package emissary.parser;
   
   import org.apache.commons.collections4.CollectionUtils;
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
   import java.io.ByteArrayOutputStream;
   import java.io.IOException;
   import java.util.List;
  import javax.annotation.Nullable;
  
  public class DataByteArraySlicer {
  
      private static final Logger logger = LoggerFactory.getLogger(DataByteArraySlicer.class);
  
      /**
       * Slice a data byte array based on a single position record
       * 
       * @param data the data to pull from
       * @param r the position record indicating offsets
       */
      public static byte[] makeDataSlice(byte[] data, PositionRecord r) {
          byte[] n = new byte[(int) r.getLength()];
          System.arraycopy(data, (int) r.getPosition(), n, 0, (int) r.getLength());
          return n;
      }
  
      /**
       * Slice a data byte array based on a list of position record
       * 
       * @param data the data to pull from
       * @param list the list of position records indicating offsets
       */
      @Nullable
      public static byte[] makeDataSlice(byte[] data, @Nullable List<PositionRecord> list) {
  
          // Nothing to do
          if (CollectionUtils.isEmpty(list)) {
              return null;
          }
  
          // Use higher performing impl when only one record
          if (list.size() == 1) {
              return makeDataSlice(data, list.get(0));
          }
  
  
          // Aggregate all the pieces using the baos
          byte[] ret = null;
  
          try {
              ByteArrayOutputStream out = new ByteArrayOutputStream();
  
              for (PositionRecord r : list) {
                  int start = (int) r.getPosition();
                  int len = (int) r.getLength();
  
                  if (len == 0) {
                      continue;
                  }
  
                  if (len > 0 && start > -1 && (len + start) <= data.length) {
                      out.write(data, start, len);
                  }
              }
  
              ret = out.toByteArray();
              out.close();
          } catch (IOException iox) {
              logger.warn("io error on bytearray stream cant happen", iox);
          }
  
          return ret;
      }
  
      /** This class is not meant to be instantiated. */
      private DataByteArraySlicer() {}
  }