/*
 * Copyright (C) 2009, Google Inc.
 * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com>
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.eclipse.jgit.lib;

import java.util.Iterator;
import java.util.NoSuchElementException;

Fast, efficient map specifically for ObjectId subclasses. 

This map provides an efficient translation from any ObjectId instance to a
cached subclass of ObjectId that has the same value.
 If object instances are stored in only one map, ObjectIdOwnerMap is a more efficient implementation. 
Type parameters:
<V> – 
           type of subclass of ObjectId that will be stored in the map./**
 * Fast, efficient map specifically for {@link org.eclipse.jgit.lib.ObjectId}
 * subclasses.
 * <p>
 * This map provides an efficient translation from any ObjectId instance to a
 * cached subclass of ObjectId that has the same value.
 * <p>
 * If object instances are stored in only one map,
 * {@link org.eclipse.jgit.lib.ObjectIdOwnerMap} is a more efficient
 * implementation.
 *
 * @param <V>
 *            type of subclass of ObjectId that will be stored in the map.
 */
public class ObjectIdSubclassMap<V extends ObjectId>
		implements Iterable<V>, ObjectIdSet {
	private static final int INITIAL_TABLE_SIZE = 2048;

	int size;

	private int grow;

	private int mask;

	V[] table;

	
Create an empty map.
/**
	 * Create an empty map.
	 */
	public ObjectIdSubclassMap() {
		initTable(INITIAL_TABLE_SIZE);
	}

	
Remove all entries from this map.
/**
	 * Remove all entries from this map.
	 */
	public void clear() {
		size = 0;
		initTable(INITIAL_TABLE_SIZE);
	}

	
Lookup an existing mapping.
Params:
toFind – 
           the object identifier to find.
Returns:
the instance mapped to toFind, or null if no mapping exists./**
	 * Lookup an existing mapping.
	 *
	 * @param toFind
	 *            the object identifier to find.
	 * @return the instance mapped to toFind, or null if no mapping exists.
	 */
	public V get(AnyObjectId toFind) {
		final int msk = mask;
		int i = toFind.w1 & msk;
		final V[] tbl = table;
		V obj;

		while ((obj = tbl[i]) != null) {
			if (AnyObjectId.isEqual(obj, toFind)) {
				return obj;
			}
			i = (i + 1) & msk;
		}
		return null;
	}

	
{@inheritDoc}

Returns true if this map contains the specified object.
/**
	 * {@inheritDoc}
	 * <p>
	 * Returns true if this map contains the specified object.
	 */
	@Override
	public boolean contains(AnyObjectId toFind) {
		return get(toFind) != null;
	}

	
Store an object for future lookup.

An existing mapping for must not be in this map. Callers must first call get(AnyObjectId) to verify there is no current mapping prior to adding a new mapping, or use addIfAbsent(ObjectId). 
Params:
newValue – 
           the object to store./**
	 * Store an object for future lookup.
	 * <p>
	 * An existing mapping for <b>must not</b> be in this map. Callers must
	 * first call {@link #get(AnyObjectId)} to verify there is no current
	 * mapping prior to adding a new mapping, or use
	 * {@link #addIfAbsent(ObjectId)}.
	 *
	 * @param newValue
	 *            the object to store.
	 */
	public <Q extends V> void add(Q newValue) {
		if (++size == grow)
			grow();
		insert(newValue);
	}

	
Store an object for future lookup.
 Stores newValue, but only if there is not already an object for the same object name. Callers can tell if the value is new by checking the return value with reference equality: 
V obj = ...;
boolean wasNew = map.addIfAbsent(obj) == obj;

Params:
newValue – 
           the object to store.
Returns:
newValue if stored, or the prior value already stored and that would have been returned had the caller used get(newValue) first./**
	 * Store an object for future lookup.
	 * <p>
	 * Stores {@code newValue}, but only if there is not already an object for
	 * the same object name. Callers can tell if the value is new by checking
	 * the return value with reference equality:
	 *
	 * <pre>
	 * V obj = ...;
	 * boolean wasNew = map.addIfAbsent(obj) == obj;
	 * </pre>
	 *
	 * @param newValue
	 *            the object to store.
	 * @return {@code newValue} if stored, or the prior value already stored and
	 *         that would have been returned had the caller used
	 *         {@code get(newValue)} first.
	 */
	public <Q extends V> V addIfAbsent(Q newValue) {
		final int msk = mask;
		int i = newValue.w1 & msk;
		final V[] tbl = table;
		V obj;

		while ((obj = tbl[i]) != null) {
			if (AnyObjectId.isEqual(obj, newValue))
				return obj;
			i = (i + 1) & msk;
		}

		if (++size == grow) {
			grow();
			insert(newValue);
		} else {
			tbl[i] = newValue;
		}
		return newValue;
	}

	
Get number of objects in map
Returns:
number of objects in map/**
	 * Get number of objects in map
	 *
	 * @return number of objects in map
	 */
	public int size() {
		return size;
	}

	
Whether size() is 0. 
Returns:
true if size() is 0./**
	 * Whether {@link #size()} is 0.
	 *
	 * @return true if {@link #size()} is 0.
	 */
	public boolean isEmpty() {
		return size == 0;
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public Iterator<V> iterator() {
		return new Iterator<V>() {
			private int found;

			private int i;

			@Override
			public boolean hasNext() {
				return found < size;
			}

			@Override
			public V next() {
				while (i < table.length) {
					final V v = table[i++];
					if (v != null) {
						found++;
						return v;
					}
				}
				throw new NoSuchElementException();
			}

			@Override
			public void remove() {
				throw new UnsupportedOperationException();
			}
		};
	}

	private void insert(V newValue) {
		final int msk = mask;
		int j = newValue.w1 & msk;
		final V[] tbl = table;
		while (tbl[j] != null)
			j = (j + 1) & msk;
		tbl[j] = newValue;
	}

	private void grow() {
		final V[] oldTable = table;
		final int oldSize = table.length;

		initTable(oldSize << 1);
		for (int i = 0; i < oldSize; i++) {
			final V obj = oldTable[i];
			if (obj != null)
				insert(obj);
		}
	}

	private void initTable(int sz) {
		grow = sz >> 1;
		mask = sz - 1;
		table = createArray(sz);
	}

	@SuppressWarnings("unchecked")
	private final V[] createArray(int sz) {
		return (V[]) new ObjectId[sz];
	}
}