// see:
// https://github.com/hunshcn/gh-proxy

// 首页静态文件
const ASSET_URL = 'https://hunshcn.github.io/gh-proxy/'
// 前缀, 如果自定义路由为 example.com/gh/*, 将 PREFIX 改为 '/gh/', 注意, 少一个杠都会错!
const PREFIX = '/'
// 分支文件使用 jsDelivr 镜像的开关, 0 为关闭, 默认关闭
const Config = {
	jsdelivr: 0
}

// 白名单，路径里面有包含字符的才会通过，e.g. ['/username/']
const whiteList = []

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',
	}),
}


const exp1 = /^(?:https?:\/\/)?github\.com\/.+?\/.+?\/(?:releases|archive)\/.*$/i
const exp2 = /^(?:https?:\/\/)?github\.com\/.+?\/.+?\/(?:blob|raw)\/.*$/i
const exp3 = /^(?:https?:\/\/)?github\.com\/.+?\/.+?\/(?:info|git-).*$/i
const exp4 = /^(?:https?:\/\/)?raw\.(?:githubusercontent|github)\.com\/.+?\/.+?\/.+?\/.+$/i
const exp5 = /^(?:https?:\/\/)?gist\.(?:githubusercontent|github)\.com\/.+?\/.+?\/.+$/i
const exp6 = /^(?:https?:\/\/)?github\.com\/.+?\/.+?\/tags.*$/i

/**
 * 入口
 * @param {Request} request
 * @returns {Promise<Response>}
 */
async function fetchHandler(request) {
	const req = request
	const urlStr = req.url
	const urlObj = new URL(urlStr)
	let path = urlObj.searchParams.get('q')
	if (path) {
		return Response.redirect('https://' + urlObj.host + PREFIX + path, 301)
	}
	// cfworker 会把路径中的 `//` 合并成 `/`
	path = urlObj.href.substr(urlObj.origin.length + PREFIX.length).replace(/^https?:\/+/, 'https://')
	// 普通文件
	if (path.search(exp1) === 0 ||
		path.search(exp3) === 0 ||
		path.search(exp4) === 0 ||
		path.search(exp5) === 0 ||
		path.search(exp6) === 0) {
		return httpHandler(req, path)
	}
	// blob/raw
	if (path.search(exp2) === 0) {
		if (Config.jsdelivr) {
			const newUrl = path.replace('/blob/', '@').replace(/^(?:https?:\/\/)?github\.com/, 'https://cdn.jsdelivr.net/gh')
			return Response.redirect(newUrl, 302)
		}
		path = path.replace('/blob/', '/raw/')
		return httpHandler(req, path)
	}
	// raw.github.com
	if (path.search(exp4) === 0) {
		const newUrl = path.replace(/(?<=com\/.+?\/.+?)\/(.+?\/)/, '@$1').replace(/^(?:https?:\/\/)?raw\.(?:githubusercontent|github)\.com/, 'https://cdn.jsdelivr.net/gh')
		return Response.redirect(newUrl, 302)
	}
	// 其他 返回静态首页
	return fetch(ASSET_URL + path)
}

/**
 * @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)
	}

	const reqHdrNew = new Headers(reqHdrRaw)

	let urlStr = pathname
	let allow = whiteList.length == 0
	for (let i of whiteList) {
		if (urlStr.includes(i)) {
			allow = true
			break
		}
	}
	if (!allow) {
		return new Response("blocked", { status: 403 })
	}
	if (urlStr.search(/^https?:\/\//) !== 0) {
		urlStr = 'https://' + urlStr
	}
	const urlObj = newUrl(urlStr)

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

/**
 * @param {string} urlStr
 */
function newUrl(urlStr) {
	try {
		return new URL(urlStr)
	} catch (err) {
		return null
	}
}
/**
 * @param {URL} urlObj
 * @param {RequestInit}  reqInit
 * @returns {Promise<Response>}
 */
async function proxy(urlObj, reqInit) {
	const res = await fetch(urlObj.href, reqInit)
	const resHdrOld = res.headers
	const resHdrNew = new Headers(resHdrOld)

	const status = res.status

	if (resHdrNew.has('location')) {
		let _location = resHdrNew.get('location')
		if (checkUrl(_location))
			resHdrNew.set('location', PREFIX + _location)
		else {
			reqInit.redirect = 'follow'
			return proxy(newUrl(_location), reqInit)
		}
	}
	resHdrNew.set('access-control-expose-headers', '*')
	resHdrNew.set('access-control-allow-origin', '*')

	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,
	})
}

function checkUrl(u) {
	for (let i of [exp1, exp2, exp3, exp4, exp5, exp6]) {
		if (u.search(i) === 0) {
			return true
		}
	}
	return false
}

function makeRes(body, status = 200, headers = {}) {
	headers['access-control-allow-origin'] = '*'
	return new Response(body, { status, headers })
}

/**
 * @typedef {Object} Env
 */
export default {
	/**
	 * @param {Request} request
	 * @param {Env} env
	 * @param {ExecutionContext} ctx
	 * @returns {Promise<Response>}
	 */
	async fetch(request, env, ctx) {
		const url = new URL(request.url);
		console.log(`Hello ${navigator.userAgent} at path ${url.pathname}!`);
		return await fetchHandler(request)
			.catch(err => makeRes('cfworker error:\n' + err.stack, 502))
	},
};