/*
 * Copyright (C) 2011 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.contacts.util;

import com.android.contacts.test.NeededForTesting;
import com.google.common.base.Preconditions;

import android.os.AsyncTask;
import android.os.Looper;

import java.util.concurrent.Executor;

/**
 * Factory methods for creating AsyncTaskExecutors.
 * <p>
 * All of the factory methods on this class check first to see if you have set a static
 * {@link AsyncTaskExecutorFactory} set through the
 * {@link #setFactoryForTest(AsyncTaskExecutorFactory)} method, and if so delegate to that instead,
 * which is one way of injecting dependencies for testing classes whose construction cannot be
 * controlled such as {@link android.app.Activity}.
 */
public final class AsyncTaskExecutors {
    /**
     * A single instance of the {@link AsyncTaskExecutorFactory}, to which we delegate if it is
     * non-null, for injecting when testing.
     */
    private static AsyncTaskExecutorFactory mInjectedAsyncTaskExecutorFactory = null;

    /**
     * Creates an AsyncTaskExecutor that submits tasks to run with
     * {@link AsyncTask#SERIAL_EXECUTOR}.
     */
    public static AsyncTaskExecutor createAsyncTaskExecutor() {
        synchronized (AsyncTaskExecutors.class) {
            if (mInjectedAsyncTaskExecutorFactory != null) {
                return mInjectedAsyncTaskExecutorFactory.createAsyncTaskExeuctor();
            }
            return new SimpleAsyncTaskExecutor(AsyncTask.SERIAL_EXECUTOR);
        }
    }

    /**
     * Creates an AsyncTaskExecutor that submits tasks to run with
     * {@link AsyncTask#THREAD_POOL_EXECUTOR}.
     */
    public static AsyncTaskExecutor createThreadPoolExecutor() {
        synchronized (AsyncTaskExecutors.class) {
            if (mInjectedAsyncTaskExecutorFactory != null) {
                return mInjectedAsyncTaskExecutorFactory.createAsyncTaskExeuctor();
            }
            return new SimpleAsyncTaskExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
        }
    }

    /** Interface for creating AsyncTaskExecutor objects. */
    public interface AsyncTaskExecutorFactory {
        AsyncTaskExecutor createAsyncTaskExeuctor();
    }

    @NeededForTesting
    public static void setFactoryForTest(AsyncTaskExecutorFactory factory) {
        synchronized (AsyncTaskExecutors.class) {
            mInjectedAsyncTaskExecutorFactory = factory;
        }
    }

    public static void checkCalledFromUiThread() {
        Preconditions.checkState(Thread.currentThread() == Looper.getMainLooper().getThread(),
                "submit method must be called from ui thread, was: " + Thread.currentThread());
    }

    private static class SimpleAsyncTaskExecutor implements AsyncTaskExecutor {
        private final Executor mExecutor;

        public SimpleAsyncTaskExecutor(Executor executor) {
            mExecutor = executor;
        }

        @Override
        public <T> AsyncTask<T, ?, ?> submit(Object identifer, AsyncTask<T, ?, ?> task,
                T... params) {
            checkCalledFromUiThread();
            return task.executeOnExecutor(mExecutor, params);
        }
    }
}