/*
 * Hunt - A refined core library for D programming language.
 *
 * Copyright (C) 2018-2019 HuntLabs
 *
 * Website: https://www.huntlabs.net/
 *
 * Licensed under the Apache-2.0 License.
 *
 */

module hunt.concurrency.AbstractExecutorService;

import hunt.concurrency.ExecutorService;
import hunt.concurrency.Future;
import hunt.concurrency.FutureTask;

import hunt.collection.ArrayList;
import hunt.collection.Collection;
import hunt.collection.Iterator;
import hunt.collection.List;

import hunt.Exceptions;
import hunt.logging;
import hunt.util.Common;
import hunt.util.DateTime;
import hunt.util.Runnable;

import std.datetime;


/**
 * Provides default implementations of {@link ExecutorService}
 * execution methods. This class implements the {@code submit},
 * {@code invokeAny} and {@code invokeAll} methods using a
 * {@link RunnableFuture} returned by {@code newTaskFor}, which defaults
 * to the {@link FutureTask} class provided in this package.  For example,
 * the implementation of {@code submit(Runnable)} creates an
 * associated {@code RunnableFuture} that is executed and
 * returned. Subclasses may override the {@code newTaskFor} methods
 * to return {@code RunnableFuture} implementations other than
 * {@code FutureTask}.
 *
 * <p><b>Extension example</b>. Here is a sketch of a class
 * that customizes {@link ThreadPoolExecutor} to use
 * a {@code CustomTask} class instead of the default {@code FutureTask}:
 * <pre> {@code
 * class CustomThreadPoolExecutor extends ThreadPoolExecutor {
 *
 *   static class CustomTask!(V) : RunnableFuture!(V) {...}
 *
 *   protected !(V) RunnableFuture!(V) newTaskFor(Callable!(V) c) {
 *       return new CustomTask!(V)(c);
 *   }
 *   protected !(V) RunnableFuture!(V) newTaskFor(Runnable r, V v) {
 *       return new CustomTask!(V)(r, v);
 *   }
 *   // ... add constructors, etc.
 * }}</pre>
 *
 * @author Doug Lea
 */
abstract class AbstractExecutorService : ExecutorService {

    /**
     * Returns a {@code RunnableFuture} for the given runnable and default
     * value.
     *
     * @param runnable the runnable task being wrapped
     * @param value the default value for the returned future
     * @param (T) the type of the given value
     * @return a {@code RunnableFuture} which, when run, will run the
     * underlying runnable and which, as a {@code Future}, will yield
     * the given value as its result and provide for cancellation of
     * the underlying task
     */
    static RunnableFuture!(T) newTaskFor(T)(Runnable runnable, T value) if(!is(T == void)) {
        return new FutureTask!(T)(runnable, value);
    }

    static RunnableFuture!(T) newTaskFor(T)(Runnable runnable) if(is(T == void)) {
        return new FutureTask!(T)(runnable);
    }

    /**
     * Returns a {@code RunnableFuture} for the given callable task.
     *
     * @param callable the callable task being wrapped
     * @param (T) the type of the callable's result
     * @return a {@code RunnableFuture} which, when run, will call the
     * underlying callable and which, as a {@code Future}, will yield
     * the callable's result as its result and provide for
     * cancellation of the underlying task
     */
    static RunnableFuture!(T) newTaskFor(T)(Callable!(T) callable) {
        return new FutureTask!(T)(callable);
    }

    /**
     * @throws RejectedExecutionException {@inheritDoc}
     * @throws NullPointerException       {@inheritDoc}
     */
    Future!(void) submit(Runnable task) {
        if (task is null) throw new NullPointerException();
        // RunnableFuture!(void) ftask = new FutureTask!(void)(task);
        RunnableFuture!(void) ftask = newTaskFor!(void)(task);
        execute(ftask);
        return ftask;
    }

    /**
     * @throws RejectedExecutionException {@inheritDoc}
     * @throws NullPointerException       {@inheritDoc}
     */
    Future!(T) submit(T)(Runnable task, T result) {
        if (task is null) throw new NullPointerException();
        RunnableFuture!(T) ftask = newTaskFor!(T)(task, result);
        execute(ftask);
        return ftask;
    }

    /**
     * @throws RejectedExecutionException {@inheritDoc}
     * @throws NullPointerException       {@inheritDoc}
     */
    Future!(T) submit(T)(Callable!(T) task) {
        if (task is null) throw new NullPointerException();
        RunnableFuture!(T) ftask = newTaskFor(task);
        execute(ftask);
        return ftask;
    }

    /**
     * the main mechanics of invokeAny.
     */
    private T doInvokeAny(T)(Collection!(Callable!(T)) tasks,
                              bool timed, long nanos) {
        if (tasks is null)
            throw new NullPointerException();
        int ntasks = tasks.size();
        if (ntasks == 0)
            throw new IllegalArgumentException();
        ArrayList!(Future!(T)) futures = new ArrayList!(Future!(T))(ntasks);
        ExecutorCompletionService!(T) ecs =
            new ExecutorCompletionService!(T)(this);

        // For efficiency, especially in executors with limited
        // parallelism, check to see if previously submitted tasks are
        // done before submitting more of them. This interleaving
        // plus the exception mechanics account for messiness of main
        // loop.

        try {
            // Record exceptions so that if we fail to obtain any
            // result, we can throw the last exception we got.
            ExecutionException ee = null;
            long deadline = timed ? Clock.currStdTime() + nanos : 0L;
            Iterator!(Callable!(T)) it = tasks.iterator();

            // Start one task for sure; the rest incrementally
            futures.add(ecs.submit(it.next()));
            --ntasks;
            int active = 1;

            for (;;) {
                Future!(T) f = ecs.poll();
                if (f is null) {
                    if (ntasks > 0) {
                        --ntasks;
                        futures.add(ecs.submit(it.next()));
                        ++active;
                    }
                    else if (active == 0)
                        break;
                    else if (timed) {
                        f = ecs.poll(nanos, NANOSECONDS);
                        if (f is null)
                            throw new TimeoutException();
                        nanos = deadline - Clock.currStdTime();
                    }
                    else
                        f = ecs.take();
                }
                if (f !is null) {
                    --active;
                    try {
                        return f.get();
                    } catch (ExecutionException eex) {
                        ee = eex;
                    } catch (RuntimeException rex) {
                        ee = new ExecutionException(rex);
                    }
                }
            }

            if (ee is null)
                ee = new ExecutionException();
            throw ee;

        } finally {
            cancelAll(futures);
        }
    }

    T invokeAny(T)(Collection!(Callable!(T)) tasks) {
        try {
            return doInvokeAny(tasks, false, 0);
        } catch (TimeoutException cannotHappen) {
            assert(false);
            return null;
        }
    }

    T invokeAny(T)(Collection!(Callable!(T)) tasks,
                           Duration timeout) {
        return doInvokeAny(tasks, true, unit.toNanos(timeout));
    }

    List!(Future!(T)) invokeAll(T)(Collection!(Callable!(T)) tasks) {
        if (tasks is null)
            throw new NullPointerException();
        ArrayList!(Future!(T)) futures = new ArrayList!(Future!(T))(tasks.size());
        try {
            foreach (Callable!(T) t ; tasks) {
                RunnableFuture!(T) f = newTaskFor(t);
                futures.add(f);
                execute(f);
            }
            for (int i = 0, size = futures.size(); i < size; i++) {
                Future!(T) f = futures.get(i);
                if (!f.isDone()) {
                    try { f.get(); }
                    catch (CancellationException ex) {
                        version(HUNT_DEBUG) warning(ex.message());
                    }
                    catch (ExecutionException) {
                        version(HUNT_DEBUG) warning(ex.message());
                    }
                }
            }
            return futures;
        } catch (Throwable t) {
            cancelAll(futures);
            throw t;
        }
    }

    List!(Future!(T)) invokeAll(T)(Collection!(Callable!(T)) tasks,
                                         Duration timeout)  {
        if (tasks is null)
            throw new NullPointerException();
        long nanos = timeout.total!(TimeUnit.HectoNanosecond)();
        long deadline = Clock.currStdTime + nanos;
        ArrayList!(Future!(T)) futures = new ArrayList!(Future!(T))(tasks.size());
        int j = 0;

        timedOut: 
        try {
            foreach (Callable!(T) t ; tasks)
                futures.add(newTaskFor(t));

            final int size = futures.size();

            // Interleave time checks and calls to execute in case
            // executor doesn't have any/much parallelism.
            for (int i = 0; i < size; i++) {
                if (((i == 0) ? nanos : deadline - Clock.currStdTime) <= 0L)
                    break timedOut;
                execute(cast(Runnable)futures.get(i));
            }

            for (; j < size; j++) {
                Future!(T) f = futures.get(j);
                if (!f.isDone()) {
                    try { f.get( Duration(deadline - Clock.currStdTime)); }
                    catch (CancellationException ex) {
                        version(HUNT_DEBUG) warning(ex.message());
                    }
                    catch (ExecutionException ex) {
                        version(HUNT_DEBUG) warning(ex.message());
                    }
                    catch (TimeoutException ex) {
                        version(HUNT_DEBUG) warning(ex.message());
                        break timedOut;
                    }
                }
            }
            return futures;
        } catch (Throwable t) {
            cancelAll(futures);
            throw t;
        }
        // Timed out before all the tasks could be completed; cancel remaining
        cancelAll(futures, j);
        return futures;
    }

    private static void cancelAll(T)(ArrayList!(Future!(T)) futures) {
        cancelAll(futures, 0);
    }

    /** Cancels all futures with index at least j. */
    private static void cancelAll(T)(ArrayList!(Future!(T)) futures, int j) {
        for (int size = futures.size(); j < size; j++)
            futures.get(j).cancel(true);
    }
}