const PREFIX = '/_/';
const TARGET = 'https://lemonarcade.com/';

const PAGE = `<!doctype html>
<html lang="en"><head>
<meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1">
<title>Google Classroom</title>
<link rel="icon" href="https://ssl.gstatic.com/classroom/favicon.png">
<style>html,body{margin:0;height:100%;overflow:hidden;background:#0b0b0b}
iframe{position:fixed;inset:0;border:0;width:100%;height:100%;display:block}</style>
</head><body>
<iframe src="${PREFIX}${TARGET}" title="app"
  allow="fullscreen; autoplay; clipboard-read; clipboard-write; encrypted-media; gamepad; microphone; camera; screen-wake-lock"
  allowfullscreen referrerpolicy="no-referrer"></iframe>
<script>
addEventListener('message', function (e) {
  if (e.data && e.data.__x === 1 && e.data.type === 'title' && e.data.value) document.title = e.data.value;
});
history.replaceState(null, '', '/#/classroom');
</script>
</body></html>`;

const SKIP = /(w3\.org|schema\.org|ogp\.me|purl\.org)/;

export default {
  async fetch(req) {
    const url = new URL(req.url);

    if (!url.pathname.startsWith(PREFIX)) {
      return new Response(PAGE, { headers: { 'content-type': 'text/html;charset=utf-8' } });
    }

    const raw = req.url.slice(req.url.indexOf(PREFIX) + PREFIX.length);
    let target;
    try { target = new URL(raw); } catch { return new Response('bad target', { status: 400 }); }

    const h = new Headers(req.headers);
    h.set('host', target.host);
    const ref = req.headers.get('referer');
    if (ref) {
      const i = ref.indexOf(PREFIX);
      if (i > -1) h.set('referer', ref.slice(i + PREFIX.length));
      else h.delete('referer');
    }
    if (req.headers.get('origin') === url.origin) h.set('origin', target.origin);

    const res = await fetch(target, {
      method: req.method,
      headers: h,
      body: ['GET','HEAD'].includes(req.method) ? undefined : req.body,
      redirect: 'manual'
    });

    const out = new Headers(res.headers);
    for (const k of ['x-frame-options','content-security-policy','content-security-policy-report-only',
                     'cross-origin-opener-policy','cross-origin-embedder-policy','cross-origin-resource-policy',
                     'permissions-policy','strict-transport-security','content-length','content-encoding','link']) out.delete(k);
    out.set('access-control-allow-origin', '*');

    if (res.status >= 300 && res.status < 400) {
      const loc = res.headers.get('location');
      if (loc) out.set('location', url.origin + PREFIX + new URL(loc, target).href);
      return new Response(null, { status: res.status, headers: out });
    }

    const sc = res.headers.getSetCookie ? res.headers.getSetCookie() : [];
    if (sc.length) {
      out.delete('set-cookie');
      for (const c of sc) out.append('set-cookie', c.replace(/;\s*Domain=[^;]+/i, ''));
    }

    const ct = out.get('content-type') || '';
    if (ct.includes('text/html') || ct.includes('text/css')) {
      const text = await res.text();
      const fixed = text.replace(/https?:\/\/[^"'\s>)\\,]+/g, m => SKIP.test(m) ? m : url.origin + PREFIX + m);
      if (ct.includes('html')) {
        const base = url.origin + PREFIX + new URL('.', target).href;
        const boot = '<base href="' + base + '"><script>(function(){'
          + 'var send=function(t,v){try{parent.postMessage({__x:1,type:t,value:v},"*")}catch(e){}};'
          + 'var last;var tick=function(){if(document.title!==last){last=document.title;send("title",last)}};'
          + 'new MutationObserver(tick).observe(document.documentElement,{subtree:true,childList:true,characterData:true});'
          + 'setInterval(tick,1000);'
          + 'var s=function(o,k,v){try{Object.defineProperty(o,k,{get:function(){return v},configurable:true})}catch(e){}};'
          + 's(window,"top",window);s(window,"parent",window);s(window,"frameElement",null);s(document,"referrer","");'
          + '})();<\/script>';
        out.set('content-type', 'text/html; charset=utf-8');
        const html = /<head[^>]*>/i.test(fixed) ? fixed.replace(/<head[^>]*>/i, m => m + boot) : boot + fixed;
        return new Response(html, { status: res.status, headers: out });
      }
      out.set('content-type', 'text/css; charset=utf-8');
      return new Response(fixed, { status: res.status, headers: out });
    }
    return new Response(res.body, { status: res.status, headers: out });
  }
};