/*
 * Copyright (C) 2004-2010 Stephen Ostermiller
 * http://ostermiller.org/contact.pl?regarding=Java+Utilities
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * See LICENSE.txt for details.
 */
package com.Ostermiller.util;

import java.io.*;
import java.util.ArrayList;

/**
 * An input stream which reads sequentially from multiple sources.
 * More information about this class is available from <a target="_top" href=
 * "http://ostermiller.org/utils/">ostermiller.org</a>.
 *
 * @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities
 * @since ostermillerutils 1.04.00
 */
public class ConcatInputStream extends InputStream {


	/**
	 * Current index to inputStreamQueue
	 *
	 * @since ostermillerutils 1.04.01
	 */
	private int inputStreamQueueIndex = 0;

	/**
	 * Queue of inputStreams that have yet to be read from.
	 *
	 * @since ostermillerutils 1.04.01
	 */
	private ArrayList<InputStream> inputStreamQueue = new ArrayList<InputStream>();

	/**
	 * A cache of the current inputStream from the inputStreamQueue
	 * to avoid unneeded access to the queue which must
	 * be synchronized.
	 *
	 * @since ostermillerutils 1.04.01
	 */
	private InputStream currentInputStream = null;

	/**
	 * true iff the client may add more inputStreams.
	 *
	 * @since ostermillerutils 1.04.01
	 */
	private boolean doneAddingInputStreams = false;

	/**
	 * Causes the addInputStream method to throw IllegalStateException
	 * and read() methods to return -1 (end of stream)
	 * when there is no more available data.
	 * <p>
	 * Calling this method when this class is no longer accepting
	 * more inputStreams has no effect.
	 *
	 * @since ostermillerutils 1.04.01
	 */
	public void lastInputStreamAdded(){
		doneAddingInputStreams = true;
	}

	/**
	 * Add the given inputStream to the queue of inputStreams from which to
	 * concatenate data.
	 *
	 * @param in InputStream to add to the concatenation.
	 * @throws IllegalStateException if more inputStreams can't be added because lastInputStreamAdded() has been called, close() has been called, or a constructor with inputStream parameters was used.
	 *
	 * @since ostermillerutils 1.04.01
	 */
	public void addInputStream(InputStream in){
		synchronized(inputStreamQueue){
			if (in == null) throw new NullPointerException();
			if (closed) throw new IllegalStateException("ConcatInputStream has been closed");
			if (doneAddingInputStreams) throw new IllegalStateException("Cannot add more inputStreams - the last inputStream has already been added.");
			inputStreamQueue.add(in);
		}
	}

	/**
	 * Add the given inputStream to the queue of inputStreams from which to
	 * concatenate data.
	 *
	 * @param in InputStream to add to the concatenation.
	 * @throws IllegalStateException if more inputStreams can't be added because lastInputStreamAdded() has been called, close() has been called, or a constructor with inputStream parameters was used.
	 * @throws NullPointerException the array of inputStreams, or any of the contents is null.
	 *
	 * @since ostermillerutils 1.04.01
	 */
	public void addInputStreams(InputStream[] in){
		for (InputStream element: in) {
			addInputStream(element);
		}
	}

	/**
	 * Gets the current inputStream, looking at the next
	 * one in the list if the current one is null.
	 *
	 * @since ostermillerutils 1.04.01
	 */
	private InputStream getCurrentInputStream(){
		if (currentInputStream == null && inputStreamQueueIndex < inputStreamQueue.size()){
			synchronized(inputStreamQueue){
				// inputStream queue index is advanced only by the nextInputStream()
				// method.  Don't do it here.
				currentInputStream = inputStreamQueue.get(inputStreamQueueIndex);
			}
		}
		return currentInputStream;
	}

	/**
	 * Indicate that we are done with the current inputStream and we should
	 * advance to the next inputStream.
	 *
	 * @since ostermillerutils 1.04.01
	 */
	private void advanceToNextInputStream(){
		currentInputStream = null;
		inputStreamQueueIndex++;
	}

	/**
	 * True iff this the close() method has been called on this stream.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	private boolean closed = false;


	/**
	 * Create a new input stream that can dynamically accept new sources.
	 * <p>
	 * New sources should be added using the addInputStream() method.
	 * When all sources have been added the lastInputStreamAdded() should
	 * be called so that read methods can return -1 (end of stream).
	 * <p>
	 * Adding new sources may by interleaved with read calls.
	 *
	 * @since ostermillerutils 1.04.01
	 */
	public ConcatInputStream(){
		// Empty constructor
	}

	/**
	 * Create a new InputStream with one source.
	 *
	 * @param in InputStream to use as a source.
	 *
	 * @throws NullPointerException if in is null
	 *
	 * @since ostermillerutils 1.04.00
	 */
	public ConcatInputStream(InputStream in){
		addInputStream(in);
		lastInputStreamAdded();
	}

	/**
	 * Create a new InputStream with two sources.
	 *
	 * @param in1 first InputStream to use as a source.
	 * @param in2 second InputStream to use as a source.
	 *
	 * @throws NullPointerException if either source is null.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	public ConcatInputStream(InputStream in1, InputStream in2){
		addInputStream(in1);
		addInputStream(in2);
		lastInputStreamAdded();
	}

	/**
	 * Create a new InputStream with an arbitrary number of sources.
	 *
	 * @param in InputStreams to use as a sources.
	 *
	 * @throws NullPointerException if the input array on any element is null.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	public ConcatInputStream(InputStream[] in){
		addInputStreams(in);
		lastInputStreamAdded();
	}

	/**
	 * Reads the next byte of data from the underlying streams. The value byte is
	 * returned as an int in the range 0 to 255. If no byte is available because
	 * the end of the stream has been reached, the value -1 is returned. This method
	 * blocks until input data is available, the end of the stream is detected, or
	 * an exception is thrown.
	 * <p>
	 * If this class in not done accepting input streams and the end of the last known
	 * stream is reached, this method will block forever unless another thread
	 * adds an input stream or interrupts.
	 *
	 * @return the next byte of data, or -1 if the end of the stream is reached.
	 *
	 * @throws IOException if an I/O error occurs.
	 */
	@Override public int read() throws IOException {
		if (closed) throw new IOException("InputStream closed");
		int r = -1;
		while (r == -1){
			InputStream in = getCurrentInputStream();
			if (in == null){
				if (doneAddingInputStreams) return -1;
				try {
					Thread.sleep(100);
				} catch (InterruptedException iox){
					throw new IOException("Interrupted");
				}
			} else {
				r = in.read();
				if (r == -1) advanceToNextInputStream();
			}
		}
		return r;
	}

	/**
	 * Reads some number of bytes from the underlying streams and stores them into
	 * the buffer array b. The number of bytes actually read is returned as an
	 * integer. This method blocks until input data is available, end of file is
	 * detected, or an exception is thrown.
	 * <p>
	 * If the length of b is zero,
	 * then no bytes are read and 0 is returned; otherwise, there is an attempt
	 * to read at least one byte.
	 * <p>
	 * The read(b) method for class InputStream has the same effect as:<br>
	 * read(b, 0, b.length)
	 * <p>
	 * If this class in not done accepting input streams and the end of the last known
	 * stream is reached, this method will block forever unless another thread
	 * adds an input stream or interrupts.
	 *
	 * @param b - Destination buffer
	 * @return The number of bytes read, or -1 if the end of the stream has been reached
	 *
	 * @throws IOException - If an I/O error occurs
	 * @throws NullPointerException - If b is null.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	@Override public int read(byte[] b) throws IOException {
		return read(b, 0, b.length);
	}

	/**
	 * Reads up to length bytes of data from the underlying streams into an array of bytes.
	 * An attempt is made to read as many as length bytes, but a smaller number may be read,
	 * possibly zero. The number of bytes actually read is returned as an integer.
	 * <p>
	 * If length is zero,
	 * then no bytes are read and 0 is returned; otherwise, there is an attempt
	 * to read at least one byte.
	 * <p>
	 * This method blocks until input data is available
	 * <p>
	 * If this class in not done accepting input streams and the end of the last known
	 * stream is reached, this method will block forever unless another thread
	 * adds an input stream or interrupts.
	 *
	 * @param b Destination buffer
	 * @param off Offset at which to start storing bytes
	 * @param len Maximum number of bytes to read
	 * @return The number of bytes read, or -1 if the end of the stream has been reached
	 *
	 * @throws IOException - If an I/O error occurs
	 * @throws NullPointerException - If b is null.
	 * @throws IndexOutOfBoundsException - if length or offset are not possible.
	 */
	@Override public int read(byte[] b, int off, int len) throws IOException {
		if (off < 0 || len < 0 || off + len > b.length) throw new IllegalArgumentException();
		if (closed) throw new IOException("InputStream closed");
		int r = -1;
		while (r == -1){
			InputStream in = getCurrentInputStream();
			if (in == null){
				if (doneAddingInputStreams) return -1;
				try {
					Thread.sleep(100);
				} catch (InterruptedException iox){
					throw new IOException("Interrupted");
				}
			} else {
				r = in.read(b, off, len);
				if (r == -1) advanceToNextInputStream();
			}
		}
		return r;
	}

	/**
	 * Skips over and discards n bytes of data from this input stream. The skip method
	 * may, for a variety of reasons, end up skipping over some smaller number of bytes,
	 * possibly 0. This may result from any of a number of conditions; reaching end of
	 * file before n bytes have been skipped is only one possibility. The actual number
	 * of bytes skipped is returned. If n is negative, no bytes are skipped.
	 * <p>
	 * If this class in not done accepting input streams and the end of the last known
	 * stream is reached, this method will block forever unless another thread
	 * adds an input stream or interrupts.
	 *
	 * @param n he number of characters to skip
	 * @return The number of characters actually skipped
	 *
	 * @throws IOException If an I/O error occurs
	 *
	 * @since ostermillerutils 1.04.00
	 */
	@Override public long skip(long n) throws IOException {
		if (closed) throw new IOException("InputStream closed");
		if (n <= 0) return 0;
		long s = -1;
		while (s <= 0){
			InputStream in = getCurrentInputStream();
			if (in == null){
				if (doneAddingInputStreams) return 0;
				try {
					Thread.sleep(100);
				} catch (InterruptedException iox){
					throw new IOException("Interrupted");
				}
			} else {
				s = in.skip(n);
				// When nothing was skipped it is a bit of a puzzle.
				// The most common cause is that the end of the underlying
				// stream was reached.  In which case calling skip on it
				// will always return zero.  If somebody were calling skip
				// until it skipped everything they needed, there would
				// be an infinite loop if we were to return zero here.
				// If we get zero, let us try to read one character so
				// we can see if we are at the end of the stream.  If so,
				// we will move to the next.
				if (s <= 0) {
					// read() will advance to the next stream for us, so don't do it again
					s = ((read()==-1)?-1:1);
				}
			}

		}
		return s;
	}

	/**
	 * Returns the number of bytes that can be read (or skipped over) from this input
	 * stream without blocking by the next caller of a method for this input stream.
	 * The next caller might be the same thread or or another thread.
	 *
	 * @throws IOException If an I/O error occurs
	 *
	 * @since ostermillerutils 1.04.00
	 */
	@Override public int available() throws IOException {
		if (closed) throw new IOException("InputStream closed");
		InputStream in = getCurrentInputStream();
		if (in == null) return 0;
		return in.available();
	}

	/**
	 * Closes this input stream and releases any system resources associated with the stream.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	@Override public void close() throws IOException {
		if (closed) return;
		for (Object element: inputStreamQueue) {
			((InputStream)element).close();
		}
		closed = true;
	}

	/**
	 * Mark not supported
	 *
	 * @since ostermillerutils 1.04.00
	 */
	@Override public void mark(int readlimit){
		// Mark not supported -- do nothing
	}

	/**
	 * Reset not supported.
	 *
	 * @throws IOException because reset is not supported.
	 *
	 * @since ostermillerutils 1.04.00
	 */
	@Override public void reset() throws IOException {
		throw new IOException("Reset not supported");
	}

	/**
	 * Does not support mark.
	 *
	 * @return false
	 *
	 * @since ostermillerutils 1.04.00
	 */
	@Override public boolean markSupported(){
		return false;
	}
}
