/*
 * Java Genetic Algorithm Library (jenetics-7.2.0).
 * Copyright (c) 2007-2023 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.internal.util;

import static java.lang.Math.ceil;
import static java.lang.Math.max;
import static java.util.Objects.requireNonNull;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;

import io.jenetics.util.Seq;

/**
 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 * @version 3.8
 * @since 2.0
 */
public abstract class Concurrency implements Executor, AutoCloseable {

        public static final int CORES = Runtime.getRuntime().availableProcessors();

        public static final Concurrency SERIAL_EXECUTOR = new SerialConcurrency();

        public abstract void execute(final Seq<? extends Runnable> runnables);

        @Override
        public abstract void close();

        /**
         * Return the underlying {@code Executor}, which is used for performing the
         * actual task execution.
         *
         * @return the underlying {@code Executor} object
         */
        public Executor getInnerExecutor() {
                return this;
        }

        /**
         * Return a new Concurrency object from the given executor.
         *
         * @param executor the underlying Executor
         * @return a new Concurrency object
         */
        public static Concurrency with(final Executor executor) {
                if (executor instanceof ForkJoinPool e) {
                        return new ForkJoinPoolConcurrency(e);
                } else if (executor instanceof ExecutorService e) {
                        return new ExecutorServiceConcurrency(e);
                } else if (executor == SERIAL_EXECUTOR) {
                        return SERIAL_EXECUTOR;
                } else {
                        return new ExecutorConcurrency(executor);
                }
        }

        /**
         * Return a new Concurrency object using the common ForkJoinPool.
         *
         * @return a new Concurrency object using the new ForkJoinPool
         */
        public static Concurrency withCommonPool() {
                return with(ForkJoinPool.commonPool());
        }


        /**
         * This Concurrency uses a ForkJoinPool.
         */
        private static final class ForkJoinPoolConcurrency extends Concurrency {
                private final List<ForkJoinTask<?>> _tasks = new ArrayList<>();
                private final ForkJoinPool _pool;

                ForkJoinPoolConcurrency(final ForkJoinPool pool) {
                        _pool = requireNonNull(pool);
                }

                @Override
                public void execute(final Runnable runnable) {
                        _tasks.add(_pool.submit(runnable));
                }

                @Override
                public void execute(final Seq<? extends Runnable> runnables) {
                        if (runnables.nonEmpty()) {
                                _tasks.add(_pool.submit(new RunnablesAction(runnables)));
                        }
                }

                @Override
                public Executor getInnerExecutor() {
                        return _pool;
                }

                @Override
                public void close() {
                        Concurrency.join(_tasks);
                }
        }

        /**
         * This Concurrency uses an ExecutorService.
         */
        private static final class ExecutorServiceConcurrency extends Concurrency {
                private final List<Future<?>> _futures = new ArrayList<>();
                private final ExecutorService _service;

                ExecutorServiceConcurrency(final ExecutorService service) {
                        _service = requireNonNull(service);
                }

                @Override
                public void execute(final Runnable command) {
                        _futures.add(_service.submit(command));
                }

                @Override
                public void execute(final Seq<? extends Runnable> runnables) {
                        if (runnables.nonEmpty()) {
                                final int[] parts = partition(
                                        runnables.size(),
                                        max(
                                                (CORES + 1)*2,
                                                (int)ceil(runnables.size()/(double)maxBatchSize())
                                        )
                                );

                                for (int i = 0; i < parts.length - 1; ++i) {
                                        execute(new RunnablesRunnable(runnables, parts[i], parts[i + 1]));
                                }
                        }
                }

                @Override
                public Executor getInnerExecutor() {
                        return _service;
                }

                @Override
                public void close() {
                        Concurrency.join(_futures);
                }

        }

        private static void join(final Iterable<? extends Future<?>> jobs) {
                Future<?> task = null;
                Iterator<? extends Future<?>> tasks = null;
                try {
                        tasks = jobs.iterator();
                        while (tasks.hasNext()) {
                                task = tasks.next();
                                task.get();
                        }
                } catch (ExecutionException e) {
                        Concurrency.cancel(task, tasks);
                        final String msg = e.getCause() != null
                                ? e.getCause().getMessage()
                                : null;
                        throw (CancellationException)new CancellationException(msg)
                                .initCause(e.getCause());
                } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                        Concurrency.cancel(task, tasks);
                        final String msg = e.getMessage();
                        throw (CancellationException)new CancellationException(msg)
                                .initCause(e);
                }
        }

        private static void cancel(
                final Future<?> task,
                final Iterator<? extends Future<?>> tasks
        ) {
                if (task != null) {
                        task.cancel(true);
                }
                if (tasks != null) {
                        tasks.forEachRemaining(t -> t.cancel(true));
                }
        }

        /**
         * This Concurrency uses an Executor.
         */
        private static final class ExecutorConcurrency extends Concurrency {
                private final List<FutureTask<?>> _tasks = new ArrayList<>();
                private final Executor _executor;

                ExecutorConcurrency(final Executor executor) {
                        _executor = requireNonNull(executor);
                }

                @Override
                public void execute(final Runnable command) {
                        final FutureTask<?> task = new FutureTask<>(command, null);
                        _tasks.add(task);
                        _executor.execute(task);
                }

                @Override
                public void execute(final Seq<? extends Runnable> runnables) {
                        if (runnables.nonEmpty()) {
                                final int[] parts = partition(
                                        runnables.size(),
                                        max(
                                                (CORES + 1)*2,
                                                (int)ceil(runnables.size()/(double)maxBatchSize())
                                        )
                                );

                                for (int i = 0; i < parts.length - 1; ++i) {
                                        execute(new RunnablesRunnable(runnables, parts[i], parts[i + 1]));
                                }
                        }
                }

                @Override
                public void close() {
                        Concurrency.join(_tasks);
                }
        }

        /**
         * This Concurrency executes the runnables within the main thread.
         */
        private static final class SerialConcurrency extends Concurrency {

                @Override
                public void execute(final Runnable command) {
                        command.run();
                }

                @Override
                public void execute(final Seq<? extends Runnable> runnables) {
                        runnables.forEach(Runnable::run);
                }

                @Override
                public void close() {
                }
        }


        /**
         * Return a array with the indexes of the partitions of an array with the
         * given size. The length of the returned array is {@code min(size, prts) + 1}.
         * <p>
         * Some examples:
         * <pre>
         *       partition(10, 3): [0, 3, 6, 10]
         *       partition(15, 6): [0, 2, 4, 6, 9, 12, 15]
         *       partition(5, 10): [0, 1, 2, 3, 4, 5]
         * </pre>
         *
         * The following examples print the start index (inclusive) and the end
         * index (exclusive) of the {@code partition(15, 6)}.
         * <pre>{@code
         * int[] parts = partition(15, 6);
         * for (int i = 0; i < parts.length - 1; ++i) {
         *     System.out.println(i + ": " + parts[i] + "\t" + parts[i + 1]);
         * }
         * }</pre>
         * <pre>
         *       0: 0   2
         *       1: 2   4
         *       2: 4   6
         *       3: 6   9
         *       4: 9   12
         *       5: 12  15
         * </pre>
         *
         * This example shows how this can be used in a concurrent environment:
         * <pre>{@code
         * try (final Concurrency c = Concurrency.start()) {
         *     final int[] parts = arrays.partition(population.size(), _maxThreads);
         *
         *     for (int i = 0; i < parts.length - 1; ++i) {
         *         final int part = i;
         *         c.execute(new Runnable() { @Override public void run() {
         *             for (int j = parts[part + 1]; --j <= parts[part];) {
         *                 population.get(j).evaluate();
         *             }
         *         }});
         *     }
         * }
         * }</pre>
         *
         * @param size the size of the array to partition.
         * @param parts the number of parts the (virtual) array should be partitioned.
         * @return the partition array with the length of {@code min(size, parts) + 1}.
         * @throws IllegalArgumentException if {@code size} or {@code p} is less than one.
         */
        private static int[] partition(final int size, final int parts) {
                if (size < 1) {
                        throw new IllegalArgumentException(
                                "Size must greater than zero: " + size
                        );
                }
                if (parts < 1) {
                        throw new IllegalArgumentException(
                                "Number of partitions must greater than zero: " + parts
                        );
                }

                final int pts = Math.min(size, parts);
                final int[] partition = new int[pts + 1];

                final int bulk = size/pts;
                final int rest = size%pts;
                assert (bulk*pts + rest) == size;

                for (int i = 0, n = pts - rest; i < n; ++i) {
                        partition[i] = i*bulk;
                }
                for (int i = 0, n = rest + 1; i < n; ++i) {
                        partition[pts - rest + i] = (pts - rest)*bulk + i*(bulk + 1);
                }

                return partition;
        }

        static int maxBatchSize() {
                return Env.maxBatchSize;
        }

        @SuppressWarnings("removal")
        private static final class Env {
                private static final int maxBatchSize = max(
                        java.security.AccessController.doPrivileged(
                                (java.security.PrivilegedAction<Integer>)() -> Integer.getInteger(
                                        "io.jenetics.concurrency.maxBatchSize",
                                        Integer.MAX_VALUE
                                )),
                        1
                );
        }

}