/*
 * Java Genetic Algorithm Library (jenetics-7.0.0).
 * 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.engine;

import static java.lang.Math.abs;
import static java.lang.Math.max;
import static java.lang.String.format;

import java.time.Duration;
import java.time.InstantSource;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.BiPredicate;
import java.util.function.Predicate;

import io.jenetics.NumericGene;
import io.jenetics.stat.DoubleMoments;
import io.jenetics.util.NanoClock;

/**
 * This class contains factory methods for creating predicates, which can be
 * used for limiting the evolution stream. Some of the <em>limit</em> predicates
 * have to maintain internal state for working properly. It is therefore
 * recommended creating new instances for every stream and don't reuse it.
 *
 * @see EvolutionStream#limit(Predicate)
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @since 3.0
 * @version 3.7
 */
public final class Limits {
        private Limits() {}

        /**
         * Return a predicate which always return {@code true}.
         *
         * @since 4.1
         *
         * @return a predicate which always return {@code true}
         */
        public static Predicate<Object> infinite() {
                return result -> true;
        }

        /**
         * Return a predicate, which will truncate the evolution stream after the
         * given number of generations. The returned predicate behaves like a call
         * of the {@link java.util.stream.Stream#limit(long)} and exists for
         * <i>completeness</i> reasons.
         *
         * @implNote
         * This predicate is mainly there for completion reason and behaves exactly
         * as the {@link java.util.stream.Stream#limit(long)} function, except for
         * the number of evaluations performed by the resulting stream. The evaluation
         * of the population is {@code max generations + 1}. This is because the
         * limiting predicate works on the {@link EvolutionResult} object, which
         * guarantees to contain an evaluated population. That means, that the
         * population must be evaluated at least once, even for a generation limit
         * of zero. If this is an unacceptable performance penalty, better use the
         * {@link java.util.stream.Stream#limit(long)} function instead.
         *
         * @since 3.1
         *
         * @param generation the number of generations after the evolution stream is
         *        truncated
         * @return a predicate which truncates the evolution stream after the given
         *        number of generations
         * @throws java.lang.IllegalArgumentException if the given {@code generation}
         *         is smaller than zero.
         */
        public static Predicate<Object> byFixedGeneration(final long generation) {
                if (generation < 0) {
                        throw new IllegalArgumentException(format(
                                "The number of generations must greater or equal than zero, " +
                                        "but was %d",
                                generation
                        ));
                }

                return new Predicate<>() {
                        private final AtomicLong _current = new AtomicLong();
                        @Override
                        public boolean test(final Object o) {
                                return _current.incrementAndGet() <= generation;
                        }
                };
        }

        /**
         * Return a predicate, which will truncate the evolution stream if no
         * better phenotype could be found after the given number of
         * {@code generations}.
         *
         * <pre>{@code
         * final Phenotype<DoubleGene, Double> result = engine.stream()
         *      // Truncate the evolution stream after 5 "steady" generations.
         *     .limit(bySteadyFitness(5))
         *      // The evolution will stop after maximal 100 generations.
         *     .limit(100)
         *     .collect(toBestPhenotype());
         * }</pre>
         *
         * @param generations the number of <i>steady</i> generations
         * @param <C> the fitness type
         * @return a predicate which truncate the evolution stream if no better
         *         phenotype could be found after a give number of
         *         {@code generations}
         * @throws IllegalArgumentException if the generation is smaller than
         *         one.
         */
        public static <C extends Comparable<? super C>>
        Predicate<EvolutionResult<?, C>> bySteadyFitness(final int generations) {
                return new SteadyFitnessLimit<>(generations);
        }

        /**
         * Return a predicate, which will truncate the evolution stream if the GA
         * execution exceeds a given time duration. This predicate is (normally)
         * used as safety net, for guaranteed stream truncation.
         *
         * <pre>{@code
         * final Phenotype<DoubleGene, Double> result = engine.stream()
         *      // Truncate the evolution stream after 5 "steady" generations.
         *     .limit(bySteadyFitness(5))
         *      // The evolution will stop after maximal 500 ms.
         *     .limit(byExecutionTime(Duration.ofMillis(500), Clock.systemUTC())
         *     .collect(toBestPhenotype());
         * }</pre>
         *
         * @since 3.1
         *
         * @param duration the duration after the evolution stream will be truncated
         * @param clock the clock used for measure the execution time
         * @return a predicate, which will truncate the evolution stream, based on
         *         the exceeded execution time
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static Predicate<Object>
        byExecutionTime(final Duration duration, final InstantSource clock) {
                return new ExecutionTimeLimit(duration, clock);
        }

        /**
         * Return a predicate, which will truncate the evolution stream if the GA
         * execution exceeds a given time duration. This predicate is (normally)
         * used as safety net, for guaranteed stream truncation.
         *
         * <pre>{@code
         * final Phenotype<DoubleGene, Double> result = engine.stream()
         *      // Truncate the evolution stream after 5 "steady" generations.
         *     .limit(bySteadyFitness(5))
         *      // The evolution will stop after maximal 500 ms.
         *     .limit(byExecutionTime(Duration.ofMillis(500))
         *     .collect(toBestPhenotype());
         * }</pre>
         *
         * @since 3.1
         *
         * @param duration the duration after the evolution stream will be truncated
         * @return a predicate, which will truncate the evolution stream, based on
         *         the exceeded execution time
         * @throws NullPointerException if the evolution {@code duration} is
         *         {@code null}
         */
        public static Predicate<Object>
        byExecutionTime(final Duration duration) {
                return byExecutionTime(duration, NanoClock.systemUTC());
        }

        /**
         * Return a predicate, which will truncated the evolution stream if the
         * best fitness of the current population becomes less than the specified
         * threshold and the objective is set to minimize the fitness. This
         * predicate also stops the evolution if the best fitness in the current
         * population becomes greater than the user-specified fitness threshold when
         * the objective is to maximize the fitness.
         *
         * <pre>{@code
         * final Phenotype<DoubleGene, Double> result = engine.stream()
         *      // Truncate the evolution stream if the best fitness is higher than
         *      // the given threshold of '2.3'.
         *     .limit(byFitnessThreshold(2.3))
         *      // The evolution will stop after maximal 250 generations; guarantees
         *      // the termination (truncation) of the evolution stream.
         *     .limit(250)
         *     .collect(toBestPhenotype());
         * }</pre>
         *
         * @since 3.1
         *
         * @param threshold the desired threshold
         * @param <C> the fitness type
         * @return the predicate which truncates the evolution stream based on the
         *         given {@code threshold}.
         * @throws NullPointerException if the given {@code threshold} is
         *        {@code null}.
         */
        public static <C extends Comparable<? super C>>
        Predicate<EvolutionResult<?, C>> byFitnessThreshold(final C threshold) {
                return new FitnessThresholdLimit<>(threshold);
        }

        /**
         * Return a predicate, which will truncate the evolution stream if the
         * fitness is converging. Two filters of different lengths are used to
         * smooth the best fitness across the generations.
         *
         * <pre>{@code
         * final Phenotype<DoubleGene, Double> result = engine.stream()
         *     .limit(byFitnessConvergence(5, 15, (s, l) -> {
         *          final double div = max(abs(s.getMean()), abs(l.getMean()));
         *          final eps = abs(s.getMean() - l.getMean())/(div <= 10E-20 ? 1.0 : div);
         *          return eps >= 10E-5
         *     }))
         *     .collect(toBestPhenotype());
         * }</pre>
         *
         * In the example above, the moving average of the short- and long filter
         * is used for determining the fitness convergence.
         *
         * @apiNote The returned predicate maintains mutable state.
         * Using it in a parallel evolution streams needs external synchronization
         * of the {@code test} method.
         *
         * @since 3.7
         *
         * @param shortFilterSize the size of the short filter
         * @param longFilterSize the size of the long filter. The long filter size
         *        also determines the minimum number of generations of the evolution
         *        stream.
         * @param proceed the predicate which determines when the evolution stream
         *        is truncated. The first parameter of the predicate contains the
         *        double statistics of the short filter and the second parameter
         *        contains the statistics of the long filter
         * @param <N> the fitness type
         * @return a new fitness convergence strategy
         * @throws NullPointerException if the {@code proceed} predicate is
         *         {@code null}
         */
        public static <N extends Number & Comparable<? super N>>
        Predicate<EvolutionResult<?, N>> byFitnessConvergence(
                final int shortFilterSize,
                final int longFilterSize,
                final BiPredicate<DoubleMoments, DoubleMoments> proceed
        ) {
                return new FitnessConvergenceLimit<>(
                        shortFilterSize,
                        longFilterSize,
                        proceed
                );
        }

        /**
         * Return a predicate, which will truncate the evolution stream if the
         * fitness is converging. Two filters of different lengths are used to
         * smooth the best fitness across the generations. When the smoothed best
         * fitness from the long filter is less than a user-specified percentage
         * away from the smoothed best fitness from the short filter, the fitness is
         * deemed as converged and the evolution terminates.
         *
         * <pre>{@code
         * final Phenotype<DoubleGene, Double> result = engine.stream()
         *     .limit(byFitnessConvergence(5, 15, 10E-4))
         *     .collect(toBestPhenotype());
         * }</pre>
         *
         * In the given example, the evolution stream stops, if the difference of the
         * mean values of the long and short filter is less than 1%. The short
         * filter calculates the mean of the best fitness values of the last 5
         * generations. The long filter uses the best fitness values of the last 15
         * generations.
         *
         * @apiNote The returned predicate maintains mutable state.
         * Using it in a parallel evolution streams needs external synchronization
         * of the {@code test} method.
         *
         * @since 3.7
         *
         * @param shortFilterSize the size of the short filter
         * @param longFilterSize the size of the long filter. The long filter size
         *        also determines the minimum number of generations of the evolution
         *        stream.
         * @param epsilon the maximal relative distance of the mean value between
         *        the short and the long filter. The {@code epsilon} must within the
         *        range of {@code [0..1]}.
         * @param <N> the fitness type
         * @return a new fitness convergence strategy
         * @throws IllegalArgumentException if {@code shortFilterSize < 1} ||
         *         {@code longFilterSize < 2} ||
         *         {@code shortFilterSize >= longFilterSize}
         * @throws IllegalArgumentException if {@code epsilon} is not in the range
         *         of {@code [0..1]}
         */
        public static <N extends Number & Comparable<? super N>>
        Predicate<EvolutionResult<?, N>> byFitnessConvergence(
                final int shortFilterSize,
                final int longFilterSize,
                final double epsilon
        ) {
                if (epsilon < 0.0 || epsilon > 1.0) {
                        throw new IllegalArgumentException(format(
                                "The given epsilon is not in the range [0, 1]: %f", epsilon
                        ));
                }

                return new FitnessConvergenceLimit<>(
                        shortFilterSize,
                        longFilterSize,
                        (s, l) -> eps(s.mean(), l.mean()) >= epsilon
                );
        }

        // Calculate the relative mean difference between short and long filter.
        private static double eps(final double s, final double l) {
                final double div = max(abs(s), abs(l));
                return abs(s - l)/(div <= 10E-20 ? 1.0 : div);
        }

        /**
         * A termination method that stops the evolution when the population is
         * deemed as converged. The population is deemed as converged when the
         * average fitness across the current population is less than a
         * user-specified percentage away from the best fitness of the current
         * population. This method takes a predicate with the <em>best</em> fitness
         * and the population fitness moments and determine whether to proceed or
         * not.
         *
         * @since 3.9
         *
         * @param proceed the predicate which determines when the evolution stream
         *        is truncated. The first parameter of the predicate contains the
         *        best fitness of the population and the second parameter contains
         *        the statistics of population fitness values
         * @param <N> the fitness type
         * @return a new fitness convergence strategy
         * @throws NullPointerException if the {@code proceed} predicate is
         *         {@code null}
         */
        public static <N extends Number & Comparable<? super N>>
        Predicate<EvolutionResult<?, N>> byPopulationConvergence(
                final BiPredicate<Double, DoubleMoments> proceed
        ) {
                return new PopulationConvergenceLimit<>(proceed);
        }

        /**
         * A termination method that stops the evolution when the population is
         * deemed as converged. The population is deemed as converged when the
         * average fitness across the current population is less than a
         * user-specified percentage away from the best fitness of the current
         * population.
         *
         * @since 3.9
         *
         * @param epsilon the maximal relative distance of the best fitness value of
         *        the population and the mean value of the population fitness values.
         * @param <N> the fitness type
         * @return a new fitness convergence strategy
         * @throws IllegalArgumentException if {@code epsilon} is not in the range
         *         of {@code [0..1]}
         */
        public static <N extends Number & Comparable<? super N>>
        Predicate<EvolutionResult<?, N>>
        byPopulationConvergence(final double epsilon) {
                if (epsilon < 0.0 || epsilon > 1.0) {
                        throw new IllegalArgumentException(format(
                                "The given epsilon is not in the range [0, 1]: %f", epsilon
                        ));
                }

                return new PopulationConvergenceLimit<>((best, moments) ->
                        eps(best, moments.mean()) >= epsilon
                );
        }

        /**
         * A termination method that stops the evolution when a user-specified
         * percentage of the genes ({@code convergedGeneRage}) that make up a
         * {@code Genotype} are deemed as converged. A gene is deemed as converged,
         * if the {@code geneConvergence} {@code Predicate<DoubleMoments>} for this
         * gene returns {@code true}.
         *
         * @since 4.0
         * @see #byGeneConvergence(double, double)
         *
         * @param geneConvergence predicate which defines when a gene is deemed as
         *        converged, by using the statistics of this gene over all genotypes
         *        of the population
         * @param convergedGeneRate the percentage of genes which must be converged
         *        for truncating the evolution stream
         * @param <G> the gene type
         * @return a new gene convergence predicate
         * @throws NullPointerException if the given gene convergence predicate is
         *         {@code null}
         * @throws IllegalArgumentException if the {@code convergedGeneRate} is not
         *         within the range {@code [0, 1]}
         */
        public static <G extends NumericGene<?, G>> Predicate<EvolutionResult<G, ?>>
        byGeneConvergence(
                final Predicate<DoubleMoments> geneConvergence,
                final double convergedGeneRate
        ) {
                return new GeneConvergenceLimit<>(geneConvergence, convergedGeneRate);
        }

        /**
         * A termination method that stops the evolution when a user-specified
         * percentage of the genes ({@code convergedGeneRage}) that make up a
         * {@code Genotype} are deemed as converged. A gene is deemed as converged
         * when the average value of that gene across all the genotypes in the
         * current population is less than a user-specified percentage
         * ({@code convergenceRate}) away from the maximum gene value across the
         * genotypes.
         * <p>
         * This method is equivalent the following code snippet:
         * <pre>{@code
         * final Predicate<EvolutionResult<DoubleGene, ?>> limit =
         *     byGeneConvergence(
         *         stat -> stat.getMax()*convergenceRate <= stat.getMean(),
         *         convergedGeneRate
         *     );
         * }</pre>
         *
         * @since 4.0
         * @see #byGeneConvergence(Predicate, double)
         *
         * @param convergenceRate the relative distance of the average gene value
         *        to its maximum value
         * @param convergedGeneRate the percentage of genes which must be converged
         *        for truncating the evolution stream
         * @param <G> the gene type
         * @return a new gene convergence predicate
         * @throws IllegalArgumentException if the {@code convergedGeneRate} or
         *         {@code convergenceRate} are not within the range {@code [0, 1]}
         */
        public static <G extends NumericGene<?, G>> Predicate<EvolutionResult<G, ?>>
        byGeneConvergence(
                final double convergenceRate,
                final double convergedGeneRate
        ) {
                return byGeneConvergence(
                        stat -> stat.max()*convergenceRate <= stat.mean(),
                        convergedGeneRate
                );
        }

}