
 
   export interface DocumentableData {
     readonly docs?: DocumentationData;
   }
 
-  export interface InstructionHolder {
-    readonly name: string;
-
-    readonly code?: string;
+  export interface CodeInstruction {
+    readonly code: string;
     readonly revertCode?: string;
-
-    readonly call?: FunctionCallsData;
   }
 
+  export interface CallInstruction {
+    readonly call: FunctionCallsData;
+  }
+
+  export type InstructionHolder = CodeInstruction | CallInstruction;
+
   export interface ParameterDefinitionData {
     readonly name: string;
     readonly optional?: boolean;
   }
 
-  export interface FunctionData extends InstructionHolder {
+  export type FunctionDefinition = {
+    readonly name: string;
     readonly parameters?: readonly ParameterDefinitionData[];
-  }
+  };
+
+  export type CodeFunctionData = FunctionDefinition & CodeInstruction;
+
+  export type CallFunctionData = FunctionDefinition & CallInstruction;
+
+  export type FunctionData = CodeFunctionData | CallFunctionData;
 
   export interface FunctionCallParametersData {
     readonly [index: string]: string;
@@ -47,10 +56,16 @@ declare module '@/application/collections/*' {
 
   export type FunctionCallsData = readonly FunctionCallData[] | FunctionCallData | undefined;
 
-  export interface ScriptData extends InstructionHolder, DocumentableData {
+  export type ScriptDefinition = DocumentableData & {
     readonly name: string;
     readonly recommend?: string;
-  }
+  };
+
+  export type CodeScriptData = ScriptDefinition & CodeInstruction;
+
+  export type CallScriptData = ScriptDefinition & CallInstruction;
+
+  export type ScriptData = CodeScriptData | CallScriptData;
 
   export interface ScriptingDefinitionData {
     readonly language: string;

src/application/collections/linux.yaml

@@ -3739,7 +3739,7 @@ functions:
       - name: prefName
       - name: jsonValue
     docs: |-
-      This script either creates or updates the `user.js` file to set specific Mozilla Firefox preferences.
+      This script modifies the `user.js` file in Firefox profiles to set specific preferences.
 
       The `user.js` file can be found in a Firefox profile folder [1] and its location depends on the type of installation:
 
@@ -3747,12 +3747,18 @@ functions:
       - Flatpak: `~/.var/app/org.mozilla.firefox/.mozilla/firefox/<profile-name>/user.js`
       - Snap: `~/snap/firefox/common/.mozilla/firefox/<profile-name>/user.js`
 
-      While the `user.js` file is optional [2], if it's present, the Firefox application will prioritize its settings over
-      those in `prefs.js` upon startup [1][2]. To prevent potential profile corruption, Mozilla advises against editing
-      `prefs.js` directly [2].
+      While the `user.js` file is optional [2], if it's present, the Firefox will prioritize its settings over
+      those in `prefs.js` upon startup [1] [2]. It's recommended not to directly edit `prefs.js` to avoid profile corruption [2].
+
+      When `user.js` is modified or deleted, corresponding changes in `prefs.js` are necessary for reversion, as Firefox
+      doesn't automatically revert these changes [3].
+
+      This script safely modifies `user.js` and ensures changes are reflected in `prefs.js` during reversion, addressing
+      issues with preference persistence [3].
 
       [1]: https://web.archive.org/web/20230811005205/https://kb.mozillazine.org/User.js_file "User.js file - MozillaZine Knowledge Base"
       [2]: https://web.archive.org/web/20221029211757/https://kb.mozillazine.org/Prefs.js_file "Prefs.js file - MozillaZine Knowledge Base"
+      [3]: https://github.com/undergroundwires/privacy.sexy/issues/282 "[BUG]: Reverting Firefox settings do not work on Linux · Issue #282 · undergroundwires/privacy.sexy | github.com"
     code: |-
       pref_name='{{ $prefName }}'
       pref_value='{{ $jsonValue }}'
@@ -3792,12 +3798,16 @@ functions:
       if [ "$total_profiles_found" -eq 0 ]; then
         echo 'No profile folders are found, no changes are made.'
       else
-        echo "Preferences verified in $total_profiles_found profiles."
+        echo "Successfully verified preferences in $total_profiles_found profiles."
       fi
     revertCode: |-
       pref_name='{{ $prefName }}'
       pref_value='{{ $jsonValue }}'
       echo "Reverting preference: \"$pref_name\" to its default."
+      if command -v 'ps' &> /dev/null && ps aux | grep -i "[f]irefox" > /dev/null; then
+        >&2 echo -e "\e[33mWarning: Firefox is currently running. Please close Firefox before executing the revert script to ensure changes are applied effectively.\e[0m"
+      fi
+      declare -a files_to_modify=('prefs.js' 'user.js')
       declare -a profile_paths=(
         ~/.mozilla/firefox/*/
         ~/.var/app/org.mozilla.firefox/.mozilla/firefox/*/
@@ -3805,31 +3815,39 @@ functions:
       )
       declare -i total_profiles_found=0
       for profile_dir in "${profile_paths[@]}"; do
-        user_js_file="${profile_dir}user.js"
-        if [ ! -f "$user_js_file" ]; then
+        if [ ! -d "$profile_dir" ]; then
           continue
         fi
-        ((total_profiles_found++))
-        echo "$user_js_file:"
-        pref_start="user_pref(\"$pref_name\","
-        pref_line="user_pref(\"$pref_name\", $pref_value);"
-        if ! grep --quiet "^$pref_start" "${user_js_file}"; then
-          echo $'\t''Skipping, preference was not configured before.'
-        elif grep --quiet "^$pref_line$" "${user_js_file}"; then
-          sed --in-place "/^$pref_line/d" "$user_js_file"
-          echo $'\t''Successfully reverted preference to default.'
-          if ! grep --quiet '[^[:space:]]' "$user_js_file"; then
-            rm "$user_js_file"
-            echo $'\t''Removed user.js file as it became empty.'
-          fi
-        else
-          echo $'\t''Skipping, the preference has value that is not configured by privacy.sexy.'
+        if [[ ! "$(basename "$profile_dir")" =~ ^[a-z0-9]{8}\..+ ]]; then
+          continue # Not a profile folder
         fi
+        ((total_profiles_found++))
+        for file_to_modify in "${files_to_modify[@]}"; do
+          config_file_path="${profile_dir}${file_to_modify}"
+          if [ ! -f "$config_file_path" ]; then
+            continue
+          fi
+          echo "$config_file_path:"
+          pref_start="user_pref(\"$pref_name\","
+          pref_line="user_pref(\"$pref_name\", $pref_value);"
+          if ! grep --quiet "^$pref_start" "${config_file_path}"; then
+            echo $'\t''Skipping, preference was not configured before.'
+          elif grep --quiet "^$pref_line$" "${config_file_path}"; then
+            sed --in-place "/^$pref_line/d" "$config_file_path"
+            echo $'\t''Successfully reverted preference to default.'
+            if ! grep --quiet '[^[:space:]]' "$config_file_path"; then
+              rm "$config_file_path"
+              echo $'\t'"Removed the file as it became empty."
+            fi
+          else
+            echo $'\t''Skipping, the preference has value that is not configured by privacy.sexy.'
+          fi
+        done
       done
       if [ "$total_profiles_found" -eq 0 ]; then
         echo 'No reversion was necessary.'
       else
-        echo "Preferences verified in $total_profiles_found profiles."
+        echo "Successfully verified preferences in $total_profiles_found profiles."
       fi
   -
     name: RenameFile

src/domain/Application.ts

@@ -8,7 +8,6 @@ export class Application implements IApplication {
     public info: IProjectInformation,
     public collections: readonly ICategoryCollection[],
   ) {
-    validateInformation(info);
     validateCollections(collections);
   }
 
@@ -16,19 +15,17 @@ export class Application implements IApplication {
     return this.collections.map((collection) => collection.os);
   }
 
-  public getCollection(operatingSystem: OperatingSystem): ICategoryCollection | undefined {
-    return this.collections.find((collection) => collection.os === operatingSystem);
-  }
-}
-
-function validateInformation(info: IProjectInformation) {
-  if (!info) {
-    throw new Error('missing project information');
+  public getCollection(operatingSystem: OperatingSystem): ICategoryCollection {
+    const collection = this.collections.find((c) => c.os === operatingSystem);
+    if (!collection) {
+      throw new Error(`Operating system "${OperatingSystem[operatingSystem]}" is not defined in application`);
+    }
+    return collection;
   }
 }
 
 function validateCollections(collections: readonly ICategoryCollection[]) {
-  if (!collections || !collections.length) {
+  if (!collections.length) {
     throw new Error('missing collections');
   }
   if (collections.filter((c) => !c).length > 0) {

src/domain/Category.ts

@@ -3,14 +3,14 @@ import { IScript } from './IScript';
 import { ICategory } from './ICategory';
 
 export class Category extends BaseEntity<number> implements ICategory {
-  private allSubScripts: ReadonlyArray<IScript> = undefined;
+  private allSubScripts?: ReadonlyArray<IScript> = undefined;
 
   constructor(
     id: number,
     public readonly name: string,
     public readonly docs: ReadonlyArray<string>,
-    public readonly subCategories?: ReadonlyArray<ICategory>,
-    public readonly scripts?: ReadonlyArray<IScript>,
+    public readonly subCategories: ReadonlyArray<ICategory>,
+    public readonly scripts: ReadonlyArray<IScript>,
   ) {
     super(id);
     validateCategory(this);
@@ -39,10 +39,7 @@ function validateCategory(category: ICategory) {
   if (!category.name) {
     throw new Error('missing name');
   }
-  if (
-    (!category.subCategories || category.subCategories.length === 0)
-      && (!category.scripts || category.scripts.length === 0)
-  ) {
+  if (category.subCategories.length === 0 && category.scripts.length === 0) {
     throw new Error('A category must have at least one sub-category or script');
   }
 }

src/domain/CategoryCollection.ts

@@ -19,9 +19,6 @@ export class CategoryCollection implements ICategoryCollection {
     public readonly actions: ReadonlyArray<ICategory>,
     public readonly scripting: IScriptingDefinition,
   ) {
-    if (!scripting) {
-      throw new Error('missing scripting definition');
-    }
     this.queryable = makeQueryable(actions);
     assertInRange(os, OperatingSystem);
     ensureValid(this.queryable);
@@ -29,17 +26,26 @@ export class CategoryCollection implements ICategoryCollection {
     ensureNoDuplicates(this.queryable.allScripts);
   }
 
-  public findCategory(categoryId: number): ICategory | undefined {
-    return this.queryable.allCategories.find((category) => category.id === categoryId);
+  public getCategory(categoryId: number): ICategory {
+    const category = this.queryable.allCategories.find((c) => c.id === categoryId);
+    if (!category) {
+      throw new Error(`Missing category with ID: "${categoryId}"`);
+    }
+    return category;
   }
 
   public getScriptsByLevel(level: RecommendationLevel): readonly IScript[] {
     assertInRange(level, RecommendationLevel);
-    return this.queryable.scriptsByLevel.get(level);
+    const scripts = this.queryable.scriptsByLevel.get(level);
+    return scripts ?? [];
   }
 
-  public findScript(scriptId: string): IScript | undefined {
-    return this.queryable.allScripts.find((script) => script.id === scriptId);
+  public getScript(scriptId: string): IScript {
+    const script = this.queryable.allScripts.find((s) => s.id === scriptId);
+    if (!script) {
+      throw new Error(`missing script: ${scriptId}`);
+    }
+    return script;
   }
 
   public getAllScripts(): IScript[] {
@@ -78,13 +84,13 @@ function ensureValid(application: IQueryableCollection) {
 }
 
 function ensureValidCategories(allCategories: readonly ICategory[]) {
-  if (!allCategories || allCategories.length === 0) {
+  if (!allCategories.length) {
     throw new Error('must consist of at least one category');
   }
 }
 
 function ensureValidScripts(allScripts: readonly IScript[]) {
-  if (!allScripts || allScripts.length === 0) {
+  if (!allScripts.length) {
     throw new Error('must consist of at least one script');
   }
   const missingRecommendationLevels = getEnumValues(RecommendationLevel)

src/domain/IApplication.ts

@@ -7,5 +7,5 @@ export interface IApplication {
   readonly collections: readonly ICategoryCollection[];
 
   getSupportedOsList(): OperatingSystem[];
-  getCollection(operatingSystem: OperatingSystem): ICategoryCollection | undefined;
+  getCollection(operatingSystem: OperatingSystem): ICategoryCollection;
 }

src/domain/ICategory.ts

@@ -5,8 +5,8 @@ import { IDocumentable } from './IDocumentable';
 export interface ICategory extends IEntity<number>, IDocumentable {
   readonly id: number;
   readonly name: string;
-  readonly subCategories?: ReadonlyArray<ICategory>;
-  readonly scripts?: ReadonlyArray<IScript>;
+  readonly subCategories: ReadonlyArray<ICategory>;
+  readonly scripts: ReadonlyArray<IScript>;
   includes(script: IScript): boolean;
   getAllScriptsRecursively(): ReadonlyArray<IScript>;
 }

src/domain/ICategoryCollection.ts

@@ -12,8 +12,8 @@ export interface ICategoryCollection {
   readonly actions: ReadonlyArray<ICategory>;
 
   getScriptsByLevel(level: RecommendationLevel): ReadonlyArray<IScript>;
-  findCategory(categoryId: number): ICategory | undefined;
-  findScript(scriptId: string): IScript | undefined;
+  getCategory(categoryId: number): ICategory;
+  getScript(scriptId: string): IScript;
   getAllScripts(): ReadonlyArray<IScript>;
   getAllCategories(): ReadonlyArray<ICategory>;
 }

src/domain/IScriptCode.ts

@@ -1,4 +1,4 @@
 export interface IScriptCode {
   readonly execute: string;
-  readonly revert: string;
+  readonly revert?: string;
 }

src/domain/ProjectInformation.ts

@@ -16,9 +16,6 @@ export class ProjectInformation implements IProjectInformation {
     if (!name) {
       throw new Error('name is undefined');
     }
-    if (!version) {
-      throw new Error('undefined version');
-    }
     if (!slogan) {
       throw new Error('undefined slogan');
     }

src/domain/Script.ts

@@ -11,9 +11,6 @@ export class Script extends BaseEntity<string> implements IScript {
     public readonly level?: RecommendationLevel,
   ) {
     super(name);
-    if (!code) {
-      throw new Error('missing code');
-    }
     validateLevel(level);
   }
 

src/domain/ScriptCode.ts

@@ -3,14 +3,14 @@ import { IScriptCode } from './IScriptCode';
 export class ScriptCode implements IScriptCode {
   constructor(
     public readonly execute: string,
-    public readonly revert: string,
+    public readonly revert: string | undefined,
   ) {
     validateCode(execute);
     validateRevertCode(revert, execute);
   }
 }
 
-function validateRevertCode(revertCode: string, execute: string) {
+function validateRevertCode(revertCode: string | undefined, execute: string) {
   if (!revertCode) {
     return;
   }
@@ -25,7 +25,7 @@ function validateRevertCode(revertCode: string, execute: string) {
 }
 
 function validateCode(code: string): void {
-  if (!code || code.length === 0) {
+  if (code.length === 0) {
     throw new Error('missing code');
   }
 }

src/infrastructure/CodeRunner.ts

@@ -6,14 +6,13 @@ export class CodeRunner {
   constructor(
     private readonly system = getWindowInjectedSystemOperations(),
     private readonly environment = RuntimeEnvironment.CurrentEnvironment,
-  ) {
-    if (!system) {
-      throw new Error('missing system operations');
-    }
-  }
+  ) { }
 
   public async runCode(code: string, folderName: string, fileExtension: string): Promise<void> {
     const { os } = this.environment;
+    if (os === undefined) {
+      throw new Error('Unidentified operating system');
+    }
     const dir = this.system.location.combinePaths(
       this.system.operatingSystem.getTempDirectory(),
       folderName,

src/infrastructure/EnvironmentVariables/EnvironmentVariablesValidator.ts

@@ -2,9 +2,6 @@ import { IEnvironmentVariables } from './IEnvironmentVariables';
 
 /* Validation is externalized to keep the environment objects simple */
 export function validateEnvironmentVariables(environment: IEnvironmentVariables): void {
-  if (!environment) {
-    throw new Error('missing environment');
-  }
   const keyValues = capturePropertyValues(environment);
   if (!Object.keys(keyValues).length) {
     throw new Error('Unable to capture key/value pairs');
@@ -30,7 +27,7 @@ function getKeysMissingValues(keyValuePairs: Record<string, unknown>): string[]
  * Necessary because code transformations can make class getters non-enumerable during bundling.
  * This ensures that even if getters are non-enumerable, their values are still captured and used.
  */
-function capturePropertyValues(instance: unknown): Record<string, unknown> {
+function capturePropertyValues(instance: object): Record<string, unknown> {
   const obj: Record<string, unknown> = {};
   const descriptors = Object.getOwnPropertyDescriptors(instance.constructor.prototype);
 

src/infrastructure/Events/EventSubscriptionCollection.ts

@@ -9,12 +9,9 @@ export class EventSubscriptionCollection implements IEventSubscriptionCollection
   }
 
   public register(subscriptions: IEventSubscription[]) {
-    if (!subscriptions || subscriptions.length === 0) {
+    if (subscriptions.length === 0) {
       throw new Error('missing subscriptions');
     }
-    if (subscriptions.some((subscription) => !subscription)) {
-      throw new Error('missing subscription in list');
-    }
     this.subscriptions.push(...subscriptions);
   }
 

src/infrastructure/Events/IEventSubscriptionCollection.ts

@@ -5,5 +5,5 @@ export interface IEventSubscriptionCollection {
 
   register(subscriptions: IEventSubscription[]): void;
   unsubscribeAll(): void;
-  unsubscribeAllAndRegister(subscriptions: IEventSubscription[]);
+  unsubscribeAllAndRegister(subscriptions: IEventSubscription[]): void;
 }

src/infrastructure/Log/ConsoleLogger.ts

@@ -1,13 +1,17 @@
 import { ILogger } from './ILogger';
 
 export class ConsoleLogger implements ILogger {
-  constructor(private readonly globalConsole: Partial<Console> = console) {
-    if (!globalConsole) {
+  constructor(private readonly consoleProxy: Partial<Console> = console) {
+    if (!consoleProxy) { // do not trust strictNullChecks for global objects
       throw new Error('missing console');
     }
   }
 
   public info(...params: unknown[]): void {
-    this.globalConsole.info(...params);
+    const logFunction = this.consoleProxy?.info;
+    if (!logFunction) {
+      throw new Error('missing "info" function');
+    }
+    logFunction.call(this.consoleProxy, ...params);
   }
 }

src/infrastructure/Log/ElectronLogger.ts

@@ -7,6 +7,11 @@ export function createElectronLogger(logger: Partial<ElectronLog>): ILogger {
     throw new Error('missing logger');
   }
   return {
-    info: (...params) => logger.info(...params),
+    info: (...params) => {
+      if (!logger.info) {
+        throw new Error('missing "info" function');
+      }
+      logger.info(...params);
+    },
   };
 }