'use strict'

/**
 * static files (404.html, sw.js, conf.js)
 */

/** @type {RequestInit} */
const PREFLIGHT_INIT = {
    status: 204,
    headers: new Headers({
        'access-control-allow-origin': '*',
        'access-control-allow-methods': 'GET,POST,PUT,PATCH,TRACE,DELETE,HEAD,OPTIONS',
        'access-control-max-age': '1728000',
    }),
}

/**
 * @param {any} body
 * @param {number} status
 * @param {Object<string, string>} headers
 */
function makeRes(body, status = 200, headers = {}) {
    headers['access-control-allow-origin'] = '*'
    return new Response(body, {status, headers})
}


/**
 * @param {string} urlStr
 */
function newUrl(urlStr) {
    try {
        return new URL(urlStr)
    } catch (err) {
        return null
    }
}


addEventListener('fetch', e => {
    const ret = fetchHandler(e)
        .catch(err => makeRes('cfworker error:\n' + err.stack, 502))
    e.respondWith(ret)
})


/**
 * @param {FetchEvent} e
 */
async function fetchHandler(e) {
  const getReqHeader = (key) => e.request.headers.get(key);

  let url = new URL(e.request.url);
  url.hostname = "code.dlang.org";

  let parameter = {
    headers: {
      'Host': 'code.dlang.org',
      'User-Agent': getReqHeader("User-Agent"),
      'Accept': getReqHeader("Accept"),
      'Accept-Language': getReqHeader("Accept-Language"),
      'Accept-Encoding': getReqHeader("Accept-Encoding"),
      'Connection': 'keep-alive',
      'Cache-Control': 'max-age=0'
    },
    cacheTtl: 3600
  };

  if (e.request.headers.has("Referer")) {
    parameter.headers.Referer = getReqHeader("Referer");
  }

  if (e.request.headers.has("Origin")) {
    parameter.headers.Origin = getReqHeader("Origin");
  }
  const exp = /.*\.zip$/
  let redirect_url = ""
  if (e.request.url.search(exp)===0) {
    await fetch(new Request(url, e.request), parameter).then( r => {
      redirect_url = r.headers.get("Location")
    })
    return httpHandler(e.request, redirect_url)
  } else {
    return fetch(new Request(url, e.request), parameter);
  }
}


/**
 * @param {Request} req
 * @param {string} pathname
 */
function httpHandler(req, pathname) {
    const reqHdrRaw = req.headers

    // preflight
    if (req.method === 'OPTIONS' &&
        reqHdrRaw.has('access-control-request-headers')
    ) {
        return new Response(null, PREFLIGHT_INIT)
    }

    let rawLen = ''

    const reqHdrNew = new Headers(reqHdrRaw)

    const refer = reqHdrNew.get('referer')

    let urlStr = pathname
    if (urlStr.startsWith('github')) {
        urlStr = 'https://' + urlStr
    }
    const urlObj = newUrl(urlStr)

    /** @type {RequestInit} */
    const reqInit = {
        method: req.method,
        headers: reqHdrNew,
        redirect: 'follow',
        body: req.body
    }
    return proxy(urlObj, reqInit, rawLen, 0)
}


/**
 *
 * @param {URL} urlObj
 * @param {RequestInit} reqInit
 */
async function proxy(urlObj, reqInit, rawLen) {
    const res = await fetch(urlObj.href, reqInit)
    const resHdrOld = res.headers
    const resHdrNew = new Headers(resHdrOld)

    // verify
    if (rawLen) {
        const newLen = resHdrOld.get('content-length') || ''
        const badLen = (rawLen !== newLen)

        if (badLen) {
            return makeRes(res.body, 400, {
                '--error': `bad len: ${newLen}, except: ${rawLen}`,
                'access-control-expose-headers': '--error',
            })
        }
    }
    const status = res.status
    resHdrNew.set('access-control-expose-headers', '*')
    resHdrNew.set('access-control-allow-origin', '*')
    resHdrNew.set('Cache-Control', 'max-age=1500')
    
    resHdrNew.delete('content-security-policy')
    resHdrNew.delete('content-security-policy-report-only')
    resHdrNew.delete('clear-site-data')

    return new Response(res.body, {
        status,
        headers: resHdrNew
    })
}