src/services/audio-capture.ts

import type {
  AudioCaptureService,
  AudioDurationCaptureProgress,
  MicPermissionState,
} from "../app/types";

const DEFAULT_THRESHOLD = 0.024;
const DEFAULT_SILENCE_MS = 900;
const DEFAULT_MAX_WAIT_MS = 12000;

export class BrowserAudioCaptureService implements AudioCaptureService {
  #stream: MediaStream | null = null;
  #audioContext: AudioContext | null = null;
  #analyser: AnalyserNode | null = null;
  #source: MediaStreamAudioSourceNode | null = null;
  #recorder: MediaRecorder | null = null;

  async ensureMicrophonePermission(): Promise<MicPermissionState> {
    try {
      await this.#ensureStream();
      return "granted";
    } catch {
      return "denied";
    }
  }

  async listenForUtterance(options: { signal?: AbortSignal } = {}): Promise<Blob> {
    const stream = await this.#ensureStream();

    if (typeof MediaRecorder === "undefined") {
      throw new Error("MediaRecorder is unavailable in this browser.");
    }

    const mimeType = BrowserAudioCaptureService.#pickMimeType();
    const recorder = mimeType
      ? new MediaRecorder(stream, { mimeType })
      : new MediaRecorder(stream);
    this.#recorder = recorder;

    const chunks: BlobPart[] = [];
    let detectedSpeech = false;
    let lastSpeechAt = 0;
    let startedAt = 0;
    let loopHandle = 0;

    recorder.ondataavailable = (event) => {
      if (event.data.size > 0) {
        chunks.push(event.data);
      }
    };

    const stop = () => {
      cancelAnimationFrame(loopHandle);
      if (recorder.state !== "inactive") {
        recorder.stop();
      }
    };

    options.signal?.addEventListener(
      "abort",
      () => {
        stop();
      },
      { once: true },
    );

    const data = new Float32Array(this.#analyser?.fftSize ?? 2048);

    const monitor = () => {
      if (!this.#analyser) {
        loopHandle = requestAnimationFrame(monitor);
        return;
      }

      this.#analyser.getFloatTimeDomainData(data);
      const rms = BrowserAudioCaptureService.#rms(data);
      const now = performance.now();

      if (rms > DEFAULT_THRESHOLD) {
        detectedSpeech = true;
        lastSpeechAt = now;
      }

      if (
        detectedSpeech &&
        lastSpeechAt > 0 &&
        now - lastSpeechAt >= DEFAULT_SILENCE_MS
      ) {
        stop();
        return;
      }

      if (!detectedSpeech && now - startedAt >= DEFAULT_MAX_WAIT_MS) {
        stop();
        return;
      }

      loopHandle = requestAnimationFrame(monitor);
    };

    const result = await new Promise<Blob>((resolve, reject) => {
      recorder.onstop = () => {
        cancelAnimationFrame(loopHandle);

        if (chunks.length === 0) {
          reject(new Error("No audio was captured."));
          return;
        }

        resolve(new Blob(chunks, { type: recorder.mimeType || "audio/webm" }));
      };

      recorder.onerror = () => {
        cancelAnimationFrame(loopHandle);
        reject(new Error("Audio capture failed."));
      };

      startedAt = performance.now();
      recorder.start(250);
      loopHandle = requestAnimationFrame(monitor);
    });

    this.#recorder = null;
    return result;
  }

  async recordForDuration(options: {
    durationMs: number;
    signal?: AbortSignal;
    onProgress?: (progress: AudioDurationCaptureProgress) => void;
  }): Promise<Blob> {
    const stream = await this.#ensureStream();

    if (typeof MediaRecorder === "undefined") {
      throw new Error("MediaRecorder is unavailable in this browser.");
    }

    const mimeType = BrowserAudioCaptureService.#pickMimeType();
    const recorder = mimeType
      ? new MediaRecorder(stream, { mimeType })
      : new MediaRecorder(stream);
    this.#recorder = recorder;

    const chunks: BlobPart[] = [];
    const durationMs = Math.max(1_000, options.durationMs);
    let timerHandle = 0;
    let progressHandle = 0;
    let startedAt = 0;
    let aborted = false;

    recorder.ondataavailable = (event) => {
      if (event.data.size > 0) {
        chunks.push(event.data);
      }
    };

    const emitProgress = (elapsedMs: number, isRecording: boolean) => {
      options.onProgress?.({
        progress: Math.max(0, Math.min(1, elapsedMs / durationMs)),
        elapsedMs,
        remainingMs: Math.max(0, durationMs - elapsedMs),
        isRecording,
      });
    };

    const stop = () => {
      window.clearTimeout(timerHandle);
      window.clearInterval(progressHandle);
      if (recorder.state !== "inactive") {
        recorder.stop();
      }
    };

    options.signal?.addEventListener(
      "abort",
      () => {
        aborted = true;
        stop();
      },
      { once: true },
    );

    try {
      return await new Promise<Blob>((resolve, reject) => {
        recorder.onstop = () => {
          window.clearTimeout(timerHandle);
          window.clearInterval(progressHandle);

          if (aborted) {
            reject(new Error("Microphone calibration was cancelled."));
            return;
          }

          if (chunks.length === 0) {
            reject(new Error("No microphone calibration audio was captured."));
            return;
          }

          emitProgress(durationMs, false);
          resolve(new Blob(chunks, { type: recorder.mimeType || "audio/webm" }));
        };

        recorder.onerror = () => {
          window.clearTimeout(timerHandle);
          window.clearInterval(progressHandle);
          reject(new Error("Microphone calibration recording failed."));
        };

        startedAt = performance.now();
        emitProgress(0, true);
        recorder.start(250);
        timerHandle = window.setTimeout(() => {
          stop();
        }, durationMs);
        progressHandle = window.setInterval(() => {
          const elapsedMs = Math.min(durationMs, performance.now() - startedAt);
          emitProgress(elapsedMs, true);
        }, 100);
      });
    } finally {
      this.#recorder = null;
    }
  }

  stop(): void {
    if (this.#recorder && this.#recorder.state !== "inactive") {
      this.#recorder.stop();
    }
  }

  async dispose(): Promise<void> {
    this.stop();
    this.#stream?.getTracks().forEach((track) => track.stop());
    this.#stream = null;
    this.#source?.disconnect();
    this.#source = null;
    this.#analyser?.disconnect();
    this.#analyser = null;
    await this.#audioContext?.close();
    this.#audioContext = null;
  }

  async #ensureStream(): Promise<MediaStream> {
    if (this.#stream) {
      return this.#stream;
    }

    const stream = await navigator.mediaDevices.getUserMedia({
      audio: {
        channelCount: 1,
        echoCancellation: true,
        noiseSuppression: true,
        autoGainControl: true,
      },
    });

    this.#stream = stream;

    this.#audioContext = new AudioContext();
    this.#source = this.#audioContext.createMediaStreamSource(stream);
    this.#analyser = this.#audioContext.createAnalyser();
    this.#analyser.fftSize = 2048;
    this.#source.connect(this.#analyser);

    return stream;
  }

  static #pickMimeType(): string | undefined {
    const candidates = [
      "audio/webm;codecs=opus",
      "audio/mp4",
      "audio/webm",
    ];

    for (const candidate of candidates) {
      if (MediaRecorder.isTypeSupported(candidate)) {
        return candidate;
      }
    }

    return undefined;
  }

  static #rms(values: Float32Array): number {
    let total = 0;
    for (const value of values) {
      total += value * value;
    }
    return Math.sqrt(total / values.length);
  }
}