/*
 * Copyright (C) 2013 The Guava Authors
 *
 * 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.google.common.collect;

import static com.google.common.collect.CollectPreconditions.checkEntryNotNull;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtIncompatible;

/**
 * Implementation of {@code Map.Entry} for {@link ImmutableMap} that adds extra
 * methods to traverse hash buckets for the key and the value. This allows reuse
 * in {@link RegularImmutableMap} and {@link RegularImmutableBiMap}, which don't
 * have to recopy the entries created by their {@code Builder} implementations.
 *
 * @author Louis Wasserman
 */
@GwtIncompatible("unnecessary")
abstract class ImmutableMapEntry<K, V> extends ImmutableEntry<K, V> {
	ImmutableMapEntry(K key, V value) {
		super(key, value);
		checkEntryNotNull(key, value);
	}

	ImmutableMapEntry(ImmutableMapEntry<K, V> contents) {
		super(contents.getKey(), contents.getValue());
		// null check would be redundant
	}

	@Nullable
	abstract ImmutableMapEntry<K, V> getNextInKeyBucket();

	@Nullable
	abstract ImmutableMapEntry<K, V> getNextInValueBucket();

	static final class TerminalEntry<K, V> extends ImmutableMapEntry<K, V> {
		TerminalEntry(ImmutableMapEntry<K, V> contents) {
			super(contents);
		}

		TerminalEntry(K key, V value) {
			super(key, value);
		}

		@Override
		@Nullable
		ImmutableMapEntry<K, V> getNextInKeyBucket() {
			return null;
		}

		@Override
		@Nullable
		ImmutableMapEntry<K, V> getNextInValueBucket() {
			return null;
		}
	}
}
