/*
 * 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.util;

import static java.util.Objects.requireNonNull;

import java.util.Comparator;
import java.util.Optional;
import java.util.Random;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.random.RandomGenerator;
import java.util.random.RandomGeneratorFactory;

/**
 * This class holds the {@link RandomGenerator} engine used for the GA. The
 * {@code RandomRegistry} is thread safe and is initialized with the
 * {@link RandomGeneratorFactory#getDefault()} PRNG.
 *
 * <h2>Setup the PRNG used for the evolution process</h2>
 * There are several ways on how to set the {@link RandomGenerator} used during
 * the evolution process.
 * <p>
 *
 * <b>Using a {@link RandomGeneratorFactory}</b><br>
 * The following example registers the <em>L128X1024MixRandom</em> random
 * generator. By using a factory, each thread gets its own generator instance,
 * which ensures thread-safety without the necessity of the created random
 * generator to be thread-safe.
 * {@snippet lang="java":
 * // This is the default setup.
 * RandomRegistry.random(RandomGeneratorFactory.getDefault());
 *
 * // Using the "L128X1024MixRandom" random generator for the evolution.
 * RandomRegistry.random(RandomGeneratorFactory.of("L128X1024MixRandom"));
 * }
 * <br>
 *
 * <b>Using a {@link RandomGenerator} {@link Supplier}</b><br>
 * If you have a random engine, which is not available as
 * {@link RandomGeneratorFactory}, it is also possible to register a
 * {@link Supplier} of the desired random generator. This method has the same
 * thread-safety property as the method above.
 * {@snippet lang="java":
 * RandomRegistry.random(() -> new MySpecialRandomGenerator());
 * }
 *
 * Register a random generator supplier is also more flexible. It allows
 * using the streaming and splitting capabilities of the random generators
 * implemented in the Java library.
 * {@snippet lang="java":
 * final Iterator<RandomGenerator> randoms =
 *     StreamableGenerator.of("L128X1024MixRandom")
 *         .rngs()
 *         .iterator();
 *
 * RandomRegistry.random(randoms::next);
 * }
 * <br>
 *
 * <b>Using a {@link RandomGenerator} instance</b><br>
 * It is also possible to set a single random generator instance for the whole
 * evolution process. When using this setup, the used random generator must be
 * thread safe.
 * {@snippet lang="java":
 * RandomRegistry.random(new Random(123456));
 * }
 * <p>
 *
 * The following code snippet shows an almost complete example of a typical
 * random generator setup.
 * {@snippet lang="java":
 * public class GA {
 *     public static void main(final String[] args) {
 *         // Initialize the registry with the factory of the PRGN.
 *         final var factory = RandomGeneratorFactory.of("L128X1024MixRandom");
 *         RandomRegistry.random(factory);
 *
 *         final Engine<DoubleGene, Double> engine = null; // @replace substring='null' replacement="..."
 *         final EvolutionResult<DoubleGene, Double> result = engine.stream()
 *             .limit(100)
 *             .collect(toBestEvolutionResult());
 *     }
 * }
 * }
 *
 * <h2>Setup of a <i>local</i> PRNG</h2>
 *
 * You can temporarily (and locally) change the implementation of the PRNG. E.g.,
 * for initialize the engine stream with the same initial population.
 * {@snippet lang="java":
 * public class GA {
 *     public static void main(final String[] args) {
 *         // Create a reproducible list of genotypes.
 *         final var factory = RandomGeneratorFactory.of("L128X1024MixRandom");
 *         final List<Genotype<DoubleGene>> genotypes =
 *             with(factory.create(123), r ->
 *                 Genotype.of(DoubleChromosome.of(0, 10)).instances()
 *                     .limit(50)
 *                     .collect(toList())
 *             );
 *
 *         final Engine<DoubleGene, Double> engine = null; // @replace substring='null' replacement="..."
 *         final EvolutionResult<DoubleGene, Double> result = engine
 *              // Initialize the evolution stream with the given genotypes.
 *             .stream(genotypes)
 *             .limit(100)
 *             .collect(toBestEvolutionResult());
 *     }
 * }
 * }
 *
 * <p>
 * The default random generator used by <em>Jenetics</em> is
 * {@code L64X256MixRandom}. Via the system property
 * {@code io.jenetics.util.defaultRandomGenerator}, it is possible to use a
 * different random generator.
 * <pre>{@code
 * java -Dio.jenetics.util.defaultRandomGenerator=L64X1024MixRandom \
 *      -cp jenetics-@__version__@.jar:app.jar \
 *          com.foo.bar.MyJeneticsApp
 * }</pre>
 *
 * @see RandomGenerator
 * @see RandomGeneratorFactory
 *
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @since 1.0
 * @version 8.0
 */
public final class RandomRegistry {
        private RandomRegistry() {}

        /**
         * Thread local wrapper for a random generator supplier (factory).
         *
         * @param <R> the type of the random generator
         */
        private static final class TLR<R extends RandomGenerator>
                extends ThreadLocal<R>
                implements Supplier<R>
        {
                private final Supplier<? extends R> _factory;

                TLR(final Supplier<? extends R> factory) {
                        _factory = requireNonNull(factory);
                }

                @Override
                protected synchronized R initialValue() {
                        return _factory.get();
                }
        }

        private static final TLR<RandomGenerator> DEFAULT_RANDOM_FACTORY =
                new TLR<>(RandomGeneratorFactory.of(Env.defaultRandomGenerator)::create);

        private static final Context<Supplier<? extends RandomGenerator>> CONTEXT =
                new Context<>(DEFAULT_RANDOM_FACTORY);

        /**
         * Return the {@link RandomGenerator} of the current scope.
         *
         * @return the {@link RandomGenerator} of the current scope
         */
        public static RandomGenerator random() {
                return CONTEXT.get().get();
        }

        /**
         * Set a new {@link RandomGenerator} for the <em>global</em> scope. The given
         * {@link RandomGenerator} <b>must</b> be thread safe, which is the case for
         * the Java {@link Random} class.
         *
         * @see #random(RandomGeneratorFactory)
         *
         * @param random the new {@link RandomGenerator} for the <em>global</em>
         *        scope
         * @throws NullPointerException if the {@code random} object is {@code null}
         */
        public static void random(final RandomGenerator random) {
                requireNonNull(random);
                CONTEXT.set(() -> random);
        }

        /**
         * Set a new {@link RandomGeneratorFactory} for the <em>global</em> scope.
         *
         * @param factory the random generator factory
         * @throws NullPointerException if the {@code factory} object is {@code null}.
         */
        public static <R extends RandomGenerator> void
        random(final RandomGeneratorFactory<? extends R> factory) {
                requireNonNull(factory);
                CONTEXT.set(new TLR<>(factory::create));
        }

        /**
         * Set a new {@link Supplier} of {@link RandomGenerator} for the
         * <em>global</em> scope.
         *
         * @param supplier the random generator supplier
         * @throws NullPointerException if the {@code supplier} object is {@code null}.
         */
        public static <R extends RandomGenerator> void
        random(final Supplier<? extends R> supplier) {
                requireNonNull(supplier);
                CONTEXT.set(new TLR<>(supplier));
        }

        /**
         * Set the random object to its default value.
         */
        public static void reset() {
                CONTEXT.reset();
        }

        /**
         * Executes the consumer code using the given {@code random} generator.
         * {@snippet lang="java":
         * final MSeq<Integer> seq = null; // @replace substring='null' replacement="..."
         * using(new Random(123), r -> {
         *     seq.shuffle();
         * });
         * }
         *
         * The example above shuffles the given integer {@code seq} <i>using</i> the
         * given {@code Random(123)} engine.
         *
         * @since 3.0
         *
         * @param random the PRNG used within the consumer
         * @param consumer the consumer which is executed with the <i>scope</i> of
         *        the given {@code random} engine.
         * @param <R> the type of the random engine
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static <R extends RandomGenerator> void using(
                final R random,
                final Consumer<? super R> consumer
        ) {
                CONTEXT.with(
                        () -> random,
                        r -> { consumer.accept(random); return null; }
                );
        }

        /**
         * Executes the consumer code using the given {@code random} generator.
         * {@snippet lang="java":
         * final MSeq<Integer> seq = null; // @replace substring='null' replacement="..."
         * using(RandomGeneratorFactory.getDefault(), r -> {
         *     seq.shuffle();
         * });
         * }
         *
         * The example above shuffles the given integer {@code seq} <i>using</i> the
         * given {@link RandomGeneratorFactory#getDefault()} factory.
         *
         * @since 7.0
         *
         * @param factory the random generator factory used within the consumer
         * @param consumer the consumer which is executed within the <i>scope</i> of
         *        the given random generator.
         * @param <R> the type of the random engine
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static <R extends RandomGenerator> void using(
                final RandomGeneratorFactory<? extends R> factory,
                final Consumer<? super R> consumer
        ) {
                CONTEXT.with(
                        new TLR<>(factory::create),
                        r -> { consumer.accept(r.get()); return null; }
                );
        }

        /**
         * Executes the consumer code using the given {@code random} generator
         * supplier.
         * {@snippet lang="java":
         * final MSeq<Integer> seq = null; // @replace substring='null' replacement="..."
         * using(() -> new MyRandomGenerator(), r -> seq.shuffle());
         * }
         *
         * @since 7.0
         *
         * @param supplier the random generator supplier used within the consumer
         * @param consumer the consumer which is executed within the <i>scope</i> of
         *        the given random generator.
         * @param <R> the type of the random engine
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static <R extends RandomGenerator> void using(
                final Supplier<? extends R> supplier,
                final Consumer<? super R> consumer
        ) {
                CONTEXT.with(
                        new TLR<>(supplier),
                        r -> { consumer.accept(r.get()); return null; }
                );
        }

        /**
         * Opens a new <em>scope</em> with the given random generator and executes
         * the given function within it. The following example shows how to create a
         * reproducible list of genotypes:
         * {@snippet lang="java":
         * final List<Genotype<DoubleGene>> genotypes =
         *     with(new LCG64ShiftRandom(123), r ->
         *         Genotype.of(DoubleChromosome.of(0, 10)).instances()
         *            .limit(50)
         *            .collect(toList())
         *     );
         * }
         *
         * @since 3.0
         *
         * @param <R> the type of the random engine
         * @param <T> the function return type
         * @param random the PRNG used for the opened scope
         * @param function the function to apply within the random scope
         * @return the object returned by the given function
         * @throws NullPointerException if one of the arguments is {@code null}
         */
        public static <R extends RandomGenerator, T> T with(
                final R random,
                final Function<? super R, ? extends T> function
        ) {
                return CONTEXT.with(
                        () -> random,
                        s -> function.apply(random)
                );
        }

        /**
         * Opens a new <em>scope</em> with the given random generator factory and
         * executes the given function within it.
         * {@snippet lang="java":
         * final List<Genotype<DoubleGene>> genotypes =
         *     with(RandomGeneratorFactory.getDefault(), random ->
         *         Genotype.of(DoubleChromosome.of(0, 10)).instances()
         *            .limit(50)
         *            .collect(toList())
         *     );
         * }
         *
         * @since 3.0
         *
         * @param <R> the type of the random engine
         * @param <T> the function return type
         * @param factory the PRNG used for the opened scope
         * @param function the function to apply within the random scope
         * @return the object returned by the given function
         * @throws NullPointerException if one of the arguments is {@code null}.
         */
        public static <R extends RandomGenerator, T> T with(
                final RandomGeneratorFactory<? extends R> factory,
                final Function<? super R, ? extends T> function
        ) {
                return CONTEXT.with(
                        new TLR<>(factory::create),
                        r -> function.apply(r.get())
                );
        }

        /**
         * Opens a new <em>scope</em> with the given random generator supplier and
         * executes the given function within it.
         * {@snippet lang="java":
         * final List<Genotype<DoubleGene>> genotypes =
         *     with(() -> new MyRandomGenerator(), random ->
         *         Genotype.of(DoubleChromosome.of(0, 10)).instances()
         *            .limit(50)
         *            .collect(toList())
         *     );
         * }
         *
         * @since 3.0
         *
         * @param <R> the type of the random engine
         * @param <T> the function return type
         * @param supplier the PRNG used for the opened scope
         * @param function the function to apply within the random scope
         * @return the object returned by the given function
         * @throws NullPointerException if one of the arguments is {@code null}.
         */
        public static <R extends RandomGenerator, T> T with(
                final Supplier<? extends R> supplier,
                final Function<? super R, ? extends T> function
        ) {
                return CONTEXT.with(
                        new TLR<>(supplier),
                        r -> function.apply(r.get())
                );
        }

        @SuppressWarnings("removal")
        private static final class Env {

                private static final String defaultRandomGenerator =
                        java.security.AccessController.doPrivileged(
                                (java.security.PrivilegedAction<String>)Env::get
                        );

                private static String get() {
                        return getConfigured()
                                .or(Env::getDefault)
                                .orElseGet(Env::getBest);
                }

                private static Optional<String> getConfigured() {
                        return Optional.ofNullable(
                                System.getProperty("io.jenetics.util.defaultRandomGenerator")
                        );
                }

                private static Optional<String> getDefault() {
                        return RandomGeneratorFactory.all()
                                .map(RandomGeneratorFactory::name)
                                .filter("L64X256MixRandom"::equals)
                                .findFirst();
                }

                private static String getBest() {
                        final var highestStateBits = Comparator
                                .<RandomGeneratorFactory<?>>comparingInt(RandomGeneratorFactory::stateBits)
                                .reversed();

                        return RandomGeneratorFactory.all()
                                .sorted(highestStateBits)
                                .map(RandomGeneratorFactory::name)
                                .findFirst()
                                .orElse("Random");
                }

        }

}