/*
 * Copyright (C) 2010-2022 Sebastiano Vigna
 *
 * 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 PACKAGE;

#if KEY_CLASS_Object
import java.util.Arrays;
import java.util.Comparator;
#endif

import java.io.Serializable;
import it.unimi.dsi.fastutil.HashCommon;
import it.unimi.dsi.fastutil.PriorityQueue;

import java.util.NoSuchElementException;

/** A type-specific array-based FIFO queue, supporting also deque operations.
 *
 * <p>Instances of this class represent a FIFO queue using a backing
 * array in a circular way. The array is enlarged and shrunk as needed. You can use the {@link #trim()} method
 * to reduce its memory usage, if necessary.
 *
 * <p>This class provides additional methods that implement a <em>deque</em> (double-ended queue).
 */

public class ARRAY_FIFO_QUEUE KEY_GENERIC implements PRIORITY_QUEUE KEY_GENERIC, Serializable {
	private static final long serialVersionUID = 0L;

	/** The standard initial capacity of a queue. */
	public static final int INITIAL_CAPACITY = 4;

	/** The backing array. */
	protected transient KEY_GENERIC_TYPE array[];

	/** The current (cached) length of {@link #array}. */
	protected transient int length;

	/** The start position in {@link #array}. It is always strictly smaller than {@link #length}.*/
	protected transient int start;

	/** The end position in {@link #array}. It is always strictly smaller than {@link #length}.
	 *  Might be actually smaller than {@link #start} because {@link #array} is used cyclically. */
	protected transient int end;

	/** Creates a new empty queue with given capacity.
	 *
	 * @implNote Because of inner limitations of the JVM, the initial
	 * capacity cannot exceed {@link it.unimi.dsi.fastutil.Arrays#MAX_ARRAY_SIZE} &minus; 1.
	 *
	 * @param capacity the initial capacity of this queue.
	 */
	SUPPRESS_WARNINGS_KEY_UNCHECKED
	public ARRAY_FIFO_QUEUE(final int capacity) {
		if (capacity > it.unimi.dsi.fastutil.Arrays.MAX_ARRAY_SIZE - 1) throw new IllegalArgumentException("Initial capacity (" + capacity + ") exceeds " + (it.unimi.dsi.fastutil.Arrays.MAX_ARRAY_SIZE - 1));
		if (capacity < 0) throw new IllegalArgumentException("Initial capacity (" + capacity + ") is negative");
		// We never build a queue with a zero-sized backing array; moreover, to
		// avoid resizing at the given capacity we need one additional element.
		array = KEY_GENERIC_ARRAY_CAST new KEY_TYPE[Math.max(1, capacity + 1)];
		length = array.length;
	}

	/** Creates a new empty queue with standard {@linkplain #INITIAL_CAPACITY initial capacity}. */
	public ARRAY_FIFO_QUEUE() {
		this(INITIAL_CAPACITY);
	}

	/** {@inheritDoc}
	 * @implSpec This implementation returns {@code null} (FIFO queues have no comparator). */
	@Override
	public KEY_COMPARATOR KEY_SUPER_GENERIC comparator() {
		return null;
	}

	@Override
	public KEY_GENERIC_TYPE DEQUEUE() {
		if (start == end) throw new NoSuchElementException();
		final KEY_GENERIC_TYPE t = array[start];
#if KEYS_REFERENCE
		array[start] = null; // Clean-up for the garbage collector.
#endif
		if (++start == length) start = 0;
		reduce();
		return t;
	}

	/** Dequeues the {@linkplain PriorityQueue#last() last} element from the queue.
	 *
	 * @return the dequeued element.
	 * @throws NoSuchElementException if the queue is empty.
	 */
	public KEY_GENERIC_TYPE DEQUEUE_LAST() {
		if (start == end) throw new NoSuchElementException();
		if (end == 0) end = length;
		final KEY_GENERIC_TYPE t = array[--end];
#if KEYS_REFERENCE
		array[end] = null; // Clean-up for the garbage collector.
#endif
		reduce();
		return t;
	}

	SUPPRESS_WARNINGS_KEY_UNCHECKED
	private final void resize(final int size, final int newLength) {
		final KEY_GENERIC_TYPE[] newArray = KEY_GENERIC_ARRAY_CAST new KEY_TYPE[newLength];
		if (start >= end) {
			if (size != 0) {
				System.arraycopy(array, start, newArray, 0, length - start);
				System.arraycopy(array, 0, newArray, length - start, end);
			}
		}
		else System.arraycopy(array, start, newArray, 0, end - start);
		start = 0;
		end = size;
		array = newArray;
		length = newLength;
	}

	private final void expand() {
		resize(length, (int)Math.min(it.unimi.dsi.fastutil.Arrays.MAX_ARRAY_SIZE, 2L * length));
	}

	private final void reduce() {
		final int size = size();
		if (length > INITIAL_CAPACITY && size <= length / 4) resize(size, length / 2);
	}

	@Override
	public void enqueue(KEY_GENERIC_TYPE x) {
		array[end++] = x;
		if (end == length) end = 0;
		if (end == start) expand();
	}

	/** Enqueues a new element as the first element (in dequeuing order) of the queue.
	 * @param x the element to enqueue.
	 */
	public void enqueueFirst(KEY_GENERIC_TYPE x) {
		if (start == 0) start = length;
		array[--start] = x;
		if (end == start) expand();
	}

	@Override
	public KEY_GENERIC_TYPE FIRST() {
		if (start == end) throw new NoSuchElementException();
		return array[start];
	}


	@Override
	public KEY_GENERIC_TYPE LAST() {
		if (start == end) throw new NoSuchElementException();
		return array[(end == 0 ? length : end) - 1];
	}

	@Override
	public void clear() {
#if KEYS_REFERENCE
		if (start <= end) Arrays.fill(array, start, end, null);
		else {
			Arrays.fill(array, start, length, null);
			Arrays.fill(array, 0, end, null);
		}
#endif
		start = end = 0;
	}

	/** Trims the queue to the smallest possible size. */
	SUPPRESS_WARNINGS_KEY_UNCHECKED
	public void trim() {
		final int size = size();
		final KEY_GENERIC_TYPE[] newArray =
#if KEYS_PRIMITIVE
											new KEY_GENERIC_TYPE[size + 1];
#else
											(KEY_GENERIC_TYPE[])new Object[size + 1];
#endif
		if (start <= end) System.arraycopy(array, start, newArray, 0, end - start);
		else {
			System.arraycopy(array, start, newArray, 0, length - start);
			System.arraycopy(array, 0, newArray, length - start, end);
		}
		start = 0;
		length = (end = size) + 1;
		array = newArray;
	}

	@Override
	public int size() {
		final int apparentLength = end - start;
		return apparentLength >= 0 ? apparentLength : length + apparentLength;
	}

	private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
		s.defaultWriteObject();
		int size = size();
		s.writeInt(size);
		for(int i = start; size-- != 0;) {
			s.WRITE_KEY(array[i++]);
			if (i == length) i = 0;
		}
	}

	SUPPRESS_WARNINGS_KEY_UNCHECKED
	private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException {
		s.defaultReadObject();
		end = s.readInt();
		array = KEY_GENERIC_ARRAY_CAST new KEY_TYPE[length = HashCommon.nextPowerOfTwo(end + 1)];
		for(int i = 0; i < end; i++) array[i] = KEY_GENERIC_CAST s.READ_KEY();
	}
}
