use std::{cmp::Reverse, collections::BTreeMap, path::PathBuf};

use tokio::fs;

use crate::adapters::AppInfo;

/// A platform-level cache of app metadata discovered from live devices.
#[derive(Debug, Clone, Default)]
pub struct AppCache {
    /// The normalized platform identifier for the cache file.
    pub platform: String,
    /// The apps currently known for that platform.
    pub apps: Vec<AppInfo>,
}

/// Persisted store for per-platform app cache files.
#[derive(Debug, Clone)]
pub struct AppCacheStore {
    root_dir: PathBuf,
}

impl AppCacheStore {
    /// Create a cache store rooted at the given directory.
    pub fn new(root_dir: PathBuf) -> Self {
        Self { root_dir }
    }

    /// Load the app cache for a single platform or return an empty cache when absent.
    pub async fn load_platform(&self, platform: &str) -> anyhow::Result<AppCache> {
        let path = self.platform_path(platform);
        let apps = match fs::read_to_string(&path).await {
            Ok(contents) => serde_json::from_str::<Vec<AppInfo>>(&contents)?,
            Err(error) if error.kind() == std::io::ErrorKind::NotFound => Vec::new(),
            Err(error) => return Err(error.into()),
        };

        Ok(AppCache {
            platform: platform.to_string(),
            apps,
        })
    }

    /// Persist the app list for a platform.
    pub async fn save_platform(&self, platform: &str, apps: &[AppInfo]) -> anyhow::Result<()> {
        fs::create_dir_all(&self.root_dir).await?;
        let contents = serde_json::to_string_pretty(apps)?;
        fs::write(self.platform_path(platform), contents).await?;
        Ok(())
    }

    /// Merge newly seen apps into the normalized, de-duplicated platform cache.
    pub async fn record_platform_apps(
        &self,
        platform: &str,
        apps: Vec<AppInfo>,
    ) -> anyhow::Result<AppCache> {
        let mut deduped = BTreeMap::new();
        for app in self.load_platform(platform).await?.apps {
            deduped.insert(app.platform_id.clone(), app);
        }
        for app in apps {
            deduped.insert(app.platform_id.clone(), app);
        }
        let apps: Vec<AppInfo> = deduped.into_values().collect();
        self.save_platform(platform, &apps).await?;
        Ok(AppCache {
            platform: platform.to_string(),
            apps,
        })
    }

    /// Resolve an app by case-insensitive name or exact ID from the persisted platform cache.
    pub async fn find_app(&self, platform: &str, query: &str) -> anyhow::Result<Option<AppInfo>> {
        let cache = self.load_platform(platform).await?;
        let normalized = normalize_query(query);

        if let Some(app) = cache.apps.iter().find(|app| {
            app.platform_id == query || app.id == query || normalize_query(&app.name) == normalized
        }) {
            return Ok(Some(app.clone()));
        }

        Ok(cache
            .apps
            .into_iter()
            .filter_map(|app| fuzzy_match_score(&normalized, &app).map(|score| (score, app)))
            .max_by_key(|(score, app)| (*score, Reverse(app.name.len())))
            .map(|(_, app)| app))
    }

    /// Remove the persisted app cache for a platform.
    pub async fn clear_platform(&self, platform: &str) -> anyhow::Result<()> {
        match fs::remove_file(self.platform_path(platform)).await {
            Ok(()) => Ok(()),
            Err(error) if error.kind() == std::io::ErrorKind::NotFound => Ok(()),
            Err(error) => Err(error.into()),
        }
    }

    fn platform_path(&self, platform: &str) -> PathBuf {
        self.root_dir.join(format!("{platform}.apps.json"))
    }
}

fn normalize_query(value: &str) -> String {
    value
        .chars()
        .filter(|character| character.is_ascii_alphanumeric())
        .flat_map(char::to_lowercase)
        .collect()
}

fn fuzzy_match_score(query: &str, app: &AppInfo) -> Option<u8> {
    if query.is_empty() {
        return None;
    }

    let name = normalize_query(&app.name);
    let id = normalize_query(&app.id);
    let platform_id = normalize_query(&app.platform_id);

    if name.starts_with(query) || id.starts_with(query) || platform_id.starts_with(query) {
        return Some(3);
    }
    if name.contains(query) || id.contains(query) || platform_id.contains(query) {
        return Some(2);
    }
    if is_subsequence(query, &name) {
        return Some(1);
    }

    None
}

fn is_subsequence(needle: &str, haystack: &str) -> bool {
    let mut needle_chars = needle.chars();
    let mut current = needle_chars.next();

    for hay in haystack.chars() {
        if current == Some(hay) {
            current = needle_chars.next();
            if current.is_none() {
                return true;
            }
        }
    }

    false
}

#[cfg(test)]
mod tests {
    use super::*;

    #[tokio::test]
    async fn cache_round_trips_and_resolves_names() {
        let temp_dir = tempfile::tempdir().expect("temp dir should exist");
        let store = AppCacheStore::new(temp_dir.path().join("cache"));
        let apps = vec![
            AppInfo {
                id: "12".to_string(),
                name: "Netflix".to_string(),
                version: None,
                platform_id: "12".to_string(),
            },
            AppInfo {
                id: "837".to_string(),
                name: "YouTube".to_string(),
                version: None,
                platform_id: "837".to_string(),
            },
        ];

        store
            .record_platform_apps("roku", apps.clone())
            .await
            .expect("apps should save");

        let loaded = store.load_platform("roku").await.expect("apps should load");
        assert_eq!(loaded.apps, apps);

        let resolved = store
            .find_app("roku", "youtube")
            .await
            .expect("app lookup should work")
            .expect("youtube should exist");
        assert_eq!(resolved.platform_id, "837");
    }

    #[tokio::test]
    async fn record_platform_apps_merges_existing_entries() {
        let temp_dir = tempfile::tempdir().expect("temp dir should exist");
        let store = AppCacheStore::new(temp_dir.path().join("cache"));

        store
            .record_platform_apps(
                "roku",
                vec![AppInfo {
                    id: "12".to_string(),
                    name: "Netflix".to_string(),
                    version: None,
                    platform_id: "12".to_string(),
                }],
            )
            .await
            .expect("first cache should save");
        store
            .record_platform_apps(
                "roku",
                vec![AppInfo {
                    id: "837".to_string(),
                    name: "YouTube".to_string(),
                    version: None,
                    platform_id: "837".to_string(),
                }],
            )
            .await
            .expect("second cache should merge");

        let loaded = store.load_platform("roku").await.expect("apps should load");
        assert_eq!(loaded.apps.len(), 2);
    }

    #[tokio::test]
    async fn clear_platform_removes_persisted_cache() {
        let temp_dir = tempfile::tempdir().expect("temp dir should exist");
        let store = AppCacheStore::new(temp_dir.path().join("cache"));

        store
            .save_platform(
                "roku",
                &[AppInfo {
                    id: "12".to_string(),
                    name: "Netflix".to_string(),
                    version: None,
                    platform_id: "12".to_string(),
                }],
            )
            .await
            .expect("apps should save");
        store
            .clear_platform("roku")
            .await
            .expect("cache should clear");

        let loaded = store.load_platform("roku").await.expect("apps should load");
        assert!(loaded.apps.is_empty());
    }

    #[tokio::test]
    async fn find_app_supports_fuzzy_name_matches() {
        let temp_dir = tempfile::tempdir().expect("temp dir should exist");
        let store = AppCacheStore::new(temp_dir.path().join("cache"));

        store
            .record_platform_apps(
                "roku",
                vec![
                    AppInfo {
                        id: "592369".to_string(),
                        name: "Jellyfin".to_string(),
                        version: None,
                        platform_id: "592369".to_string(),
                    },
                    AppInfo {
                        id: "12".to_string(),
                        name: "Netflix".to_string(),
                        version: None,
                        platform_id: "12".to_string(),
                    },
                ],
            )
            .await
            .expect("apps should save");

        let resolved = store
            .find_app("roku", "jelly")
            .await
            .expect("lookup should work")
            .expect("jellyfin should resolve");
        assert_eq!(resolved.name, "Jellyfin");
    }
}