export class Stereo48kToMono16kDownsampler {
  private readonly pendingMono48k: number[] = [];

  pushStereo48kChunk(chunk: Buffer): Int16Array {
    if (chunk.length < 4) {
      return new Int16Array();
    }

    for (let offset = 0; offset + 3 < chunk.length; offset += 4) {
      const left = chunk.readInt16LE(offset);
      const right = chunk.readInt16LE(offset + 2);
      this.pendingMono48k.push(Math.round((left + right) / 2));
    }

    const outputLength = Math.floor(this.pendingMono48k.length / 3);
    if (outputLength === 0) {
      return new Int16Array();
    }

    const output = new Int16Array(outputLength);
    let readIndex = 0;
    for (let index = 0; index < outputLength; index += 1) {
      const a = this.pendingMono48k[readIndex];
      const b = this.pendingMono48k[readIndex + 1];
      const c = this.pendingMono48k[readIndex + 2];
      output[index] = Math.round((a + b + c) / 3);
      readIndex += 3;
    }

    this.pendingMono48k.splice(0, readIndex);
    return output;
  }
}

export function int16ArrayToFloat32(input: Int16Array): Float32Array {
  const output = new Float32Array(input.length);
  for (let index = 0; index < input.length; index += 1) {
    output[index] = input[index] / 32768;
  }
  return output;
}

export function float32ToPcm16Buffer(input: Float32Array): Buffer {
  const buffer = Buffer.allocUnsafe(input.length * 2);
  for (let index = 0; index < input.length; index += 1) {
    const value = Math.max(-1, Math.min(1, input[index]));
    const scaled = value < 0 ? value * 32768 : value * 32767;
    buffer.writeInt16LE(Math.round(scaled), index * 2);
  }
  return buffer;
}

export function takeFrame(source: number[], frameSize: number): Int16Array | null {
  if (source.length < frameSize) {
    return null;
  }

  const values = source.splice(0, frameSize);
  return Int16Array.from(values);
}