feat(mcp): MCP connector

packages/mcp/src/hub-bridge.js

@@ -0,0 +1,136 @@
+#!/usr/bin/env node
+import { readFileSync } from 'node:fs'
+import http from 'node:http'
+import { fileURLToPath } from 'node:url'
+import { WebSocketServer } from 'ws'
+
+const EXT_ID = 'akldabonmimlicnjlflnapfeklbfemhj'
+const STORE_URL = `https://chromewebstore.google.com/detail/page-agent-ext/${EXT_ID}`
+
+const launcherTemplate = readFileSync(
+	fileURLToPath(new URL('./launcher.html', import.meta.url)),
+	'utf-8'
+)
+
+/**
+ * HTTP + WebSocket bridge to the hub.html extension tab.
+ * - HTTP serves the launcher page (triggers extension to open hub)
+ * - WS carries execute/stop commands and result/error responses
+ */
+export class HubBridge {
+	/** @type {number} */
+	port
+
+	/** @type {http.Server} */
+	#httpServer
+
+	/** @type {WebSocketServer} */
+	#wss
+
+	/** @type {import('ws').WebSocket | null} */
+	#hub = null
+
+	/** @type {{ resolve: (r: {success: boolean, data: string}) => void, reject: (e: Error) => void } | null} */
+	#pendingTask = null
+
+	/** @param {number} port */
+	constructor(port) {
+		this.port = port
+		this.#httpServer = http.createServer((_req, res) => {
+			const html = launcherTemplate
+				.replaceAll('__EXT_ID__', EXT_ID)
+				.replaceAll('__STORE_URL__', STORE_URL)
+				.replaceAll('__WS_PORT__', String(port))
+			res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' })
+			res.end(html)
+		})
+		this.#wss = new WebSocketServer({ server: this.#httpServer })
+		this.#wss.on('connection', (ws) => this.#onConnection(ws))
+	}
+
+	/** @returns {Promise<void>} */
+	async start() {
+		return new Promise((resolve, reject) => {
+			this.#httpServer.on('error', (/** @type {NodeJS.ErrnoException} */ err) => {
+				if (err.code === 'EADDRINUSE') {
+					reject(
+						new Error(`Port ${this.port} is in use. Another Page Agent MCP server may be running.`)
+					)
+				} else {
+					reject(err)
+				}
+			})
+			this.#httpServer.listen(this.port, () => {
+				console.error(`[page-agent-mcp] HTTP + WS on http://localhost:${this.port}`)
+				resolve()
+			})
+		})
+	}
+
+	get connected() {
+		return this.#hub?.readyState === 1
+	}
+
+	get busy() {
+		return this.#pendingTask !== null
+	}
+
+	/**
+	 * @param {string} task
+	 * @param {Record<string, unknown>} [config]
+	 * @returns {Promise<{success: boolean, data: string}>}
+	 */
+	async executeTask(task, config) {
+		if (!this.connected) throw new Error('Hub is not connected. Is the extension running?')
+		if (this.#pendingTask) throw new Error('Agent is already running a task.')
+
+		return new Promise((resolve, reject) => {
+			this.#pendingTask = { resolve, reject }
+			this.#hub.send(JSON.stringify({ type: 'execute', task, config }))
+		})
+	}
+
+	stopTask() {
+		if (this.connected) {
+			this.#hub.send(JSON.stringify({ type: 'stop' }))
+		}
+	}
+
+	/** @param {import('ws').WebSocket} ws */
+	#onConnection(ws) {
+		if (this.#hub && this.#hub.readyState === 1) {
+			ws.close(4000, 'Another hub is already connected')
+			return
+		}
+
+		this.#hub = ws
+		console.error('[page-agent-mcp] Hub connected')
+
+		ws.on('message', (/** @type {Buffer} */ rawData) => {
+			/** @type {{ type: string, success?: boolean, data?: string, message?: string }} */
+			let msg
+			try {
+				msg = JSON.parse(rawData.toString('utf-8'))
+			} catch {
+				return
+			}
+
+			if (msg.type === 'result') {
+				this.#pendingTask?.resolve({ success: msg.success ?? false, data: msg.data ?? '' })
+				this.#pendingTask = null
+			} else if (msg.type === 'error') {
+				this.#pendingTask?.reject(new Error(msg.message ?? 'Unknown error from hub'))
+				this.#pendingTask = null
+			}
+		})
+
+		ws.on('close', () => {
+			console.error('[page-agent-mcp] Hub disconnected')
+			if (this.#hub === ws) this.#hub = null
+			if (this.#pendingTask) {
+				this.#pendingTask.reject(new Error('Hub disconnected while task was running'))
+				this.#pendingTask = null
+			}
+		})
+	}
+}