/**
 * Express server with WebSocket proxy for TASTE Voice Bot frontend
 *
 * Architecture:
 * - Browser connects to this server on port 3000 (HTTP + WebSocket)
 * - Server serves static files from current directory
 * - WebSocket requests to /ws/* are proxied internally to backend
 * - Browser never directly connects to backend port
 */

const express = require('express');
const { createProxyMiddleware } = require('http-proxy-middleware');
const path = require('path');

// Read backend configuration from environment variables
const BACKEND_HOST = process.env.BACKEND_HOST || 'localhost';
const BACKEND_PORT = process.env.BACKEND_PORT || '8000';
const BACKEND_WS_PATH = process.env.BACKEND_WS_PATH || '/ws/orchestrator';
const FRONTEND_PORT = process.env.FRONTEND_PORT || '3000';

// Parse BACKEND_HOST to extract protocol and hostname
let backendUrl;
try {
    // If BACKEND_HOST includes protocol (http:// or https://), parse it
    if (BACKEND_HOST.includes('://')) {
        const url = new URL(BACKEND_HOST);
        const protocol = url.protocol === 'https:' ? 'https' : 'http';
        const wsProtocol = url.protocol === 'https:' ? 'wss' : 'ws';
        const host = url.hostname;
        const port = url.port || BACKEND_PORT;
        backendUrl = {
            http: `${protocol}://${host}:${port}`,
            ws: `${wsProtocol}://${host}:${port}`,
            display: `${protocol}://${host}:${port}`
        };
    } else {
        // BACKEND_HOST is just hostname
        backendUrl = {
            http: `http://${BACKEND_HOST}:${BACKEND_PORT}`,
            ws: `ws://${BACKEND_HOST}:${BACKEND_PORT}`,
            display: `http://${BACKEND_HOST}:${BACKEND_PORT}`
        };
    }
} catch (e) {
    // Fallback to simple hostname
    backendUrl = {
        http: `http://${BACKEND_HOST}:${BACKEND_PORT}`,
        ws: `ws://${BACKEND_HOST}:${BACKEND_PORT}`,
        display: `http://${BACKEND_HOST}:${BACKEND_PORT}`
    };
}

const app = express();

// Serve static files from current directory
app.use(express.static(__dirname));

// WebSocket proxy middleware
const wsProxy = createProxyMiddleware({
    target: backendUrl.http,
    changeOrigin: true,
    ws: true, // Enable WebSocket proxying
    logLevel: 'info',
    onError: (err, req, res) => {
        console.error('Proxy error:', err);
        if (res.writeHead) {
            res.writeHead(502, { 'Content-Type': 'text/plain' });
            res.end('Bad Gateway: Could not connect to backend');
        }
    },
    onProxyReqWs: (proxyReq, req, socket, options, head) => {
        console.log(`[WS Proxy] ${req.url} -> ${backendUrl.ws}${req.url}`);
    }
});

// Apply WebSocket proxy to /ws/* paths
app.use('/ws', wsProxy);

// Start server
const server = app.listen(FRONTEND_PORT, () => {
    console.log('=================================');
    console.log('TASTE Voice Bot Frontend Server');
    console.log('=================================');
    console.log(`Frontend: http://localhost:${FRONTEND_PORT}`);
    console.log(`Backend:  ${backendUrl.display}`);
    console.log(`WS Proxy: /ws/* -> ${backendUrl.ws}/ws/*`);
    console.log('=================================');
});

// Enable WebSocket upgrade handling
server.on('upgrade', (req, socket, head) => {
    if (req.url.startsWith('/ws')) {
        wsProxy.upgrade(req, socket, head);
    } else {
        socket.destroy();
    }
});

// Graceful shutdown
process.on('SIGTERM', () => {
    console.log('SIGTERM received, shutting down gracefully...');
    server.close(() => {
        console.log('Server closed');
        process.exit(0);
    });
});

process.on('SIGINT', () => {
    console.log('SIGINT received, shutting down gracefully...');
    server.close(() => {
        console.log('Server closed');
        process.exit(0);
    });
});