package kingsy101;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

public class BlockInputStream extends FilterInputStream {

  public BlockInputStream (InputStream in, int blockSize) {
    super (in);
    if (blockSize <= 0)
      throw new IllegalArgumentException ("blockSize");

    this.blockSize = blockSize;
  }

  /**
   * Reads one block out of the underlying input source. If the source ends
   * before a complete block can be read, the returned block will be shorter
   * than the block size; otherwise, this will read until a complete block is
   * read or the input source fails.
   * 
   * @return the read block.
   * @throws IOException
   *             if the input source fails.
   */
  public byte[] readBlock () throws IOException {
    byte[] buffer = new byte[blockSize];

    int totalRead = 0;

    while (totalRead < blockSize) {
      int read = in.read (buffer, totalRead, blockSize - totalRead);
      if (read == -1)
        return truncateBlock (buffer, totalRead);
      totalRead += read;
    }

    return buffer;
  }

  private byte[] truncateBlock (byte[] buffer, int totalRead) {
    byte[] truncatedBuffer = new byte[totalRead];
    System.arraycopy (buffer, 0, truncatedBuffer, 0, totalRead);
    return truncatedBuffer;
  }

  private final int blockSize;
}