/*******************************************************************************
 * Copyright 2011 See AUTHORS file.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/

package com.badlogic.gdx.utils;

/** A simple linked list that pools its nodes.
 * @author mzechner */
public class PooledLinkedList<T> {
	static final class Item<T> {
		public T payload;
		public Item<T> next;
		public Item<T> prev;
	}

	private Item<T> head;
	private Item<T> tail;
	private Item<T> iter;
	private Item<T> curr;
	private int size = 0;

	private final Pool<Item<T>> pool;

	public PooledLinkedList (int maxPoolSize) {
		this.pool = new Pool<Item<T>>(16, maxPoolSize) {
			@Override
			protected Item<T> newObject () {
				return new Item<T>();
			}
		};
	}

	/** Adds the specified object to the end of the list regardless of iteration status */
	public void add (T object) {
		Item<T> item = pool.obtain();
		item.payload = object;
		item.next = null;
		item.prev = null;

		if (head == null) {
			head = item;
			tail = item;
			size++;
			return;
		}

		item.prev = tail;
		tail.next = item;
		tail = item;
		size++;
	}

	/** Adds the specified object to the head of the list regardless of iteration status */
	public void addFirst (T object) {
		Item<T> item = pool.obtain();
		item.payload = object;
		item.next = head;
		item.prev = null;

		if (head != null) {
			head.prev = item;
		} else {
			tail = item;
		}

		head = item;

		size++;
	}

	/** Returns the number of items in the list */
	public int size () {
		return size;
	}

	/** Starts iterating over the list's items from the head of the list */
	public void iter () {
		iter = head;
	}

	/** Starts iterating over the list's items from the tail of the list */
	public void iterReverse () {
		iter = tail;
	}

	/** Gets the next item in the list
	 * 
	 * @return the next item in the list or null if there are no more items */
	public @Null T next () {
		if (iter == null) return null;

		T payload = iter.payload;
		curr = iter;
		iter = iter.next;
		return payload;
	}

	/** Gets the previous item in the list
	 * 
	 * @return the previous item in the list or null if there are no more items */
	public @Null T previous () {
		if (iter == null) return null;

		T payload = iter.payload;
		curr = iter;
		iter = iter.prev;
		return payload;
	}

	/** Removes the current list item based on the iterator position. */
	public void remove () {
		if (curr == null) return;

		size--;

		Item<T> c = curr;
		Item<T> n = curr.next;
		Item<T> p = curr.prev;
		pool.free(curr);
		curr = null;

		if (size == 0) {
			head = null;
			tail = null;
			return;
		}

		if (c == head) {
			n.prev = null;
			head = n;
			return;
		}

		if (c == tail) {
			p.next = null;
			tail = p;
			return;
		}

		p.next = n;
		n.prev = p;
	}

	/** Removes the tail of the list regardless of iteration status */
	public @Null T removeLast () {
		if (tail == null) {
			return null;
		}

		T payload = tail.payload;

		size--;

		Item<T> p = tail.prev;
		pool.free(tail);

		if (size == 0) {
			head = null;
			tail = null;
		} else {
			tail = p;
			tail.next = null;
		}

		return payload;
	}

	public void clear () {
		iter();
		T v = null;
		while ((v = next()) != null)
			remove();
	}

}
