import Foundation
import Network

/// Caches library data (albums, artists, playlists, songs) to disk for offline browsing.
/// Also monitors network connectivity.
class LibraryCache: ObservableObject {
    static let shared = LibraryCache()
    
    @Published var isOffline = false
    
    private let fileManager = FileManager.default
    private let cacheDir: URL
    private let monitor = NWPathMonitor()
    private let monitorQueue = DispatchQueue(label: "com.navidromeplayer.network")
    
    private init() {
        let caches = fileManager.urls(for: .cachesDirectory, in: .userDomainMask).first!
        cacheDir = caches.appendingPathComponent("LibraryCache", isDirectory: true)
        try? fileManager.createDirectory(at: cacheDir, withIntermediateDirectories: true)
        // Allow background access — prevents -54 sandbox errors
        try? (cacheDir as NSURL).setResourceValue(
            URLFileProtection.completeUntilFirstUserAuthentication,
            forKey: .fileProtectionKey
        )
        
        // Set file protection to allow background access — prevents -54 sandbox errors
        try? (cacheDir as NSURL).setResourceValue(
            URLFileProtection.completeUntilFirstUserAuthentication,
            forKey: .fileProtectionKey
        )
        
        // Monitor network status
        monitor.pathUpdateHandler = { [weak self] path in
            DispatchQueue.main.async {
                self?.isOffline = (path.status != .satisfied)
            }
        }
        monitor.start(queue: monitorQueue)
    }
    
    deinit {
        monitor.cancel()
    }
    
    // MARK: - Generic Cache Read/Write
    
    private func cacheURL(for key: String) -> URL {
        cacheDir.appendingPathComponent("\(key).json")
    }
    
    func save<T: Encodable>(_ data: T, key: String) {
        if let encoded = try? JSONEncoder().encode(data) {
            try? encoded.write(to: cacheURL(for: key), options: .atomic)
        }
    }
    
    func load<T: Decodable>(_ type: T.Type, key: String) -> T? {
        let url = cacheURL(for: key)
        guard let data = try? Data(contentsOf: url) else { return nil }
        return try? JSONDecoder().decode(type, from: data)
    }
    
    // MARK: - Typed Helpers
    
    func cacheAlbums(_ albums: [Album], key: String = "recent_albums") {
        save(albums, key: key)
    }
    func loadAlbums(key: String = "recent_albums") -> [Album]? {
        load([Album].self, key: key)
    }
    
    func cacheArtists(_ artists: [ArtistIndex]) {
        save(artists, key: "artists")
    }
    func loadArtists() -> [ArtistIndex]? {
        load([ArtistIndex].self, key: "artists")
    }
    
    func cachePlaylists(_ playlists: [Playlist]) {
        save(playlists, key: "playlists")
    }
    func loadPlaylists() -> [Playlist]? {
        load([Playlist].self, key: "playlists")
    }
    
    func cacheAlbumDetail(_ album: AlbumWithSongs) {
        save(album, key: "album_\(album.id)")
    }
    func loadAlbumDetail(id: String) -> AlbumWithSongs? {
        load(AlbumWithSongs.self, key: "album_\(id)")
    }
    
    func cacheArtistDetail(_ artist: ArtistWithAlbums) {
        save(artist, key: "artist_\(artist.id)")
    }
    func loadArtistDetail(id: String) -> ArtistWithAlbums? {
        load(ArtistWithAlbums.self, key: "artist_\(id)")
    }
    
    func cacheRadioStations(_ stations: [RadioStation]) {
        save(stations, key: "radio_stations")
    }
    func loadRadioStations() -> [RadioStation]? {
        load([RadioStation].self, key: "radio_stations")
    }
    
    // MARK: - Download Status Check
    
    /// Returns set of song IDs that are downloaded for offline playback
    func downloadedSongIds() -> Set<String> {
        let key = "offline_catalog"
        guard let data = UserDefaults.standard.data(forKey: key),
              let songs = try? JSONDecoder().decode([DownloadedSong].self, from: data) else {
            return []
        }
        return Set(songs.map { $0.id })
    }
    
    // MARK: - Clear
    
    func clearAll() {
        if let files = try? fileManager.contentsOfDirectory(at: cacheDir, includingPropertiesForKeys: nil) {
            for file in files { try? fileManager.removeItem(at: file) }
        }
    }
}