/*
 * Copyright (C) 2017 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 androidx.arch.core.executor;

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

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.annotation.RequiresApi;
import androidx.annotation.RestrictTo;

import java.lang.reflect.InvocationTargetException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * @hide
 */
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP_PREFIX)
public class DefaultTaskExecutor extends TaskExecutor {

    private final Object mLock = new Object();

    private final ExecutorService mDiskIO = Executors.newFixedThreadPool(4, new ThreadFactory() {
        private static final String THREAD_NAME_STEM = "arch_disk_io_";

        private final AtomicInteger mThreadId = new AtomicInteger(0);

        @Override
        public Thread newThread(Runnable r) {
            Thread t = new Thread(r);
            t.setName(THREAD_NAME_STEM + mThreadId.getAndIncrement());
            return t;
        }
    });

    @Nullable
    private volatile Handler mMainHandler;

    @Override
    public void executeOnDiskIO(Runnable runnable) {
        mDiskIO.execute(runnable);
    }

    @Override
    public void postToMainThread(Runnable runnable) {
        if (mMainHandler == null) {
            synchronized (mLock) {
                if (mMainHandler == null) {
                    mMainHandler = createAsync(Looper.getMainLooper());
                }
            }
        }
        //noinspection ConstantConditions
        mMainHandler.post(runnable);
    }

    @Override
    public boolean isMainThread() {
        return Looper.getMainLooper().getThread() == Thread.currentThread();
    }

    @SuppressWarnings("JavaReflectionMemberAccess")
    @NonNull
    private static Handler createAsync(@NonNull Looper looper) {
        if (Build.VERSION.SDK_INT >= 28) {
            return Api28Impl.createAsync(looper);
        } else if (Build.VERSION.SDK_INT >= 17) {
            try {
                // This constructor was added as private in JB MR1:
                // https://android.googlesource.com/platform/frameworks/base/+/refs/heads/jb-mr1-release/core/java/android/os/Handler.java
                return Handler.class.getDeclaredConstructor(Looper.class, Handler.Callback.class,
                        boolean.class)
                        .newInstance(looper, null, true);
            } catch (IllegalAccessException ignored) {
            } catch (InstantiationException ignored) {
            } catch (NoSuchMethodException ignored) {
            } catch (InvocationTargetException e) {
                return new Handler(looper);
            }
        }
        return new Handler(looper);
    }

    @RequiresApi(28)
    private static class Api28Impl {
        private Api28Impl() {
            // Non-instantiable.
        }

        @NonNull
        public static Handler createAsync(@NonNull Looper looper) {
            return Handler.createAsync(looper);
        }
    }
}
