/*

* Copyright 2020 Google LLC

*

* Licensed under the Apache License, Version 2.0 (the "License");

* you may not use this file except in compliance with the License.

* You may obtain a copy of the License at

*

* https://www.apache.org/licenses/LICENSE-2.0

*

* Unless required by applicable law or agreed to in writing, software

* distributed under the License is distributed on an "AS IS" BASIS,

* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

* See the License for the specific language governing permissions and

* limitations under the License.

*/

const {doRedirect} = require('./env');

const redirectsYaml = require('redirects-yaml');

const YAML = require('js-yaml');

const fs = require('fs');

const path = require('path');

// Included for types only.

// eslint-disable-next-line no-unused-vars

const express = require('express');

/**

* @param {redirectsYaml.RedirectLine[]} redirects

* @param {string[]=} staticPaths

*/

function buildCheckHandlerInternal(redirects, staticPaths = undefined) {

let checker = () => true;

if (staticPaths) {

// Ensure that staticPath is never blank (this ensures it's always ".").

const alwaysStaticPaths = staticPaths.map(staticPath => staticPath || '.');

checker = s => {

for (const staticPath of alwaysStaticPaths) {

// This is passed the folder name, not "/index.html". We just assume that any folder that

// exists can be redirected to.

const check = path.join(staticPath, s);

if (fs.existsSync(check)) {

return true;

}

}

return false;

};

}

return redirectsYaml.buildHandlers(redirects, checker);

}

/**

* Builds HTTP middleware that serves redirects for a redirects.yaml

* configuration file.

*

* @param {string} filename to load configuration from

* @param {string[]=} staticPaths to check if content exists

* @param {number=} code to use

* @return {express.RequestHandler}

*/

function buildRedirectHandler(filename, staticPaths = undefined, code = 301) {

const raw = YAML.load(fs.readFileSync(filename, 'utf-8'));

const {redirects} =

/** @type {{ redirects: redirectsYaml.RedirectLine[] }} */ (raw);

const handler = buildCheckHandlerInternal(redirects, staticPaths);

/** @type {express.RequestHandler} */

return (req, res, next) => {

const target = handler(req.url);

if (target !== null && target !== req.url) {

return doRedirect(res, target, code);

}

// If we didn't match normally but the URL contains a dot, then check it again with those

// replaced with underscores. There are various bad links to APIs with ".", when the generated

// pages actually use "_".

if (req.url.includes('.')) {

let update = req.url.replace(/\./g, '_');

if (update.endsWith('_html')) {

update = update.slice(0, -5) + '.html';

}

const target = handler(update);

if (target !== null && target !== req.url) {

return doRedirect(res, target, code);

}

}

return next();

};

}

module.exports = {

buildCheckHandlerInternal,

buildRedirectHandler,

};