/*
 * 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.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.IOUtils;


An output stream which will retain data in memory until a specified
threshold is reached, and only then commit it to disk. If the stream is
closed before the threshold is reached, the data will not be written to
disk at all.

This class originated in FileUpload processing. In this use case, you do
not know in advance the size of the file being uploaded. If the file is small
you want to store it in memory (for speed), but if the file is large you want
to store it to file (to avoid memory issues).
/**
 * An output stream which will retain data in memory until a specified
 * threshold is reached, and only then commit it to disk. If the stream is
 * closed before the threshold is reached, the data will not be written to
 * disk at all.
 * <p>
 * This class originated in FileUpload processing. In this use case, you do
 * not know in advance the size of the file being uploaded. If the file is small
 * you want to store it in memory (for speed), but if the file is large you want
 * to store it to file (to avoid memory issues).
 *
 */
public class DeferredFileOutputStream
    extends ThresholdingOutputStream
{
    // ----------------------------------------------------------- Data members


    
The output stream to which data will be written prior to the threshold
being reached.
/**
     * The output stream to which data will be written prior to the threshold
     * being reached.
     */
    private ByteArrayOutputStream memoryOutputStream;


    
The output stream to which data will be written at any given time. This
will always be one of memoryOutputStream or
diskOutputStream.
/**
     * The output stream to which data will be written at any given time. This
     * will always be one of <code>memoryOutputStream</code> or
     * <code>diskOutputStream</code>.
     */
    private OutputStream currentOutputStream;


    
The file to which output will be directed if the threshold is exceeded.
/**
     * The file to which output will be directed if the threshold is exceeded.
     */
    private File outputFile;

    
The temporary file prefix.
/**
     * The temporary file prefix.
     */
    private final String prefix;

    
The temporary file suffix.
/**
     * The temporary file suffix.
     */
    private final String suffix;

    
The directory to use for temporary files.
/**
     * The directory to use for temporary files.
     */
    private final File directory;


    
True when close() has been called successfully.
/**
     * True when close() has been called successfully.
     */
    private boolean closed = false;

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


    
Constructs an instance of this class which will trigger an event at the
specified threshold, and save data to a file beyond that point.
The initial buffer size will default to 1024 bytes which is ByteArrayOutputStream's default buffer size.
Params:
threshold –  The number of bytes at which to trigger an event.
outputFile – The file to which data is saved beyond the threshold./**
     * Constructs an instance of this class which will trigger an event at the
     * specified threshold, and save data to a file beyond that point.
     * The initial buffer size will default to 1024 bytes which is ByteArrayOutputStream's default buffer size.
     *
     * @param threshold  The number of bytes at which to trigger an event.
     * @param outputFile The file to which data is saved beyond the threshold.
     */
    public DeferredFileOutputStream(final int threshold, final File outputFile)
    {
        this(threshold,  outputFile, null, null, null, ByteArrayOutputStream.DEFAULT_SIZE);
    }

    
Constructs an instance of this class which will trigger an event at the
specified threshold, and save data to a file beyond that point.
Params:
threshold –  The number of bytes at which to trigger an event.
initialBufferSize – The initial size of the in memory buffer.
outputFile – The file to which data is saved beyond the threshold.
Since:
2.5/**
     * Constructs an instance of this class which will trigger an event at the
     * specified threshold, and save data to a file beyond that point.
     *
     * @param threshold  The number of bytes at which to trigger an event.
     * @param initialBufferSize The initial size of the in memory buffer.
     * @param outputFile The file to which data is saved beyond the threshold.
     *
     * @since 2.5
     */
    public DeferredFileOutputStream(final int threshold, final int initialBufferSize, final File outputFile)
    {
        this(threshold, outputFile, null, null, null, initialBufferSize);
        if (initialBufferSize < 0) {
            throw new IllegalArgumentException("Initial buffer size must be atleast 0.");
        }
    }

    
Constructs an instance of this class which will trigger an event at the
specified threshold, and save data to a temporary file beyond that point.
The initial buffer size will default to 32 bytes which is ByteArrayOutputStream's default buffer size.
Params:
threshold –  The number of bytes at which to trigger an event.
prefix – Prefix to use for the temporary file.
suffix – Suffix to use for the temporary file.
directory – Temporary file directory.
Since:
1.4/**
     * Constructs an instance of this class which will trigger an event at the
     * specified threshold, and save data to a temporary file beyond that point.
     * The initial buffer size will default to 32 bytes which is ByteArrayOutputStream's default buffer size.
     *
     * @param threshold  The number of bytes at which to trigger an event.
     * @param prefix Prefix to use for the temporary file.
     * @param suffix Suffix to use for the temporary file.
     * @param directory Temporary file directory.
     *
     * @since 1.4
     */
    public DeferredFileOutputStream(final int threshold, final String prefix, final String suffix, final File directory)
    {
        this(threshold, null, prefix, suffix, directory, ByteArrayOutputStream.DEFAULT_SIZE);
        if (prefix == null) {
            throw new IllegalArgumentException("Temporary file prefix is missing");
        }
    }

    
Constructs an instance of this class which will trigger an event at the
specified threshold, and save data to a temporary file beyond that point.
Params:
threshold –  The number of bytes at which to trigger an event.
initialBufferSize – The initial size of the in memory buffer.
prefix – Prefix to use for the temporary file.
suffix – Suffix to use for the temporary file.
directory – Temporary file directory.
Since:
2.5/**
     * Constructs an instance of this class which will trigger an event at the
     * specified threshold, and save data to a temporary file beyond that point.
     *
     * @param threshold  The number of bytes at which to trigger an event.
     * @param initialBufferSize The initial size of the in memory buffer.
     * @param prefix Prefix to use for the temporary file.
     * @param suffix Suffix to use for the temporary file.
     * @param directory Temporary file directory.
     *
     * @since 2.5
     */
    public DeferredFileOutputStream(final int threshold, final int initialBufferSize, final String prefix,
                                    final String suffix, final File directory)
    {
        this(threshold, null, prefix, suffix, directory, initialBufferSize);
        if (prefix == null) {
            throw new IllegalArgumentException("Temporary file prefix is missing");
        }
        if (initialBufferSize < 0) {
            throw new IllegalArgumentException("Initial buffer size must be atleast 0.");
        }
    }

    
Constructs an instance of this class which will trigger an event at the
specified threshold, and save data either to a file beyond that point.
Params:
threshold –  The number of bytes at which to trigger an event.
outputFile – The file to which data is saved beyond the threshold.
prefix – Prefix to use for the temporary file.
suffix – Suffix to use for the temporary file.
directory – Temporary file directory.
initialBufferSize – The initial size of the in memory buffer./**
     * Constructs an instance of this class which will trigger an event at the
     * specified threshold, and save data either to a file beyond that point.
     *
     * @param threshold  The number of bytes at which to trigger an event.
     * @param outputFile The file to which data is saved beyond the threshold.
     * @param prefix Prefix to use for the temporary file.
     * @param suffix Suffix to use for the temporary file.
     * @param directory Temporary file directory.
     * @param initialBufferSize The initial size of the in memory buffer.
     */
    private DeferredFileOutputStream(final int threshold, final File outputFile, final String prefix,
                                     final String suffix, final File directory, final int initialBufferSize) {
        super(threshold);
        this.outputFile = outputFile;
        this.prefix = prefix;
        this.suffix = suffix;
        this.directory = directory;

        memoryOutputStream = new ByteArrayOutputStream(initialBufferSize);
        currentOutputStream = memoryOutputStream;
    }


    // --------------------------------------- ThresholdingOutputStream methods


    
Returns the current output stream. This may be memory based or disk
based, depending on the current state with respect to the threshold.
Throws:
IOException – if an error occurs.
Returns:
The underlying output stream./**
     * Returns the current output stream. This may be memory based or disk
     * based, depending on the current state with respect to the threshold.
     *
     * @return The underlying output stream.
     *
     * @throws IOException if an error occurs.
     */
    @Override
    protected OutputStream getStream() throws IOException
    {
        return currentOutputStream;
    }


    
Switches the underlying output stream from a memory based stream to one
that is backed by disk. This is the point at which we realise that too
much data is being written to keep in memory, so we elect to switch to
disk-based storage.
Throws:
IOException – if an error occurs./**
     * Switches the underlying output stream from a memory based stream to one
     * that is backed by disk. This is the point at which we realise that too
     * much data is being written to keep in memory, so we elect to switch to
     * disk-based storage.
     *
     * @throws IOException if an error occurs.
     */
    @Override
    protected void thresholdReached() throws IOException
    {
        if (prefix != null) {
            outputFile = File.createTempFile(prefix, suffix, directory);
        }
        FileUtils.forceMkdirParent(outputFile);
        final FileOutputStream fos = new FileOutputStream(outputFile);
        try {
            memoryOutputStream.writeTo(fos);
        } catch (final IOException e){
            fos.close();
            throw e;
        }
        currentOutputStream = fos;
        memoryOutputStream = null;
    }


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


    
Determines whether or not the data for this output stream has been
retained in memory.
Returns:
true if the data is available in memory; false otherwise./**
     * Determines whether or not the data for this output stream has been
     * retained in memory.
     *
     * @return {@code true} if the data is available in memory;
     *         {@code false} otherwise.
     */
    public boolean isInMemory()
    {
        return !isThresholdExceeded();
    }


    
Returns the data for this output stream as an array of bytes, assuming that the data has been retained in memory. If the data was written to disk, this method returns null. 
Returns:
The data for this output stream, or null if no such data is available./**
     * Returns the data for this output stream as an array of bytes, assuming
     * that the data has been retained in memory. If the data was written to
     * disk, this method returns {@code null}.
     *
     * @return The data for this output stream, or {@code null} if no such
     *         data is available.
     */
    public byte[] getData()
    {
        if (memoryOutputStream != null)
        {
            return memoryOutputStream.toByteArray();
        }
        return null;
    }


    
Returns either the output file specified in the constructor or
the temporary file created or null.

If the constructor specifying the file is used then it returns that
same output file, even when threshold has not been reached.
 If constructor specifying a temporary file prefix/suffix is used then the temporary file created once the threshold is reached is returned If the threshold was not reached then null is returned. 
Returns:
The file for this output stream, or null if no such file exists./**
     * Returns either the output file specified in the constructor or
     * the temporary file created or null.
     * <p>
     * If the constructor specifying the file is used then it returns that
     * same output file, even when threshold has not been reached.
     * <p>
     * If constructor specifying a temporary file prefix/suffix is used
     * then the temporary file created once the threshold is reached is returned
     * If the threshold was not reached then {@code null} is returned.
     *
     * @return The file for this output stream, or {@code null} if no such
     *         file exists.
     */
    public File getFile()
    {
        return outputFile;
    }


    
Closes underlying output stream, and mark this as closed
Throws:
IOException – if an error occurs./**
     * Closes underlying output stream, and mark this as closed
     *
     * @throws IOException if an error occurs.
     */
    @Override
    public void close() throws IOException
    {
        super.close();
        closed = true;
    }


    
Writes the data from this output stream to the specified output stream,
after it has been closed.
Params:
out – output stream to write to.
Throws:
IOException – if this stream is not yet closed or an error occurs./**
     * Writes the data from this output stream to the specified output stream,
     * after it has been closed.
     *
     * @param out output stream to write to.
     * @throws IOException if this stream is not yet closed or an error occurs.
     */
    public void writeTo(final OutputStream out) throws IOException
    {
        // we may only need to check if this is closed if we are working with a file
        // but we should force the habit of closing wether we are working with
        // a file or memory.
        if (!closed) {
            throw new IOException("Stream not closed");
        }

        if (isInMemory()) {
            memoryOutputStream.writeTo(out);
        } else {
            try (FileInputStream fis = new FileInputStream(outputFile)) {
                IOUtils.copy(fis, out);
            }
        }
    }
}