/*
 * Copyright 2021 Google LLC
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
 */

/** @typedef {import('./intervalometer.js').SequenceState} SequenceState */

export const supportsSpeech = 'speechSynthesis' in globalThis;

/**
 * Speaks the run out loud: a countdown into each frame, and the odd status
 * announcement. Useful when you're in front of the camera rather than at the
 * laptop, or holding still for a long exposure.
 *
 * Driven from the intervalometer's state updates (~5/s) rather than its own
 * timer, so it can't drift away from what the sequence is actually doing. Each
 * second is spoken at most once, tracked by the second it belongs to.
 */
export class Narrator {
  enabled = false;
  /** Seconds before a frame to start counting. */
  countFrom = 5;
  announceFrames = false;
  /** Empty means the browser's default voice. */
  voiceURI = '';

  /** @type {number | null} */
  #lastSecond = null;
  #lastNextAt = 0;
  /** @type {string} */
  #lastPhase = 'idle';
  /** @type {SpeechSynthesisVoice[]} */
  #voices = [];

  constructor() {
    if (!supportsSpeech) return;
    this.#loadVoices();
    // Voices arrive asynchronously, and on some platforms only after this fires.
    speechSynthesis.onvoiceschanged = () => this.#loadVoices();
  }

  #loadVoices() {
    this.#voices = speechSynthesis.getVoices();
  }

  get voices() {
    return this.#voices;
  }

  /**
   * @param {string} text
   * @param {{ interrupt?: boolean }} [options]
   */
  say(text, { interrupt = false } = {}) {
    if (!supportsSpeech || !this.enabled) return;
    // A countdown that queues up behind a stale announcement is worse than
    // silence, so anything time-critical clears the queue first.
    if (interrupt) speechSynthesis.cancel();
    let utterance = new SpeechSynthesisUtterance(text);
    let voice = this.#voices.find(v => v.voiceURI === this.voiceURI);
    if (voice) utterance.voice = voice;
    // Slightly quick, so a spoken "three" lands nearer the second it names.
    utterance.rate = 1.1;
    speechSynthesis.speak(utterance);
  }

  cancel() {
    if (supportsSpeech) speechSynthesis.cancel();
  }

  /** Forget what's been spoken, e.g. when a new sequence starts. */
  reset() {
    this.#lastSecond = null;
    this.#lastNextAt = 0;
    this.#lastPhase = 'idle';
    this.cancel();
  }

  /**
   * Called on every sequence state update.
   * @param {SequenceState} state
   */
  update(state) {
    if (!this.enabled || !supportsSpeech) {
      this.#lastPhase = state.phase;
      return;
    }

    // A new target time means a new frame to count into.
    if (state.nextAt !== this.#lastNextAt) {
      this.#lastNextAt = state.nextAt;
      this.#lastSecond = null;
    }

    if (state.phase === 'waiting' || state.phase === 'delay') {
      // Never start counting from further out than the gap actually is - with a
      // 3s interval and a count of 5 you'd otherwise talk over the last frame.
      let gapSeconds =
        state.phase === 'delay'
          ? Infinity
          : Math.round(state.intervalMs / 1000) - 1;
      let limit = Math.max(0, Math.min(this.countFrom, gapSeconds));
      let remaining = Math.ceil((state.nextAt - Date.now()) / 1000);
      if (remaining >= 1 && remaining <= limit && remaining !== this.#lastSecond) {
        this.#lastSecond = remaining;
        this.say(String(remaining));
      }
    }

    if (state.phase !== this.#lastPhase) {
      this.#announcePhase(state);
      this.#lastPhase = state.phase;
    }
  }

  /** @param {SequenceState} state */
  #announcePhase(state) {
    switch (state.phase) {
      case 'capturing':
        if (this.announceFrames) {
          this.say(
            state.total
              ? `Frame ${state.taken + 1} of ${state.total}`
              : `Frame ${state.taken + 1}`
          );
        }
        break;
      case 'done':
        this.say(
          `Sequence complete. ${state.taken} frame${
            state.taken === 1 ? '' : 's'
          }.`,
          { interrupt: true }
        );
        break;
      case 'stopped':
        this.say('Sequence stopped.', { interrupt: true });
        break;
      case 'failed':
        this.say('Sequence failed.', { interrupt: true });
        break;
    }
  }
}