import * as fs from 'fs';
import * as path from 'path';
import * as smartrx from '@push.rocks/smartrx';
import type { IWatcher, IWatcherOptions, IWatchEvent, TWatchEventType } from './interfaces.js';

/**
 * Node.js/Bun file watcher using native fs.watch API
 */
export class NodeWatcher implements IWatcher {
  private watchers: Map<string, fs.FSWatcher> = new Map();
  private watchedFiles: Set<string> = new Set();
  private _isWatching = false;

  // Debounce: pending emits per file path
  private pendingEmits: Map<string, NodeJS.Timeout> = new Map();

  // Restart tracking
  private restartDelays: Map<string, number> = new Map();
  private restartAttempts: Map<string, number> = new Map();
  private healthCheckInterval: NodeJS.Timeout | null = null;

  // Inode tracking - detect when directories are replaced (atomic saves, etc.)
  // fs.watch watches the inode, not the path. If inode changes, we need to restart.
  private watchedInodes: Map<string, bigint> = new Map();

  // Configuration constants
  private static readonly MAX_RETRIES = 3;
  private static readonly INITIAL_RESTART_DELAY = 1000;
  private static readonly MAX_RESTART_DELAY = 30000;
  private static readonly HEALTH_CHECK_INTERVAL = 30000;

  public readonly events$ = new smartrx.rxjs.Subject<IWatchEvent>();

  constructor(private options: IWatcherOptions) {}

  /**
   * Safely emit an event, catching any subscriber errors
   */
  private safeEmit(event: IWatchEvent): void {
    try {
      this.events$.next(event);
    } catch (error) {
      console.error('[smartwatch] Subscriber threw error (isolated):', error);
      // Don't let subscriber errors kill the watcher
    }
  }

  /**
   * Restart a watcher after an error with exponential backoff
   */
  private async restartWatcher(basePath: string, error: Error): Promise<void> {
    const attempts = (this.restartAttempts.get(basePath) || 0) + 1;
    this.restartAttempts.set(basePath, attempts);

    console.log(`[smartwatch] Watcher error for ${basePath}: ${error.message}`);
    console.log(`[smartwatch] Restart attempt ${attempts}/${NodeWatcher.MAX_RETRIES}`);

    if (attempts > NodeWatcher.MAX_RETRIES) {
      console.error(`[smartwatch] Max retries exceeded for ${basePath}, giving up`);
      this.safeEmit({
        type: 'error',
        path: basePath,
        error: new Error(`Max restart retries (${NodeWatcher.MAX_RETRIES}) exceeded`)
      });
      return;
    }

    // Close failed watcher
    const oldWatcher = this.watchers.get(basePath);
    if (oldWatcher) {
      try {
        oldWatcher.close();
      } catch {
        // Ignore close errors
      }
      this.watchers.delete(basePath);
    }

    // Exponential backoff
    const delay = this.restartDelays.get(basePath) || NodeWatcher.INITIAL_RESTART_DELAY;
    console.log(`[smartwatch] Waiting ${delay}ms before restart...`);
    await new Promise((resolve) => setTimeout(resolve, delay));
    this.restartDelays.set(basePath, Math.min(delay * 2, NodeWatcher.MAX_RESTART_DELAY));

    try {
      await this.watchPath(basePath, 0);
      console.log(`[smartwatch] Successfully restarted watcher for ${basePath}`);
      this.restartDelays.set(basePath, NodeWatcher.INITIAL_RESTART_DELAY);
      this.restartAttempts.set(basePath, 0);
    } catch (restartError) {
      console.error(`[smartwatch] Restart failed for ${basePath}:`, restartError);
      this.restartWatcher(basePath, restartError as Error); // Recursive retry
    }
  }

  /**
   * Start periodic health checks to detect silent failures
   * Checks for:
   * 1. Path no longer exists
   * 2. Inode changed (directory was replaced - fs.watch watches inode, not path!)
   */
  private startHealthCheck(): void {
    console.log('[smartwatch] Starting health check (every 30s)');
    this.healthCheckInterval = setInterval(async () => {
      console.log(`[smartwatch] Health check: ${this.watchers.size} watchers active`);
      for (const [basePath] of this.watchers) {
        try {
          const stats = await fs.promises.stat(basePath);
          const currentInode = stats.ino;
          const previousInode = this.watchedInodes.get(basePath);

          if (!stats) {
            console.error(`[smartwatch] Health check failed: ${basePath} no longer exists`);
            this.safeEmit({
              type: 'error',
              path: basePath,
              error: new Error('Watched path no longer exists')
            });
            this.restartWatcher(basePath, new Error('Watched path disappeared'));
          } else if (previousInode !== undefined && BigInt(currentInode) !== previousInode) {
            // CRITICAL: Inode changed! fs.watch is now watching a stale inode.
            // This happens when the directory is replaced (atomic operations, git checkout, etc.)
            console.warn(`[smartwatch] Inode changed for ${basePath}: ${previousInode} -> ${currentInode}`);
            console.warn('[smartwatch] fs.watch watches inode, not path - restarting watcher');
            this.restartWatcher(basePath, new Error('Inode changed - directory was replaced'));
          }
        } catch (error: any) {
          if (error.code === 'ENOENT') {
            console.error(`[smartwatch] Health check failed: ${basePath} no longer exists`);
            this.restartWatcher(basePath, new Error('Watched path disappeared'));
          } else if (error.code === 'ENOSPC') {
            // inotify watch limit exceeded - critical system issue
            console.error(`[smartwatch] ENOSPC: inotify watch limit exceeded!`);
            console.error('[smartwatch] Fix: echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p');
            this.safeEmit({ type: 'error', path: basePath, error });
          } else {
            console.error(`[smartwatch] Health check error for ${basePath}:`, error);
          }
        }
      }
    }, NodeWatcher.HEALTH_CHECK_INTERVAL);
  }

  /**
   * Stop health check interval
   */
  private stopHealthCheck(): void {
    if (this.healthCheckInterval) {
      clearInterval(this.healthCheckInterval);
      this.healthCheckInterval = null;
      console.log('[smartwatch] Stopped health check');
    }
  }

  /**
   * Check if a file is a temporary file created by editors
   */
  private isTemporaryFile(filePath: string): boolean {
    const basename = path.basename(filePath);
    // Editor temp files: *.tmp.*, *.swp, *.swx, *~, .#*
    if (basename.includes('.tmp.')) return true;
    if (basename.endsWith('.swp') || basename.endsWith('.swx')) return true;
    if (basename.endsWith('~')) return true;
    if (basename.startsWith('.#')) return true;
    return false;
  }

  get isWatching(): boolean {
    return this._isWatching;
  }

  async start(): Promise<void> {
    if (this._isWatching) {
      return;
    }

    console.log(`[smartwatch] Starting watcher for ${this.options.basePaths.length} base path(s)...`);

    try {
      // Start watching each base path
      for (const basePath of this.options.basePaths) {
        await this.watchPath(basePath, 0);
      }

      this._isWatching = true;

      // Start health check monitoring
      this.startHealthCheck();

      // Perform initial scan to emit 'add' events for existing files
      for (const basePath of this.options.basePaths) {
        await this.scanDirectory(basePath, 0);
      }

      // Emit ready event
      this.safeEmit({ type: 'ready', path: '' });
      console.log(`[smartwatch] Watcher started with ${this.watchers.size} active watcher(s)`);
    } catch (error: any) {
      console.error('[smartwatch] Failed to start watcher:', error);
      this.safeEmit({ type: 'error', path: '', error });
      throw error;
    }
  }

  async stop(): Promise<void> {
    console.log('[smartwatch] Stopping watcher...');
    this._isWatching = false;

    // Stop health check monitoring
    this.stopHealthCheck();

    // Cancel all pending debounced emits
    for (const timeout of this.pendingEmits.values()) {
      clearTimeout(timeout);
    }
    this.pendingEmits.clear();

    // Close all watchers
    for (const [watchPath, watcher] of this.watchers) {
      console.log(`[smartwatch] Closing watcher for: ${watchPath}`);
      watcher.close();
    }
    this.watchers.clear();
    this.watchedFiles.clear();

    // Clear restart tracking state
    this.restartDelays.clear();
    this.restartAttempts.clear();
    this.watchedInodes.clear();

    console.log('[smartwatch] Watcher stopped');
  }

  /**
   * Start watching a path (file or directory)
   */
  private async watchPath(watchPath: string, depth: number): Promise<void> {
    if (depth > this.options.depth) {
      return;
    }

    try {
      const stats = await this.statSafe(watchPath);
      if (!stats) {
        return;
      }

      if (stats.isDirectory()) {
        // Store inode for health check - fs.watch watches inode, not path!
        // If inode changes (directory replaced), watcher becomes stale
        this.watchedInodes.set(watchPath, BigInt(stats.ino));

        // Watch the directory with recursive option (Node.js 20+ supports this on all platforms)
        const watcher = fs.watch(
          watchPath,
          { recursive: true, persistent: true },
          (eventType, filename) => {
            if (filename) {
              this.handleFsEvent(watchPath, filename, eventType);
            }
          }
        );

        watcher.on('error', (error: NodeJS.ErrnoException) => {
          console.error(`[smartwatch] FSWatcher error event on ${watchPath}:`, error);

          // Detect inotify watch limit exceeded - common cause of "stops working"
          if (error.code === 'ENOSPC') {
            console.error('[smartwatch] CRITICAL: inotify watch limit exceeded!');
            console.error('[smartwatch] Fix with: echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p');
          }

          this.safeEmit({ type: 'error', path: watchPath, error });
          if (this._isWatching) {
            this.restartWatcher(watchPath, error);
          }
        });

        // Handle 'close' event - fs.watch can close without error
        watcher.on('close', () => {
          console.warn(`[smartwatch] FSWatcher closed unexpectedly for ${watchPath}`);
          if (this._isWatching) {
            this.restartWatcher(watchPath, new Error('Watcher closed unexpectedly'));
          }
        });

        this.watchers.set(watchPath, watcher);
        console.log(`[smartwatch] Started watching: ${watchPath}`);
      }
    } catch (error: any) {
      console.error(`[smartwatch] Failed to watch path ${watchPath}:`, error);
      this.safeEmit({ type: 'error', path: watchPath, error });
    }
  }

  /**
   * Handle raw fs.watch events - debounce and normalize them
   */
  private handleFsEvent(
    basePath: string,
    filename: string,
    eventType: 'rename' | 'change' | string
  ): void {
    const fullPath = path.join(basePath, filename);

    // Skip temporary files - but ONLY pure temp files, not the target of atomic writes
    // Atomic writes: editor writes to file.tmp.xxx then renames to file
    // We need to detect the final file, so only skip files that ARE temp files
    // and haven't been renamed to the real file yet
    if (this.isTemporaryFile(fullPath)) {
      // For temp files, we still want to track if they get renamed TO a real file
      // The 'rename' event fires for both source and target, so we'll catch the real file
      console.log(`[smartwatch] Skipping temp file event: ${filename}`);
      return;
    }

    // Debounce: cancel any pending emit for this file
    const existing = this.pendingEmits.get(fullPath);
    if (existing) {
      clearTimeout(existing);
    }

    // Schedule debounced emit
    const timeout = setTimeout(() => {
      this.pendingEmits.delete(fullPath);
      this.emitFileEvent(fullPath, eventType);
    }, this.options.debounceMs);

    this.pendingEmits.set(fullPath, timeout);
  }

  /**
   * Emit the actual file event after debounce
   */
  private async emitFileEvent(
    fullPath: string,
    eventType: 'rename' | 'change' | string
  ): Promise<void> {
    try {
      const stats = await this.statSafe(fullPath);

      if (eventType === 'rename') {
        // 'rename' can mean add or unlink - check if file exists
        if (stats) {
          // File exists - it's either a new file or was renamed to this location
          if (stats.isDirectory()) {
            if (!this.watchedFiles.has(fullPath)) {
              this.watchedFiles.add(fullPath);
              this.safeEmit({ type: 'addDir', path: fullPath, stats });
            }
          } else {
            const wasWatched = this.watchedFiles.has(fullPath);
            this.watchedFiles.add(fullPath);
            this.safeEmit({
              type: wasWatched ? 'change' : 'add',
              path: fullPath,
              stats
            });
          }
        } else {
          // File doesn't exist - it was deleted
          if (this.watchedFiles.has(fullPath)) {
            const wasDir = this.isKnownDirectory(fullPath);
            this.watchedFiles.delete(fullPath);
            this.safeEmit({
              type: wasDir ? 'unlinkDir' : 'unlink',
              path: fullPath
            });
          }
        }
      } else if (eventType === 'change') {
        // File was modified
        if (stats && !stats.isDirectory()) {
          const wasWatched = this.watchedFiles.has(fullPath);
          if (!wasWatched) {
            // This is actually an 'add' - file wasn't being watched before
            this.watchedFiles.add(fullPath);
            this.safeEmit({ type: 'add', path: fullPath, stats });
          } else {
            this.safeEmit({ type: 'change', path: fullPath, stats });
          }
        } else if (!stats && this.watchedFiles.has(fullPath)) {
          // File was deleted
          this.watchedFiles.delete(fullPath);
          this.safeEmit({ type: 'unlink', path: fullPath });
        }
      }
    } catch (error: any) {
      this.safeEmit({ type: 'error', path: fullPath, error });
    }
  }

  /**
   * Scan directory and emit 'add' events for existing files
   */
  private async scanDirectory(dirPath: string, depth: number): Promise<void> {
    if (depth > this.options.depth) {
      return;
    }

    try {
      const entries = await fs.promises.readdir(dirPath, { withFileTypes: true });

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

        // Skip temp files during initial scan too
        if (this.isTemporaryFile(fullPath)) {
          continue;
        }

        const stats = await this.statSafe(fullPath);

        if (!stats) {
          continue;
        }

        if (entry.isDirectory()) {
          this.watchedFiles.add(fullPath);
          this.safeEmit({ type: 'addDir', path: fullPath, stats });
          await this.scanDirectory(fullPath, depth + 1);
        } else if (entry.isFile()) {
          this.watchedFiles.add(fullPath);
          this.safeEmit({ type: 'add', path: fullPath, stats });
        }
      }
    } catch (error: any) {
      if (error.code !== 'ENOENT' && error.code !== 'EACCES') {
        this.safeEmit({ type: 'error', path: dirPath, error });
      }
    }
  }

  /**
   * Safely stat a path, returning null if it doesn't exist
   */
  private async statSafe(filePath: string): Promise<fs.Stats | null> {
    try {
      return await (this.options.followSymlinks
        ? fs.promises.stat(filePath)
        : fs.promises.lstat(filePath));
    } catch (error: any) {
      // Only silently return null for expected "file doesn't exist" errors
      if (error.code === 'ENOENT' || error.code === 'ENOTDIR') {
        return null;
      }
      // Log other errors (permission, I/O) but still return null
      console.warn(`[smartwatch] statSafe warning for ${filePath}: ${error.code} - ${error.message}`);
      return null;
    }
  }

  /**
   * Check if a path was known to be a directory (for proper unlink event type)
   */
  private isKnownDirectory(filePath: string): boolean {
    // Check if any watched files are children of this path
    for (const watched of this.watchedFiles) {
      if (watched.startsWith(filePath + path.sep)) {
        return true;
      }
    }
    return false;
  }
}