/* 
 * 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.ArrayDeque;
import java.util.Deque;
import java.util.Iterator;

/**
 * An iterator that supports queuing elements after/before the current iterator;
 *
 * @author bjculkin
 *
 * @param <E> The type of element this iterator iterates over
 */
public class QueuedIterator<E> implements Iterator<E> {
	private Iterator<E> cur;

	private Deque<Iterator<E>> pending;

	/**
	 * Static method for constructing iterators.
	 * 
	 * @param <E> The type of element this iterator iterates over
	 * 
	 * @return A queued iterator.
	 */
	public static <E> QueuedIterator<E> queued() {
		return new QueuedIterator<>();
	}

	/**
	 * Static method for constructing iterators.
	 *
	 * @param <E> The type of element this iterator iterates over
	 * 
	 * @param vals The values to iterate over.
	 *
	 * @return A queued iterator.
	 */
	@SafeVarargs
	public static <E> QueuedIterator<E> queued(E... vals) {
		return new QueuedIterator<>(new ArrayIterator<>(vals));
	}

	/**
	 * Static method for constructing iterators.
	 *
	 * @param <E> The type of element this iterator iterates over
	 * 
	 * @param itrs The iterators to use.
	 *
	 * @return A queued iterator over the provided iterators.
	 */
	@SafeVarargs
	public static <E> QueuedIterator<E> queued(Iterator<E>... itrs) {
		return new QueuedIterator<>(itrs);
	}

	/**
	 * Static method for constructing iterators.
	 *
	 * @param <E> The type of element this iterator iterates over
	 * 
	 * @param itrs The iterables to use.
	 *
	 * @return A queued iterator over the provided iterables.
	 */
	@SafeVarargs
	public static <E> QueuedIterator<E> queued(Iterable<E>... itrs) {
		return new QueuedIterator<>(itrs);
	}

	/**
	 * Create a new queued iterator that starts blank.
	 */
	public QueuedIterator() {
		pending = new ArrayDeque<>();
	}

	/**
	 * Create a new queued iterator with a set of initial sources.
	 *
	 * @param inits
	 *              The set of initial iterators to use.
	 */
	@SafeVarargs
	public QueuedIterator(Iterator<E>... inits) {
		this();

		for (Iterator<E> init : inits) pending.add(init);
	}

	/**
	 * Create a new queued iterator with a set of initial sources.
	 *
	 * @param inits
	 *              The set of initial iterables to use.
	 */
	@SafeVarargs
	public QueuedIterator(Iterable<E>... inits) {
		this();

		for (Iterable<E> init : inits) pending.add(init.iterator());
	}

	/**
	 * Create a new queued iterator with a set of initial values.
	 *
	 * @param vals
	 *             The set of initial values to use.
	 */
	@SafeVarargs
	public QueuedIterator(E... vals) {
		this(new ArrayIterator<>(vals));
	}

	/**
	 * Add a new iterator who we will iterate through first.
	 *
	 * @param itr
	 *            The iterator to go through first.
	 */
	public void before(Iterator<E> itr) {
		pending.push(cur);

		cur = itr;
	}

	/**
	 * Add a new iterable who we will iterate through first.
	 *
	 * @param itr
	 *            The iterable to go through first.
	 */
	public void before(Iterable<E> itr) {
		before(itr.iterator());
	}

	/**
	 * Add a new set of values who we will iterate through first.
	 *
	 * @param vals
	 *             Values to iterate over first.
	 */
	public void before(@SuppressWarnings("unchecked") E... vals) {
		before(new ArrayIterator<>(vals));
	}

	/**
	 * Add a new iterator who we will iterate through next.
	 *
	 * @param itr
	 *            The iterator to go through next.
	 */
	public void after(Iterator<E> itr) {
		pending.push(itr);
	}

	/**
	 * Add a new iterable who we will iterate through next.
	 *
	 * @param itr
	 *            The iterable to go through next.
	 */
	public void after(Iterable<E> itr) {
		after(itr.iterator());
	}

	/**
	 * Add a new set of values who we will iterate through next.
	 *
	 * @param vals
	 *             The values to iterate over next.
	 */
	public void after(@SuppressWarnings("unchecked") E... vals) {
		after(new ArrayIterator<>(vals));
	}

	/**
	 * Add a new iterator who we will iterate through last.
	 *
	 * @param itr
	 *            The iterator to go through last.
	 */
	public void last(Iterator<E> itr) {
		pending.add(itr);
	}

	/**
	 * Add a new iterable who we will iterate through last.
	 *
	 * @param itr
	 *            The iterable to go through last.
	 */
	public void last(Iterable<E> itr) {
		last(itr.iterator());
	}

	/**
	 * Add a new set of values who we will iterate through last.
	 *
	 * @param vals
	 *             The values we will iterate over.
	 */
	public void last(@SuppressWarnings("unchecked") E... vals) {
		last(new ArrayIterator<>(vals));
	}

	@Override
	public boolean hasNext() {
		while (cur == null || !cur.hasNext()) {
			if (pending.isEmpty()) return false;

			cur = pending.pop();
		}

		return cur.hasNext();
	}

	@Override
	public E next() {
		while (cur == null || !cur.hasNext()) {
			if (pending.isEmpty()) return null;

			cur = pending.pop();
		}

		return cur.next();
	}
}