const express = require('express');
const { chromium } = require('playwright');
const cheerio = require('cheerio');
const cors = require('cors');

const app = express();
app.use(cors());
app.use(express.json());

const requestQueue = [];
let isProcessing = false;
let browserInstance = null; // Globally cached single browser instance

// Initialize the master browser process on boot
async function initBrowser() {
    try {
        console.log("[System Init]: Launching master Chromium process...");
        browserInstance = await chromium.launch({
            headless: true,
            args: [
                '--no-sandbox',
                '--disable-setuid-sandbox',
                '--disable-dev-shm-usage', // Vital for low memory containers
                '--disable-accelerated-2d-canvas',
                '--disable-gpu'
            ]
        });
        console.log("[System Init]: Headless Chromium ready to snatch.");
    } catch (err) {
        console.error("[System Init Error]: Failed launching master browser:", err.message);
    }
}

// Queue Processing Loop
async function processQueue() {
    if (isProcessing || requestQueue.length === 0) return;
    
    isProcessing = true;
    const currentTask = requestQueue.shift();

    // Ensure browser didn't crash or close unexpectedly under heavy workloads
    if (!browserInstance) {
        await initBrowser();
    }

    let context = null;
    let page = null;

    try {
        const { targetUrl, requestedAssets, res } = currentTask;
        console.log(`\n[Snatch Worker]: Processing -> ${targetUrl}`);

        // Create an isolated, completely fresh browser context (simulates a new device context)
        context = await browserInstance.newContext({
            userAgent: 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36',
            viewport: { width: 1280, height: 800 },
            deviceScaleFactor: 1,
            bypassCSP: true // Bypass Content Security Policy to pull stylesheets freely
        });

        page = await context.newPage();

        // Navigate to the page and wait until network connections completely settle down
        await page.goto(targetUrl, {
            timeout: 25000, 
            waitUntil: 'networkidle' // Crucial: Waits for all dynamic React/JS loads to finish
        });

        // Pull the fully compiled, javascript-rendered DOM tree structure string
        const renderedHtml = await page.content();
        const $ = cheerio.load(renderedHtml);
        
        let extractedCss = "";
        let extractedJs = "";

        // 1. Asset Extractor: CSS Elements
        if (requestedAssets.includes('css')) {
            $('style').each((_, el) => { 
                extractedCss += `/* --- Inline Style --- */\n${$(el).text()}\n\n`; 
            });
            $('link[rel="stylesheet"]').each((_, el) => {
                const href = $(el).attr('href');
                if (href) {
                    const absUrl = href.startsWith('http') ? href : new URL(href, targetUrl).href;
                    extractedCss += `/* External Reference: ${absUrl} */\n`;
                }
            });
        }

        // 2. Asset Extractor: JS Elements
        if (requestedAssets.includes('js')) {
            $('script').each((_, el) => {
                const text = $(el).text();
                const src = $(el).attr('src');
                if (text.trim()) {
                    extractedJs += `// --- Inline Script ---\n${text.trim()}\n\n`;
                } else if (src) {
                    const absUrl = src.startsWith('http') ? src : new URL(src, targetUrl).href;
                    extractedJs += `// External Reference: ${absUrl}\n`;
                }
            });
        }

        // 3. Asset Extractor: Clean, isolated HTML document frame body
        let cleanHtml = "";
        if (requestedAssets.includes('html')) {
            $('script, style, link[rel="stylesheet"]').remove();
            cleanHtml = $('body').html() || $.html();
        }

        // Send payload back cleanly
        res.json({
            html: requestedAssets.includes('html') ? cleanHtml.trim() : null,
            css: requestedAssets.includes('css') ? extractedCss.trim() : null,
            js: requestedAssets.includes('js') ? extractedJs.trim() : null
        });

        console.log(`[Snatch Worker]: Successfully sent assets back to frontend client.`);

    } catch (error) {
        console.error(`[Snatch Worker Error]: Execution hit a wall:`, error.message);
        currentTask.res.status(500).json({ error: "Playwright Snatcher failed execution task: " + error.message });
    } finally {
        // Clean up individual tabs to completely prevent memory leaks
        if (page) await page.close().catch(() => {});
        if (context) await context.close().catch(() => {});
        
        isProcessing = false;
        // Moderate pacing backoff time window delay
        setTimeout(processQueue, 150);
    }
}

// Operational Status Route Mapping
app.get('/', (req, res) => {
    res.json({
        engine: "CodeSnatch Ultimate Playwright Cluster",
        status: "operational",
        browserProcessAlive: !!browserInstance,
        backlogLength: requestQueue.length
    });
});

// Primary Scrape Ingestion Route
app.get('/scrape', (req, res) => {
    const targetUrl = req.query.url;
    const requestedAssets = req.query.assets ? req.query.assets.split(',') : ['html', 'css', 'js'];

    if (!targetUrl) {
        return res.status(400).json({ error: "Missing required query parameter 'url'." });
    }

    requestQueue.push({ targetUrl, requestedAssets, res });
    console.log(`[Traffic]: Enqueued new web page target. Backlog count: ${requestQueue.length}`);
    
    processQueue();
});

// Standard system shutdown handling to cleanly close Chromium process
process.on('SIGTERM', async () => {
    if (browserInstance) await browserInstance.close();
    process.exit(0);
});

const PORT = process.env.PORT || 7860;
app.listen(PORT, async () => {
    console.log(`=== Ultimate CodeSnatch Backend Listening on Port: ${PORT} ===`);
    await initBrowser(); // Instantly spin up browser engine instance when web server activates
});