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Java utility library
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/*
 * Copyright 2018 OmniFaces
 *
 * 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 org.omnifaces.utils;

import java.util.Comparator;
import java.util.function.Predicate;

public final class Comparators {

	private Comparators() {
	}

	/**
	 * Create a new {@link Comparator} that places values that match the given {@link Predicate} before values that do not.
	 *
	 * If either both values match the predicate or both do not match the predicate, the order is determined by the given comparator.
	 *
	 * @param predicate the predicate to use to sort the values
	 * @param comparator the comparator to use to sort any pairs of values that either both do or do not match the predicate
	 * @param  the type of the values
	 *
	 * @return the new comparator
	 */
	public static  Comparator firstWhen(Predicate predicate, Comparator comparator) {
		return firstOrLastWhen(true, predicate, comparator);
	}

	/**
	 * Create a new {@link Comparator} that places values that match the given {@link Predicate} after  values that do not.
	 *
	 * If either both values match the predicate or both do not match the predicate, the order is determined by the given comparator.
	 *
	 * @param predicate the predicate to use to sort the values
	 * @param comparator the comparator to use to sort any pairs of values that either both do or do not match the predicate
	 * @param  the type of the values
	 *
	 * @return the new comparator
	 */
	public static  Comparator lastWhen(Predicate predicate, Comparator comparator) {
		return firstOrLastWhen(false, predicate, comparator);
	}

	private static  Comparator firstOrLastWhen(boolean matchesFirst, Predicate predicate, Comparator comparator) {
		final int direction = matchesFirst ? -1 : 1;

		return (t1, t2) -> {
			boolean t1Matches = predicate.test(t1);
			boolean t2Matches = predicate.test(t2);

			if (t1Matches != t2Matches) {
				return t1Matches ? direction : -1 * direction;
			}

			return comparator.compare(t1, t2);
		};
	}
}