/*
 * 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.output;

import java.io.IOException;
import java.io.OutputStream;


An output stream which triggers an event when a specified number of bytes of
data have been written to it. The event can be used, for example, to throw
an exception if a maximum has been reached, or to switch the underlying
stream type when the threshold is exceeded.

This class overrides all OutputStream methods. However, these
overrides ultimately call the corresponding methods in the underlying output
stream implementation.

NOTE: This implementation may trigger the event before the threshold
is actually reached, since it triggers when a pending write operation would
cause the threshold to be exceeded.
/**
 * An output stream which triggers an event when a specified number of bytes of
 * data have been written to it. The event can be used, for example, to throw
 * an exception if a maximum has been reached, or to switch the underlying
 * stream type when the threshold is exceeded.
 * <p>
 * This class overrides all <code>OutputStream</code> methods. However, these
 * overrides ultimately call the corresponding methods in the underlying output
 * stream implementation.
 * <p>
 * NOTE: This implementation may trigger the event <em>before</em> the threshold
 * is actually reached, since it triggers when a pending write operation would
 * cause the threshold to be exceeded.
 *
 */
public abstract class ThresholdingOutputStream
    extends OutputStream
{

    // ----------------------------------------------------------- Data members


    
The threshold at which the event will be triggered.
/**
     * The threshold at which the event will be triggered.
     */
    private final int threshold;


    
The number of bytes written to the output stream.
/**
     * The number of bytes written to the output stream.
     */
    private long written;


    
Whether or not the configured threshold has been exceeded.
/**
     * Whether or not the configured threshold has been exceeded.
     */
    private boolean thresholdExceeded;


    // ----------------------------------------------------------- Constructors


    
Constructs an instance of this class which will trigger an event at the
specified threshold.
Params:
threshold – The number of bytes at which to trigger an event./**
     * Constructs an instance of this class which will trigger an event at the
     * specified threshold.
     *
     * @param threshold The number of bytes at which to trigger an event.
     */
    public ThresholdingOutputStream(final int threshold)
    {
        this.threshold = threshold;
    }


    // --------------------------------------------------- OutputStream methods


    
Writes the specified byte to this output stream.
Params:
b – The byte to be written.
Throws:
IOException – if an error occurs./**
     * Writes the specified byte to this output stream.
     *
     * @param b The byte to be written.
     *
     * @throws IOException if an error occurs.
     */
    @Override
    public void write(final int b) throws IOException
    {
        checkThreshold(1);
        getStream().write(b);
        written++;
    }


    
Writes b.length bytes from the specified byte array to this
output stream.
Params:
b – The array of bytes to be written.
Throws:
IOException – if an error occurs./**
     * Writes <code>b.length</code> bytes from the specified byte array to this
     * output stream.
     *
     * @param b The array of bytes to be written.
     *
     * @throws IOException if an error occurs.
     */
    @Override
    public void write(final byte b[]) throws IOException
    {
        checkThreshold(b.length);
        getStream().write(b);
        written += b.length;
    }


    
Writes len bytes from the specified byte array starting at
offset off to this output stream.
Params:
b –   The byte array from which the data will be written.
off – The start offset in the byte array.
len – The number of bytes to write.
Throws:
IOException – if an error occurs./**
     * Writes <code>len</code> bytes from the specified byte array starting at
     * offset <code>off</code> to this output stream.
     *
     * @param b   The byte array from which the data will be written.
     * @param off The start offset in the byte array.
     * @param len The number of bytes to write.
     *
     * @throws IOException if an error occurs.
     */
    @Override
    public void write(final byte b[], final int off, final int len) throws IOException
    {
        checkThreshold(len);
        getStream().write(b, off, len);
        written += len;
    }


    
Flushes this output stream and forces any buffered output bytes to be
written out.
Throws:
IOException – if an error occurs./**
     * Flushes this output stream and forces any buffered output bytes to be
     * written out.
     *
     * @throws IOException if an error occurs.
     */
    @Override
    public void flush() throws IOException
    {
        getStream().flush();
    }


    
Closes this output stream and releases any system resources associated
with this stream.
Throws:
IOException – if an error occurs./**
     * Closes this output stream and releases any system resources associated
     * with this stream.
     *
     * @throws IOException if an error occurs.
     */
    @Override
    public void close() throws IOException
    {
        try
        {
            flush();
        }
        catch (final IOException ignored)
        {
            // ignore
        }
        getStream().close();
    }


    // --------------------------------------------------------- Public methods


    
Returns the threshold, in bytes, at which an event will be triggered.
Returns:
The threshold point, in bytes./**
     * Returns the threshold, in bytes, at which an event will be triggered.
     *
     * @return The threshold point, in bytes.
     */
    public int getThreshold()
    {
        return threshold;
    }


    
Returns the number of bytes that have been written to this output stream.
Returns:
The number of bytes written./**
     * Returns the number of bytes that have been written to this output stream.
     *
     * @return The number of bytes written.
     */
    public long getByteCount()
    {
        return written;
    }


    
Determines whether or not the configured threshold has been exceeded for
this output stream.
Returns:
true if the threshold has been reached; false otherwise./**
     * Determines whether or not the configured threshold has been exceeded for
     * this output stream.
     *
     * @return {@code true} if the threshold has been reached;
     *         {@code false} otherwise.
     */
    public boolean isThresholdExceeded()
    {
        return written > threshold;
    }


    // ------------------------------------------------------ Protected methods


    
Checks to see if writing the specified number of bytes would cause the
configured threshold to be exceeded. If so, triggers an event to allow
a concrete implementation to take action on this.
Params:
count – The number of bytes about to be written to the underlying
             output stream.
Throws:
IOException – if an error occurs./**
     * Checks to see if writing the specified number of bytes would cause the
     * configured threshold to be exceeded. If so, triggers an event to allow
     * a concrete implementation to take action on this.
     *
     * @param count The number of bytes about to be written to the underlying
     *              output stream.
     *
     * @throws IOException if an error occurs.
     */
    protected void checkThreshold(final int count) throws IOException
    {
        if (!thresholdExceeded && written + count > threshold)
        {
            thresholdExceeded = true;
            thresholdReached();
        }
    }

    
Resets the byteCount to zero. You can call this from thresholdReached() if you want the event to be triggered again. /**
     * Resets the byteCount to zero.  You can call this from
     * {@link #thresholdReached()} if you want the event to be triggered again.
     */
    protected void resetByteCount()
    {
        this.thresholdExceeded = false;
        this.written = 0;
    }

    
Sets the byteCount to count.  Useful for re-opening an output stream
that has previously been written to.
Params:
count – The number of bytes that have already been written to the
output stream
Since:
2.5/**
     * Sets the byteCount to count.  Useful for re-opening an output stream
     * that has previously been written to.
     *
     * @param count The number of bytes that have already been written to the
     * output stream
     *
     * @since 2.5
     */
    protected void setByteCount(final long count) {
        this.written = count;
    }


    // ------------------------------------------------------- Abstract methods


    
Returns the underlying output stream, to which the corresponding
OutputStream methods in this class will ultimately delegate.
Throws:
IOException – if an error occurs.
Returns:
The underlying output stream./**
     * Returns the underlying output stream, to which the corresponding
     * <code>OutputStream</code> methods in this class will ultimately delegate.
     *
     * @return The underlying output stream.
     *
     * @throws IOException if an error occurs.
     */
    protected abstract OutputStream getStream() throws IOException;


    
Indicates that the configured threshold has been reached, and that a
subclass should take whatever action necessary on this event. This may
include changing the underlying output stream.
Throws:
IOException – if an error occurs./**
     * Indicates that the configured threshold has been reached, and that a
     * subclass should take whatever action necessary on this event. This may
     * include changing the underlying output stream.
     *
     * @throws IOException if an error occurs.
     */
    protected abstract void thresholdReached() throws IOException;
}