Refactor text utilities and expand their usage

This commit refactors existing text utility functions into the
application layer for broad reuse and integrates them across
the codebase. Initially, these utilities were confined to test
code, which limited their application.

Changes:

- Move text utilities to the application layer.
- Centralize text utilities into dedicated files for better
  maintainability.
- Improve robustness of utility functions with added type checks.
- Replace duplicated logic with centralized utility functions
  throughout the codebase.
- Expand unit tests to cover refactored code parts.

src/application/Common/Text/FilterEmptyStrings.ts

@@ -0,0 +1,25 @@
+import { isArray } from '@/TypeHelpers';
+
+export type OptionalString = string | undefined | null;
+
+export function filterEmptyStrings(
+  texts: readonly OptionalString[],
+  isArrayType: typeof isArray = isArray,
+): string[] {
+  if (!isArrayType(texts)) {
+    throw new Error(`Invalid input: Expected an array, but received type ${typeof texts}.`);
+  }
+  assertArrayItemsAreStringLike(texts);
+  return texts
+    .filter((title): title is string => Boolean(title));
+}
+
+function assertArrayItemsAreStringLike(
+  texts: readonly unknown[],
+): asserts texts is readonly OptionalString[] {
+  const invalidItems = texts.filter((item) => !(typeof item === 'string' || item === undefined || item === null));
+  if (invalidItems.length > 0) {
+    const invalidTypes = invalidItems.map((item) => typeof item).join(', ');
+    throw new Error(`Invalid array items: Expected items as string, undefined, or null. Received invalid types: ${invalidTypes}.`);
+  }
+}

src/application/Common/Text/IndentText.ts

@@ -0,0 +1,29 @@
+import { isString } from '@/TypeHelpers';
+import { splitTextIntoLines } from './SplitTextIntoLines';
+
+export function indentText(
+  text: string,
+  indentLevel = 1,
+  utilities: TextIndentationUtilities = DefaultUtilities,
+): string {
+  if (!utilities.isStringType(text)) {
+    throw new Error(`Indentation error: The input must be a string. Received type: ${typeof text}.`);
+  }
+  if (indentLevel <= 0) {
+    throw new Error(`Indentation error: The indent level must be a positive integer. Received: ${indentLevel}.`);
+  }
+  const indentation = '\t'.repeat(indentLevel);
+  return utilities.splitIntoLines(text)
+    .map((line) => (line ? `${indentation}${line}` : line))
+    .join('\n');
+}
+
+interface TextIndentationUtilities {
+  readonly splitIntoLines: typeof splitTextIntoLines;
+  readonly isStringType: typeof isString;
+}
+
+const DefaultUtilities: TextIndentationUtilities = {
+  splitIntoLines: splitTextIntoLines,
+  isStringType: isString,
+};

src/application/Common/Text/SplitTextIntoLines.ts

@@ -0,0 +1,11 @@
+import { isString } from '@/TypeHelpers';
+
+export function splitTextIntoLines(
+  text: string,
+  isStringType = isString,
+): string[] {
+  if (!isStringType(text)) {
+    throw new Error(`Line splitting error: Expected a string but received type '${typeof text}'.`);
+  }
+  return text.split(/\r\n|\r|\n/);
+}