/*

 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.

 */

/*

 * Licensed to the Apache Software Foundation (ASF) under one or more

 * contributor license agreements.  See the NOTICE file distributed with

 * this work for additional information regarding copyright ownership.

 * The ASF licenses this file to You 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.

 */

/*

 * $Id: MultiHashtable.java,v 1.2.4.1 2005/09/05 11:18:51 pvedula Exp $

 */

package com.sun.org.apache.xalan.internal.xsltc.compiler.util;

import java.util.HashMap;

import java.util.HashSet;

import java.util.Map;

import java.util.Set;

/**

 * @author Jacek Ambroziak

 * @author Santiago Pericas-Geertsen

 * @param <K>

 * @param <V>

 */

public final class MultiHashtable<K,V> {

    static final long serialVersionUID = -6151608290510033572L;

    private final Map<K, Set<V>> map = new HashMap<>();

    private boolean modifiable = true;

    /**

     * Associates the specified key with a set of values. If the map previously

     * contained a mapping for the key, the value is added to the set.

     * @param key key with which the specified value is to be associated

     * @param value value to be added to a set that is associated with the specified key

     * @return the set that is associated with the specified key.

     * @throw UnsupportedOperationException is the MultiHashtable is not modifiable.

     */

    public Set<V> put(K key, V value) {

        if (modifiable) {

            Set<V> set = map.computeIfAbsent(key, k -> new HashSet<>());

            set.add(value);

            return set;

        }

        throw new UnsupportedOperationException("The MultiHashtable instance is not modifiable.");

    }

    /**

     * Maps a key to a value in a set that is associated with the specified key.

     * The mapping is performed by evaluating whether an item in the set equals

     * the specified value.

     *

     * @param key key with which the specified value is to be associated

     * @param value value in a set that is associated with the specified key

     * @return the item in the set if a match is found.

     */

    public V maps(K key, V value) {

        if (key == null) return null;

        final Set<V> set = map.get(key);

        if (set != null) {

            for (V v : set) {

                if (v.equals(value)) {

                    return v;

                }

            }

        }

        return null;

    }

    /**

     * Makes the MultiHashtable unmodifiable.  This method allows modules to set the table

     * as "read-only" so that only query operation, that is maps, is allowed. Any attempts

     * to modify the returned map result in an UnsupportedOperationException.

     */

    public void makeUnmodifiable() {

        modifiable = false;

    }

}