package it.unimi.dsi.fastutil.io;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.FileChannel;
import java.nio.channels.WritableByteChannel;

/*
 * Copyright (C) 2005-2019 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.
 */

import it.unimi.dsi.fastutil.bytes.ByteArrays;

A repositionable MeasurableInputStream based on cached data received by a WritableByteChannel whose first bytes can be inspected directly. 
An instance of this class acts as a buffer holding the bytes written through its WritableByteChannel interface (which can be easily turned into an OutputStream using Channels.newOutputStream(WritableByteChannel)). The data can be discarded at any time using clear(). The first inspectable bytes of buffer contains the first bytes written. When buffer is full, the bytes are written to an overflow
file.
At any time, the stream of bytes written since creation (or since the last clear()) are available as a fully implemented MeasurableInputStream which also implements RepositionableStream and supports marking. Note that you must arbitrate carefully write and read accesses, as it is always possible to call write(ByteBuffer) and thus modify the length of the MeasurableInputStream. 
The method close() makes the MeasurableInputStream and WritableByteChannel state-changing methods temporarily throw an IOException, but does not otherwise modify the state of the stream. You can reopen the stream later, or clear it. The method dispose() can be used to release the resources associated with the stream. 
Buffering
This class provides no form of buffering except for the memory buffer described above, both when reading and when writing. Users should consider wrapping instances of this class with a FastBufferedInputStream, as reads after the buffer has been exhausted will be performed directly on a RandomAccessFile. /** A {@linkplain RepositionableStream repositionable} {@link MeasurableInputStream} based on
 * cached data received by a {@link WritableByteChannel} whose first bytes can be inspected directly.
 *
 * <p>An instance of this class acts as a buffer holding the bytes written through its
 * {@link WritableByteChannel} interface (which can be easily turned into an {@link OutputStream} using
 * {@link Channels#newOutputStream(WritableByteChannel)}). The data can be discarded at any time using
 * {@link #clear()}. The first {@link #inspectable} bytes of {@link #buffer} contains the first
 * bytes written. When {@link #buffer} is full, the bytes are written to an <em>overflow
 * file</em>.
 *
 * <p>At any time, the stream of bytes written since creation (or since the last {@link #clear()})
 * are available as a fully implemented {@link MeasurableInputStream} which also implements
 * {@link RepositionableStream} and {@linkplain #mark(int) supports marking}.
 * Note that you must arbitrate carefully write and read accesses,
 * as it is always possible to call {@link #write(ByteBuffer)}
 * and thus modify the {@linkplain #length() length} of the {@link MeasurableInputStream}.
 *
 * <p>The method {@link #close()} makes the {@link MeasurableInputStream} and {@link WritableByteChannel} state-changing methods temporarily throw an {@link IOException}, but
 * does not otherwise modify the state of the stream. You can {@linkplain #reopen() reopen} the stream
 * later, or {@linkplain #clear() clear} it.
 * The method {@link #dispose()} can be used to release
 * the resources associated with the stream.
 *
 * <h2>Buffering</h2>
 *
 * <p>This class provides no form of buffering except for the memory buffer described above, both
 * when reading and when writing. Users should consider wrapping instances of this class with a
 * {@link FastBufferedInputStream}, as reads after the buffer has been exhausted will be performed
 * directly on a {@link RandomAccessFile}. */
public class InspectableFileCachedInputStream extends MeasurableInputStream implements RepositionableStream, WritableByteChannel {
	public static final boolean DEBUG = false;

	
The default buffer size (64KiB). /** The default buffer size (64KiB). */
	public static final int DEFAULT_BUFFER_SIZE = 64 * 1024;

	
The inspection buffer. The first inspectable bytes contain the first part of the input stream. The buffer is available for inspection, but users should not modify its content. /** The inspection buffer. The first {@link #inspectable} bytes contain the first part of the input stream.
	 * The buffer is available for inspection, but users should not modify its content. */
	public final byte[] buffer;

	
The number of valid bytes currently in buffer. /** The number of valid bytes currently in {@link #buffer}. */
	public int inspectable;

	
The overflow file used by this stream: it is created at construction time, and deleted on close(). /** The overflow file used by this stream: it is created at construction time, and deleted on {@link #close()}. */
	private final File overflowFile;

	
The random access file used to access the overflow file. /** The random access file used to access the overflow file. */
	private final RandomAccessFile randomAccessFile;

	
randomAccessFile#getChannel(), cached. /** {@link #randomAccessFile randomAccessFile#getChannel()}, cached. */
	private final FileChannel fileChannel;

	
The position on this stream (i.e., the index of the next byte to be returned). /** The position on this stream (i.e., the index of the next byte to be returned). */
	private long position;

	
The mark, if set, or -1. /** The {@linkplain #mark(int) mark}, if set, or -1. */
	private long mark;

	
The write position of the overflow file. When inspectable is equal to buffer.length, the length of the stream is inspectable + writePosition. /** The write position of the {@link #randomAccessFile overflow file}. When {@link #inspectable} is equal
	 * to {@link #buffer buffer.length}, the length of the stream is {@link #inspectable} + {@link #writePosition}.  */
	private long writePosition;


	
Creates a new instance with specified buffer size and overlow-file directory.
Params:
bufferSize – the buffer size, in bytes.
overflowFile – the directory where the overflow file should be created, or null for the default temporary directory./** Creates a new instance with specified buffer size and overlow-file directory.
	 *
	 * @param bufferSize the buffer size, in bytes.
	 * @param overflowFile the directory where the overflow file should be created, or {@code null} for the default temporary directory.
	 */
	public InspectableFileCachedInputStream(final int bufferSize, final File overflowFile) throws IOException {
		if (bufferSize <= 0) throw new IllegalArgumentException("Illegal buffer size " + bufferSize);
		if (overflowFile != null) this.overflowFile = overflowFile;
		else (this.overflowFile = File.createTempFile(getClass().getSimpleName(), "overflow")).deleteOnExit();
		buffer = new byte[bufferSize];
		randomAccessFile = new RandomAccessFile(this.overflowFile, "rw");
		fileChannel = randomAccessFile.getChannel();
		mark = -1;
	}

	
Creates a new instance with specified buffer size and default overflow-file directory.
Params:
bufferSize – the buffer size, in bytes./** Creates a new instance with specified buffer size and default overflow-file directory.
	 *
	 * @param bufferSize the buffer size, in bytes.
	 */
	public InspectableFileCachedInputStream(final int bufferSize) throws IOException {
		this(bufferSize, null);
	}

	
Creates a new instance with default buffer size and overflow-file directory. /** Creates a new instance with default buffer size and overflow-file directory. */
	public InspectableFileCachedInputStream() throws IOException {
		this(DEFAULT_BUFFER_SIZE);
	}

	private void ensureOpen() throws IOException {
		if (position == -1) throw new IOException("This " + getClass().getSimpleName() + " is closed");
	}

	
Clears the content of this InspectableFileCachedInputStream, zeroing the length of the represented stream. /** Clears the content of this {@link InspectableFileCachedInputStream}, zeroing the length of the represented
	 * stream. */
	public void clear() throws IOException {
		if (! fileChannel.isOpen()) throw new IOException("This " + getClass().getSimpleName() + " is closed");
		writePosition = position = inspectable = 0;
		mark = -1;
	}

	
Appends the content of a specified buffer to the end of the currently represented stream.
Params:
byteBuffer – a byte buffer.
Returns:
the number of bytes appended (i.e., byteBuffer.remaining())./** Appends the content of a specified buffer to the end of the currently represented stream.
	 *
	 * @param byteBuffer a byte buffer.
	 * @return the number of bytes appended (i.e., {@link ByteBuffer#remaining() byteBuffer.remaining()}).
	 */
	@Override
	public int write(final ByteBuffer byteBuffer) throws IOException {
		ensureOpen();
		final int remaining = byteBuffer.remaining();

		if (inspectable < buffer.length) {
			// Still some space in the inspectable buffer.
			final int toBuffer = Math.min(buffer.length - inspectable, remaining);
			byteBuffer.get(buffer, inspectable, toBuffer);
			inspectable += toBuffer;
		}

		if (byteBuffer.hasRemaining()) {
			fileChannel.position(writePosition);
			writePosition += fileChannel.write(byteBuffer);
		}

		return remaining;
	}

	
Truncates the overflow file to a given size if possible.
Params:
size – the new size; the final size is the maximum between the current write position (i.e., the length
of the represented stream minus the length of the inspection buffer) and this value./** Truncates the overflow file to a given size if possible.
	 *
	 * @param size the new size; the final size is the maximum between the current write position (i.e., the length
	 * of the represented stream minus the length of the inspection buffer) and this value.
	 */
	public void truncate(final long size) throws FileNotFoundException, IOException {
		fileChannel.truncate(Math.max(size, writePosition));
	}

	
Makes the stream unreadable until the next clear(). 
See Also:
reopen()/** Makes the stream unreadable until the next {@link #clear()}.
	 *
	 * @see #reopen()
	 */
	@Override
	public void close() {
		position = -1;
	}

	
Makes the stream readable again after a close(). 
See Also:
close()/** Makes the stream readable again after a {@link #close()}.
	 *
	 * @see #close()
	 */
	public void reopen() throws IOException {
		if (! fileChannel.isOpen()) throw new IOException("This " + getClass().getSimpleName() + " is closed");
		position = 0;
	}

	
Disposes this stream, deleting the overflow file. After that, the stream is unusable. /** Disposes this stream, deleting the overflow file. After that, the stream is unusable. */
	public void dispose() throws IOException {
		position = -1;
		randomAccessFile.close();
		overflowFile.delete();
	}

	@SuppressWarnings("deprecation")
	@Override
	protected void finalize() throws Throwable {
		try {
			dispose();
		}
		finally {
			super.finalize();
		}
	}

	@Override
	public int available() throws IOException {
		ensureOpen();
		return (int)Math.min(Integer.MAX_VALUE, length() - position);
	}

	@Override
	public int read(final byte[] b, int offset, int length) throws IOException {
		ensureOpen();
		if (length == 0) return 0;
		if (position == length()) return -1; // Nothing to read.
		ByteArrays.ensureOffsetLength(b, offset, length);
		int read = 0;

		if (position < inspectable) {
			/* The first min(inspectable - readPosition, length) bytes should be taken from the buffer. */
			final int toCopy = Math.min(inspectable - (int)position, length);
			System.arraycopy(buffer, (int)position, b, offset, toCopy);
			length -= toCopy;
			offset += toCopy;
			position += toCopy;
			read = toCopy;
		}

		if (length > 0) { // We want to read more.
			if (position == length()) return read != 0 ? read : -1; // There's nothing more to read.
			fileChannel.position(position - inspectable);
			final int toRead = (int)Math.min(length() - position, length);
			// This is *intentionally* not a readFully(). Let the language to its stuff.
			final int t = randomAccessFile.read(b, offset, toRead);
			position += t;
			read += t;
		}

		return read;
	}

	@Override
	public int read(final byte[] b) throws IOException {
		return read(b, 0, b.length);
	}

	@Override
	public long skip(final long n) throws IOException {
		ensureOpen();
		final long toSkip = Math.min(n, length() - position);
		position += toSkip;
		return toSkip;
	}

	@Override
	public int read() throws IOException {
		ensureOpen();
		if (position == length()) return -1; // Nothing to read
		if (position < inspectable) return buffer[(int)position++] & 0xFF;
		fileChannel.position(position - inspectable);
		position++;
		return randomAccessFile.read();
	}

	@Override
	public long length() throws IOException {
		ensureOpen();
		return inspectable + writePosition;
	}

	@Override
	public long position() throws IOException {
		ensureOpen();
		return position;
	}

	
Positions the input stream.
Params:
position – the new position (will be minimized with length())./** Positions the input stream.
	 *
	 * @param position the new position (will be minimized with {@link #length()}).
	 */
	@Override
	public void position(final long position) throws IOException {
		this.position = Math.min(position, length());
	}

	@Override
	public boolean isOpen() {
		return position != -1;
	}

	@Override
	public void mark(final int readlimit) {
		mark = position;
	}

	@Override
	public void reset() throws IOException {
		ensureOpen();
		if (mark == -1) throw new IOException("Mark has not been set");
		position(mark);
	}

	@Override
	public boolean markSupported() {
		return true;
	}
}