/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * 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 com.android.settingslib.utils;

import android.os.Handler;
import android.os.Looper;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class ThreadUtils {

    private static volatile Thread sMainThread;
    private static volatile Handler sMainThreadHandler;
    private static volatile ExecutorService sThreadExecutor;

    /**
     * Returns true if the current thread is the UI thread.
     */
    public static boolean isMainThread() {
        if (sMainThread == null) {
            sMainThread = Looper.getMainLooper().getThread();
        }
        return Thread.currentThread() == sMainThread;
    }

    /**
     * Returns a shared UI thread handler.
     */
    public static Handler getUiThreadHandler() {
        if (sMainThreadHandler == null) {
            sMainThreadHandler = new Handler(Looper.getMainLooper());
        }

        return sMainThreadHandler;
    }

    /**
     * Checks that the current thread is the UI thread. Otherwise throws an exception.
     */
    public static void ensureMainThread() {
        if (!isMainThread()) {
            throw new RuntimeException("Must be called on the UI thread");
        }
    }

    /**
     * Posts runnable in background using shared background thread pool.
     *
     * @Return A future of the task that can be monitored for updates or cancelled.
     */
    public static Future postOnBackgroundThread(Runnable runnable) {
        return getThreadExecutor().submit(runnable);
    }

    /**
     * Posts callable in background using shared background thread pool.
     *
     * @Return A future of the task that can be monitored for updates or cancelled.
     */
    public static Future postOnBackgroundThread(Callable callable) {
        return getThreadExecutor().submit(callable);
    }

    /**
     * Posts the runnable on the main thread.
     */
    public static void postOnMainThread(Runnable runnable) {
        getUiThreadHandler().post(runnable);
    }

    private static synchronized ExecutorService getThreadExecutor() {
        if (sThreadExecutor == null) {
            sThreadExecutor = Executors.newFixedThreadPool(
                    Runtime.getRuntime().availableProcessors());
        }
        return sThreadExecutor;
    }
}
