/**
 * Get video ID.
 *
 * There are a few type of video URL formats.
 *  - https://www.youtube.com/watch?v=VIDEO_ID
 *  - https://m.youtube.com/watch?v=VIDEO_ID
 *  - https://youtu.be/VIDEO_ID
 *  - https://www.youtube.com/v/VIDEO_ID
 *  - https://www.youtube.com/embed/VIDEO_ID
 *  - https://music.youtube.com/watch?v=VIDEO_ID
 *  - https://gaming.youtube.com/watch?v=VIDEO_ID
 *
 * @param {string} link
 * @return {string}
 * @throws {Error} If unable to find a id
 * @throws {TypeError} If videoid doesn't match specs
 */
const validQueryDomains = new Set([
  'youtube.com',
  'www.youtube.com',
  'm.youtube.com',
  'music.youtube.com',
  'gaming.youtube.com',
]);
const validPathDomains = /^https?:\/\/(youtu\.be\/|(www\.)?youtube\.com\/(embed|v|shorts)\/)/;
exports.getURLVideoID = link => {
  const parsed = new URL(link);
  let id = parsed.searchParams.get('v');
  if (validPathDomains.test(link) && !id) {
    const paths = parsed.pathname.split('/');
    id = parsed.host === 'youtu.be' ? paths[1] : paths[2];
  } else if (parsed.hostname && !validQueryDomains.has(parsed.hostname)) {
    throw Error('Not a YouTube domain');
  }
  if (!id) {
    throw Error(`No video id found: ${link}`);
  }
  id = id.substring(0, 11);
  if (!exports.validateID(id)) {
    throw TypeError(`Video id (${id}) does not match expected ` +
      `format (${idRegex.toString()})`);
  }
  return id;
};


/**
 * Gets video ID either from a url or by checking if the given string
 * matches the video ID format.
 *
 * @param {string} str
 * @returns {string}
 * @throws {Error} If unable to find a id
 * @throws {TypeError} If videoid doesn't match specs
 */
const urlRegex = /^https?:\/\//;
exports.getVideoID = str => {
  if (exports.validateID(str)) {
    return str;
  } else if (urlRegex.test(str)) {
    return exports.getURLVideoID(str);
  } else {
    throw Error(`No video id found: ${str}`);
  }
};


/**
 * Returns true if given id satifies YouTube's id format.
 *
 * @param {string} id
 * @return {boolean}
 */
const idRegex = /^[a-zA-Z0-9-_]{11}$/;
exports.validateID = id => idRegex.test(id);


/**
 * Checks wether the input string includes a valid id.
 *
 * @param {string} string
 * @returns {boolean}
 */
exports.validateURL = string => {
  try {
    exports.getURLVideoID(string);
    return true;
  } catch (e) {
    return false;
  }
};