package edu.jiangxin.apktoolbox.convert.protobuf.unsupervised;
   
   import org.apache.commons.lang3.ArrayUtils;
   
   import java.math.BigInteger;
   import java.nio.ByteOrder;
   import java.util.Map;
   
   public class BufferReader {
  
      private byte[] buffer;
      private int offset;
      private int savedOffset;
  
      public BufferReader(byte[] buffer) {
          this.buffer = buffer;
          offset = 0;
      }
  
      public int getOffset() {
          return offset;
      }
  
      public BigInteger readVarInt() {
          Map<String, Object> result = VarintUtils.decodeVarint(buffer, offset);
          offset += (int) result.get("length");
          return (BigInteger) result.get("value");
      }
  
      public byte[] readBuffer(int length) {
          this.checkByte(length);
          byte[] result = ArrayUtils.subarray(buffer, offset, offset + length);
          offset += length;
          return result;
      }
  
      public void trySkipGrpcHeader() {
          int backupOffset = offset;
          if (buffer.length > 0 && buffer[offset] == 0 && leftBytes() >= 5) {
              offset++;
              int length = ByteUtil.bytesToInt(buffer, offset, ByteOrder.BIG_ENDIAN);
              offset += 4;
  
              if (length > leftBytes()) {
                  offset = backupOffset;
              }
          }
      }
  
      public int leftBytes() {
          return buffer.length - offset;
      }
  
      public void checkByte(int length) {
          int bytesAvailable = leftBytes();
          if (length > bytesAvailable) {
              throw new RuntimeException("Not enough bytes left. Requested: " + length + " left: " + bytesAvailable);
          } else if (length < 0) {
              throw new RuntimeException("The length should be greater than 0");
          }
      }
  
      public void checkpoint() {
          this.savedOffset = offset;
      }
  
      public void resetToCheckpoint() {
          offset = this.savedOffset;
      }
  
  }