CollectionUtils.java

// SPDX-License-Identifier: MIT

package lermitage.intellij.extra.icons.utils;

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

/** To avoid using Apache Commons Collection 3 (no longer bundled with IDE) or 4 just for a few operations. */
public class CollectionUtils {

    @SuppressWarnings("BooleanMethodIsAlwaysInverted")
    public static boolean isEqualCollection(final Collection<?> a, final Collection<?> b) {
        if (a.size() != b.size()) {
            return false;
        }
        final CardinalityHelper<Object> helper = new CardinalityHelper<>(a, b);
        if (helper.cardinalityA.size() != helper.cardinalityB.size()) {
            return false;
        }
        for (final Object obj : helper.cardinalityA.keySet()) {
            if (helper.freqA(obj) != helper.freqB(obj)) {
                return false;
            }
        }
        return true;
    }

    //
    // The rest of the code has been duplicated from org.apache.commons:commons-collections4, then applied quick-fixes by IDE
    //

    private static class CardinalityHelper<O> {

        /** Contains the cardinality for each object in collection A. */
        final Map<O, Integer> cardinalityA;

        /** Contains the cardinality for each object in collection B. */
        final Map<O, Integer> cardinalityB;

        /**
         * Create a new CardinalityHelper for two collections.
         * @param a the first collection
         * @param b the second collection
         */
        public CardinalityHelper(final Iterable<? extends O> a, final Iterable<? extends O> b) {
            cardinalityA = getCardinalityMap(a);
            cardinalityB = getCardinalityMap(b);
        }

        /**
         * Returns the frequency of this object in collection A.
         * @param obj the object
         * @return the frequency of the object in collection A
         */
        public int freqA(final Object obj) {
            return getFreq(obj, cardinalityA);
        }

        /**
         * Returns the frequency of this object in collection B.
         * @param obj the object
         * @return the frequency of the object in collection B
         */
        public int freqB(final Object obj) {
            return getFreq(obj, cardinalityB);
        }

        private int getFreq(final Object obj, final Map<?, Integer> freqMap) {
            final Integer count = freqMap.get(obj);
            if (count != null) {
                return count;
            }
            return 0;
        }
    }

    public static <O> Map<O, Integer> getCardinalityMap(final Iterable<? extends O> coll) {
        final Map<O, Integer> count = new HashMap<>();
        for (final O obj : coll) {
            count.merge(obj, 1, Integer::sum);
        }
        return count;
    }

}