package it.unimi.dsi.fastutil.io;

/*		 
 * Copyright (C) 2005-2014 Sebastiano Vigna 
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License. 
 */

/** Simple, fast and repositionable byte-array input stream.
 *
 * <p><strong>Warning</strong>: this class implements the correct semantics
 * of {@link #read(byte[], int, int)} as described in {@link java.io.InputStream}.
 * The implementation given in {@link java.io.ByteArrayInputStream} is broken,
 * but it will never be fixed because it's too late.
 *
 * @author Sebastiano Vigna
 */

public class FastByteArrayInputStream extends MeasurableInputStream implements RepositionableStream {

	/** The array backing the input stream. */
	public byte[] array;

	/** The first valid entry. */
	public int offset;

	/** The number of valid bytes in {@link #array} starting from {@link #offset}. */
	public int length;

	/** The current position as a distance from {@link #offset}. */
	private int position;

	/** The current mark as a position, or -1 if no mark exists. */
	private int mark;

	/** Creates a new array input stream using a given array fragment.
	 *
	 * @param array the backing array.
	 * @param offset the first valid entry of the array.
	 * @param length the number of valid bytes.
	 */
	public FastByteArrayInputStream( final byte[] array, final int offset, final int length ) {
		this.array = array;
		this.offset = offset;
		this.length = length;
	}

	/** Creates a new array input stream using a given array. 
	 *
	 * @param array the backing array.
	 */
	public FastByteArrayInputStream( final byte[] array ) {
		this( array, 0, array.length );
	}

	public boolean markSupported() {
		return true;
	}

	public void reset() {
		position = mark;
	}

	/** Closing a fast byte array input stream has no effect. */
	public void close() {}

	public void mark( final int dummy ) {
		mark = position;
	}

	public int available() {
		return length - position;
	}

	public long skip( long n ) {
		if ( n <= length - position ) {
			position += (int)n;
			return n;
		}
		n = length - position;
		position = length;
		return n;
	}

	public int read() {
		if ( length == position ) return -1;
		return array[ offset + position++ ] & 0xFF;
	}

	/** Reads bytes from this byte-array input stream as 
	 * specified in {@link java.io.InputStream#read(byte[], int, int)}.
	 * Note that the implementation given in {@link java.io.ByteArrayInputStream#read(byte[], int, int)}
	 * will return -1 on a zero-length read at EOF, contrarily to the specification. We won't.
	 */
	
	public int read( final byte b[], final int offset, final int length ) {
		if ( this.length == this.position ) return length == 0 ? 0 : -1;
		final int n = Math.min( length, this.length - this.position );
		System.arraycopy( array, this.offset + this.position, b, offset, n );
		this.position += n;
		return n;
	}

	public long position() {
		return position;
	}

	public void position( final long newPosition ) {
		position = (int)Math.min( newPosition, length );
	}

	@Override
	public long length() {
		return length;
	}
}
