class PacketConverter {
 final _log = new Logger('PacketConverter');
 final packets = new ListQueue<List<int>>();
 final messages = new ListQueue<List<int>>();
 final MAX_DOC_SIZE = 32 * 1024 * 1024;
 bool headerMode = true;
 int bytesToRead = 4;
 List<int> buffer;
 int readPos = 0;
 List<int> messageBuffer;
 int messagesConverted = 0;
 final lengthBuffer = new BsonBinary(4);

 addPacket(List<int> packet) {
   packets.addLast(packet);
   //print('addPacket to $this');
   if (headerMode) {
     handleHeader();
   } else {
     handleBody();
   }
 }
 handleHeader(){
   if (bytesAvailable()>=4) {
     headerMode = false;
     lengthBuffer.rewind();
     readIntoBuffer(lengthBuffer.byteList,0);
     int len = lengthBuffer.readInt32();
     if (len > MAX_DOC_SIZE) {
       throw new MongoDartError('Message length $len over maximum document size');
     }
     messageBuffer = new List<int>(len);
     handleBody();
   }
 }
 handleBody(){
   if (bytesAvailable()>=messageBuffer.length-4) {
     headerMode = true;
     messageBuffer.setRange(0,4,lengthBuffer.byteList);
     readIntoBuffer(messageBuffer,4);
     messagesConverted++;
     messages.addLast(messageBuffer);
     handleHeader();
   }
 }
 /// Length of all packets with current read position on first packet subtracted
 int bytesAvailable() => packets.fold(- readPos,(value, element) => value + element.length) ;
 void readIntoBuffer(List<int> buffer, int pos) {
   if(buffer.length - pos > bytesAvailable()) {
//      print('$this $buffer $pos');
     throw new MongoDartError('Bad state. Read buffer too big');
   }
   int writePos = pos;
   while (writePos < buffer.length) {
     writePos += _readPacketIntoBuffer(buffer, writePos);
   }
   if (writePos < buffer.length) {
     throw new MongoDartError('Bad state. Buffer was not written fully');
   }
 }
 int _readPacketIntoBuffer(List<int> buffer, int pos) {
   int bytesRead = min(buffer.length - pos,packets.first.length - readPos);
   buffer.setRange(pos,pos+bytesRead,packets.first,readPos);
   if (readPos + bytesRead == packets.first.length) {
     readPos = 0;
     packets.removeFirst();
   } else {
     readPos += bytesRead;
   }
   return bytesRead;
 }
 String toString() => 'PacketConverter(readPos: $readPos, headerMode: $headerMode, packets: $packets)';
 bool get isClear => this.packets.isEmpty && messages.isEmpty && headerMode;
}