tikhomirov@51: /*
tikhomirov@51:  * Copyright (c) 2011 Artem Tikhomirov 
tikhomirov@51:  */
tikhomirov@51: package com.tmate.hgkit.fs;
tikhomirov@51: 
tikhomirov@51: import java.io.IOException;
tikhomirov@51: 
tikhomirov@51: /**
tikhomirov@51:  * XXX Perhaps, DataAccessSlice? Unlike FilterInputStream, we limit amount of data read from DataAccess being filtered.
tikhomirov@51:  *   
tikhomirov@51:  * @author artem
tikhomirov@51:  */
tikhomirov@51: public class FilterDataAccess extends DataAccess {
tikhomirov@51: 	private final DataAccess dataAccess;
tikhomirov@51: 	private final long offset;
tikhomirov@51: 	private final int length;
tikhomirov@51: 	private int count;
tikhomirov@51: 
tikhomirov@51: 	public FilterDataAccess(DataAccess dataAccess, long offset, int length) {
tikhomirov@51: 		this.dataAccess = dataAccess;
tikhomirov@51: 		this.offset = offset;
tikhomirov@51: 		this.length = length;
tikhomirov@51: 		count = length;
tikhomirov@51: 	}
tikhomirov@51: 
tikhomirov@51: 	protected int available() {
tikhomirov@51: 		return count;
tikhomirov@51: 	}
tikhomirov@51: 
tikhomirov@51: 	@Override
tikhomirov@51: 	public void reset() throws IOException {
tikhomirov@51: 		count = length;
tikhomirov@51: 	}
tikhomirov@51: 	
tikhomirov@51: 	@Override
tikhomirov@51: 	public boolean isEmpty() {
tikhomirov@51: 		return count <= 0;
tikhomirov@51: 	}
tikhomirov@51: 	
tikhomirov@51: 	@Override
tikhomirov@51: 	public long length() {
tikhomirov@51: 		return length;
tikhomirov@51: 	}
tikhomirov@51: 
tikhomirov@51: 	@Override
tikhomirov@51: 	public void seek(long localOffset) throws IOException {
tikhomirov@51: 		if (localOffset < 0 || localOffset > length) {
tikhomirov@51: 			throw new IllegalArgumentException();
tikhomirov@51: 		}
tikhomirov@51: 		dataAccess.seek(offset + localOffset);
tikhomirov@51: 		count = (int) (length - localOffset);
tikhomirov@51: 	}
tikhomirov@51: 
tikhomirov@51: 	@Override
tikhomirov@51: 	public void skip(int bytes) throws IOException {
tikhomirov@51: 		int newCount = count - bytes;
tikhomirov@51: 		if (newCount < 0 || newCount > length) {
tikhomirov@51: 			throw new IllegalArgumentException();
tikhomirov@51: 		}
tikhomirov@51: 		seek(length - newCount);
tikhomirov@51: 		/*
tikhomirov@51: 		 can't use next code because don't want to rewind backing DataAccess on reset()
tikhomirov@51: 		 i.e. this.reset() modifies state of this instance only, while filtered DA may go further.
tikhomirov@51: 		 Only actual this.skip/seek/read would rewind it to desired position 
tikhomirov@51: 	  		dataAccess.skip(bytes);
tikhomirov@51: 			count = newCount;
tikhomirov@51: 		 */
tikhomirov@51: 
tikhomirov@51: 	}
tikhomirov@51: 
tikhomirov@51: 	@Override
tikhomirov@51: 	public byte readByte() throws IOException {
tikhomirov@51: 		if (count <= 0) {
tikhomirov@51: 			throw new IllegalArgumentException("Underflow"); // XXX be descriptive
tikhomirov@51: 		}
tikhomirov@51: 		if (count == length) {
tikhomirov@51: 			dataAccess.seek(offset);
tikhomirov@51: 		}
tikhomirov@51: 		count--;
tikhomirov@51: 		return dataAccess.readByte();
tikhomirov@51: 	}
tikhomirov@51: 
tikhomirov@51: 	@Override
tikhomirov@51: 	public void readBytes(byte[] b, int off, int len) throws IOException {
tikhomirov@51: 		if (count <= 0 || len > count) {
tikhomirov@51: 			throw new IllegalArgumentException("Underflow"); // XXX be descriptive
tikhomirov@51: 		}
tikhomirov@51: 		if (count == length) {
tikhomirov@51: 			dataAccess.seek(offset);
tikhomirov@51: 		}
tikhomirov@51: 		dataAccess.readBytes(b, off, len);
tikhomirov@51: 		count -= len;
tikhomirov@51: 	}
tikhomirov@51: 
tikhomirov@51: 	// done shall be no-op, as we have no idea what's going on with DataAccess we filter
tikhomirov@51: }