import { Database } from "bun:sqlite";
import { createHash } from "crypto";
import { watch, type FSWatcher } from "fs";
import { readdir, stat } from "fs/promises";
import { join, relative } from "path";
import { parseFile } from "music-metadata";
import { upsertTrack, type Track } from "./db";

const HASH_CHUNK_SIZE = 64 * 1024; // 64KB
const AUDIO_EXTENSIONS = new Set([".mp3", ".ogg", ".flac", ".wav", ".m4a", ".aac", ".opus", ".wma"]);

export interface LibraryTrack extends Track {
  filename: string;
  filepath: string;
  available: boolean;
}

interface CacheEntry {
  path: string;
  track_id: string;
  size: number;
  mtime_ms: number;
  cached_at: number;
}

type LibraryEventType = "added" | "removed" | "changed";
type LibraryEventCallback = (track: LibraryTrack) => void;

export class Library {
  private cacheDb: Database;
  private musicDir: string;
  private trackMap = new Map<string, string>(); // trackId -> filepath
  private trackInfo = new Map<string, LibraryTrack>(); // trackId -> full info
  private watcher: FSWatcher | null = null;
  private eventListeners = new Map<LibraryEventType, Set<LibraryEventCallback>>();
  private pendingFiles = new Map<string, NodeJS.Timeout>(); // filepath -> debounce timer

  constructor(musicDir: string, cacheDbPath: string = "./library_cache.db") {
    this.musicDir = musicDir;
    this.cacheDb = new Database(cacheDbPath);
    this.initCacheDb();
  }

  private initCacheDb(): void {
    this.cacheDb.run(`
      CREATE TABLE IF NOT EXISTS file_cache (
        path TEXT PRIMARY KEY,
        track_id TEXT NOT NULL,
        size INTEGER NOT NULL,
        mtime_ms INTEGER NOT NULL,
        cached_at INTEGER DEFAULT (unixepoch())
      )
    `);
    this.cacheDb.run(`CREATE INDEX IF NOT EXISTS idx_file_cache_track ON file_cache(track_id)`);
  }

  async computeTrackId(filePath: string): Promise<string> {
    const file = Bun.file(filePath);
    const size = file.size;

    // Read first 64KB
    const chunk = await file.slice(0, HASH_CHUNK_SIZE).arrayBuffer();

    // Get duration from metadata
    let duration = 0;
    try {
      const metadata = await parseFile(filePath, { duration: true });
      duration = metadata.format.duration || 0;
    } catch {
      // If metadata parsing fails, use size only
    }

    // Hash: size + duration + first 64KB
    const hash = createHash("sha256");
    hash.update(`${size}:${duration.toFixed(3)}:`);
    hash.update(new Uint8Array(chunk));

    return "sha256:" + hash.digest("hex").substring(0, 32);
  }

  private getCacheEntry(relativePath: string): CacheEntry | null {
    return this.cacheDb.query("SELECT * FROM file_cache WHERE path = ?").get(relativePath) as CacheEntry | null;
  }

  private setCacheEntry(relativePath: string, trackId: string, size: number, mtimeMs: number): void {
    this.cacheDb.query(`
      INSERT OR REPLACE INTO file_cache (path, track_id, size, mtime_ms, cached_at)
      VALUES (?, ?, ?, ?, unixepoch())
    `).run(relativePath, trackId, size, mtimeMs);
  }

  private removeCacheEntry(relativePath: string): void {
    this.cacheDb.query("DELETE FROM file_cache WHERE path = ?").run(relativePath);
  }

  private isAudioFile(filename: string): boolean {
    const ext = filename.substring(filename.lastIndexOf(".")).toLowerCase();
    return AUDIO_EXTENSIONS.has(ext);
  }

  private async processFile(filePath: string): Promise<LibraryTrack | null> {
    const relativePath = relative(this.musicDir, filePath);
    const filename = filePath.substring(filePath.lastIndexOf("/") + 1).replace(/\\/g, "/").split("/").pop() || filePath;

    try {
      const fileStat = await stat(filePath);
      const size = fileStat.size;
      const mtimeMs = fileStat.mtimeMs;

      // Check cache
      const cached = this.getCacheEntry(relativePath);
      let trackId: string;

      if (cached && cached.size === size && cached.mtime_ms === Math.floor(mtimeMs)) {
        trackId = cached.track_id;
      } else {
        // Compute new hash
        trackId = await this.computeTrackId(filePath);
        this.setCacheEntry(relativePath, trackId, size, Math.floor(mtimeMs));
      }

      // Get metadata
      let title = filename.replace(/\.[^.]+$/, "");
      let artist: string | null = null;
      let album: string | null = null;
      let duration = 0;

      try {
        const metadata = await parseFile(filePath, { duration: true });
        title = metadata.common.title || title;
        artist = metadata.common.artist || null;
        album = metadata.common.album || null;
        duration = metadata.format.duration || 0;
      } catch {
        // Use defaults
      }

      const track: LibraryTrack = {
        id: trackId,
        filename,
        filepath: filePath,
        title,
        artist,
        album,
        duration,
        size,
        available: true,
        created_at: Math.floor(Date.now() / 1000),
      };

      // Upsert to main database
      upsertTrack({
        id: trackId,
        title,
        artist,
        album,
        duration,
        size,
      });

      return track;
    } catch (e) {
      console.error(`[Library] Failed to process ${filePath}:`, e);
      return null;
    }
  }

  async scan(): Promise<void> {
    console.log(`[Library] Scanning ${this.musicDir}...`);
    const startTime = Date.now();
    let processed = 0;
    let cached = 0;

    const scanDir = async (dir: string) => {
      const entries = await readdir(dir, { withFileTypes: true });

      for (const entry of entries) {
        const fullPath = join(dir, entry.name);

        if (entry.isDirectory()) {
          await scanDir(fullPath);
        } else if (entry.isFile() && this.isAudioFile(entry.name)) {
          const relativePath = relative(this.musicDir, fullPath);
          const cacheEntry = this.getCacheEntry(relativePath);

          // Quick check if cache is valid
          if (cacheEntry) {
            try {
              const fileStat = await stat(fullPath);
              if (cacheEntry.size === fileStat.size && cacheEntry.mtime_ms === Math.floor(fileStat.mtimeMs)) {
                // Cache hit - reuse existing data
                const existingTrack = this.trackInfo.get(cacheEntry.track_id);
                if (!existingTrack) {
                  // Need metadata but skip hashing
                  const track = await this.processFile(fullPath);
                  if (track) {
                    this.trackMap.set(track.id, fullPath);
                    this.trackInfo.set(track.id, track);
                  }
                } else {
                  this.trackMap.set(cacheEntry.track_id, fullPath);
                }
                cached++;
                continue;
              }
            } catch {}
          }

          const track = await this.processFile(fullPath);
          if (track) {
            this.trackMap.set(track.id, fullPath);
            this.trackInfo.set(track.id, track);
            processed++;
          }
        }
      }
    };

    await scanDir(this.musicDir);

    const elapsed = Date.now() - startTime;
    console.log(`[Library] Scan complete: ${this.trackMap.size} tracks (${processed} processed, ${cached} cached) in ${elapsed}ms`);
  }

  startWatching(): void {
    if (this.watcher) return;

    console.log(`[Library] Watching ${this.musicDir} for changes...`);

    this.watcher = watch(this.musicDir, { recursive: true }, async (event, filename) => {
      if (!filename) return;

      // Normalize path separators
      const normalizedFilename = filename.replace(/\\/g, "/");
      if (!this.isAudioFile(normalizedFilename)) return;

      const fullPath = join(this.musicDir, filename);

      // Debounce: wait 5 seconds after last change before processing
      const existing = this.pendingFiles.get(fullPath);
      if (existing) clearTimeout(existing);

      this.pendingFiles.set(fullPath, setTimeout(async () => {
        this.pendingFiles.delete(fullPath);
        await this.processFileChange(fullPath);
      }, 5000));
    });
  }

  private async processFileChange(fullPath: string): Promise<void> {
    try {
      const exists = await Bun.file(fullPath).exists();

      if (exists) {
        // File added or modified
        const track = await this.processFile(fullPath);
        if (track) {
          const wasNew = !this.trackMap.has(track.id);
          this.trackMap.set(track.id, fullPath);
          this.trackInfo.set(track.id, track);
          this.emit(wasNew ? "added" : "changed", track);
          console.log(`[Library] ${wasNew ? "Added" : "Updated"}: ${track.title}`);
        }
      } else {
        // File deleted
        const relativePath = relative(this.musicDir, fullPath);
        const cacheEntry = this.getCacheEntry(relativePath);

        if (cacheEntry) {
          const track = this.trackInfo.get(cacheEntry.track_id);
          if (track) {
            track.available = false;
            this.trackMap.delete(cacheEntry.track_id);
            this.emit("removed", track);
            console.log(`[Library] Removed: ${track.title}`);
          }
          this.removeCacheEntry(relativePath);
        }
      }
    } catch (e) {
      console.error(`[Library] Watch error for ${fullPath}:`, e);
    }
  }

  stopWatching(): void {
    if (this.watcher) {
      this.watcher.close();
      this.watcher = null;
    }
  }

  // Event handling
  on(event: LibraryEventType, callback: LibraryEventCallback): void {
    if (!this.eventListeners.has(event)) {
      this.eventListeners.set(event, new Set());
    }
    this.eventListeners.get(event)!.add(callback);
  }

  off(event: LibraryEventType, callback: LibraryEventCallback): void {
    this.eventListeners.get(event)?.delete(callback);
  }

  private emit(event: LibraryEventType, track: LibraryTrack): void {
    this.eventListeners.get(event)?.forEach((cb) => cb(track));
  }

  // Accessors
  getTrack(id: string): LibraryTrack | null {
    return this.trackInfo.get(id) || null;
  }

  getFilePath(id: string): string | null {
    return this.trackMap.get(id) || null;
  }

  getAllTracks(): LibraryTrack[] {
    return Array.from(this.trackInfo.values()).filter((t) => t.available);
  }

  getTrackCount(): number {
    return this.trackMap.size;
  }

  // Check if a track ID is available (file exists)
  isAvailable(id: string): boolean {
    return this.trackMap.has(id);
  }
}