import 'dart:typed_data';

enum G711Type {
  uLaw,
  aLaw,
}

class G711Decoder {
  Uint8List g711Encode(Uint8List pcmData, G711Type g711Type) {
    List<int> g711Data = [];

    for (int sample in pcmData) {
      int sign = (sample < 0) ? 0x80 : 0;
      int magnitude = (sample < 0) ? -sample : sample;

      int exponent = 7;
      while (magnitude < (1 << exponent) && exponent > 0) {
        exponent--;
      }

      int mantissa = (magnitude >> (exponent - 4)) & 0x0F;

      if (g711Type == G711Type.uLaw) {
        // μ-law encoding
        int value = ~(sign | ((exponent << 4) & 0x70) | (mantissa >> 4));
        g711Data.add(value & 0xFF);
      } else {
        // A-law encoding
        int value = sign | ((exponent << 4) & 0x70) | (mantissa >> 4);
        g711Data.add(value & 0xFF);
      }
    }

    return Uint8List.fromList(g711Data);
  }

  List<int> pcm16ToG711u(List<int> pcm16Data) {
    List<int> g711uData = [];

    for (int i = 0; i < pcm16Data.length; i += 2) {
      int pcmSample = (pcm16Data[i + 1] << 8) | pcm16Data[i];
      int g711Sample = pcmToG711u(pcmSample);

      // 将 G.711 样本拆分成两个字节
      g711uData.add(g711Sample & 0xFF);
      g711uData.add((g711Sample >> 8) & 0xFF);
    }

    return g711uData;
  }

  int pcmToG711u(int pcmSample) {
    const int MULAW_BIAS = 0x84;
    const int CLIP = 32635;

    // 剪裁 PCM 样本
    if (pcmSample > CLIP) {
      pcmSample = CLIP;
    } else if (pcmSample < -CLIP) {
      pcmSample = -CLIP;
    }

    // 增加偏置并取反
    pcmSample += MULAW_BIAS;
    pcmSample = ~pcmSample & 0xFF;

    return pcmSample;
  }
}