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

const app = express();
const PORT = 7860;

// --- CONFIGURATION ---
// Minimum free RAM (in Megabytes) required to accept a new request
const MIN_FREE_RAM_MB = 500; 
// How often to check the queue (in milliseconds)
const QUEUE_CHECK_INTERVAL_MS = 2000; 

const requestQueue = [];

// Get current free RAM in MB
const getFreeRamMB = () => os.freemem() / (1024 * 1024);

// 🧠 RAM MONITORING & QUEUEING MIDDLEWARE
app.use((req, res, next) => {
    // We only want to queue Heavy requests (usually POST requests with files)
    // GET requests like status checks can bypass this if needed, but let's queue all for safety
    const freeRam = getFreeRamMB();
    
    if (freeRam > MIN_FREE_RAM_MB) {
        next(); // Enough RAM, process immediately
    } else {
        console.log(`⚠️ [RAM LOW: ${freeRam.toFixed(2)} MB] Queuing request: ${req.method} ${req.url}`);
        requestQueue.push({ req, res, next, time: Date.now() });
    }
});

// 🔄 QUEUE PROCESSOR LOOP
setInterval(() => {
    if (requestQueue.length > 0) {
        const freeRam = getFreeRamMB();
        if (freeRam > MIN_FREE_RAM_MB) {
            // Remove the first request from the queue
            const { req, res, next, time } = requestQueue.shift();
            const waitTime = ((Date.now() - time) / 1000).toFixed(1);
            console.log(`✅ [RAM OK: ${freeRam.toFixed(2)} MB] Processing queued request: ${req.method} ${req.url} (Waited ${waitTime}s)`);
            next(); // Continue processing
        }
    }
}, QUEUE_CHECK_INTERVAL_MS);


// 🔀 REVERSE PROXY ROUTES
const proxyOptions = {
    changeOrigin: true,
    proxyTimeout: 300000, // 5 minutes timeout for heavy tasks
};

app.use('/visuals', createProxyMiddleware({ target: 'http://127.0.0.1:7861', pathRewrite: {'^/visuals': ''}, ...proxyOptions }));
app.use('/audio_server', createProxyMiddleware({ target: 'http://127.0.0.1:7862', pathRewrite: {'^/audio_server': ''}, ...proxyOptions }));
app.use('/cipher_sticker', createProxyMiddleware({ target: 'http://127.0.0.1:7863', pathRewrite: {'^/cipher_sticker': ''}, ...proxyOptions }));
app.use('/scanner', createProxyMiddleware({ target: 'http://127.0.0.1:7864', pathRewrite: {'^/scanner': ''}, ...proxyOptions }));

// Status Route
app.get('/', (req, res) => {
    res.json({
        message: '🚀 Cipher-MD Smart API Gateway is Running!',
        status: 'Active',
        ram_monitoring: true,
        free_ram_mb: Math.round(getFreeRamMB()),
        queued_requests: requestQueue.length
    });
});

app.listen(PORT, () => {
    console.log(`\n======================================================`);
    console.log(`🚀 SMART API GATEWAY RUNNING ON PORT ${PORT}`);
    console.log(`🧠 RAM THRESHOLD: ${MIN_FREE_RAM_MB} MB`);
    console.log(`======================================================\n`);
});