/// NALU相关工具类与结构体
import 'dart:typed_data';

/// NALU单元结构体
class NaluUnit {
  final int type; // NALU类型
  final List<int> data;
  NaluUnit(this.type, this.data);
}

class NaluUtils {
  /// 分离一帧数据中的所有NALU单元
  static List<NaluUnit> splitNalus(List<int> data) {
    final List<NaluUnit> nalus = [];
    int i = 0;
    List<int> startCodes = [];
    // 先找到所有起始码位置
    while (i < data.length - 3) {
      if (i < data.length - 4 &&
          data[i] == 0 && data[i + 1] == 0 && data[i + 2] == 0 && data[i + 3] == 1) {
        startCodes.add(i);
        i += 4;
      } else if (data[i] == 0 && data[i + 1] == 0 && data[i + 2] == 1) {
        startCodes.add(i);
        i += 3;
      } else {
        i++;
      }
    }
    // 补上结尾
    startCodes.add(data.length);
    // 分割NALU
    int nalusTotalLen = 0;
    for (int idx = 0; idx < startCodes.length - 1; idx++) {
      int start = startCodes[idx];
      int next = startCodes[idx + 1];
      int skip = (data[start] == 0 && data[start + 1] == 0 && data[start + 2] == 0 && data[start + 3] == 1) ? 4 : 3;
      int naluStart = start + skip;
      if (naluStart < next) {
        final nalu = data.sublist(start, next);
        nalusTotalLen += nalu.length;
        if (nalu.isNotEmpty) {
          nalus.add(NaluUnit(getNaluType(nalu), nalu));
        }
      }
    }
    if (nalus.isEmpty && data.isNotEmpty) {
      nalus.add(NaluUnit(getNaluType(data), data));
    } else if (nalusTotalLen < data.length) {
      nalus.add(NaluUnit(getNaluType(data.sublist(nalusTotalLen)), data.sublist(nalusTotalLen)));
    }
    return nalus;
  }

  /// 获取NALU类型
  static int getNaluType(List<int> nalu) {
    if (nalu.isEmpty) return -1;
    int offset = 0;
    if (nalu.length >= 4 && nalu[0] == 0x00 && nalu[1] == 0x00) {
      if (nalu[2] == 0x01)
        offset = 3;
      else if (nalu[2] == 0x00 && nalu[3] == 0x01)
        offset = 4;
    }
    if (nalu.length > offset) {
      return nalu[offset] & 0x1F;
    }
    return -1;
  }

  /// 提取所有指定type的NALU并拼接返回
  static List<int> filterNalusByType(List<int> frameData, int type) {
    final nalus = splitNalus(frameData);
    final filtered = nalus.where((nalu) => nalu.type == type).toList();
    final result = <int>[];
    for (final nalu in filtered) {
      result.addAll(nalu.data);
    }
    return result;
  }
}