/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */
package org.apache.commons.io.input;

import static org.apache.commons.io.IOUtils.EOF;

import java.io.EOFException;
import java.io.IOException;
import java.io.InputStream;

A functional, light weight InputStream that emulates a stream of a specified size. 
 This implementation provides a light weight object for testing with an InputStream where the contents don't matter. 
 One use case would be for testing the handling of large InputStream as it can emulate that scenario without the overhead of actually processing large numbers of bytes - significantly speeding up test execution times. 

This implementation returns zero from the method that
reads a byte and leaves the array unchanged in the read
methods that are passed a byte array.
If alternative data is required the processByte() and
processBytes() methods can be implemented to generate
data, for example:
 public class TestInputStream extends NullInputStream {
     public TestInputStream(int size) {
         super(size);
     }
     protected int processByte() {
         return ... // return required value here
     }
     protected void processBytes(byte[] bytes, int offset, int length) {
         for (int i = offset; i < length; i++) {
             bytes[i] = ... // set array value here
         }
     }
 }

Since:
1.3
Version:
$Id$/**
 * A functional, light weight {@link InputStream} that emulates
 * a stream of a specified size.
 * <p>
 * This implementation provides a light weight
 * object for testing with an {@link InputStream}
 * where the contents don't matter.
 * <p>
 * One use case would be for testing the handling of
 * large {@link InputStream} as it can emulate that
 * scenario without the overhead of actually processing
 * large numbers of bytes - significantly speeding up
 * test execution times.
 * <p>
 * This implementation returns zero from the method that
 * reads a byte and leaves the array unchanged in the read
 * methods that are passed a byte array.
 * If alternative data is required the <code>processByte()</code> and
 * <code>processBytes()</code> methods can be implemented to generate
 * data, for example:
 *
 * <pre>
 *  public class TestInputStream extends NullInputStream {
 *      public TestInputStream(int size) {
 *          super(size);
 *      }
 *      protected int processByte() {
 *          return ... // return required value here
 *      }
 *      protected void processBytes(byte[] bytes, int offset, int length) {
 *          for (int i = offset; i &lt; length; i++) {
 *              bytes[i] = ... // set array value here
 *          }
 *      }
 *  }
 * </pre>
 *
 * @since 1.3
 * @version $Id$
 */
public class NullInputStream extends InputStream {

    private final long size;
    private long position;
    private long mark = -1;
    private long readlimit;
    private boolean eof;
    private final boolean throwEofException;
    private final boolean markSupported;

    
Create an InputStream that emulates a specified size which supports marking and does not throw EOFException. 
Params:
size – The size of the input stream to emulate./**
     * Create an {@link InputStream} that emulates a specified size
     * which supports marking and does not throw EOFException.
     *
     * @param size The size of the input stream to emulate.
     */
    public NullInputStream(final long size) {
       this(size, true, false);
    }

    
Create an InputStream that emulates a specified size with option settings. 
Params:
size – The size of the input stream to emulate.
markSupported – Whether this instance will support
the mark() functionality.
throwEofException – Whether this implementation will throw an EOFException or return -1 when the end of file is reached./**
     * Create an {@link InputStream} that emulates a specified
     * size with option settings.
     *
     * @param size The size of the input stream to emulate.
     * @param markSupported Whether this instance will support
     * the <code>mark()</code> functionality.
     * @param throwEofException Whether this implementation
     * will throw an {@link EOFException} or return -1 when the
     * end of file is reached.
     */
    public NullInputStream(final long size, final boolean markSupported, final boolean throwEofException) {
       this.size = size;
       this.markSupported = markSupported;
       this.throwEofException = throwEofException;
    }

    
Return the current position.
Returns:
the current position./**
     * Return the current position.
     *
     * @return the current position.
     */
    public long getPosition() {
        return position;
    }

    
Return the size this InputStream emulates. 
Returns:
The size of the input stream to emulate./**
     * Return the size this {@link InputStream} emulates.
     *
     * @return The size of the input stream to emulate.
     */
    public long getSize() {
        return size;
    }

    
Return the number of bytes that can be read.
Returns:
The number of bytes that can be read./**
     * Return the number of bytes that can be read.
     *
     * @return The number of bytes that can be read.
     */
    @Override
    public int available() {
        final long avail = size - position;
        if (avail <= 0) {
            return 0;
        } else if (avail > Integer.MAX_VALUE) {
            return Integer.MAX_VALUE;
        } else {
            return (int)avail;
        }
    }

    
Close this input stream - resets the internal state to
the initial values.
Throws:
IOException – If an error occurs./**
     * Close this input stream - resets the internal state to
     * the initial values.
     *
     * @throws IOException If an error occurs.
     */
    @Override
    public void close() throws IOException {
        eof = false;
        position = 0;
        mark = -1;
    }

    
Mark the current position.
Params:
readlimit – The number of bytes before this marked position
is invalid.
Throws:
UnsupportedOperationException – if mark is not supported./**
     * Mark the current position.
     *
     * @param readlimit The number of bytes before this marked position
     * is invalid.
     * @throws UnsupportedOperationException if mark is not supported.
     */
    @Override
    public synchronized void mark(final int readlimit) {
        if (!markSupported) {
            throw new UnsupportedOperationException("Mark not supported");
        }
        mark = position;
        this.readlimit = readlimit;
    }

    
Indicates whether mark is supported.
Returns:
Whether mark is supported or not./**
     * Indicates whether <i>mark</i> is supported.
     *
     * @return Whether <i>mark</i> is supported or not.
     */
    @Override
    public boolean markSupported() {
        return markSupported;
    }

    
Read a byte.
Throws:
EOFException – if the end of file is reached and
throwEofException is set to true.
IOException – if trying to read past the end of file.
Returns:
Either The byte value returned by processByte()
or -1 if the end of file has been reached and
throwEofException is set to false./**
     * Read a byte.
     *
     * @return Either The byte value returned by <code>processByte()</code>
     * or <code>-1</code> if the end of file has been reached and
     * <code>throwEofException</code> is set to {@code false}.
     * @throws EOFException if the end of file is reached and
     * <code>throwEofException</code> is set to {@code true}.
     * @throws IOException if trying to read past the end of file.
     */
    @Override
    public int read() throws IOException {
        if (eof) {
            throw new IOException("Read after end of file");
        }
        if (position == size) {
            return doEndOfFile();
        }
        position++;
        return processByte();
    }

    
Read some bytes into the specified array.
Params:
bytes – The byte array to read into
Throws:
EOFException – if the end of file is reached and
throwEofException is set to true.
IOException – if trying to read past the end of file.
Returns:
The number of bytes read or -1
if the end of file has been reached and
throwEofException is set to false./**
     * Read some bytes into the specified array.
     *
     * @param bytes The byte array to read into
     * @return The number of bytes read or <code>-1</code>
     * if the end of file has been reached and
     * <code>throwEofException</code> is set to {@code false}.
     * @throws EOFException if the end of file is reached and
     * <code>throwEofException</code> is set to {@code true}.
     * @throws IOException if trying to read past the end of file.
     */
    @Override
    public int read(final byte[] bytes) throws IOException {
        return read(bytes, 0, bytes.length);
    }

    
Read the specified number bytes into an array.
Params:
bytes – The byte array to read into.
offset – The offset to start reading bytes into.
length – The number of bytes to read.
Throws:
EOFException – if the end of file is reached and
throwEofException is set to true.
IOException – if trying to read past the end of file.
Returns:
The number of bytes read or -1
if the end of file has been reached and
throwEofException is set to false./**
     * Read the specified number bytes into an array.
     *
     * @param bytes The byte array to read into.
     * @param offset The offset to start reading bytes into.
     * @param length The number of bytes to read.
     * @return The number of bytes read or <code>-1</code>
     * if the end of file has been reached and
     * <code>throwEofException</code> is set to {@code false}.
     * @throws EOFException if the end of file is reached and
     * <code>throwEofException</code> is set to {@code true}.
     * @throws IOException if trying to read past the end of file.
     */
    @Override
    public int read(final byte[] bytes, final int offset, final int length) throws IOException {
        if (eof) {
            throw new IOException("Read after end of file");
        }
        if (position == size) {
            return doEndOfFile();
        }
        position += length;
        int returnLength = length;
        if (position > size) {
            returnLength = length - (int)(position - size);
            position = size;
        }
        processBytes(bytes, offset, returnLength);
        return returnLength;
    }

    
Reset the stream to the point when mark was last called.
Throws:
UnsupportedOperationException – if mark is not supported.
IOException – If no position has been marked
or the read limit has been exceed since the last position was
marked./**
     * Reset the stream to the point when mark was last called.
     *
     * @throws UnsupportedOperationException if mark is not supported.
     * @throws IOException If no position has been marked
     * or the read limit has been exceed since the last position was
     * marked.
     */
    @Override
    public synchronized void reset() throws IOException {
        if (!markSupported) {
            throw new UnsupportedOperationException("Mark not supported");
        }
        if (mark < 0) {
            throw new IOException("No position has been marked");
        }
        if (position > mark + readlimit) {
            throw new IOException("Marked position [" + mark +
                    "] is no longer valid - passed the read limit [" +
                    readlimit + "]");
        }
        position = mark;
        eof = false;
    }

    
Skip a specified number of bytes.
Params:
numberOfBytes – The number of bytes to skip.
Throws:
EOFException – if the end of file is reached and
throwEofException is set to true.
IOException – if trying to read past the end of file.
Returns:
The number of bytes skipped or -1
if the end of file has been reached and
throwEofException is set to false./**
     * Skip a specified number of bytes.
     *
     * @param numberOfBytes The number of bytes to skip.
     * @return The number of bytes skipped or <code>-1</code>
     * if the end of file has been reached and
     * <code>throwEofException</code> is set to {@code false}.
     * @throws EOFException if the end of file is reached and
     * <code>throwEofException</code> is set to {@code true}.
     * @throws IOException if trying to read past the end of file.
     */
    @Override
    public long skip(final long numberOfBytes) throws IOException {
        if (eof) {
            throw new IOException("Skip after end of file");
        }
        if (position == size) {
            return doEndOfFile();
        }
        position += numberOfBytes;
        long returnLength = numberOfBytes;
        if (position > size) {
            returnLength = numberOfBytes - (position - size);
            position = size;
        }
        return returnLength;
    }

    
Return a byte value for the  read() method.

This implementation returns zero.
Returns:
This implementation always returns zero./**
     * Return a byte value for the  <code>read()</code> method.
     * <p>
     * This implementation returns zero.
     *
     * @return This implementation always returns zero.
     */
    protected int processByte() {
        // do nothing - overridable by subclass
        return 0;
    }

    
Process the bytes for the read(byte[], offset, length)
method.

This implementation leaves the byte array unchanged.
Params:
bytes – The byte array
offset – The offset to start at.
length – The number of bytes./**
     * Process the bytes for the <code>read(byte[], offset, length)</code>
     * method.
     * <p>
     * This implementation leaves the byte array unchanged.
     *
     * @param bytes The byte array
     * @param offset The offset to start at.
     * @param length The number of bytes.
     */
    protected void processBytes(final byte[] bytes, final int offset, final int length) {
        // do nothing - overridable by subclass
    }

    
Handle End of File.
Throws:
EOFException – if throwEofException is set to true.
Returns:
-1 if throwEofException is set to false/**
     * Handle End of File.
     *
     * @return <code>-1</code> if <code>throwEofException</code> is
     * set to {@code false}
     * @throws EOFException if <code>throwEofException</code> is set
     * to {@code true}.
     */
    private int doEndOfFile() throws EOFException {
        eof = true;
        if (throwEofException) {
            throw new EOFException();
        }
        return EOF;
    }

}