export default {
  async fetch(request, env, context) {
    return await handleRequest(request, env, context)
  }
}

async function handleRequest(request, {pageUrl, codeUrl}, context) {
  const url = new URL(request.url);
  const allowOrigin = request.headers.get('Origin') || url.origin;
  const pathPrefix = '/b23/';
  const pathname = url.pathname.startsWith(pathPrefix) ? url.pathname.slice(pathPrefix.length - 1) : url.pathname;

  const routeJsonResult = '/g';

  const response = await caches.default.match(request);
  if (response) { return response; }

  if (pathname === '/' || pathname === '/index.html') {
    const {status, body} = await fetch(pageUrl);
    return new Response(body, {
      status,
      headers: {
        "content-type": "text/html; charset=utf-8",
      }
    });
  }

  if (pathname === '/worker.js') {
    const {status, body} = await fetch(codeUrl);
    return new Response(body, {
      status,
      headers: {
        "content-type": "text/plain;charset=utf-8"
      }
    });
  }

  // invalid pathnames should be handled here
  if (pathname.includes('.')) {
    return new Response("400 Bad Request.", {
      status: 400,
      headers: {
        'Cache-Control': 'public, max-age=31536000',
      },
    });
  }

  if (request.method === "OPTIONS") {
    // Handle CORS preflight requests
    if (
      request.headers.get("Origin") !== null &&
      request.headers.get("Access-Control-Request-Method") !== null &&
      request.headers.get("Access-Control-Request-Headers") !== null
    ) {
      return new Response(null, {
        headers: {
          "Access-Control-Allow-Origin": allowOrigin,
          "Access-Control-Allow-Methods": "GET,HEAD,OPTIONS",
          "Access-Control-Max-Age": "86400",
          "Access-Control-Allow-Headers": request.headers.get(
            "Access-Control-Request-Headers"
          ),
        },
      });
    } else {
      // Handle standard OPTIONS request.
      return new Response(null, {
        headers: {
          Allow: "GET, HEAD, POST, OPTIONS",
        },
      });
    }
  }

  const g = pathname.startsWith(routeJsonResult);

  const b23 = new URL(g ? pathname.slice(routeJsonResult.length) : pathname, 'https://b23.tv');

  const paramsToReserve = [
    'p', 'page', 't', 'itemsId', 'tab', 'topic_id', 'vote_id'
  ];

  let returned;

  await fetch(b23, {
    redirect: "manual",
  })
    .then((response) => {
      if (response.status === 302 || response.status === 301) {
        const orgUrl = new URL(response.headers.get('Location') || 'https://www.bilibili.com/');
        const newUrl = new URL(orgUrl.pathname, orgUrl.origin);
        const search = new URLSearchParams();
        orgUrl.searchParams.forEach((value, key) => {
          if (paramsToReserve.includes(key)) { search.append(key, value); }
        });
        newUrl.search = search.toString();
        if (g) {
          returned = new Response(JSON.stringify({
            'stripped': newUrl.toString(),
            'url': response.headers.get('Location'),
            'oq': b23.toString(),
          }), {
            status: 200,
            headers: {
              'Content-Type': 'application/json; charset=utf-8',
              'Cache-Control': 'public, max-age=31536000',
              'Referrer-Policy': 'no-referrer',
              'Access-Control-Allow-Origin': allowOrigin,
            },
          });
          return;
        }
        const modifiedHeaders = new Headers(response.headers);
        modifiedHeaders.set('Access-Control-Allow-Origin', allowOrigin);
        modifiedHeaders.set('Cache-Control', 'public, max-age=31536000');
        modifiedHeaders.set('Referrer-Policy', 'no-referrer');
        modifiedHeaders.set('Location', newUrl.toString());
        returned = new Response(response.body, {
          ...response,
          headers: modifiedHeaders,
        });
        context.waitUntil(caches.default.put(request, returned.clone()));
      } else {
        const modifiedHeaders = new Headers(response.headers);
        modifiedHeaders.set('Access-Control-Allow-Origin', allowOrigin);
        returned = new Response(response.body, {
          status: Number.parseInt(response.headers.get('bili-status-code').slice(1)),
          headers: modifiedHeaders,
        });
      }
    });

  return returned;
}