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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.prog.op;

import static java.lang.String.format;
import static java.util.Objects.requireNonNull;
import static io.jenetics.internal.util.SerialIO.readNullableString;
import static io.jenetics.internal.util.SerialIO.writeNullableString;

import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInput;
import java.io.ObjectInputStream;
import java.io.ObjectOutput;
import java.io.Serial;
import java.io.Serializable;
import java.util.Objects;
import java.util.function.Supplier;

import io.jenetics.internal.util.Lazy;

/**
 * Implementation of an ephemeral constant. It causes the insertion of
 * a mutable constant into the operation tree. Every time this terminal
 * is chosen, a different value is generated which is then used for that
 * particular terminal, and which will remain fixed for the given tree. The main
 * usage would be to introduce random terminal values.
 *
 * {@snippet lang="java":
 * final Random random = null; // @replace substring='null' replacement="..."
 * final Op val = EphemeralConst.of(random::nextDouble);
 * }
 *
 * Serialization
 * Although the {@code EphemeralConst} class implements the {@link Serializable}
 * interface, the serialization will fail if the const supplier is not
 * serializable as well. This can be achieved by casting the
 * supplier to a {@link Serializable}.
 * {@snippet lang="java":
 * final Random random = new Random();
 * final EphemeralConst object = EphemeralConst.of(
 *     "R",
 *     (Supplier & Serializable)random::nextInt
 * );
 * }
 * The serialization of the constant will fail, if the lambda has to
 * capture variables form a non-serializable context (class). In such a
 * case, it is advisable to create a dedicated supplier class.
 * {@snippet lang="java":
 * final class RandomInt implements Supplier, Serializable {
 *     private final Random rnd = new Random();
 *     private final int min;
 *     private final int max;
 *
 *     private RandomInt(final int min, final int max) {
 *         this.min = min;
 *         this.max = max;
 *     }
 *
 *     @Override
 *     public Integer get() {
 *         return rnd.nextInt(max - min) + min;
 *     }
 * }
 * }
 *
 *
 * @author Franz Wilhelmstötter
 * @version 7.0
 * @since 3.9
 */
public final class EphemeralConst
	extends Val
	implements Op, Serializable
{

	@Serial
	private static final long serialVersionUID = 1L;

	private final Lazy _value;
	private final Supplier _supplier;

	private EphemeralConst(
		final String name,
		final Lazy value,
		final Supplier supplier
	) {
		super(name);
		_value = requireNonNull(value);
		_supplier = requireNonNull(supplier);
	}

	private EphemeralConst(final String name, final Supplier supplier) {
		this(name, Lazy.of(supplier), supplier);
	}

	/**
	 * Return a newly created, uninitialized constant of type {@code T}.
	 *
	 * @return a newly created, uninitialized constant of type {@code T}
	 */
	@Override
	public Op get() {
		return new EphemeralConst<>(name(), _supplier);
	}

	/**
	 * Fixes and returns the constant value.
	 *
	 * @since 5.0
	 *
	 * @return the constant value
	 */
	@Override
	public T value() {
		return _value.get();
	}

	@Override
	public String toString() {
		return name() != null
			? format("%s(%s)", name(), value())
			: Objects.toString(value());
	}

	/**
	 * Create a new ephemeral constant with the given {@code name} and value
	 * {@code supplier}. For every newly created operation tree, a new constant
	 * value is chosen for this terminal operation. The value is then kept
	 * constant for this tree.
	 *
	 * @param name the name of the ephemeral constant
	 * @param supplier the value supplier
	 * @param  the constant type
	 * @return a new ephemeral constant
	 * @throws NullPointerException if one of the arguments is {@code null}
	 */
	public static  EphemeralConst of(
		final String name,
		final Supplier supplier
	) {
		return new EphemeralConst<>(requireNonNull(name), supplier);
	}

	/**
	 * Create a new ephemeral constant with the given value {@code supplier}.
	 * For every newly created operation tree, a new constant value is chosen
	 * for this terminal operation. The value is then kept constant for this tree.
	 *
	 * @param supplier the value supplier
	 * @param  the constant type
	 * @return a new ephemeral constant
	 * @throws NullPointerException if the {@code supplier} is {@code null}
	 */
	public static  EphemeralConst of(final Supplier supplier) {
		return new EphemeralConst<>(null, supplier);
	}


	/* *************************************************************************
	 *  Java object serialization
	 * ************************************************************************/

	@Serial
	private Object writeReplace() {
		return new SerialProxy(SerialProxy.EPHEMERAL_CONST, this);
	}

	@Serial
	private void readObject(final ObjectInputStream stream)
		throws InvalidObjectException
	{
		throw new InvalidObjectException("Serialization proxy required.");
	}

	void write(final ObjectOutput out) throws IOException {
		writeNullableString(name(), out);
		out.writeObject(value());
		out.writeObject(_supplier);
	}

	@SuppressWarnings({"unchecked", "rawtypes"})
	static EphemeralConst read(final ObjectInput in)
		throws IOException, ClassNotFoundException
	{
		final String name = readNullableString(in);
		final Object value = in.readObject();
		final Supplier supplier = (Supplier)in.readObject();

		return new EphemeralConst(name, Lazy.ofValue(value), supplier);
	}

}