/*
 * Copyright 2015 Open Networking Laboratory
 *
 * 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 org.onlab.util;

import java.util.Collection;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * Executor service wrapper for shared executors with safeguards on shutdown
 * to prevent inadvertent shutdown.
 */
class SharedExecutorService implements ExecutorService {

    private static final String NOT_ALLOWED = "Shutdown of shared executor is not allowed";

    private ExecutorService executor;

    /**
     * Creates a wrapper for the given executor service.
     *
     * @param executor executor service to wrap
     */
    SharedExecutorService(ExecutorService executor) {
        this.executor = executor;
    }

    /**
     * Returns the backing executor service.
     *
     * @return backing executor service
     */
    ExecutorService backingExecutor() {
        return executor;
    }

    /**
     * Swaps the backing executor with a new one and shuts down the old one.
     *
     * @param executor new executor service
     */
    void setBackingExecutor(ExecutorService executor) {
        ExecutorService oldExecutor = this.executor;
        this.executor = executor;
        oldExecutor.shutdown();
    }

    @Override
    public void shutdown() {
        throw new UnsupportedOperationException(NOT_ALLOWED);
    }

    @Override
    public List<Runnable> shutdownNow() {
        throw new UnsupportedOperationException(NOT_ALLOWED);
    }

    @Override
    public boolean isShutdown() {
        return executor.isShutdown();
    }

    @Override
    public boolean isTerminated() {
        return executor.isTerminated();
    }

    @Override
    public boolean awaitTermination(long timeout, TimeUnit unit)
            throws InterruptedException {
        return executor.awaitTermination(timeout, unit);
    }

    @Override
    public <T> Future<T> submit(Callable<T> task) {
        return executor.submit(task);
    }

    @Override
    public <T> Future<T> submit(Runnable task, T result) {
        return executor.submit(task, result);
    }

    @Override
    public Future<?> submit(Runnable task) {
        return executor.submit(task);
    }

    @Override
    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
            throws InterruptedException {
        return executor.invokeAll(tasks);
    }

    @Override
    public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
                                         long timeout, TimeUnit unit)
            throws InterruptedException {
        return executor.invokeAll(tasks, timeout, unit);
    }

    @Override
    public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
            throws InterruptedException, ExecutionException {
        return executor.invokeAny(tasks);
    }

    @Override
    public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
                           long timeout, TimeUnit unit)
            throws InterruptedException, ExecutionException, TimeoutException {
        return executor.invokeAny(tasks, timeout, unit);
    }

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

}