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/*
 * Java Genetic Algorithm Library (jenetics-8.1.0).
 * Copyright (c) 2007-2024 Franz Wilhelmstötter
 *
 * 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.
 *
 * Author:
 *    Franz Wilhelmstötter ([email protected])
 */
package io.jenetics.ext;

import static java.lang.String.format;
import static java.util.Objects.requireNonNull;

import io.jenetics.Gene;
import io.jenetics.Optimize;
import io.jenetics.Phenotype;
import io.jenetics.Selector;
import io.jenetics.stat.MinMax;
import io.jenetics.util.ISeq;
import io.jenetics.util.MSeq;
import io.jenetics.util.Seq;

/**
 * Selector implementation which is part of the
 * Weasel program
 * algorithm. The Weasel program is a thought experiment by Richard
 * Dawkins to illustrate the functioning of the evolution: random mutation
 * combined with non-random cumulative selection.
 * 
 * The selector always returns populations which only contains "{@code count}"
 * instances of the best {@link Phenotype}.
 * 
 * {@link io.jenetics.engine.Engine} setup for the Weasel program:
 * {@snippet lang="java":
 * final Engine engine = Engine.builder(problem)
 *      // Set the 'WeaselSelector'.
 *     .selector(new WeaselSelector<>())
 *      // Disable survivors selector.
 *     .offspringFraction(1)
 *      // Set the 'WeaselMutator'.
 *     .alterers(new WeaselMutator<>(0.05))
 *     .build();
 * }
 *
 * @see Weasel program
 * @see WeaselMutator
 *
 * @param  the gene type
 * @param  the fitness result type
 *
 * @author Franz Wilhelmstötter
 * @since 3.5
 * @version 5.0
 */
public class WeaselSelector<
	G extends Gene,
	C extends Comparable
>
	implements Selector
{
	@Override
	public ISeq> select(
		final Seq> population,
		final int count,
		final Optimize opt
	) {
		requireNonNull(population, "Population");
		requireNonNull(opt, "Optimization");
		if (count < 0) {
			throw new IllegalArgumentException(format(
				"Selection count must be greater or equal then zero, but was %s",
				count
			));
		}

		final MinMax> minMax = population.stream()
			.collect(MinMax.toMinMax(opt.ascending()));

		final MSeq> result = MSeq.ofLength(count);
		return result.fill(minMax::max).toISeq();
	}

	@Override
	public String toString() {
		return "WeaselSelector";
	}

}