/*
 * 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 android.support.v4.app;

import android.app.Service;
import android.app.job.JobInfo;
import android.app.job.JobParameters;
import android.app.job.JobScheduler;
import android.app.job.JobServiceEngine;
import android.app.job.JobWorkItem;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Build;
import android.os.IBinder;
import android.os.PowerManager;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.annotation.RequiresApi;
import android.support.v4.os.BuildCompat;
import android.util.Log;

import java.util.ArrayList;
import java.util.HashMap;

/**
 * Helper for processing work that has been enqueued for a job/service.  When running on
 * {@link android.os.Build.VERSION_CODES#O Android O} or later, the work will be dispatched
 * as a job via {@link android.app.job.JobScheduler#enqueue JobScheduler.enqueue}.  When running
 * on older versions of the platform, it will use
 * {@link android.content.Context#startService Context.startService}.
 *
 * <p>You must publish your subclass in your manifest for the system to interact with.  This
 * should be published as a {@link android.app.job.JobService}, as described for that class,
 * since on O and later platforms it will be executed that way.</p>
 *
 * <p>Use {@link #enqueueWork(Context, Class, int, Intent)} to enqueue new work to be
 * dispatched to and handled by your service.  It will be executed in
 * {@link #onHandleWork(Intent)}.</p>
 *
 * <p>You do not need to use {@link android.support.v4.content.WakefulBroadcastReceiver}
 * when using this class.  When running on {@link android.os.Build.VERSION_CODES#O Android O},
 * the JobScheduler will take care of wake locks for you (holding a wake lock from the time
 * you enqueue work until the job has been dispatched and while it is running).  When running
 * on previous versions of the platform, this wake lock handling is emulated in the class here
 * by directly calling the PowerManager; this means the application must request the
 * {@link android.Manifest.permission#WAKE_LOCK} permission.</p>
 *
 * <p>There are a few important differences in behavior when running on
 * {@link android.os.Build.VERSION_CODES#O Android O} or later as a Job vs. pre-O:</p>
 *
 * <ul>
 *     <li><p>When running as a pre-O service, the act of enqueueing work will generally start
 *     the service immediately, regardless of whether the device is dozing or in other
 *     conditions.  When running as a Job, it will be subject to standard JobScheduler
 *     policies for a Job with a {@link android.app.job.JobInfo.Builder#setOverrideDeadline(long)}
 *     of 0: the job will not run while the device is dozing, it may get delayed more than
 *     a service if the device is under strong memory pressure with lots of demand to run
 *     jobs.</p></li>
 *     <li><p>When running as a pre-O service, the normal service execution semantics apply:
 *     the service can run indefinitely, though the longer it runs the more likely the system
 *     will be to outright kill its process, and under memory pressure one should expect
 *     the process to be killed even of recently started services.  When running as a Job,
 *     the typical {@link android.app.job.JobService} execution time limit will apply, after
 *     which the job will be stopped (cleanly, not by killing the process) and rescheduled
 *     to continue its execution later.  Job are generally not killed when the system is
 *     under memory pressure, since the number of concurrent jobs is adjusted based on the
 *     memory state of the device.</p></li>
 * </ul>
 *
 * <p>Here is an example implementation of this class:</p>
 *
 * {@sample frameworks/support/samples/Support4Demos/src/com/example/android/supportv4/app/SimpleJobIntentService.java
 *      complete}
 */
public abstract class JobIntentService extends Service {
    static final String TAG = "JobIntentService";

    static final boolean DEBUG = false;

    CompatJobEngine mJobImpl;
    WorkEnqueuer mCompatWorkEnqueuer;
    CommandProcessor mCurProcessor;

    final ArrayList<CompatWorkItem> mCompatQueue;

    static final Object sLock = new Object();
    static final HashMap<Class, WorkEnqueuer> sClassWorkEnqueuer = new HashMap<>();

    /**
     * Base class for the target service we can deliver work to and the implementation of
     * how to deliver that work.
     */
    abstract static class WorkEnqueuer {
        final ComponentName mComponentName;

        boolean mHasJobId;
        int mJobId;

        WorkEnqueuer(Context context, Class cls) {
            mComponentName = new ComponentName(context, cls);
        }

        void ensureJobId(int jobId) {
            if (!mHasJobId) {
                mHasJobId = true;
                mJobId = jobId;
            } else if (mJobId != jobId) {
                throw new IllegalArgumentException("Given job ID " + jobId
                        + " is different than previous " + mJobId);
            }
        }

        abstract void enqueueWork(Intent work);

        public void serviceCreated() {
        }

        public void serviceStartReceived() {
        }

        public void serviceDestroyed() {
        }
    }

    /**
     * Get rid of lint warnings about API levels.
     */
    interface CompatJobEngine {
        IBinder compatGetBinder();
        GenericWorkItem dequeueWork();
    }

    /**
     * An implementation of WorkEnqueuer that works for pre-O (raw Service-based).
     */
    static final class CompatWorkEnqueuer extends WorkEnqueuer {
        private final Context mContext;
        private final PowerManager.WakeLock mLaunchWakeLock;
        private final PowerManager.WakeLock mRunWakeLock;
        boolean mLaunchingService;
        boolean mServiceRunning;

        CompatWorkEnqueuer(Context context, Class cls) {
            super(context, cls);
            mContext = context.getApplicationContext();
            // Make wake locks.  We need two, because the launch wake lock wants to have
            // a timeout, and the system does not do the right thing if you mix timeout and
            // non timeout (or even changing the timeout duration) in one wake lock.
            PowerManager pm = ((PowerManager) context.getSystemService(Context.POWER_SERVICE));
            mLaunchWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, cls.getName());
            mLaunchWakeLock.setReferenceCounted(false);
            mRunWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, cls.getName());
            mRunWakeLock.setReferenceCounted(false);
        }

        @Override
        void enqueueWork(Intent work) {
            Intent intent = new Intent(work);
            intent.setComponent(mComponentName);
            if (DEBUG) Log.d(TAG, "Starting service for work: " + work);
            if (mContext.startService(intent) != null) {
                synchronized (this) {
                    if (!mLaunchingService) {
                        mLaunchingService = true;
                        if (!mServiceRunning) {
                            // If the service is not already holding the wake lock for
                            // itself, acquire it now to keep the system running until
                            // we get this work dispatched.  We use a timeout here to
                            // protect against whatever problem may cause is to not get
                            // the work.
                            mLaunchWakeLock.acquire(60 * 1000);
                        }
                    }
                }
            }
        }

        @Override
        public void serviceCreated() {
            synchronized (this) {
                // We hold the wake lock as long as the service is running.
                if (!mServiceRunning) {
                    mServiceRunning = true;
                    mRunWakeLock.acquire();
                    mLaunchWakeLock.release();
                }
            }
        }

        @Override
        public void serviceStartReceived() {
            synchronized (this) {
                // Once we have started processing work, we can count whatever last
                // enqueueWork() that happened as handled.
                mLaunchingService = false;
            }
        }

        @Override
        public void serviceDestroyed() {
            synchronized (this) {
                // If we are transitioning back to a wakelock with a timeout, do the same
                // as if we had enqueued work without the service running.
                if (mLaunchingService) {
                    mLaunchWakeLock.acquire(60 * 1000);
                }
                mServiceRunning = false;
                mRunWakeLock.release();
            }
        }
    }

    /**
     * Implementation of a JobServiceEngine for interaction with JobIntentService.
     */
    @RequiresApi(26)
    static final class JobServiceEngineImpl extends JobServiceEngine
            implements JobIntentService.CompatJobEngine {
        static final String TAG = "JobServiceEngineImpl";

        static final boolean DEBUG = false;

        final JobIntentService mService;
        JobParameters mParams;

        final class WrapperWorkItem implements JobIntentService.GenericWorkItem {
            final JobWorkItem mJobWork;

            WrapperWorkItem(JobWorkItem jobWork) {
                mJobWork = jobWork;
            }

            @Override
            public Intent getIntent() {
                return mJobWork.getIntent();
            }

            @Override
            public void complete() {
                mParams.completeWork(mJobWork);
            }
        }

        JobServiceEngineImpl(JobIntentService service) {
            super(service);
            mService = service;
        }

        @Override
        public IBinder compatGetBinder() {
            return getBinder();
        }

        @Override
        public boolean onStartJob(JobParameters params) {
            if (DEBUG) Log.d(TAG, "onStartJob: " + params);
            mParams = params;
            // We can now start dequeuing work!
            mService.ensureProcessorRunningLocked();
            return true;
        }

        @Override
        public boolean onStopJob(JobParameters params) {
            if (DEBUG) Log.d(TAG, "onStartJob: " + params);
            return mService.onStopCurrentWork();
        }

        /**
         * Dequeue some work.
         */
        @Override
        public JobIntentService.GenericWorkItem dequeueWork() {
            JobWorkItem work = mParams.dequeueWork();
            if (work != null) {
                return new WrapperWorkItem(work);
            } else {
                return null;
            }
        }
    }

    @RequiresApi(26)
    static final class JobWorkEnqueuer extends JobIntentService.WorkEnqueuer {
        private final JobInfo mJobInfo;
        private final JobScheduler mJobScheduler;

        JobWorkEnqueuer(Context context, Class cls, int jobId) {
            super(context, cls);
            ensureJobId(jobId);
            JobInfo.Builder b = new JobInfo.Builder(jobId, mComponentName);
            mJobInfo = b.setOverrideDeadline(0).build();
            mJobScheduler = (JobScheduler) context.getApplicationContext().getSystemService(
                    Context.JOB_SCHEDULER_SERVICE);
        }

        @Override
        void enqueueWork(Intent work) {
            if (DEBUG) Log.d(TAG, "Enqueueing work: " + work);
            mJobScheduler.enqueue(mJobInfo, new JobWorkItem(work));
        }
    }

    /**
     * Abstract definition of an item of work that is being dispatched.
     */
    interface GenericWorkItem {
        Intent getIntent();
        void complete();
    }

    /**
     * An implementation of GenericWorkItem that dispatches work for pre-O platforms: intents
     * received through a raw service's onStartCommand.
     */
    final class CompatWorkItem implements GenericWorkItem {
        final Intent mIntent;
        final int mStartId;

        CompatWorkItem(Intent intent, int startId) {
            mIntent = intent;
            mStartId = startId;
        }

        @Override
        public Intent getIntent() {
            return mIntent;
        }

        @Override
        public void complete() {
            if (DEBUG) Log.d(TAG, "Stopping self: #" + mStartId);
            stopSelf(mStartId);
        }
    }

    /**
     * This is a task to dequeue and process work in the background.
     */
    final class CommandProcessor extends AsyncTask<Void, Void, Void> {
        @Override
        protected Void doInBackground(Void... params) {
            GenericWorkItem work;

            if (DEBUG) Log.d(TAG, "Starting to dequeue work...");

            while ((work = dequeueWork()) != null) {
                if (DEBUG) Log.d(TAG, "Processing next work: " + work);
                onHandleWork(work.getIntent());
                if (DEBUG) Log.d(TAG, "Completing work: " + work);
                work.complete();
            }

            if (DEBUG) Log.d(TAG, "Done processing work!");

            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            if (mCompatQueue != null) {
                synchronized (mCompatQueue) {
                    mCurProcessor = null;
                    checkForMoreCompatWorkLocked();
                }
            }
        }
    }

    /**
     * Default empty constructor.
     */
    public JobIntentService() {
        if (Build.VERSION.SDK_INT >= 26) {
            mCompatQueue = null;
        } else {
            mCompatQueue = new ArrayList<>();
        }
    }

    @Override
    public void onCreate() {
        super.onCreate();
        if (DEBUG) Log.d(TAG, "CREATING: " + this);
        if (Build.VERSION.SDK_INT >= 26) {
            mJobImpl = new JobServiceEngineImpl(this);
            mCompatWorkEnqueuer = null;
        } else {
            mJobImpl = null;
            mCompatWorkEnqueuer = getWorkEnqueuer(this, this.getClass(), false, 0);
            mCompatWorkEnqueuer.serviceCreated();
        }
    }

    /**
     * Processes start commands when running as a pre-O service, enqueueing them to be
     * later dispatched in {@link #onHandleWork(Intent)}.
     */
    @Override
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
        if (mCompatQueue != null) {
            mCompatWorkEnqueuer.serviceStartReceived();
            if (DEBUG) Log.d(TAG, "Received compat start command #" + startId + ": " + intent);
            synchronized (mCompatQueue) {
                mCompatQueue.add(new CompatWorkItem(intent != null ? intent : new Intent(),
                        startId));
                ensureProcessorRunningLocked();
            }
            return START_REDELIVER_INTENT;
        } else {
            if (DEBUG) Log.d(TAG, "Ignoring start command: " + intent);
            return START_NOT_STICKY;
        }
    }

    /**
     * Returns the IBinder for the {@link android.app.job.JobServiceEngine} when
     * running as a JobService on O and later platforms.
     */
    @Override
    public IBinder onBind(@NonNull Intent intent) {
        if (mJobImpl != null) {
            IBinder engine = mJobImpl.compatGetBinder();
            if (DEBUG) Log.d(TAG, "Returning engine: " + engine);
            return engine;
        } else {
            return null;
        }
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if (mCompatWorkEnqueuer != null) {
            mCompatWorkEnqueuer.serviceDestroyed();
        }
    }

    /**
     * Call this to enqueue work for your subclass of {@link JobIntentService}.  This will
     * either directly start the service (when running on pre-O platforms) or enqueue work
     * for it as a job (when running on O and later).  In either case, a wake lock will be
     * held for you to ensure you continue running.  The work you enqueue will ultimately
     * appear at {@link #onHandleWork(Intent)}.
     *
     * @param context Context this is being called from.
     * @param cls The concrete class the work should be dispatched to (this is the class that
     * is published in your manifest).
     * @param jobId A unique job ID for scheduling; must be the same value for all work
     * enqueued for the same class.
     * @param work The Intent of work to enqueue.
     */
    public static void enqueueWork(@NonNull Context context, @NonNull Class cls, int jobId,
            @NonNull Intent work) {
        if (work == null) {
            throw new IllegalArgumentException("work must not be null");
        }
        synchronized (sLock) {
            WorkEnqueuer we = getWorkEnqueuer(context, cls, true, jobId);
            we.ensureJobId(jobId);
            we.enqueueWork(work);
        }
    }

    static WorkEnqueuer getWorkEnqueuer(Context context, Class cls, boolean hasJobId, int jobId) {
        WorkEnqueuer we = sClassWorkEnqueuer.get(cls);
        if (we == null) {
            if (BuildCompat.isAtLeastO()) {
                if (!hasJobId) {
                    throw new IllegalArgumentException("Can't be here without a job id");
                }
                we = new JobWorkEnqueuer(context, cls, jobId);
            } else {
                we = new CompatWorkEnqueuer(context, cls);
            }
            sClassWorkEnqueuer.put(cls, we);
        }
        return we;
    }

    /**
     * Called serially for each work dispatched to and processed by the service.  This
     * method is called on a background thread, so you can do long blocking operations
     * here.  Upon returning, that work will be considered complete and either the next
     * pending work dispatched here or the overall service destroyed now that it has
     * nothing else to do.
     *
     * <p>Be aware that when running as a job, you are limited by the maximum job execution
     * time and any single or total sequential items of work that exceeds that limit will
     * cause the service to be stopped while in progress and later restarted with the
     * last unfinished work.  (There is currently no limit on execution duration when
     * running as a pre-O plain Service.)</p>
     *
     * @param intent The intent describing the work to now be processed.
     */
    protected abstract void onHandleWork(@NonNull Intent intent);

    /**
     * This will be called if the JobScheduler has decided to stop this job.  The job for
     * this service does not have any constraints specified, so this will only generally happen
     * if the service exceeds the job's maximum execution time.
     *
     * @return True to indicate to the JobManager whether you'd like to reschedule this work,
     * false to drop this and all following work. Regardless of the value returned, your service
     * must stop executing or the system will ultimately kill it.  The default implementation
     * returns true, and that is most likely what you want to return as well (so no work gets
     * lost).
     */
    public boolean onStopCurrentWork() {
        return true;
    }

    void ensureProcessorRunningLocked() {
        if (mCurProcessor == null) {
            mCurProcessor = new CommandProcessor();
            if (DEBUG) Log.d(TAG, "Starting processor: " + mCurProcessor);
            mCurProcessor.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
        }
    }

    void checkForMoreCompatWorkLocked() {
        // The async task has finished, but we may have gotten more work scheduled in the
        // meantime.  If so,
        if (mCompatQueue != null && mCompatQueue.size() > 0) {
            ensureProcessorRunningLocked();
        }
    }

    GenericWorkItem dequeueWork() {
        if (mJobImpl != null) {
            return mJobImpl.dequeueWork();
        } else {
            synchronized (mCompatQueue) {
                if (mCompatQueue.size() > 0) {
                    return mCompatQueue.remove(0);
                } else {
                    return null;
                }
            }
        }
    }
}