package emissary.core.channels;
   
   import org.apache.commons.io.IOUtils;
   
   import java.io.IOException;
   import java.nio.ByteBuffer;
   import java.nio.channels.SeekableByteChannel;
   import java.util.Arrays;
   
  import static org.junit.jupiter.api.Assertions.assertArrayEquals;
  import static org.junit.jupiter.api.Assertions.assertEquals;
  
  public class ChannelTestHelper {
      private ChannelTestHelper() {}
  
      public static void checkByteArrayAgainstSbc(final byte[] bytesToVerify, final SeekableByteChannelFactory sbcf)
              throws IOException {
          try (SeekableByteChannel sbc = sbcf.create()) {
              int startIndex;
              int length;
              for (startIndex = 0; startIndex < bytesToVerify.length; startIndex++) {
                  for (length = bytesToVerify.length - startIndex; length > 0; length--) {
                      checkSegment(sbc, bytesToVerify, startIndex, length);
                  }
              }
  
              // Do the same as above but starting from the end of the string/file
              for (startIndex = (bytesToVerify.length - 1); startIndex > -1; startIndex--) {
                  for (length = bytesToVerify.length - startIndex; length > 0; length--) {
                      checkSegment(sbc, bytesToVerify, startIndex, length);
                  }
              }
          }
      }
  
      private static void checkSegment(final SeekableByteChannel sbc, final byte[] bytesToVerify, final int startIndex,
              final int length) throws IOException {
          sbc.position(startIndex);
          assertEquals(startIndex, sbc.position(), "Setting initial position of sbc is incorrect!");
  
          final ByteBuffer buff = ByteBuffer.allocate(length);
          final int bytesRead = IOUtils.read(sbc, buff);
  
          assertEquals(length, bytesRead, "bytesRead value is incorrect!");
          assertEquals(startIndex + length, sbc.position(), "Sbc position after read is incorrect!");
          assertArrayEquals(Arrays.copyOfRange(bytesToVerify, startIndex, startIndex + length), buff.array(),
                  "Bytes read are incorrect!");
      }
  }