Portfolio/tests/helpers/fake-audio-context.ts

export type AudioParamEvent =
  | { readonly kind: 'set'; readonly value: number; readonly at: number }
  | { readonly kind: 'linear'; readonly value: number; readonly at: number }
  | { readonly kind: 'exponential'; readonly value: number; readonly at: number }
  | { readonly kind: 'target'; readonly value: number; readonly at: number; readonly constant: number }
  | { readonly kind: 'cancel'; readonly at: number }
  | { readonly kind: 'hold'; readonly at: number };

export interface FakeAudioParamRecord {
  readonly param: AudioParam;
  readonly events: AudioParamEvent[];
}

export interface FakeSourceRecord {
  readonly kind: 'buffer' | 'oscillator';
  readonly node: AudioScheduledSourceNode;
  readonly starts: Array<{ at: number; offset: number; duration: number | null }>;
  readonly stops: number[];
  disconnectCount: number;
  emitEnded(): void;
}

export interface FakeAudioHarness {
  readonly context: AudioContext;
  readonly params: FakeAudioParamRecord[];
  readonly sources: FakeSourceRecord[];
  readonly gainNodes: readonly GainNode[];
  readonly buffers: AudioBuffer[];
  readonly destination: AudioNode;
  setCurrentTime(seconds: number): void;
  decodedBuffer(durationSeconds: number, channels?: number): AudioBuffer;
  emitContextState(state: AudioContextState | 'interrupted'): void;
}

const createParam = (
  records: FakeAudioParamRecord[],
  initial = 0,
): AudioParam => {
  const events: AudioParamEvent[] = [];
  const parameter = {
    value: initial,
    defaultValue: initial,
    minValue: Number.NEGATIVE_INFINITY,
    maxValue: Number.POSITIVE_INFINITY,
    automationRate: 'a-rate' as const,
    setValueAtTime(this: { value: number }, value: number, at: number) {
      this.value = value;
      events.push({ kind: 'set', value, at });
      return this as unknown as AudioParam;
    },
    linearRampToValueAtTime(this: { value: number }, value: number, at: number) {
      this.value = value;
      events.push({ kind: 'linear', value, at });
      return this as unknown as AudioParam;
    },
    exponentialRampToValueAtTime(this: { value: number }, value: number, at: number) {
      this.value = value;
      events.push({ kind: 'exponential', value, at });
      return this as unknown as AudioParam;
    },
    setTargetAtTime(this: { value: number }, value: number, at: number, constant: number) {
      this.value = value;
      events.push({ kind: 'target', value, at, constant });
      return this as unknown as AudioParam;
    },
    cancelScheduledValues(at: number) {
      events.push({ kind: 'cancel', at });
      return this as unknown as AudioParam;
    },
    cancelAndHoldAtTime(at: number) {
      events.push({ kind: 'hold', at });
      return this as unknown as AudioParam;
    },
    setValueCurveAtTime() {
      throw new Error('Unexpected value-curve scheduling in focused audio tests.');
    },
  } as unknown as AudioParam;
  records.push({ param: parameter, events });
  return parameter;
};

interface DisconnectableNode extends AudioNode {
  disconnectCount: number;
}

function createNode(): DisconnectableNode {
  const node = {
    disconnectCount: 0,
    connect(destination: AudioNode | AudioParam) {
      return destination;
    },
    disconnect(this: { disconnectCount: number }) {
      this.disconnectCount += 1;
    },
  } as unknown as DisconnectableNode;
  return node;
}

export function createFakeAudioHarness(): FakeAudioHarness {
  const params: FakeAudioParamRecord[] = [];
  const sources: FakeSourceRecord[] = [];
  const gainNodes: GainNode[] = [];
  const buffers: AudioBuffer[] = [];
  const stateListeners = new Set<() => void>();
  const sampleRate = 48_000;
  let currentTime = 0;
  let state: AudioContextState | 'interrupted' = 'suspended';

  const decodedBuffer = (durationSeconds: number, channels = 2): AudioBuffer => {
    const length = Math.max(1, Math.round(durationSeconds * sampleRate));
    const data = Array.from({ length: channels }, () => new Float32Array(length));
    const buffer = {
      sampleRate,
      length,
      duration: length / sampleRate,
      numberOfChannels: channels,
      getChannelData(channel: number) {
        const samples = data[channel];
        if (samples === undefined) throw new RangeError(`Missing channel ${channel}.`);
        return samples;
      },
    } as unknown as AudioBuffer;
    buffers.push(buffer);
    return buffer;
  };

  const destination = createNode();

  const createScheduledSource = (kind: FakeSourceRecord['kind']): AudioScheduledSourceNode => {
    const node = createNode() as AudioScheduledSourceNode & DisconnectableNode;
    const starts: FakeSourceRecord['starts'] = [];
    const stops: number[] = [];
    const endedListeners = new Set<() => void>();
    const record: FakeSourceRecord = {
      kind,
      node,
      starts,
      stops,
      get disconnectCount() {
        return node.disconnectCount;
      },
      set disconnectCount(value: number) {
        node.disconnectCount = value;
      },
      emitEnded() {
        for (const listener of endedListeners) listener();
        endedListeners.clear();
      },
    };
    Object.assign(node, {
      start(at = 0, offset = 0, duration?: number) {
        starts.push({ at, offset, duration: duration ?? null });
      },
      stop(at = 0) {
        stops.push(at);
      },
      addEventListener(type: string, listener: () => void, options?: AddEventListenerOptions) {
        if (type === 'ended') endedListeners.add(listener);
        if (options?.once !== true) return;
      },
      removeEventListener(type: string, listener: () => void) {
        if (type === 'ended') endedListeners.delete(listener);
      },
    });
    sources.push(record);
    return node;
  };

  const context = {
    get currentTime() {
      return currentTime;
    },
    get state() {
      return state;
    },
    sampleRate,
    destination,
    createGain() {
      const node = Object.assign(createNode(), { gain: createParam(params, 1) }) as GainNode;
      gainNodes.push(node);
      return node;
    },
    createBiquadFilter() {
      return Object.assign(createNode(), {
        type: 'lowpass' as BiquadFilterType,
        frequency: createParam(params),
        detune: createParam(params),
        Q: createParam(params),
        gain: createParam(params),
      }) as unknown as BiquadFilterNode;
    },
    createStereoPanner() {
      return Object.assign(createNode(), { pan: createParam(params) }) as StereoPannerNode;
    },
    createBuffer(numberOfChannels: number, length: number, bufferSampleRate: number) {
      const data = Array.from(
        { length: numberOfChannels },
        () => new Float32Array(length),
      );
      const buffer = {
        sampleRate: bufferSampleRate,
        length,
        duration: length / bufferSampleRate,
        numberOfChannels,
        getChannelData(channel: number) {
          const samples = data[channel];
          if (samples === undefined) throw new RangeError(`Missing channel ${channel}.`);
          return samples;
        },
      } as unknown as AudioBuffer;
      buffers.push(buffer);
      return buffer;
    },
    createBufferSource() {
      return Object.assign(createScheduledSource('buffer'), {
        buffer: null as AudioBuffer | null,
        loop: false,
        loopStart: 0,
        loopEnd: 0,
        playbackRate: createParam(params, 1),
        detune: createParam(params),
      }) as AudioBufferSourceNode;
    },
    createOscillator() {
      return Object.assign(createScheduledSource('oscillator'), {
        type: 'sine' as OscillatorType,
        frequency: createParam(params, 440),
        detune: createParam(params),
      }) as OscillatorNode;
    },
    async decodeAudioData() {
      return decodedBuffer(1);
    },
    async resume() {
      state = 'running';
    },
    async suspend() {
      state = 'suspended';
    },
    async close() {
      state = 'closed';
    },
    addEventListener(type: string, listener: () => void) {
      if (type === 'statechange') stateListeners.add(listener);
    },
    removeEventListener(type: string, listener: () => void) {
      if (type === 'statechange') stateListeners.delete(listener);
    },
  } as unknown as AudioContext;

  return {
    context,
    params,
    sources,
    gainNodes,
    buffers,
    destination,
    setCurrentTime(seconds) {
      currentTime = seconds;
    },
    decodedBuffer,
    emitContextState(nextState) {
      state = nextState;
      for (const listener of stateListeners) listener();
    },
  };
}