const express = require("express");
const axios = require("axios");
const fs = require("fs");
const path = require("path");
const https = require("https");
const crypto = require("crypto");

const app = express();
const PORT = 7860;
const DOWNLOAD_DIR = path.join(__dirname, "downloads");

// Ensure the downloads directory exists
if (!fs.existsSync(DOWNLOAD_DIR)) {
    fs.mkdirSync(DOWNLOAD_DIR, { recursive: true });
}

// Axios instance to ignore SSL verification
const axiosInstance = axios.create({
    httpsAgent: new https.Agent({ rejectUnauthorized: false }),
    timeout: 300000, // 5 minutes timeout
});

// Function to generate a unique request ID
const generateRequestId = () => crypto.randomBytes(6).toString("hex");

// Function to validate URLs
const isValidUrl = (url) => {
    try {
        new URL(url);
        return true;
    } catch (error) {
        return false;
    }
};

// Function to delete files after a delay (default: 10 minutes)
const scheduleFileDeletion = (filePath, delay = 600000) => {
    setTimeout(() => {
        fs.unlink(filePath, (err) => {
            if (!err) {
                console.log(`✅ Deleted file: ${filePath}`);
            }
        });
    }, delay);
};

// **Download Function with Integrity Check**
const downloadFile = async (fileUrl, filePath, requestId) => {
    let retries = 3; // Retry up to 3 times

    while (retries > 0) {
        try {
            console.log(`⬇️ [${requestId}] Downloading: ${fileUrl}`);

            const response = await axiosInstance({
                url: fileUrl,
                method: "GET",
                responseType: "stream",
                headers: { "User-Agent": "Mozilla/5.0", "Accept": "*/*" }
            });

            const totalSize = response.headers["content-length"]; // Get file size
            console.log(`📏 [${requestId}] Expected size: ${totalSize} bytes`);

            const writer = fs.createWriteStream(filePath);
            response.data.pipe(writer);

            await new Promise((resolve, reject) => {
                writer.on("finish", resolve);
                writer.on("error", reject);
            });

            // Verify file size
            const fileSize = fs.statSync(filePath).size;
            if (totalSize && fileSize < totalSize * 0.9) { // Allow minor variance
                console.error(`⚠️ [${requestId}] Download incomplete: ${fileSize} bytes (expected ${totalSize} bytes)`);
                fs.unlinkSync(filePath);
                throw new Error("Incomplete download, retrying...");
            }

            console.log(`✅ [${requestId}] Download complete: ${filePath}`);
            return true;

        } catch (error) {
            console.error(`❌ [${requestId}] Download failed: ${error.message}`);
            retries--;

            if (retries === 0) {
                console.error(`⛔ [${requestId}] All retries failed, skipping.`);
            }
        }
    }

    return false;
};

// **API Route - Responds Immediately, Processes in Background**
app.get("/download", async (req, res) => {
    const fileUrl = req.query.url;

    // Validate URL before processing
    if (!fileUrl || !isValidUrl(fileUrl)) {
        return res.status(400).json({ error: "❌ Invalid or missing URL parameter" });
    }

    // Generate a unique request ID
    const requestId = generateRequestId();
    console.log(`📥 [${requestId}] Received request for: ${fileUrl}`);

    // Extract file extension from URL
    const fileExt = path.extname(new URL(fileUrl).pathname) || ".dat"; // Default to ".dat" if no extension
    const filename = `${requestId}${fileExt}`;
    const filePath = path.join(DOWNLOAD_DIR, filename);

    const hostUrl = `${req.protocol}://${req.get("host")}`;
    const servedUrl = `${hostUrl}/files/${filename}`;

    // **Respond to the client immediately**
    res.json({ message: "Processing in background", fileUrl: servedUrl });

    // **Background Processing (Download)**
    (async () => {
        const success = await downloadFile(fileUrl, filePath, requestId);
        if (success) {
            scheduleFileDeletion(filePath);
        }
    })();
});

// Serve files from downloads directory
app.use("/files", express.static(DOWNLOAD_DIR));

// Start the server with an extended timeout
const server = app.listen(PORT, () => {
    console.log(`🚀 Server running on port ${PORT}`);
});

// Increase Express server timeout to 10 minutes
server.timeout = 600000;