import http from 'node:http';
import fs from 'node:fs';
import path from 'node:path';

const PORT = Number(process.env.PORT || 80);
const DIST_DIR = path.resolve(process.cwd(), 'dist');

const DASHSCOPE_BASE_URL = 'https://dashscope.aliyuncs.com/compatible-mode/v1';

function getContentType(filePath) {
  const ext = path.extname(filePath).toLowerCase();
  switch (ext) {
    case '.html':
      return 'text/html; charset=utf-8';
    case '.js':
      return 'text/javascript; charset=utf-8';
    case '.css':
      return 'text/css; charset=utf-8';
    case '.svg':
      return 'image/svg+xml';
    case '.png':
      return 'image/png';
    case '.jpg':
    case '.jpeg':
      return 'image/jpeg';
    case '.ico':
      return 'image/x-icon';
    case '.json':
      return 'application/json; charset=utf-8';
    case '.map':
      return 'application/json; charset=utf-8';
    case '.woff2':
      return 'font/woff2';
    case '.txt':
      return 'text/plain; charset=utf-8';
    default:
      return 'application/octet-stream';
  }
}

function sendJson(res, statusCode, body) {
  const payload = JSON.stringify(body);
  res.statusCode = statusCode;
  res.setHeader('Content-Type', 'application/json; charset=utf-8');
  res.setHeader('Cache-Control', 'no-store');
  res.end(payload);
}

async function readJsonBody(req) {
  const chunks = [];
  for await (const chunk of req) chunks.push(chunk);
  const raw = Buffer.concat(chunks).toString('utf-8');
  if (!raw) return null;
  return JSON.parse(raw);
}

function applyApiCorsHeaders(req, res) {
  const origin = req.headers.origin;
  if (!origin) return;
  res.setHeader('Access-Control-Allow-Origin', origin);
  res.setHeader('Vary', 'Origin');
  res.setHeader('Access-Control-Allow-Credentials', 'true');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type, Authorization');
  res.setHeader('Access-Control-Allow-Methods', 'POST, OPTIONS');
}

async function handleChatCompletions(req, res) {
  applyApiCorsHeaders(req, res);

  if (req.method === 'OPTIONS') {
    res.statusCode = 204;
    res.end();
    return;
  }

  if (req.method !== 'POST') {
    sendJson(res, 405, { error: 'Method Not Allowed' });
    return;
  }

  const apiKey =
    process.env.DASHSCOPE_API_KEY ||
    process.env.VITE_API_KEY ||
    process.env.DASHSCOPE_KEY;

  if (!apiKey) {
    sendJson(res, 500, { error: 'Missing DASHSCOPE_API_KEY in server environment' });
    return;
  }

  let body;
  try {
    body = await readJsonBody(req);
  } catch (e) {
    sendJson(res, 400, { error: 'Invalid JSON request body' });
    return;
  }

  const upstreamUrl = `${DASHSCOPE_BASE_URL}/chat/completions`;
  const abortController = new AbortController();

  req.on('close', () => {
    abortController.abort();
  });

  let upstream;
  try {
    upstream = await fetch(upstreamUrl, {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${apiKey}`,
      },
      body: JSON.stringify(body ?? {}),
      signal: abortController.signal,
    });
  } catch (e) {
    sendJson(res, 502, { error: 'Upstream request failed' });
    return;
  }

  const isStream = Boolean(body && body.stream);

  res.statusCode = upstream.status;
  res.setHeader(
    'Content-Type',
    upstream.headers.get('content-type') ||
      (isStream ? 'text/event-stream; charset=utf-8' : 'application/json; charset=utf-8')
  );

  // Help prevent buffering in common reverse proxies.
  res.setHeader('Cache-Control', isStream ? 'no-cache, no-transform' : 'no-store');
  res.setHeader('X-Accel-Buffering', 'no');

  // For streaming: flush headers ASAP so the browser can start rendering.
  if (isStream) {
    res.setHeader('Connection', 'keep-alive');
  }
  if (typeof res.flushHeaders === 'function') res.flushHeaders();

  if (!upstream.body) {
    const text = await upstream.text().catch(() => '');
    res.end(text);
    return;
  }

  try {
    const reader = upstream.body.getReader();
    while (true) {
      const { done, value } = await reader.read();
      if (done) break;
      if (value) res.write(Buffer.from(value));
    }
  } catch (e) {
    // If client disconnected, ignore; otherwise just end response.
  } finally {
    res.end();
  }
}

function serveStatic(req, res, url) {
  if (req.method !== 'GET' && req.method !== 'HEAD') {
    res.statusCode = 405;
    res.end('Method Not Allowed');
    return;
  }

  const pathname = decodeURIComponent(url.pathname);

  // Prevent path traversal.
  const safePath = path.normalize(pathname).replace(/^(\.\.(\/|\\|$))+/, '');
  const fsPath = path.join(DIST_DIR, safePath);

  let resolved = fsPath;

  try {
    if (pathname.endsWith('/')) {
      resolved = path.join(fsPath, 'index.html');
    } else if (fs.existsSync(resolved) && fs.statSync(resolved).isDirectory()) {
      resolved = path.join(resolved, 'index.html');
    }
  } catch {
    // ignore
  }

  try {
    if (!fs.existsSync(resolved) || !fs.statSync(resolved).isFile()) {
      // SPA history fallback.
      resolved = path.join(DIST_DIR, 'index.html');
    }
  } catch {
    resolved = path.join(DIST_DIR, 'index.html');
  }

  const isAsset = pathname.startsWith('/assets/');
  const contentType = getContentType(resolved);

  res.statusCode = 200;
  res.setHeader('Content-Type', contentType);
  res.setHeader(
    'Cache-Control',
    isAsset ? 'public, max-age=31536000, immutable' : 'no-cache'
  );

  if (req.method === 'HEAD') {
    res.end();
    return;
  }

  fs.createReadStream(resolved).pipe(res);
}

const server = http.createServer(async (req, res) => {
  try {
    const url = new URL(req.url || '/', `http://${req.headers.host || 'localhost'}`);

    if (url.pathname === '/api/chat/completions') {
      await handleChatCompletions(req, res);
      return;
    }

    serveStatic(req, res, url);
  } catch (e) {
    res.statusCode = 500;
    res.end('Internal Server Error');
  }
});

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