kitaev@213: /*
kitaev@213:  * Copyright (c) 2011 TMate Software Ltd
kitaev@213:  *  
kitaev@213:  * This program is free software; you can redistribute it and/or modify
kitaev@213:  * it under the terms of the GNU General Public License as published by
kitaev@213:  * the Free Software Foundation; version 2 of the License.
kitaev@213:  *
kitaev@213:  * This program is distributed in the hope that it will be useful,
kitaev@213:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
kitaev@213:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
kitaev@213:  * GNU General Public License for more details.
kitaev@213:  *
kitaev@213:  * For information on how to redistribute this software under
kitaev@213:  * the terms of a license other than GNU General Public License
kitaev@213:  * contact TMate Software at support@hg4j.com
kitaev@213:  */
kitaev@213: package org.tmatesoft.hg.internal;
kitaev@213: 
kitaev@213: import java.io.IOException;
kitaev@213: 
kitaev@213: 
kitaev@213: /**
kitaev@213:  * XXX Perhaps, DataAccessSlice? Unlike FilterInputStream, we limit amount of data read from DataAccess being filtered.
kitaev@213:  *   
kitaev@213:  *   
kitaev@213:  * @author Artem Tikhomirov
kitaev@213:  * @author TMate Software Ltd.
kitaev@213:  */
kitaev@213: public class FilterDataAccess extends DataAccess {
kitaev@213: 	private final DataAccess dataAccess;
kitaev@213: 	private final int offset;
kitaev@213: 	private final int length;
kitaev@213: 	private int count;
kitaev@213: 
kitaev@213: 	public FilterDataAccess(DataAccess dataAccess, int offset, int length) {
kitaev@213: 		this.dataAccess = dataAccess;
kitaev@213: 		this.offset = offset;
kitaev@213: 		this.length = length;
kitaev@213: 		count = length;
kitaev@213: 	}
kitaev@213: 
kitaev@213: 	protected int available() {
kitaev@213: 		return count;
kitaev@213: 	}
kitaev@213: 
kitaev@213: 	@Override
kitaev@213: 	public FilterDataAccess reset() throws IOException {
kitaev@213: 		count = length;
kitaev@213: 		return this;
kitaev@213: 	}
kitaev@213: 	
kitaev@213: 	@Override
kitaev@213: 	public boolean isEmpty() {
kitaev@213: 		return count <= 0;
kitaev@213: 	}
kitaev@213: 	
kitaev@213: 	@Override
kitaev@213: 	public int length() {
kitaev@213: 		return length;
kitaev@213: 	}
kitaev@213: 
kitaev@213: 	@Override
kitaev@213: 	public void seek(int localOffset) throws IOException {
kitaev@213: 		if (localOffset < 0 || localOffset > length) {
kitaev@213: 			throw new IllegalArgumentException();
kitaev@213: 		}
kitaev@213: 		dataAccess.seek(offset + localOffset);
kitaev@213: 		count = (int) (length - localOffset);
kitaev@213: 	}
kitaev@213: 
kitaev@213: 	@Override
kitaev@213: 	public void skip(int bytes) throws IOException {
kitaev@213: 		int newCount = count - bytes;
kitaev@213: 		if (newCount < 0 || newCount > length) {
kitaev@213: 			throw new IllegalArgumentException();
kitaev@213: 		}
kitaev@213: 		seek(length - newCount);
kitaev@213: 		/*
kitaev@213: 		 can't use next code because don't want to rewind backing DataAccess on reset()
kitaev@213: 		 i.e. this.reset() modifies state of this instance only, while filtered DA may go further.
kitaev@213: 		 Only actual this.skip/seek/read would rewind it to desired position 
kitaev@213: 	  		dataAccess.skip(bytes);
kitaev@213: 			count = newCount;
kitaev@213: 		 */
kitaev@213: 
kitaev@213: 	}
kitaev@213: 
kitaev@213: 	@Override
kitaev@213: 	public byte readByte() throws IOException {
kitaev@213: 		if (count <= 0) {
kitaev@213: 			throw new IllegalArgumentException("Underflow"); // XXX be descriptive
kitaev@213: 		}
kitaev@213: 		if (count == length) {
kitaev@213: 			dataAccess.seek(offset);
kitaev@213: 		}
kitaev@213: 		count--;
kitaev@213: 		return dataAccess.readByte();
kitaev@213: 	}
kitaev@213: 
kitaev@213: 	@Override
kitaev@213: 	public void readBytes(byte[] b, int off, int len) throws IOException {
kitaev@213: 		if (len == 0) {
kitaev@213: 			return;
kitaev@213: 		}
kitaev@213: 		if (count <= 0 || len > count) {
kitaev@213: 			throw new IllegalArgumentException(String.format("Underflow. Bytes left: %d, asked to read %d", count, len));
kitaev@213: 		}
kitaev@213: 		if (count == length) {
kitaev@213: 			dataAccess.seek(offset);
kitaev@213: 		}
kitaev@213: 		dataAccess.readBytes(b, off, len);
kitaev@213: 		count -= len;
kitaev@213: 	}
kitaev@213: 
kitaev@213: 	// done shall be no-op, as we have no idea what's going on with DataAccess we filter
kitaev@213: }