byte_streams.dart

library realdb.io;

import "dart:async";
import "dart:io";
import "dart:typed_data";

abstract class ByteStream {
  Future<int> read();
  Future<int> getPosition();

  Future skip(int count) async {
    for (var i = 1; i <= count; i++) {
      await read();
    }
  }

  Future close() async {}
}

class ByteDataStream extends ByteStream {
  final ByteData data;
  
  int _pos = -1;

  ByteDataStream(this.data);

  @override
  Future<int> getPosition() async {
    return _pos;
  }

  @override
  Future<int> read() async {
    _pos++;
    return data.getUint8(_pos);
  }
}

class FileByteStream extends ByteStream {
  final RandomAccessFile file;

  FileByteStream(this.file);

  @override
  Future<int> read() => file.readByte();

  @override
  Future<int> getPosition() => file.position();

  @override
  Future skip(int count) async =>
    file.setPosition((await file.position()) + count);

  @override
  Future close() async => await file.close();
}

class ChunkedFileByteStream extends FileByteStream {
  final int chunkSize;

  int _pos = -1;
  int _buffPos = -1;
  Uint8List _buff;

  ChunkedFileByteStream(this.chunkSize, RandomAccessFile file) : super(file) {
    _buff = new Uint8List(chunkSize);
  }

  @override
  Future<int> read() async {
    _pos++;
    if (_buffPos == -1 || _buffPos == chunkSize - 1) {
      await file.readInto(_buff);
      _buffPos = -1;
    }
    _buffPos++;

    return _buff[_buffPos];
  }

  @override
  Future<int> getPosition() async {
    return _pos;
  }

  @override
  Future skip(int count) async {
    await file.setPosition((await file.position()) + count);
    _pos += count;
  }
}