/*
 * 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 (franz.wilhelmstoetter@gmail.com)
 */
package io.jenetics;

import static java.lang.String.format;
import static java.util.Objects.requireNonNull;
import static io.jenetics.internal.util.Hashes.hash;
import static io.jenetics.internal.util.SerialIO.readLong;
import static io.jenetics.internal.util.SerialIO.writeLong;

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.NoSuchElementException;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Function;

import io.jenetics.util.Verifiable;

/**
 * The {@code Phenotype} consists of a {@link Genotype}, the current generation
 * and an optional fitness value. Once the fitness has been evaluated, a new
 * {@code Phenotype} instance, with the calculated fitness, can be created with
 * the {@link #withFitness(Comparable)}.
 *
 * @see Genotype
 *
 * @implNote
 * This class is immutable and thread-safe.
 *
 * @param <G> the gene type
 * @param <C> the fitness result type
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @since 1.0
 * @version 6.0
 */
public final class Phenotype<
        G extends Gene<?, G>,
        C extends Comparable<? super C>
>
        implements
                Comparable<Phenotype<G, C>>,
                Verifiable,
                Serializable
{
        @Serial
        private static final long serialVersionUID = 6L;

        private final Genotype<G> _genotype;
        private final long _generation;
        private final C _fitness;

        /**
         * Create a new phenotype from the given arguments.
         *
         * @param genotype the genotype of this phenotype.
         * @param generation the current generation of the generated phenotype.
         * @param fitness the known fitness of the phenotype, maybe {@code null}
         * @throws NullPointerException if the genotype is {@code null}.
         * @throws IllegalArgumentException if the given {@code generation} is
         *         {@code < 0}.
         */
        private Phenotype(
                final Genotype<G> genotype,
                final long generation,
                final C fitness
        ) {
                if (generation < 0) {
                        throw new IllegalArgumentException(format(
                                "Generation must not < 0 and was %s.", generation
                        ));
                }

                _genotype = requireNonNull(genotype, "Genotype");
                _generation = generation;
                _fitness = fitness;
        }

        /**
         * Applies the given fitness function to the underlying genotype and return
         * a new phenotype with the (newly) evaluated fitness function, if not
         * already evaluated. If the fitness value is already set {@code this}
         * phenotype is returned.
         *
         * @since 5.0
         *
         * @param ff the fitness function
         * @return an evaluated phenotype or {@code this} if the fitness value is
         *         already set
         * @throws NullPointerException if the given fitness function is {@code null}
         */
        public Phenotype<G, C>
        eval(final Function<? super Genotype<G>, ? extends C> ff) {
                requireNonNull(ff);
                return _fitness == null ? withFitness(ff.apply(_genotype)) : this;
        }

        /**
         * This method returns a copy of the {@code Genotype}, to guarantee a
         * immutable class.
         *
         * @return the cloned {@code Genotype} of this {@code Phenotype}.
         * @throws NullPointerException if one of the arguments is {@code null}.
         */
        public Genotype<G> genotype() {
                return _genotype;
        }

        /**
         * A phenotype instance can be created with or without fitness value.
         * Initially, the phenotype is created without fitness value. The
         * fitness evaluation strategy is responsible for creating phenotypes with
         * fitness value assigned.
         *
         * @since 4.2
         *
         * @see #nonEvaluated()
         *
         * @return {@code true} is this phenotype has a fitness value assigned,
         *         {@code false} otherwise
         */
        public boolean isEvaluated() {
                return _fitness != null;
        }

        /**
         * A phenotype instance can be created with or without fitness value.
         * Initially, the phenotype is created without fitness value. The
         * fitness evaluation strategy is responsible for creating phenotypes with
         * fitness value assigned.
         *
         * @since 5.0
         *
         * @see #isEvaluated()
         *
         * @return {@code false} is this phenotype has a fitness value assigned,
         *         {@code true} otherwise
         */
        public boolean nonEvaluated() {
                return _fitness == null;
        }

        /**
         * Return the fitness value of this {@code Phenotype}.
         *
         * @see #fitnessOptional()
         *
         * @return The fitness value of this {@code Phenotype}.
         * @throws NoSuchElementException if {@link #isEvaluated()} returns
         *         {@code false}
         */
        public C fitness() {
                if (_fitness == null) {
                        throw new NoSuchElementException(
                                "Phenotype has no assigned fitness value."
                        );
                }

                return _fitness;
        }

        /**
         * Return the fitness value of {@code this} phenotype, or
         * {@link Optional#empty()} if not evaluated yet.
         *
         * @since 5.0
         *
         * @see #fitness()
         *
         * @return the fitness value
         */
        public Optional<C> fitnessOptional() {
                return Optional.ofNullable(_fitness);
        }

        /**
         * Return the generation this {@link Phenotype} was created.
         *
         * @see #age(long)
         *
         * @return The generation this {@link Phenotype} was created.
         */
        public long generation() {
                return _generation;
        }

        /**
         * Return the age of this phenotype depending on the given current generation.
         *
         * @see #generation()
         *
         * @param currentGeneration the current generation evaluated by the GA.
         * @return the age of this phenotype:
         *          {@code currentGeneration - this.getGeneration()}.
         */
        public long age(final long currentGeneration) {
                return currentGeneration - _generation;
        }

        /**
         * Return a phenotype, where the fitness is set to {@code null}. If
         * {@code this} phenotype isn't evaluated, {@code this} instance is returned.
         *
         * @since 6.0
         *
         * @return a phenotype, where the fitness is set to {@code null}
         */
        public Phenotype<G, C> nullifyFitness() {
                return _fitness != null ? of(_genotype, _generation) : this;
        }

        /**
         * Test whether this phenotype is valid. The phenotype is valid if its
         * {@link Genotype} is valid.
         *
         * @return true if this phenotype is valid, false otherwise.
         */
        @Override
        public boolean isValid() {
                return _genotype.isValid();
        }

        @Override
        public int compareTo(final Phenotype<G, C> pt) {
                if (isEvaluated()) {
                        return pt.isEvaluated() ? fitness().compareTo(pt.fitness()) : 1;
                } else {
                        return pt.isEvaluated() ? -1 : 0;
                }
        }

        @Override
        public int hashCode() {
                return hash(_generation, hash(_fitness, hash(_genotype)));
        }

        @Override
        public boolean equals(final Object obj) {
                return obj instanceof Phenotype<?, ?> other &&
                        _generation == other._generation &&
                        Objects.equals(_fitness, other._fitness) &&
                        Objects.equals(_genotype, other._genotype);
        }

        @Override
        public String toString() {
                return _genotype + " -> " + _fitness;
        }

        /**
         * Return a new {@code Phenotype} object with the given <em>raw</em> fitness
         * value. The returned phenotype is automatically <em>evaluated</em>:
         * {@code isEvaluated() == true}
         *
         * @since 4.2
         *
         * @param fitness the phenotypes' fitness value
         * @throws NullPointerException if the given {@code fitness} value is
         *         {@code null}
         * @return a new phenotype with the given fitness value
         */
        public Phenotype<G, C> withFitness(final C fitness) {
                return Phenotype.of(
                        _genotype,
                        _generation,
                        requireNonNull(fitness)
                );
        }

        /**
         * Return a new {@code Phenotype} object with the given generation.
         *
         * @since 5.0
         *
         * @param generation the generation of the newly created phenotype
         * @return a new phenotype with the given generation
         */
        public Phenotype<G, C> withGeneration(final long generation) {
                return Phenotype.of(
                        _genotype,
                        generation,
                        _fitness
                );
        }


        /* *************************************************************************
         *  Static factory methods.
         * ************************************************************************/

        /**
         * Create a new phenotype from the given arguments. The phenotype is created
         * with a non-assigned fitness function and the call of {@link #isEvaluated()}
         * will return {@code false}.
         *
         * @param <G> the gene type of the chromosome
         * @param <C> the fitness value type
         * @param genotype the genotype of this phenotype.
         * @param generation the current generation of the generated phenotype.
         * @return a new phenotype object
         * @throws NullPointerException if one of the arguments is {@code null}.
         * @throws IllegalArgumentException if the given {@code generation} is
         *         {@code < 0}.
         */
        public static <G extends Gene<?, G>, C extends Comparable<? super C>>
        Phenotype<G, C> of(final Genotype<G> genotype, final long generation) {
                return new Phenotype<>(
                        genotype,
                        generation,
                        null
                );
        }

        /**
         * Create a new phenotype from the given arguments.
         *
         * @param <G> the gene type of the chromosome
         * @param <C> the fitness value type
         * @param genotype the genotype of this phenotype.
         * @param generation the current generation of the generated phenotype.
         * @param fitness the known fitness of the phenotype.
         * @return a new phenotype object
         * @throws NullPointerException if one of the arguments is {@code null}.
         * @throws IllegalArgumentException if the given {@code generation} is
         *         {@code < 0}.
         */
        public static <G extends Gene<?, G>, C extends Comparable<? super C>>
        Phenotype<G, C> of(
                final Genotype<G> genotype,
                final long generation,
                final C fitness
        ) {
                return new Phenotype<>(
                        genotype,
                        generation,
                        requireNonNull(fitness)
                );
        }


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

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

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

        void write(final ObjectOutput out) throws IOException {
                writeLong(_generation, out);
                out.writeObject(_genotype);
                out.writeObject(_fitness);
        }

        @SuppressWarnings({"unchecked", "rawtypes"})
        static Object read(final ObjectInput in)
                throws IOException, ClassNotFoundException
        {
                final var generation = readLong(in);
                final var genotype = (Genotype)in.readObject();
                final var fitness = (Comparable)in.readObject();

                return new Phenotype(genotype, generation, fitness);
        }

}