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';
import { WriteStabilizer } from '../utils/write-stabilizer.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;
  private writeStabilizer: WriteStabilizer;
  private recentEvents: Map<string, number> = new Map();
  private throttleMs = 50;

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

  constructor(private options: IWatcherOptions) {
    this.writeStabilizer = new WriteStabilizer(
      options.stabilityThreshold,
      options.pollInterval
    );
  }

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

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

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

      this._isWatching = true;

      // 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.events$.next({ type: 'ready', path: '' });
    } catch (error: any) {
      this.events$.next({ type: 'error', path: '', error });
      throw error;
    }
  }

  async stop(): Promise<void> {
    this._isWatching = false;
    this.writeStabilizer.cancelAll();

    // Close all watchers
    for (const [watchPath, watcher] of this.watchers) {
      watcher.close();
    }
    this.watchers.clear();
    this.watchedFiles.clear();
    this.recentEvents.clear();
  }

  /**
   * 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()) {
        // 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) => {
          this.events$.next({ type: 'error', path: watchPath, error });
        });

        this.watchers.set(watchPath, watcher);
      }
    } catch (error: any) {
      this.events$.next({ type: 'error', path: watchPath, error });
    }
  }

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

    // Throttle duplicate events
    if (!this.shouldEmit(fullPath, eventType)) {
      return;
    }

    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.events$.next({ type: 'addDir', path: fullPath, stats });
            }
          } else {
            // Wait for write to stabilize before emitting
            try {
              const stableStats = await this.writeStabilizer.waitForWriteFinish(fullPath);
              const wasWatched = this.watchedFiles.has(fullPath);
              this.watchedFiles.add(fullPath);
              this.events$.next({
                type: wasWatched ? 'change' : 'add',
                path: fullPath,
                stats: stableStats
              });
            } catch {
              // File was deleted during stabilization
              if (this.watchedFiles.has(fullPath)) {
                this.watchedFiles.delete(fullPath);
                this.events$.next({ type: 'unlink', path: fullPath });
              }
            }
          }
        } else {
          // File doesn't exist - it was deleted
          if (this.watchedFiles.has(fullPath)) {
            const wasDir = this.isKnownDirectory(fullPath);
            this.watchedFiles.delete(fullPath);
            this.events$.next({
              type: wasDir ? 'unlinkDir' : 'unlink',
              path: fullPath
            });
          }
        }
      } else if (eventType === 'change') {
        // File was modified
        if (stats && !stats.isDirectory()) {
          try {
            const stableStats = await this.writeStabilizer.waitForWriteFinish(fullPath);
            // Check if this is a new file (not yet in watchedFiles)
            const wasWatched = this.watchedFiles.has(fullPath);
            if (!wasWatched) {
              // This is actually an 'add' - file wasn't being watched before
              this.watchedFiles.add(fullPath);
              this.events$.next({ type: 'add', path: fullPath, stats: stableStats });
            } else {
              this.events$.next({ type: 'change', path: fullPath, stats: stableStats });
            }
          } catch {
            // File was deleted during write
            if (this.watchedFiles.has(fullPath)) {
              this.watchedFiles.delete(fullPath);
              this.events$.next({ type: 'unlink', path: fullPath });
            }
          }
        }
      }
    } catch (error: any) {
      this.events$.next({ 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);
        const stats = await this.statSafe(fullPath);

        if (!stats) {
          continue;
        }

        if (entry.isDirectory()) {
          this.watchedFiles.add(fullPath);
          this.events$.next({ type: 'addDir', path: fullPath, stats });
          await this.scanDirectory(fullPath, depth + 1);
        } else if (entry.isFile()) {
          this.watchedFiles.add(fullPath);
          this.events$.next({ type: 'add', path: fullPath, stats });
        }
      }
    } catch (error: any) {
      if (error.code !== 'ENOENT' && error.code !== 'EACCES') {
        this.events$.next({ 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 {
      if (this.options.followSymlinks) {
        return await fs.promises.stat(filePath);
      } else {
        return await fs.promises.lstat(filePath);
      }
    } catch {
      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;
  }

  /**
   * Throttle duplicate events
   */
  private shouldEmit(filePath: string, eventType: string): boolean {
    const key = `${filePath}:${eventType}`;
    const now = Date.now();
    const lastEmit = this.recentEvents.get(key);

    if (lastEmit && now - lastEmit < this.throttleMs) {
      return false;
    }

    this.recentEvents.set(key, now);

    // Clean up old entries periodically
    if (this.recentEvents.size > 1000) {
      const cutoff = now - this.throttleMs * 2;
      for (const [k, time] of this.recentEvents) {
        if (time < cutoff) {
          this.recentEvents.delete(k);
        }
      }
    }

    return true;
  }
}