/**
 * Copyright 2013 Netflix, Inc.
 * 
 * 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.
 */
package rx.concurrency;

import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;

import rx.Scheduler;

/**
 * Static factory methods for creating Schedulers.
 */
public class Schedulers {
    private static final ScheduledExecutorService COMPUTATION_EXECUTOR = createComputationExecutor();
    private static final Executor IO_EXECUTOR = createIOExecutor();

    private Schedulers() {

    }

    /**
     * {@link Scheduler} that executes work immediately on the current thread.
     * 
     * @return {@link ImmediateScheduler} instance
     */
    public static Scheduler immediate() {
        return ImmediateScheduler.getInstance();
    }

    /**
     * {@link Scheduler} that queues work on the current thread to be executed after the current work completes.
     * 
     * @return {@link CurrentThreadScheduler} instance
     */
    public static Scheduler currentThread() {
        return CurrentThreadScheduler.getInstance();
    }

    /**
     * {@link Scheduler} that creates a new {@link Thread} for each unit of work.
     * 
     * @return {@link NewThreadScheduler} instance
     */
    public static Scheduler newThread() {
        return NewThreadScheduler.getInstance();
    }

    /**
     * {@link Scheduler} that queues work on the EventQueue thread to be executed on the Swing UI Thread.
     * 
     * @return {@link NewThreadScheduler} instance
     */
    public static Scheduler eventQueue() {
        return EventQueueScheduler.getInstance();
    }

    /**
     * {@link Scheduler} that queues work on an {@link Executor}.
     * <p>
     * Note that this does not support scheduled actions with a delay.
     * 
     * @return {@link ExecutorScheduler} instance
     */
    public static Scheduler executor(Executor executor) {
        return new ExecutorScheduler(executor);
    }

    /**
     * {@link Scheduler} that queues work on an {@link ScheduledExecutorService}.
     * 
     * @return {@link ExecutorScheduler} instance
     */
    public static Scheduler executor(ScheduledExecutorService executor) {
        return new ExecutorScheduler(executor);
    }

    /**
     * {@link Scheduler} intended for computational work.
     * <p>
     * The implementation is backed by a {@link ScheduledExecutorService} thread-pool sized to the number of CPU cores.
     * <p>
     * This can be used for event-loops, processing callbacks and other computational work.
     * <p>
     * Do not perform IO-bound work on this scheduler. Use {@link #threadPoolForComputation()} instead.
     * 
     * @return {@link ExecutorScheduler} for computation-bound work.
     */
    public static Scheduler threadPoolForComputation() {
        return executor(COMPUTATION_EXECUTOR);
    }

    /**
     * {@link Scheduler} intended for IO-bound work.
     * <p>
     * The implementation is backed by an {@link Executor} thread-pool that will grow as needed.
     * <p>
     * This can be used for asynchronously performing blocking IO.
     * <p>
     * Do not perform computational work on this scheduler. Use {@link #threadPoolForComputation()} instead.
     * 
     * @return {@link ExecutorScheduler} for IO-bound work.
     */
    public static Scheduler threadPoolForIO() {
        return executor(IO_EXECUTOR);
    }

    private static ScheduledExecutorService createComputationExecutor() {
        int cores = Runtime.getRuntime().availableProcessors();
        return Executors.newScheduledThreadPool(cores, new ThreadFactory() {
            final AtomicInteger counter = new AtomicInteger();

            @Override
            public Thread newThread(Runnable r) {
                Thread t = new Thread(r, "RxComputationThreadPool-" + counter.incrementAndGet());
                t.setDaemon(true);
                return t;
            }
        });
    }

    private static Executor createIOExecutor() {
        Executor result = Executors.newCachedThreadPool(new ThreadFactory() {
            final AtomicLong counter = new AtomicLong();

            @Override
            public Thread newThread(Runnable r) {
                Thread t = new Thread(r, "RxIOThreadPool-" + counter.incrementAndGet());
                t.setDaemon(true);
                return t;
            }
        });

        return result;
    }
}