type PlaybackMessage =
  | { kind: "config"; inputRate: number }
  | { kind: "audio"; samples: Float32Array; sequence: number }
  | { kind: "clear" | "finish"; sequence: number };

class AudioPlaybackProcessor extends AudioWorkletProcessor {
  private rate = 16000;
  private queue: Float32Array[] = [];
  private offset = 0;
  private fraction = 0;
  private playing = false;
  private fadeIn = 0;
  private fadeOut = 0;
  private lastSample = 0;
  private sequence = 0;
  private finished = false;

  constructor() {
    super();
    this.port.onmessage = (event: MessageEvent<PlaybackMessage>) => {
      const data = event.data;
      switch (data.kind) {
        case "config":
          if (data.inputRate > 0) {
            this.rate = data.inputRate;
          }
          break;
        case "audio":
          this.sequence = data.sequence;
          this.finished = false;
          if (data.samples.length) {
            this.queue.push(data.samples);
          }
          break;
        case "clear":
          this.sequence = data.sequence;
          this.finished = true;
          this.queue = [];
          this.offset = 0;
          this.fraction = 0;
          this.fadeOut = 32;
          break;
        case "finish":
          this.sequence = data.sequence;
          this.finished = true;
          break;
      }
    };
  }
  private bufferedMs() {
    return (this.queue.reduce((sum, buffer) => sum + buffer.length, -this.offset) / this.rate) * 1000;
  }
  private read(): number | null {
    const head = this.queue[0];
    if (!head) {
      return null;
    }
    const a = head[this.offset] ?? 0;
    const b = head[this.offset + 1] ?? this.queue[1]?.[0] ?? a;
    return a + (b - a) * this.fraction;
  }
  private advance() {
    this.fraction += this.rate / sampleRate;
    while (this.fraction >= 1) {
      this.fraction--;
      this.offset++;
    }
    while (this.queue[0] && this.offset >= this.queue[0].length) {
      this.offset -= this.queue[0].length;
      this.queue.shift();
    }
  }
  process(_inputs: Float32Array[][], outputs: Float32Array[][]) {
    const channels = outputs[0];
    const output = channels?.[0];
    if (!output) {
      return true;
    }
    for (let index = 0; index < output.length; index++) {
      let value = 0;
      if (!this.playing && this.queue.length && (this.finished || this.bufferedMs() >= 90)) {
        this.playing = true;
        this.fadeIn = 32;
        this.fadeOut = 0;
      }
      if (this.playing) {
        const sample = this.read();
        if (sample === null) {
          value = this.lastSample * (1 - 1 / 32);
          this.lastSample = value;
          if (Math.abs(value) < 1e-4) {
            this.playing = false;
            this.lastSample = 0;
          }
        } else {
          value = sample;
          this.lastSample = sample;
          this.advance();
        }
        if (this.fadeIn > 0) {
          value *= 1 - this.fadeIn-- / 32;
        }
        if (this.fadeOut > 0) {
          value *= this.fadeOut-- / 32;
          if (!this.fadeOut) {
            this.playing = false;
            this.lastSample = 0;
          }
        }
      }
      output[index] = value;
      const stereo = channels?.[1];
      if (stereo) {
        stereo[index] = value;
      }
    }
    if (this.finished && !this.playing && !this.queue.length) {
      this.finished = false;
      this.port.postMessage({ kind: "drained", sequence: this.sequence });
    }
    return true;
  }
}
registerProcessor("audio-playback", AudioPlaybackProcessor);