/*
 * 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.
 */

package org.apache.fesod.common.util;

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.TreeMap;

public class MapUtils {

    private MapUtils() {}

    /**
     * Creates a <i>mutable</i>, empty {@code HashMap} instance.
     *
     * <p><b>Note:</b> if mutability is not required, use ImmutableMap.of() instead.
     *
     * <p><b>Note:</b> if {@code K} is an {@code enum} type, use newEnumMap instead.
     *
     * <p><b>Note for Java 7 and later:</b> this method is now unnecessary and should be treated as
     * deprecated. Instead, use the {@code HashMap} constructor directly, taking advantage of the new
     * <a href="http://goo.gl/iz2Wi">"diamond" syntax</a>.
     *
     * @return a new, empty {@code HashMap}
     */
    public static <K, V> HashMap<K, V> newHashMap() {
        return new HashMap<>(16);
    }

    /**
     * Creates a <i>mutable</i>, empty {@code TreeMap} instance using the natural ordering of its
     * elements.
     *
     * <p><b>Note:</b> if mutability is not required, use ImmutableSortedMap.of() instead.
     *
     * <p><b>Note for Java 7 and later:</b> this method is now unnecessary and should be treated as
     * deprecated. Instead, use the {@code TreeMap} constructor directly, taking advantage of the new
     * <a href="http://goo.gl/iz2Wi">"diamond" syntax</a>.
     *
     * @return a new, empty {@code TreeMap}
     */
    public static <K extends Comparable, V> TreeMap<K, V> newTreeMap() {
        return new TreeMap<>();
    }

    /**
     * Creates a {@code HashMap} instance, with a high enough "initial capacity" that it <i>should</i>
     * hold {@code expectedSize} elements without growth. This behavior cannot be broadly guaranteed,
     * but it is observed to be true for OpenJDK 1.7. It also can't be guaranteed that the method
     * isn't inadvertently <i>oversizing</i> the returned map.
     *
     * @param expectedSize the number of entries you expect to add to the returned map
     * @return a new, empty {@code HashMap} with enough capacity to hold {@code expectedSize} entries
     * without resizing
     * @throws IllegalArgumentException if {@code expectedSize} is negative
     */
    public static <K, V> HashMap<K, V> newHashMapWithExpectedSize(int expectedSize) {
        return new HashMap<>(capacity(expectedSize));
    }

    /**
     * Creates a <i>mutable</i>, empty, insertion-ordered {@code LinkedHashMap} instance.
     *
     * <p><b>Note:</b> if mutability is not required, use  ImmutableMap.of() instead.
     *
     * <p><b>Note for Java 7 and later:</b> this method is now unnecessary and should be treated as
     * deprecated. Instead, use the {@code LinkedHashMap} constructor directly, taking advantage of
     * the new <a href="http://goo.gl/iz2Wi">"diamond" syntax</a>.
     *
     * @return a new, empty {@code LinkedHashMap}
     */
    public static <K, V> LinkedHashMap<K, V> newLinkedHashMap() {
        return new LinkedHashMap<>();
    }

    /**
     * Creates a {@code LinkedHashMap} instance, with a high enough "initial capacity" that it
     * <i>should</i> hold {@code expectedSize} elements without growth. This behavior cannot be
     * broadly guaranteed, but it is observed to be true for OpenJDK 1.7. It also can't be guaranteed
     * that the method isn't inadvertently <i>oversizing</i> the returned map.
     *
     * @param expectedSize the number of entries you expect to add to the returned map
     * @return a new, empty {@code LinkedHashMap} with enough capacity to hold {@code expectedSize}
     * entries without resizing
     * @throws IllegalArgumentException if {@code expectedSize} is negative
     */
    public static <K, V> LinkedHashMap<K, V> newLinkedHashMapWithExpectedSize(int expectedSize) {
        return new LinkedHashMap<>(capacity(expectedSize));
    }

    /**
     * Returns a capacity that is sufficient to keep the map from being resized as long as it grows no
     * larger than expectedSize and the load factor is ≥ its default (0.75).
     */
    static int capacity(int expectedSize) {
        if (expectedSize < 3) {
            return expectedSize + 1;
        }
        if (expectedSize < IntUtils.MAX_POWER_OF_TWO) {
            // This is the calculation used in JDK8 to resize when a putAll
            // happens; it seems to be the most conservative calculation we
            // can make.  0.75 is the default load factor.
            return (int) ((float) expectedSize / 0.75F + 1.0F);
        }
        return Integer.MAX_VALUE;
    }
}
