/* 
 * esodata - data structures and other things, of varying utility
 * Copyright 2022, Ben Culkin
 * 
 * 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 <https://www.gnu.org/licenses/>.
 */
package bjc.data;

import java.util.*;

/*
 * @TODO Oct 6, 2020 - Ben Culkin - :CleverCache
 * 
 * In the future, there are certain efficiencies we could take with our cached 
 * elements; namely, the case where we repeat the same element multiple times,
 *  or the case where we have a mixture of identical (and probably sizable) elements
 * 
 *  The general downside to these of course, is that these efficiencies would cost
 *  us something in terms of complexity, as well as not benefiting iterators which
 *  aren't large enough.
 *  
 *  Still an interesting thought as to the best way to implement such a thing though.
 */

/**
 * An iterator which can go back to the beginning of its iteration sequence at
 * any point.
 * 
 * @author Ben Culkin
 *
 * @param <T>
 *            The type iterated over.
 */
public class ResettableIterator<T> implements Iterator<T> {
	private List<T> cache;
	private Iterator<T> backing;

	private boolean isRepeating = false;
	private Iterator<T> cacheIterator;

	/**
	 * Create a new resettable iterator.
	 * 
	 * @param itr
	 *            The iterator to iterate over.
	 */
	public ResettableIterator(Iterator<T> itr) {
		backing = itr;

		cache = new ArrayList<>();
	}

	/**
	 * Create a new resettable iterator.
	 * 
	 * @param itr
	 *            The iterable to iterate over.
	 */
	public ResettableIterator(Iterable<T> itr) {
		this(itr.iterator());
	}

	@Override
	public boolean hasNext() {
		if (isRepeating) return cacheIterator.hasNext() ? true : backing.hasNext();
		return backing.hasNext();
	}

	@Override
	public T next() {
		if (isRepeating) {
			if (cacheIterator.hasNext()) {
				return cacheIterator.next();
			}
			
			cacheIterator = null;
			isRepeating = false;
		}

		T itm = backing.next();

		cache.add(itm);

		return itm;
	}

	/**
	 * Reset this iterator to its starting point.
	 */
	public void reset() {
		isRepeating = true;

		cacheIterator = cache.iterator();
	}

	/**
	 * Clears the cache of items.
	 * 
	 * This will immediately return the iterator to the last actual item from the
	 * sequence, as well as making that the first item to be iterated over in the
	 * future.
	 */
	public void clearCache() {
		isRepeating = false;
		cacheIterator = null;

		cache = new ArrayList<>();
	}
}