const http = require('http');
const fs = require('fs');
const path = require('path');

const PORT = process.env.PORT || 24710;
const HOST = process.env.HOST || '0.0.0.0';
const ROOT = __dirname;

const MIME = {
  '.html': 'text/html; charset=utf-8',
  '.js':   'application/javascript',
  '.wasm': 'application/wasm',
  '.data': 'application/octet-stream',
  '.css':  'text/css',
  '.png':  'image/png',
  '.ico':  'image/x-icon',
  '.svg':  'image/svg+xml',
  '.json': 'application/json',
  '.jpg':  'image/jpeg',
  '.jpeg': 'image/jpeg',
  '.mp4':  'video/mp4',
  '.m4v':  'video/mp4',
  '.webm': 'video/webm',
  '.ogg':  'video/ogg',
};

function extType(p) {
  return MIME[path.extname(p).toLowerCase()] || 'application/octet-stream';
}

function originalCompressedPath(fp) {
  if (fp.endsWith('.unityweb')) return fp.slice(0, -'.unityweb'.length);
  if (fp.endsWith('.gz')) return fp.slice(0, -'.gz'.length);
  if (fp.endsWith('.br')) return fp.slice(0, -'.br'.length);
  return fp;
}

function headersForFile(fp, size, encoding) {
  const originalPath = originalCompressedPath(fp);
  const fileName = path.basename(originalPath);
  const isHashedBuildAsset = /\/Build\/[a-f0-9]{32}\./.test(fp);
  const headers = {
    'Content-Type': extType(originalPath),
    'Content-Length': size,
    'X-Content-Type-Options': 'nosniff',
    'Accept-Ranges': 'bytes',
  };

  if (encoding != null) {
    headers['Content-Encoding'] = encoding;
    headers['Cache-Control'] = isHashedBuildAsset
      ? 'public, max-age=31536000, immutable'
      : 'public, max-age=604800';
  } else if (/\.(mp4|m4v|webm|ogg)$/i.test(fp)) {
    headers['Cache-Control'] = 'public, max-age=31536000, immutable';
  } else if (fileName === 'ServiceWorker.js' || fileName === 'index.html' || fileName === 'manifest.webmanifest') {
    headers['Cache-Control'] = 'no-cache';
  } else if (isHashedBuildAsset) {
    headers['Cache-Control'] = 'public, max-age=31536000, immutable';
  } else {
    headers['Cache-Control'] = 'public, max-age=3600';
  }

  return headers;
}

function addValidators(headers, stat) {
  headers['ETag'] = `"${stat.size.toString(16)}-${Math.floor(stat.mtimeMs).toString(16)}"`;
  headers['Last-Modified'] = stat.mtime.toUTCString();
  return headers;
}

function isFresh(req, headers) {
  const ifNoneMatch = req.headers['if-none-match'];
  if (ifNoneMatch && ifNoneMatch === headers['ETag']) return true;

  const ifModifiedSince = req.headers['if-modified-since'];
  if (ifModifiedSince && headers['Last-Modified']) {
    return new Date(ifModifiedSince).getTime() >= new Date(headers['Last-Modified']).getTime();
  }

  return false;
}

function detectUnityEncoding(fp, callback) {
  if (fp.endsWith('.gz')) {
    callback(null, 'gzip');
    return;
  }

  if (fp.endsWith('.br')) {
    callback(null, 'br');
    return;
  }

  if (!fp.endsWith('.unityweb')) {
    callback(null, null);
    return;
  }

  fs.open(fp, 'r', (openErr, fd) => {
    if (openErr) { callback(openErr); return; }
    const buf = Buffer.alloc(2);
    fs.read(fd, buf, 0, 2, 0, (readErr) => {
      fs.close(fd, () => {});
      if (readErr) { callback(readErr); return; }
      callback(null, buf[0] === 0x1f && buf[1] === 0x8b ? 'gzip' : 'br');
    });
  });
}

// 首页：基于原始 index.html，注入启动封面（不修改任何 Unity 加载逻辑）
function serveIndex(res) {
  try {
    let html = fs.readFileSync(path.join(ROOT, 'index.html'), 'utf-8');

    // 注入到 </head> 之前的 CSS
    const css = `
    <style>
      #landing-overlay {
        position: fixed; inset: 0; z-index: 9999;
        display: flex; flex-direction: column;
        align-items: center; justify-content: center;
        background: radial-gradient(ellipse at center, #2a2526 0%, #1a1516 70%, #0d0a0b 100%);
        transition: opacity 0.5s ease;
      }
      #landing-overlay.hidden { opacity: 0; pointer-events: none; }
      #landing-overlay .logo-area { margin-bottom: 60px; text-align: center; }
      #landing-overlay .logo-area .icon {
        width: 120px; height: 120px; margin: 0 auto 30px;
        background: url('TemplateData/unity-logo-light.png') no-repeat center;
        background-size: contain;
        filter: drop-shadow(0 0 30px rgba(255,255,255,0.15));
      }
      #landing-overlay h1 {
        font-size: clamp(24px, 4vw, 42px);
        font-weight: 700; letter-spacing: 0.08em; color: #fff;
        text-shadow: 0 2px 20px rgba(255,255,255,0.2);
      }
      #landing-overlay .subtitle {
        margin-top: 12px;
        font-size: clamp(14px, 1.8vw, 18px);
        color: rgba(255,255,255,0.45); letter-spacing: 0.15em;
      }
      #landing-btn {
        display: inline-flex; align-items: center; gap: 12px;
        padding: 16px 56px;
        font-size: clamp(16px, 2vw, 20px);
        font-weight: 600; letter-spacing: 0.1em; color: #fff;
        background: linear-gradient(135deg, #4a90d9 0%, #357abd 100%);
        border: none; border-radius: 50px; cursor: pointer;
        transition: transform 0.2s ease, box-shadow 0.2s ease;
        box-shadow: 0 8px 32px rgba(74, 144, 217, 0.35);
      }
      #landing-btn:hover {
        transform: translateY(-2px) scale(1.03);
        box-shadow: 0 12px 40px rgba(74, 144, 217, 0.5);
      }
      #landing-btn:active { transform: translateY(0) scale(0.98); }
      #landing-btn .arrow {
        display: inline-block; font-size: 1.2em;
        transition: transform 0.2s ease;
      }
      #landing-btn:hover .arrow { transform: translateX(4px); }
      #landing-overlay .hint {
        margin-top: 40px; font-size: 13px;
        color: rgba(255,255,255,0.25); letter-spacing: 0.05em;
      }
    </style>`;

    // 注入到 <body> 最前面的 overlay
    const overlay = `
  <div id="landing-overlay">
    <div class="logo-area">
      <div class="icon"></div>
      <h1>运动伤害现场急救虚拟仿真实验</h1>
      <p class="subtitle">VIRTUAL SIMULATION EXPERIMENT</p>
    </div>
    <button id="landing-btn" onclick="enterExperiment()">
      进入全屏实验
      <span class="arrow">→</span>
    </button>
    <p class="hint">点击按钮进入全屏沉浸式实验环境</p>
  </div>`;

    // 注入到 </body> 之前的 JS（不修改原始 Unity 加载逻辑）
    const js = `
  <script>
    (function() {
      var overlay = document.getElementById('landing-overlay');

      window.enterExperiment = function() {
        var el = document.documentElement;
        var requestFS = el.requestFullscreen || el.webkitRequestFullscreen
                     || el.msRequestFullscreen || el.mozRequestFullScreen;

        function go() {
          overlay.classList.add('hidden');
        }

        if (requestFS) {
          requestFS.call(el).then(go).catch(function(err) {
            console.warn('全屏请求失败:', err);
            go();
          });
        } else {
          go();
        }
      };
    })();
  </script>`;

    html = html.replace('</head>', css + '\n</head>');
    html = html.replace('<body>', '<body>\n' + overlay);
    html = html.replace('</body>', js + '\n</body>');

    res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
    res.end(html);
  } catch (err) {
    res.writeHead(500);
    res.end('Internal Server Error');
    console.error(err);
  }
}

// 静态文件
function serveStatic(req, res) {
  let requestPath;
  try {
    requestPath = decodeURIComponent(req.url.split('?')[0]);
  } catch (err) {
    res.writeHead(400);
    res.end('Bad Request');
    return;
  }

  let fp = path.join(ROOT, requestPath);
  if (!fp.startsWith(ROOT)) { res.writeHead(403); res.end('Forbidden'); return; }
  fs.stat(fp, (err, stat) => {
    if (err || !stat.isFile()) { res.writeHead(404); res.end('Not Found'); return; }

    detectUnityEncoding(fp, (encodingErr, encoding) => {
      if (encodingErr) { res.writeHead(500); res.end('Internal Server Error'); return; }

      const range = req.headers.range;
      if (range) {
        const match = /^bytes=(\d*)-(\d*)$/.exec(range);
        if (!match) {
          res.writeHead(416, { 'Content-Range': `bytes */${stat.size}` });
          res.end();
          return;
        }

        let start;
        let end;
        if (match[1] === '' && match[2] !== '') {
          const suffixLength = parseInt(match[2], 10);
          start = Math.max(stat.size - suffixLength, 0);
          end = stat.size - 1;
        } else {
          start = match[1] === '' ? 0 : parseInt(match[1], 10);
          end = match[2] === '' ? stat.size - 1 : parseInt(match[2], 10);
        }
        if (Number.isNaN(start) || Number.isNaN(end) || start > end || end >= stat.size) {
          res.writeHead(416, { 'Content-Range': `bytes */${stat.size}` });
          res.end();
          return;
        }

        const headers = addValidators(headersForFile(fp, end - start + 1, encoding), stat);
        headers['Content-Range'] = `bytes ${start}-${end}/${stat.size}`;
        res.writeHead(206, headers);
        fs.createReadStream(fp, { start, end }).pipe(res);
        return;
      }

      const headers = addValidators(headersForFile(fp, stat.size, encoding), stat);
      if (isFresh(req, headers)) {
        delete headers['Content-Length'];
        res.writeHead(304, headers);
        res.end();
        return;
      }

      res.writeHead(200, headers);
      fs.createReadStream(fp).pipe(res);
    });
  });
}

http.createServer((req, res) => {
  if (req.url === '/' || req.url === '/index.html') return serveIndex(res);
  serveStatic(req, res);
}).listen(PORT, HOST, () => {
  console.log('');
  console.log('  ╔══════════════════════════════════════════════════╗');
  console.log('  ║  运动伤害现场急救虚拟仿真实验 - WebGL Server       ║');
  console.log('  ║                                                  ║');
  console.log('  ║  Server running at: http://' + HOST + ':' + PORT + '          ║');
  console.log('  ║  Press Ctrl+C to stop                            ║');
  console.log('  ╚══════════════════════════════════════════════════╝');
  console.log('');
});