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package com.hfg.util.io;

import java.io.FilterReader;
import java.io.IOException;
import java.io.Reader;

import com.hfg.math.Range;

//------------------------------------------------------------------------------
/**
 FilterReader that provides the specified segment of the stream.
 
 @author J. Alex Taylor, hairyfatguy.com
 
 */
//------------------------------------------------------------------------------
// com.hfg Library
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//
// J. Alex Taylor, President, Founder, CEO, COO, CFO, OOPS hairyfatguy.com
// [email protected]
//------------------------------------------------------------------------------

public class SegmentReader extends FilterReader
{
   private Range mSegment;
   private char[]  mBuffer;
   private int     mBufferLimit;
   private int     mBufferIndex;
   private boolean mEndOfStreamReached;
   private int     mNumBytes;

   //###########################################################################
   // CONSTRUCTORS
   //###########################################################################

   //---------------------------------------------------------------------------
   public SegmentReader(Reader inReader, Range inSegment)
   {
      super(inReader);
      mSegment = inSegment;
      if (mSegment != null
          && null == mSegment.getStart())
      {
         mSegment.setStart(1);
      }
   }

   //###########################################################################
   // PUBLIC METHODS
   //###########################################################################

   //---------------------------------------------------------------------------
   @Override
   public int read(char[] inBuffer, int inOffset, int inMaxReadLength)
         throws IOException
   {
      int theChar;
      int numCharsRead = 0;
      do
      {
         theChar = read();
         if (theChar > 0)
         {
            inBuffer[inOffset++] = (char) theChar;
            numCharsRead++;
         }
      }
      while (theChar >= 0
            && numCharsRead < inMaxReadLength);

      return (theChar < 0 && 0 == numCharsRead ? -1 : numCharsRead);
   }

   //---------------------------------------------------------------------------
   @Override
   public int read()
         throws IOException
   {
      if (null == mBuffer)
      {
         // Initialize
         mBuffer = new char[8196];

         if (mSegment != null
             && mSegment.getStart() > 1)
         {
            super.in.skip(mSegment.getStart() - 1);
         }
      }

      if (mBufferIndex >= mBufferLimit)
      {
         fillBuffer();
      }

      return (mEndOfStreamReached ? -1 : mBuffer[mBufferIndex++]);
   }

   //###########################################################################
   // PRIVATE METHODS
   //###########################################################################

   //---------------------------------------------------------------------------
   private void fillBuffer()
         throws IOException
   {
      int fillSize = mBuffer.length;
      if (mSegment !=  null
          && mSegment.getEnd() != null)
      {
         int remainingBytesToRead = mSegment.length().intValue() - mNumBytes;
         fillSize = Math.min(fillSize, remainingBytesToRead);
      }

      if (fillSize > 0)
      {
         mBufferLimit = super.in.read(mBuffer, 0, fillSize);
         if (mBufferLimit > 0)
         {
            mNumBytes += mBufferLimit;
         }
      }
      else
      {
         mBufferLimit = -1;
      }

      if (-1 == mBufferLimit)
      {
         mEndOfStreamReached = true;
      }

      // Reset the index
      mBufferIndex = 0;
   }
}