"use strict";

/*
  Copyright 2018 Google LLC

  Use of this source code is governed by an MIT-style
  license that can be found in the LICENSE file or at
  https://opensource.org/licenses/MIT.
*/
const errors = require('./errors');

const escapeRegExp = require('./escape-regexp');

module.exports = modifyURLPrefix => {
  if (!modifyURLPrefix || typeof modifyURLPrefix !== 'object' || Array.isArray(modifyURLPrefix)) {
    throw new Error(errors['modify-url-prefix-bad-prefixes']);
  } // If there are no entries in modifyURLPrefix, just return an identity
  // function as a shortcut.


  if (Object.keys(modifyURLPrefix).length === 0) {
    return entry => entry;
  }

  Object.keys(modifyURLPrefix).forEach(key => {
    if (typeof modifyURLPrefix[key] !== 'string') {
      throw new Error(errors['modify-url-prefix-bad-prefixes']);
    }
  }); // Escape the user input so it's safe to use in a regex.

  const safeModifyURLPrefixes = Object.keys(modifyURLPrefix).map(escapeRegExp); // Join all the `modifyURLPrefix` keys so a single regex can be used.

  const prefixMatchesStrings = safeModifyURLPrefixes.join('|'); // Add `^` to the front the prefix matches so it only matches the start of
  // a string.

  const modifyRegex = new RegExp(`^(${prefixMatchesStrings})`);
  return originalManifest => {
    const manifest = originalManifest.map(entry => {
      if (typeof entry.url !== 'string') {
        throw new Error(errors['manifest-entry-bad-url']);
      }

      entry.url = entry.url.replace(modifyRegex, match => {
        return modifyURLPrefix[match];
      });
      return entry;
    });
    return {
      manifest
    };
  };
};