/*
 * Java Genetic Algorithm Library (jenetics-7.1.0).
 * Copyright (c) 2007-2022 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 (franz.wilhelmstoetter@gmail.com)
 */
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 <em>ephemeral</em> constant. It causes the insertion of
 * a <em>mutable</em> 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.
 *
 * <pre>{@code
 * final Random random = ...;
 * final Op<Double> val = EphemeralConst.of(random::nextDouble);
 * }</pre>
 *
 * <b>Serialization</b>
 * Although the {@code EphemeralConst} class implements the {@link Serializable}
 * interface, the serialization will fail if the <em>const</em> supplier is not
 * <em>serializable</em> as well. This can be achieved by <em>casting</em> the
 * supplier to a {@link Serializable}.
 * <pre>{@code
 * final Random random = new Random();
 * final EphemeralConst<Integer> object = EphemeralConst.of(
 *     "R",
 *     (Supplier<Integer> & Serializable)random::nextInt
 * );
 * }</pre>
 * The serialization of the <em>constant</em> will fail, if the lambda has to
 * capture variables form a <em>non</em>-serializable context (class). In such a
 * case it is advisable to create a dedicated supplier class.
 * <pre>{@code
 * final class RandomInt implements Supplier<Integer>, 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;
 *     }
 * }
 * }</pre>
 *
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 7.0
 * @since 3.9
 */
public final class EphemeralConst<T>
        extends Val<T>
        implements Op<T>, Serializable
{

        @Serial
        private static final long serialVersionUID = 1L;

        private final Lazy<T> _value;
        private final Supplier<T> _supplier;

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

        private EphemeralConst(final String name, final Supplier<T> 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<T> 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 than kept
         * constant for this tree.
         *
         * @param name the name of the ephemeral constant
         * @param supplier the value supplier
         * @param <T> the constant type
         * @return a new ephemeral constant
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static <T> EphemeralConst<T> of(
                final String name,
                final Supplier<T> 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 than kept constant for this tree.
         *
         * @param supplier the value supplier
         * @param <T> the constant type
         * @return a new ephemeral constant
         * @throws NullPointerException if the {@code supplier} is {@code null}
         */
        public static <T> EphemeralConst<T> of(final Supplier<T> 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);
        }

}