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Module contains external API of the evitaDB.
There is a newer version: 2024.9.3
/*
 *
 *                         _ _        ____  ____
 *               _____   _(_) |_ __ _|  _ \| __ )
 *              / _ \ \ / / | __/ _` | | | |  _ \
 *             |  __/\ V /| | || (_| | |_| | |_) |
 *              \___| \_/ |_|\__\__,_|____/|____/
 *
 *   Copyright (c) 2023
 *
 *   Licensed under the Business Source License, Version 1.1 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *   https://github.com/FgForrest/evitaDB/blob/main/LICENSE
 *
 *   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 io.evitadb.utils;

import java.util.Collections;
import java.util.EnumSet;
import java.util.LinkedHashSet;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collectors;

/**
 * Copy of {@link Collectors} methods that are not available in JDK.
 *
 * @author Jan Novotný ([email protected]), FG Forrest a.s. (c) 2023
 */
public class CollectorUtils {
	static final Set CH_UNORDERED_NOID
		= Collections.unmodifiableSet(EnumSet.of(Collector.Characteristics.UNORDERED));

	/**
	 * Returns a {@code Collector} that accumulates the input elements into an
	 * unmodifiable Set. The returned
	 * Collector disallows null values and will throw {@code NullPointerException}
	 * if it is presented with a null value. If the input contains duplicate elements,
	 * an arbitrary element of the duplicates is preserved.
	 *
	 * This is an {@link Collector.Characteristics#UNORDERED unordered}
	 * Collector.
	 *
	 * @param  the type of the input elements
	 * @return a {@code Collector} that accumulates the input elements into an
	 * unmodifiable Set
	 * @see Collectors#toUnmodifiableSet()
	 */
	@SuppressWarnings("unchecked")
	public static  Collector> toUnmodifiableLinkedHashSet() {
		return new CollectorImpl<>(LinkedHashSet::new, Set::add,
			(left, right) -> {
				if (left.size() < right.size()) {
					right.addAll(left); return right;
				} else {
					left.addAll(right); return left;
				}
			},
			set -> (Set)Collections.unmodifiableSet(set),
			CH_UNORDERED_NOID);
	}

	@SuppressWarnings("unchecked")
	private static  Function castingIdentity() {
		return i -> (R) i;
	}

	/**
	 * Simple implementation class for {@code Collector}.
	 *
	 * @param  the type of elements to be collected
	 * @param  the type of the result
	 */
	static class CollectorImpl implements Collector {
		private final Supplier supplier;
		private final BiConsumer accumulator;
		private final BinaryOperator combiner;
		private final Function finisher;
		private final Set characteristics;

		CollectorImpl(Supplier supplier,
		              BiConsumer accumulator,
		              BinaryOperator combiner,
		              Function finisher,
		              Set characteristics) {
			this.supplier = supplier;
			this.accumulator = accumulator;
			this.combiner = combiner;
			this.finisher = finisher;
			this.characteristics = characteristics;
		}

		CollectorImpl(Supplier supplier,
		              BiConsumer accumulator,
		              BinaryOperator combiner,
		              Set characteristics) {
			this(supplier, accumulator, combiner, castingIdentity(), characteristics);
		}

		@Override
		public BiConsumer accumulator() {
			return accumulator;
		}

		@Override
		public Supplier supplier() {
			return supplier;
		}

		@Override
		public BinaryOperator combiner() {
			return combiner;
		}

		@Override
		public Function finisher() {
			return finisher;
		}

		@Override
		public Set characteristics() {
			return characteristics;
		}
	}

}