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package org.scijava.util;

import java.util.Enumeration;
import java.util.Iterator;

/**
 * A class that provides more thorough support for iteration. Any
 * {@link Enumeration}, {@link Iterator} or {@link Iterable} object can be
 * provided to the constructor, and the resultant {@code IteratorPlus} will
 * provide all three access mechanisms. In the case of {@link #iterator()} it
 * simply returns {@code this}, for more convenient usage with for-each loops. Note, however, that because of this fact, multiple calls
 * to {#iterator()} will produce the same {@link Iterator} every time (in fact,
 * the {@link IteratorPlus} object itself).
 * 
 * For example, let's say you have an {@code Enumeration} and you want
 * to loop over it with the for-each syntax. You could write:
 * 
 * {@code
 * final Enumeration en = ...;
 * for (final String s : new IteratorPlus(en))
 *   // do something with the string
 * }
 * 
 * The same technique works with {@link Iterator}.
 * 
 * 
 * @author Curtis Rueden
 */
public class IteratorPlus implements Enumeration, Iterator,
	Iterable
{

	/** The backing {@link Iterator}. */
	private final Iterator iterator;

	// -- Constructors --

	public IteratorPlus(final Iterable iterable) {
		this(iterable.iterator());
	}

	public IteratorPlus(final Enumeration enumeration) {
		this(new EnumerationIterator<>(enumeration));
	}

	public IteratorPlus(final Iterator iterator) {
		this.iterator = iterator;
	}

	// -- Enumeration methods --

	@Override
	public boolean hasMoreElements() {
		return hasNext();
	}

	@Override
	public E nextElement() {
		return next();
	}

	// -- Iterator methods --

	@Override
	public boolean hasNext() {
		return iterator.hasNext();
	}

	@Override
	public E next() {
		return iterator.next();
	}

	@Override
	public void remove() {
		iterator.remove();
	}

	// -- Iterable methods --

	@Override
	public Iterator iterator() {
		return this;
	}

	// -- Helper classes --

	/**
	 * A helper class for translating an {@link Enumeration} into an
	 * {@link Iterator}.
	 */
	private static class EnumerationIterator implements Iterator {

		private final Enumeration enumeration;

		private EnumerationIterator(final Enumeration enumeration) {
			this.enumeration = enumeration;
		}

		@Override
		public boolean hasNext() {
			return enumeration.hasMoreElements();
		}

		@Override
		public E next() {
			return enumeration.nextElement();
		}

		@Override
		public void remove() {
			throw new UnsupportedOperationException();
		}
	}

}