const { Track } = require('./track')
const { from_seconds_to_string } = require('./helpers/duration')

// side effect
function shuffle_array(arr) {
  for (let i = arr.length - 1; i > 0; i--) {
    const j = Math.floor(Math.random() * (i + 1));
    [arr[i], arr[j]] = [arr[j], arr[i]];
  }
}

/**
 * @class
 */
class Playlist {
  #current_index
  #tracks
  #name
  #touched

  /**
   * @constructor
   * @param {Object} parameters={}
   * @param {Track[]} [parameters.tracks=[]] The tracks that compose the playlist
   * @param {number} [parameters.current_index=0] The id of the currently played track
   */
  constructor({ tracks = [], current_index = 0, name = null } = {}) {
    this.#current_index = current_index
    this.#tracks = tracks.map(t => t instanceof Track ? t : new Track(t))
    this.#name = name
    this.#touched = false
  }

  /**
   * @method
   * @returns {Playlist} A copy of the current playlist
   */
  clone() {
    return new Playlist({
      current_index: this.#current_index,
      tracks: this.#tracks.map(t => t.clone()),
      name: this.#name
    })
  }

  /**
   * @method
   * @desc Shuffle the track list
   * @returns {Playlist} The current playlist
   */
  shuffle() {
    shuffle_array(this.#tracks)
    this.#touched = true
    return this
  }

  /**
   * @method
   * @returns {Object} A JSON object that describe the tracklist
   */
  toJSON() {
    return this.#tracks
  }

  map_tracks(callback) {
    const current = this.get_current_track()
    return this.#tracks.map((t, idx, all) => callback(t, idx, all, current))
  }

  next({ loop = 0 }) {
    this.#current_index = (this.#current_index + 1)
    if (loop > 0) {
      this.#current_index %= this.#tracks.length
    }
    return this
  }

  previous({ loop = 0 }) {
    this.#current_index = this.#current_index - 1
    if (this.#current_index < 0) this.#current_index = 0
    if (loop > 0) {
      this.#current_index %= this.#tracks.length
    }
    return this
  }

  goto(idx) {
    if (this.#tracks[idx - 1] == null) {
      return false
    }
    this.#current_index = idx - 1
    return true
  }

  /**
   * @returns {Track|null} The track that is currenly played, or <code>null</code> if it doesn't exist
   */
  get_current_track() {
    return this.#tracks[this.#current_index] ?? null
  }

  /**
   * @param {number} track_index The index of the track to be retrieved
   * @returns {Track|null} The track that is looked for, or <code>null</code> if it doesn't exist
   */
  get_track_by_index(track_index) {
    return this.#tracks[track_index] ?? null
  }

  /**
   * @method
   * @desc Add a new track a the end of the playlist
   * @param {Track}
   * @returns {Playlist} The current playlist
   */
  push(track) {
    this.#tracks.push(track)
    this.#touched = true
    return this
  }

  /**
   * @method
   * @desc Remove a track from the playlist
   * @param {number} The index of the track to remove
   * @returns {boolean} <code>true</code> if the element was successfully removed, <code>false</code> otherwise
   */
  delete(track_index) {
    if (track_index >= this.#tracks.length) {
      return false
    }
    if (track_index < this.#current_index) {
      this.#current_index -= 1
    }
    delete this.#tracks[track_index]
    this.#tracks = this.#tracks.filter(Boolean)
    this.#touched = true
    return true
  }

  /**
   * @method
   * @returns {boolean} <code>true</code> if the playlist is empty, <code>false</code> otherwise
   */
  is_empty() {
    return this.#tracks.length === 0
  }

  /**
   * @method
   * @returns {number} The number of tracks in the playlist
   */
  get_length() {
    return this.#tracks.length
  }

  /**
   * @method
   * @return {number} The duration of the playlist, in seconds
   */
  get_duration() {
    return this.#tracks.reduce((a, t) => a + t.get_length(), 0)
  }

  /**
   * @method
   * @return {durationString} The duration of the playlist, as a string
   */
  get_duration_as_string() {
    return from_seconds_to_string(this.get_duration())
  }

  /**
   * @method
   * @returns {string} a string representation of the playlist
   */
  toString() {
    return this.#tracks.join(', ')
  }

  get_name() {
    return this.#name || "(unamed)"
  }

  set_name(name = null) {
    this.#name = name
  }

  is_named() {
    return Boolean(this.#name)
  }

  untouch() {
    this.#touched = false
  }

  is_touched() {
    return this.#touched
  }
}

module.exports = { Playlist }