/*		 
 * Copyright (C) 2003-2014 Paolo Boldi and 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 #keyclass(Object)
import java.util.Arrays;
import java.util.Comparator;
import it.unimi.dsi.fastutil.AbstractPriorityQueue;
#endif

import java.util.NoSuchElementException;

/** A type-specific array-based priority queue.
 *
 * <P>Instances of this class represent a priority queue using a backing
 * array&mdash;all operations are performed directly on the array. The array is
 * enlarged as needed, but it is never shrunk. Use the {@link #trim()} method
 * to reduce its size, if necessary.
 *
 * <P>This implementation is extremely inefficient, but it is difficult to beat
 * when the size of the queue is very small.
 */

public class ARRAY_PRIORITY_QUEUE KEY_GENERIC extends ABSTRACT_PRIORITY_QUEUE KEY_GENERIC {

	/** The backing array. */
	SUPPRESS_WARNINGS_KEY_UNCHECKED
	protected KEY_GENERIC_TYPE array[] = KEY_GENERIC_ARRAY_CAST ARRAYS.EMPTY_ARRAY;

	/** The number of elements in this queue. */
	protected int size;
	
	/** The type-specific comparator used in this queue. */
	protected KEY_COMPARATOR KEY_SUPER_GENERIC c;

	/** The first index, cached, if {@link #firstIndexValid} is true. */
	protected int firstIndex;

	/** Whether {@link #firstIndex} contains a valid value. */
	protected boolean firstIndexValid;

	/** Creates a new empty queue with a given capacity and comparator.
	 *
	 * @param capacity the initial capacity of this queue.
	 * @param c the comparator used in this queue, or <code>null</code> for the natural order.
	 */
	SUPPRESS_WARNINGS_KEY_UNCHECKED
	public ARRAY_PRIORITY_QUEUE( int capacity, KEY_COMPARATOR KEY_SUPER_GENERIC c ) {
		if ( capacity > 0 ) this.array = KEY_GENERIC_ARRAY_CAST new KEY_TYPE[ capacity ];
		this.c = c;
	}

	/** Creates a new empty queue with a given capacity and using the natural order.
	 *
	 * @param capacity the initial capacity of this queue.
	 */
	public ARRAY_PRIORITY_QUEUE( int capacity ) {
		this( capacity, null );
	}

	/** Creates a new empty queue with a given comparator.
	 *
	 * @param c the comparator used in this queue, or <code>null</code> for the natural order.
	 */
	public ARRAY_PRIORITY_QUEUE( KEY_COMPARATOR KEY_SUPER_GENERIC c ) {
		this( 0, c );
	}

	/** Creates a new empty queue using the natural order. 
	 */
	public ARRAY_PRIORITY_QUEUE() {
		this( 0, null );
	}

	/** Wraps a given array in a queue using a given comparator.
	 *
	 * <P>The queue returned by this method will be backed by the given array.
	 *
	 * @param a an array.
	 * @param size the number of elements to be included in the queue.
	 * @param c the comparator used in this queue, or <code>null</code> for the natural order.
	 */
	public ARRAY_PRIORITY_QUEUE( final KEY_GENERIC_TYPE[] a, int size, final KEY_COMPARATOR KEY_SUPER_GENERIC c ) {
		this( c );
		this.array = a;
		this.size = size;
	}


	/** Wraps a given array in a queue using a given comparator.
	 *
	 * <P>The queue returned by this method will be backed by the given array.
	 *
	 * @param a an array.
	 * @param c the comparator used in this queue, or <code>null</code> for the natural order.
	 */
	public ARRAY_PRIORITY_QUEUE( final KEY_GENERIC_TYPE[] a, final KEY_COMPARATOR KEY_SUPER_GENERIC c ) {
		this( a, a.length, c );
	}

	/** Wraps a given array in a queue using the natural order.
	 *
	 * <P>The queue returned by this method will be backed by the given array.
	 *
	 * @param a an array.
	 * @param size the number of elements to be included in the queue.
	 */
	public ARRAY_PRIORITY_QUEUE( final KEY_GENERIC_TYPE[] a, int size ) {
		this( a, size, null );
	}


	/** Wraps a given array in a queue using the natural order.
	 *
	 * <P>The queue returned by this method will be backed by the given array.
	 *
	 * @param a an array.
	 */
	public ARRAY_PRIORITY_QUEUE( final KEY_GENERIC_TYPE[] a ) {
		this( a, a.length );
	}



	/** Returns the index of the smallest element. */

	SUPPRESS_WARNINGS_KEY_UNCHECKED
	private int findFirst() {
		if ( firstIndexValid ) return this.firstIndex;
		firstIndexValid = true;
		int i = size;
		int firstIndex = --i;
		KEY_GENERIC_TYPE first = array[ firstIndex ];

		if ( c == null ) { while( i-- != 0 ) if ( KEY_LESS( array[ i ], first ) ) first = array[ firstIndex = i ]; }
		else while( i-- != 0 ) { if ( c.compare( array[ i ], first ) < 0 ) first = array[ firstIndex = i ]; }

		return this.firstIndex = firstIndex;
	}

	private void ensureNonEmpty() {
		if ( size == 0 ) throw new NoSuchElementException();
	}

	SUPPRESS_WARNINGS_KEY_UNCHECKED
	public void enqueue( KEY_GENERIC_TYPE x ) {
		if ( size == array.length ) array = ARRAYS.grow( array, size + 1 );
		if ( firstIndexValid ) {
			if ( c == null ) { if ( KEY_LESS( x, array[ firstIndex ] ) ) firstIndex = size; }
			else if ( c.compare( x, array[ firstIndex ] ) < 0 ) firstIndex = size;
		}
		else firstIndexValid = false;
		array[ size++ ] = x;
	}

	public KEY_GENERIC_TYPE DEQUEUE() {
		ensureNonEmpty();
		final int first = findFirst();
		final KEY_GENERIC_TYPE result = array[ first ];
		System.arraycopy( array, first + 1, array, first, --size - first );
#if #keyclass(Object)
		array[ size ] = null;
#endif
		firstIndexValid = false;
		return result;
	}

	public KEY_GENERIC_TYPE FIRST() {
		ensureNonEmpty();
		return array[ findFirst() ];
	}

	public void changed() {
		ensureNonEmpty();
		firstIndexValid = false;
	}

	public int size() { return size; }

	public void clear() { 
#if #keyclass(Object)
		Arrays.fill( array, 0, size, null );
#endif
		size = 0; 
		firstIndexValid = false;
	}

	/** Trims the underlying array so that it has exactly {@link #size()} elements.
	 */

	public void trim() {
		array = ARRAYS.trim( array, size );
	}

	public KEY_COMPARATOR KEY_SUPER_GENERIC comparator() { return c; }
}
