flutter_vid/lib/us/vid_us_data_reader.dart

import 'dart:convert';
import 'dart:typed_data';

class VidUsDataReader {
  late final ByteBuffer _buffer;
  late int _index;

  VidUsDataReader(Uint8List data, [int offset = 0]) {
    _buffer = data.buffer;
    _index = data.offsetInBytes + offset;
  }

  ///Read int value from binary data(little endian),
  int readInt([int index = -1]) {
    if (index == -1) {
      var intData = _buffer.asByteData(_index, 4);
      _index += 4;
      return intData.getInt32(0, Endian.little);
    } else {
      var intData = _buffer.asByteData(index, 4);
      _index = index + 4;
      return intData.getInt32(0, Endian.little);
    }
  }

  ///Read string from the binary data, the string format is utf8
  String readString([int index = -1]) {
    if (index == -1) {
      var dataLength = readInt();
      var stringData = _buffer.asUint8List(_index, dataLength);
      _index += dataLength;
      return utf8.decode(stringData);
    } else {
      var dataLength = readInt(index);
      var stringData = _buffer.asUint8List(_index, dataLength);
      _index += dataLength;
      return utf8.decode(stringData);
    }
  }

  ///Read int16 value from binary data(little endian)
  int readInt16([int index = -1]) {
    if (index == -1) {
      var intData = _buffer.asByteData(_index, 2);
      _index += 2;
      return intData.getInt16(0, Endian.little);
    } else {
      var intData = _buffer.asByteData(index, 2);
      _index = index + 2;
      return intData.getInt16(0, Endian.little);
    }
  }

  ///Read int64 value from binary data(little endian)
  ///this method is not support in web platform use readInt64V2 instead.
  int readInt64([int index = -1]) {
    if (index == -1) {
      var intData = _buffer.asByteData(_index, 8);
      _index += 8;
      return intData.getInt64(0, Endian.little);
    } else {
      var intData = _buffer.asByteData(index, 8);
      _index = index + 8;
      return intData.getInt64(0, Endian.little);
    }
  }

  ///Read int64 value from binary data(little endian)
  ///this method use two int32 to support read int64 on web platform
  int readInt64V2([int index = -1]) {
    if (index == -1) {
      int low = readInt();
      int high = readInt();
      int value = high >> 32;
      value |= low;
      return value;
    } else {
      int low = readInt(index);
      int high = readInt();
      int value = high >> 32;
      value |= low;
      return value;
    }
  }

  ///Read float value from binary data(little endian)
  double readFloat([int index = -1]) {
    if (index == -1) {
      var floatData = _buffer.asByteData(_index, 4);
      _index += 4;
      return floatData.getFloat32(0, Endian.little);
    } else {
      var floatData = _buffer.asByteData(index, 4);
      _index = index + 4;
      return floatData.getFloat32(0, Endian.little);
    }
  }

  ///Read double value from binary data(little endian)
  double readDouble([int index = -1]) {
    if (index == -1) {
      var floatData = _buffer.asByteData(_index, 8);
      _index += 8;
      return floatData.getFloat64(0, Endian.little);
    } else {
      var floatData = _buffer.asByteData(index, 8);
      _index = index + 8;
      return floatData.getFloat64(0, Endian.little);
    }
  }

  ///Read bool value from binary data
  bool readBool([int index = -1]) {
    if (index == -1) {
      var boolData = _buffer.asByteData(_index, 1);
      _index++;
      return boolData.getInt8(0) == 1;
    } else {
      var boolData = _buffer.asByteData(index, 1);
      _index++;
      return boolData.getInt8(0) == 1;
    }
  }

  ///Read byte value from binary data
  int readByte([int index = -1]) {
    if (index == -1) {
      var byteData = _buffer.asByteData(_index, 1);
      _index++;
      return byteData.getInt8(0);
    } else {
      var byteData = _buffer.asByteData(index, 1);
      _index++;
      return byteData.getInt8(0);
    }
  }

  ///Read bytes from the binary data.
  Uint8List readBytes([int index = -1]) {
    var dataLength = readInt(index);
    var bytes = _buffer.asUint8List(_index, dataLength);
    _index += dataLength;
    return bytes;
  }

  int _readLong(Uint8List longData) {
    int low = longData.buffer
        .asByteData(longData.offsetInBytes)
        .getInt32(0, Endian.little);
    int high = longData.buffer
        .asByteData(longData.offsetInBytes)
        .getInt32(4, Endian.little);
    int value = high >> 32;
    value |= low;
    return value;
  }

  ///Read a group of int64 values from the binary data.
  List<int> readLongs() {
    var longData = readBytes();
    var longCount = longData.length ~/ 8;
    List<int> result = [];
    for (var i = 0; i < longCount; i++) {
      result.add(_readLong(
          longData.buffer.asUint8List(longData.offsetInBytes + i * 8, 8)));
    }
    return result;
  }
}