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A system for running GOAL multi-agent systems.
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/**
 * The GOAL Runtime Environment. Copyright (C) 2015 Koen Hindriks.
 *
 * 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 3 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.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program. If not, see .
 */
package goal.util;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * An Iterable that will 'stitch' an iteration of iterations.

 * 

 * Using {@code yield return} as an indicator what the {@code next()} method of
 * the {@link #iterator()} should return, the following pseudo-code describes
 * the working of this class:

 * 

 * 
 *   for (Iterable<? extends T> subIter : allIters)

 *     for (T value : subIter)

 *       yield return value;
 * 
 *
 * @param 
 *            The value the iterable's iterator will iterate over.
 */
public class IterableStitcher implements Iterable {
	/**
	 * The iterable whose iterator iterates over the collections of values that this
	 * stitcher stitches.
	 */
	private final Iterable> baseIterable;

	/**
	 * Creates a new {@link IterableStitcher}, which will stitch the given iterable
	 * of iterables.
	 *
	 * @param baseIterable
	 *            The iteration of iterables to stitch together.
	 */
	public IterableStitcher(Iterable> baseIterable) {
		this.baseIterable = baseIterable;
	}

	@Override
	public Iterator iterator() {
		return new StitchIterator(this.baseIterable);
	}

	/**
	 * Iterator for the {@link IterableStitcher}. Takes one Iterable and iterates
	 * over its values. Once the iterable's iterator is exhausted, the next iterable
	 * is taken. This repeats until all iterables have been iterated over.
	 */
	private class StitchIterator implements Iterator {
		/** The iterator to stitch. */
		private final Iterator> innerIterator;
		/**
		 * The iterator to use for the next value in {@link #next()}, as well as for
		 * {@link #hasNext()}
		 */
		private Iterator currentIterator;
		/** The iterator last used to generate the value for next(). */
		private Iterator lastUsedIterator;

		/**
		 * Creates a new {@link StitchIterator}.
		 *
		 * @param iterable
		 *            the existing iterable.
		 */
		public StitchIterator(Iterable> iterable) {
			this.innerIterator = iterable.iterator();
			// initialize the current iterator
			this.nextIterator();
		}

		/**
		 * Finds the next iterator in {@link #innerIterator} that can provide a value
		 * for {@link #next()}. That iterator is stored in {@link #currentIterator}.
		 */
		private void nextIterator() {
			this.currentIterator = null;
			while (this.innerIterator.hasNext() && this.currentIterator == null) {
				this.currentIterator = this.innerIterator.next().iterator();
				// skip the iterator if it does not have any
				if (!this.currentIterator.hasNext()) {
					this.currentIterator = null;
				}
			}
		}

		@Override
		public boolean hasNext() {
			// the current iterator is removed when it does not have any
			// more items.
			return this.currentIterator != null;
		}

		@Override
		public T next() {
			if (this.currentIterator == null) {
				throw new NoSuchElementException();
			}

			T value = this.currentIterator.next();
			// save the current iterator, in order to support #remove()
			this.lastUsedIterator = this.currentIterator;
			// make sure to update the current iterator if it is empty,
			// so that #hasNext can return the proper value.
			if (!this.currentIterator.hasNext()) {
				this.nextIterator();
			}
			return value;
		}

		@Override
		public void remove() {
			this.lastUsedIterator.remove();
		}
	}
}