const http = require('http');
const https = require('https');
const url = require('url');
const fs = require('fs');
const path = require('path');
const crypto = require('crypto');
const EventEmitter = require('events');

// Configuration
const PORT = process.env.PORT || 9520; 
const API_BASE = process.env.API_BASE || 'http://127.0.0.1:9558/api';
const CACHE_DIR = process.env.CACHE_DIR ? path.resolve(process.env.CACHE_DIR) : path.join(__dirname, '.cache');

// Ensure cache directory exists
if (!fs.existsSync(CACHE_DIR)) {
    fs.mkdirSync(CACHE_DIR, { recursive: true });
}

// Active downloads manager
// Key -> { emitter: EventEmitter, currentSize: number, totalSize: number, path: string, done: boolean, error: any }
const activeDownloads = new Map();

// Helper to fetch JSON from API
function fetchApi(token) {
    return new Promise((resolve, reject) => {
        const apiUrl = new URL(API_BASE);
        if (token) {
            apiUrl.searchParams.set('token', token);
        }
        
        const req = http.get(apiUrl, (res) => {
            if (res.statusCode !== 200) {
                res.resume(); 
                return reject(new Error(`API Status Code: ${res.statusCode}`));
            }

            let data = '';
            res.on('data', chunk => data += chunk);
            res.on('end', () => {
                try {
                    const json = JSON.parse(data);
                    resolve(json);
                } catch (e) {
                    reject(e);
                }
            });
        });

        req.on('error', reject);
        req.setTimeout(30000, () => {
            req.destroy();
            reject(new Error('API Request Timeout'));
        });
    });
}

// Helper to determine cache key
function getCacheKey(apiData) {
    if (apiData.data && apiData.data.uniqid) {
        return apiData.data.uniqid;
    }
    // Fallback to hash of URL
    if (apiData.data && apiData.data.url) {
        return crypto.createHash('md5').update(apiData.data.url).digest('hex');
    }
    return null;
}

// Helper to get cache paths
function getCachePaths(key) {
    const subDir = key.substring(0, 1);
    const dir = path.join(CACHE_DIR, subDir);
    if (!fs.existsSync(dir)) {
        fs.mkdirSync(dir, { recursive: true });
    }
    return {
        content: path.join(dir, `${key}.data`),
        meta: path.join(dir, `${key}.meta`)
    };
}

// Helper to parse Range header
function parseRange(range, totalSize) {
    if (!range || range.indexOf('bytes=') !== 0) return null;
    
    const parts = range.replace(/bytes=/, "").split("-");
    const partialStart = parts[0];
    const partialEnd = parts[1];

    const start = parseInt(partialStart, 10);
    const end = partialEnd ? parseInt(partialEnd, 10) : totalSize - 1;
    
    if (isNaN(start) || isNaN(end) || start > end || start >= totalSize) return null;
    
    return { start, end };
}

// Serve file from cache (Completed file)
function serveCompletedCache(req, res, cachePaths, apiData) {
    const { content } = cachePaths;
    const responseHeaders = { ...apiData.data.headers };
    
    if (!responseHeaders['Access-Control-Allow-Origin']) {
        responseHeaders['Access-Control-Allow-Origin'] = '*';
    }
    
    fs.stat(content, (err, stats) => {
        if (err) {
            res.writeHead(500);
            res.end('Cache file missing');
            return;
        }

        const totalSize = stats.size;
        const range = req.headers.range;
        
        if (range) {
            const parsed = parseRange(range, totalSize);
            if (parsed) {
                const { start, end } = parsed;
                const chunksize = (end - start) + 1;
                
                responseHeaders['Content-Range'] = `bytes ${start}-${end}/${totalSize}`;
                responseHeaders['Accept-Ranges'] = 'bytes';
                responseHeaders['Content-Length'] = chunksize;
                
                res.writeHead(206, responseHeaders);
                
                const stream = fs.createReadStream(content, { start, end });
                stream.pipe(res);
                return;
            }
        }

        responseHeaders['Content-Length'] = totalSize;
        responseHeaders['Accept-Ranges'] = 'bytes';
        
        res.writeHead(200, responseHeaders);
        const stream = fs.createReadStream(content);
        stream.pipe(res);
    });
}

// Start download if needed, and serve the growing file
function downloadAndServe(req, res, apiData, cachePaths, key) {
    let task = activeDownloads.get(key);

    // 1. If no task exists, create one
    if (!task) {
        task = {
            emitter: new EventEmitter(),
            currentSize: 0,
            totalSize: 0, // unknown initially
            path: cachePaths.content,
            done: false,
            error: null
        };
        activeDownloads.set(key, task);

        // Start download process
        const targetUrl = apiData.data.url;
        const protocol = targetUrl.startsWith('https') ? https : http;
        
        const proxyReq = protocol.get(targetUrl, (proxyRes) => {
            if (proxyRes.statusCode !== 200) {
                task.error = new Error(`Upstream ${proxyRes.statusCode}`);
                task.emitter.emit('error', task.error);
                activeDownloads.delete(key);
                return;
            }

            // Save meta
            const metaPath = cachePaths.meta.replace('.meta', '.thumb.meta');
            fs.writeFileSync(metaPath, JSON.stringify(apiData));

            const totalSize = parseInt(proxyRes.headers['content-length'] || '0', 10);
            task.totalSize = totalSize;

            const fileStream = fs.createWriteStream(task.path);
            
            proxyRes.on('data', chunk => {
                fileStream.write(chunk);
                task.currentSize += chunk.length;
                task.emitter.emit('progress', task.currentSize);
            });

            proxyRes.on('end', () => {
                fileStream.end();
                task.done = true;
                task.emitter.emit('done');
                activeDownloads.delete(key);
            });

            proxyRes.on('error', (err) => {
                fileStream.end();
                fs.unlink(task.path, () => {});
                task.error = err;
                task.emitter.emit('error', err);
                activeDownloads.delete(key);
            });
        });

        proxyReq.on('error', (err) => {
            task.error = err;
            task.emitter.emit('error', err);
            activeDownloads.delete(key);
        });
    }

    // 2. Serve from the growing file (Tailing logic)
    serveGrowingFile(req, res, task, apiData);
}

function serveGrowingFile(req, res, task, apiData) {
    const responseHeaders = { ...apiData.data.headers };
    if (!responseHeaders['Access-Control-Allow-Origin']) {
        responseHeaders['Access-Control-Allow-Origin'] = '*';
    }

    // Handle Range request if present (only supports simple start range for now)
    const range = req.headers.range;
    let start = 0;
    
    if (range) {
        const parts = range.replace(/bytes=/, "").split("-");
        start = parseInt(parts[0], 10);
        if (isNaN(start)) start = 0;
        
        // Note: We don't know the end yet properly, or we support open-ended
        responseHeaders['Accept-Ranges'] = 'bytes';
        // We can't strictly send Content-Range with /totalSize if we don't know it yet,
        // but often we do from upstream Content-Length.
        if (task.totalSize) {
             responseHeaders['Content-Range'] = `bytes ${start}-${task.totalSize-1}/${task.totalSize}`;
             responseHeaders['Content-Length'] = task.totalSize - start;
        }
        res.writeHead(206, responseHeaders);
    } else {
        if (task.totalSize) {
            responseHeaders['Content-Length'] = task.totalSize;
        }
        res.writeHead(200, responseHeaders);
    }

    // Stream logic
    let bytesSent = start;
    let fd = null;
    let ended = false;
    let isReading = false;

    // Open file for reading
    // We might need to wait for file to be created?
    // Usually writeStream creates it immediately.
    
    function openAndStream() {
        fs.open(task.path, 'r', (err, fileDesc) => {
            if (err) {
                // If file not found yet, wait a bit
                if (err.code === 'ENOENT' && !task.error && !task.done) {
                    setTimeout(openAndStream, 100);
                    return;
                }
                if (!res.headersSent) res.writeHead(500);
                res.end();
                return;
            }
            fd = fileDesc;
            pump();
        });
    }

    function onTaskDone() {
        pump();
    }
    
    function onTaskError(err) {
        close();
    }
    
    // Subscribe to permanent events
    task.emitter.on('done', onTaskDone);
    task.emitter.on('error', onTaskError);

    function pump() {
        if (ended || isReading) return;
        if (task.error) {
            res.end(); // Upstream error
            return;
        }

        // Determine how much we can read
        // Available bytes in file = task.currentSize
        const available = task.currentSize - bytesSent;

        if (available > 0) {
            isReading = true;
            const buffer = Buffer.alloc(Math.min(available, 64 * 1024)); // 64KB chunks
            fs.read(fd, buffer, 0, buffer.length, bytesSent, (err, bytesRead) => {
                isReading = false;
                if (err) {
                    close();
                    return;
                }
                
                if (bytesRead > 0) {
                    const chunk = buffer.slice(0, bytesRead);
                    const canContinue = res.write(chunk);
                    bytesSent += bytesRead;
                    
                    if (canContinue) {
                        pump();
                    } else {
                        res.once('drain', pump);
                    }
                } else {
                    // Should not happen if available > 0, but safety check
                    wait();
                }
            });
        } else {
            // No data available yet
            if (task.done) {
                close(); // We are done
            } else {
                wait();
            }
        }
    }

    function wait() {
        if (ended) return;
        task.emitter.once('progress', pump);
    }

    function close() {
        if (ended) return;
        ended = true;
        if (fd) fs.close(fd, () => {});
        res.end();
        
        // Cleanup listeners
        task.emitter.removeListener('progress', pump);
        task.emitter.removeListener('done', onTaskDone);
        task.emitter.removeListener('error', onTaskError);
    }

    res.on('close', close);
    res.on('error', close);

    openAndStream();
}


const server = http.createServer(async (req, res) => {
    // Basic CORS
    res.setHeader('Access-Control-Allow-Origin', '*');
    res.setHeader('Access-Control-Allow-Methods', 'GET, OPTIONS');
    
    if (req.method === 'OPTIONS') {
        res.writeHead(200);
        res.end();
        return;
    }

    // Ignore favicon
    if (req.url === '/favicon.ico') {
        res.writeHead(204);
        res.end();
        return;
    }

    try {
        const token = req.url.substring(1); 

        if (!token) {
            res.writeHead(400);
            res.end('Missing token');
            return;
        }

        // 1. Get API Data
        let apiData;
        try {
            apiData = await fetchApi(token);
        } catch (e) {
            console.error('API Fetch Error:', e.message);
            res.writeHead(502);
            res.end('API Error');
            return;
        }

        if (apiData.code !== 200 || !apiData.data || !apiData.data.url) {
            res.writeHead(404);
            res.end('Invalid API response');
            return;
        }

        const key = getCacheKey(apiData);
        if (!key) {
            res.writeHead(500);
            res.end('Could not generate cache key');
            return;
        }

        const cachePaths = getCachePaths(key);

        // 2. Check Cache
        // If file exists and is NOT currently being downloaded
        if (activeDownloads.has(key)) {
             // Join the active download stream
             downloadAndServe(req, res, apiData, cachePaths, key);
        } else if (fs.existsSync(cachePaths.content) && fs.existsSync(cachePaths.meta)) {
             serveCompletedCache(req, res, cachePaths, apiData);
        } else {
             // Start new download
             downloadAndServe(req, res, apiData, cachePaths, key);
        }

    } catch (err) {
        console.error('Server Error:', err);
        if (!res.headersSent) {
            res.writeHead(500);
            res.end('Internal Server Error');
        }
    }
});

server.listen(PORT, () => {
    console.log(`Server running on port ${PORT}`);
});