AugmentedMap.java

/**
 * The MIT License (MIT)
 *
 * Copyright (c) 2015 Georgy Vlasov
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.tenidwa.collections.utils;

import com.google.common.collect.ForwardingMap;
import com.google.common.collect.ImmutableMap;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;

/**
 * A map that augments another map with more values. For every key that is
 * not in the base map, a key-value pair will be present in the augmented
 * map, with the value generated by the augmentaiton function.
 * @author Georgy Vlasov (suseika@tendiwa.org)
 * @version $Id$
 * @since 0.7.0
 */
public final class AugmentedMap<K, V> extends ForwardingMap<K, V> {
    /**
     * Map delegate.
     */
    private final transient Map<K, V> delegate;

    /**
     * Ctor.
     * @param base Base map to augment.
     * @param keys Keys of the augmented map.
     * @param augmentation Function used to generate the new values.
     */
    public AugmentedMap(
        final Map<K, V> base,
        final Set<? extends K> keys,
        final Function<K, V> augmentation
    ) {
        this.delegate = AugmentedMap.createDelegate(base, keys, augmentation);
    }

    /**
     * Creates map delegate.
     * @param base Base map to augment.
     * @param keys Keys to the augmented map.
     * @param augmentation Function used to generate the new values.
     * @param <K> Key
     * @param <V> Value
     * @return A copy of the {@code base} map augmented with new values.
     */
    private static <K, V> ImmutableMap<K, V> createDelegate(
        final Map<K, V> base,
        final Set<? extends K> keys,
        final Function<K, V> augmentation
    ) {
        final ImmutableMap.Builder<K, V> builder = ImmutableMap.builder();
        builder.putAll(base);
        keys.stream()
            .filter(key -> !base.containsKey(key))
            .forEach(key -> builder.put(key, augmentation.apply(key)));
        return builder.build();
    }

    @Override
    protected Map<K, V> delegate() {
        return this.delegate;
    }
}