/**

* Resource Events Emitter

*

* Singleton EventEmitter for resource change notifications.

* Handlers emit 'change' events here, WebSocket broadcasts to subscribers.

*/

import { EventEmitter } from 'events';

import { watch } from 'fs';

import { join, relative } from 'path';

// Singleton event emitter for resource changes

export const resourceEvents = new EventEmitter();

// Increase max listeners since many WebSocket connections may subscribe

resourceEvents.setMaxListeners(1000);

/**

* Emit a resource change event

* @param {string} resourceUrl - Full URL of the changed resource

*/

export function emitChange(resourceUrl) {

resourceEvents.emit('change', resourceUrl);

}

/**

* Start watching filesystem for changes and emit notifications

* @param {string} rootDir - Directory to watch

* @param {string} baseUrl - Base URL for constructing resource URLs (e.g., http://localhost:3000)

*/

export function startFileWatcher(rootDir, baseUrl) {

// Debounce map to avoid duplicate events (editors often save multiple times)

const debounceMap = new Map();

const DEBOUNCE_MS = 100;

try {

const watcher = watch(rootDir, { recursive: true }, (eventType, filename) => {

if (!filename) return;

// Skip hidden files and common temp files

if (filename.startsWith('.') || filename.endsWith('~') || filename.endsWith('.swp')) {

return;

}

// Debounce: skip if we just emitted for this file

const now = Date.now();

const lastEmit = debounceMap.get(filename);

if (lastEmit && now - lastEmit < DEBOUNCE_MS) {

return;

}

debounceMap.set(filename, now);

// Clean up old debounce entries periodically

if (debounceMap.size > 1000) {

for (const [key, time] of debounceMap) {

if (now - time > 5000) debounceMap.delete(key);

}

}

// Construct resource URL

const resourcePath = '/' + filename.replace(/\\/g, '/');

const resourceUrl = baseUrl.replace(/\/$/, '') + resourcePath;

emitChange(resourceUrl);

});

// Handle watcher errors gracefully

watcher.on('error', (err) => {

console.error('File watcher error:', err.message);

});

return watcher;

} catch (err) {

console.error('Failed to start file watcher:', err.message);

return null;

}

}