Signal-Android/app/src/main/java/org/thoughtcrime/securesms/jobs/ForegroundServiceUtil.kt

package org.thoughtcrime.securesms.jobs

import android.app.AlarmManager
import android.app.ForegroundServiceStartNotAllowedException
import android.app.PendingIntent
import android.content.BroadcastReceiver
import android.content.Context
import android.content.Intent
import android.os.Build
import android.os.SystemClock
import androidx.core.content.ContextCompat
import org.signal.core.util.PendingIntentFlags
import org.signal.core.util.logging.Log
import org.thoughtcrime.securesms.dependencies.ApplicationDependencies
import org.thoughtcrime.securesms.service.GenericForegroundService
import org.thoughtcrime.securesms.service.NotificationController
import org.thoughtcrime.securesms.util.ServiceUtil
import java.util.concurrent.CountDownLatch
import java.util.concurrent.TimeUnit
import java.util.concurrent.locks.ReentrantLock
import kotlin.concurrent.withLock
import kotlin.time.Duration.Companion.minutes

/**
 * Helps start foreground services from the background.
 */
object ForegroundServiceUtil {

  private val TAG = Log.tag(ForegroundServiceUtil::class.java)

  private val updateMutex: ReentrantLock = ReentrantLock()
  private var activeLatch: CountDownLatch? = null

  private val DEFAULT_TIMEOUT: Long = 1.minutes.inWholeMilliseconds

  /**
   * A simple wrapper around [ContextCompat.startForegroundService], but makes the possible failure part of the contract by forcing the caller to handle the
   * [UnableToStartException].
   */
  @JvmStatic
  @Throws(UnableToStartException::class)
  fun start(context: Context, intent: Intent) {
    if (Build.VERSION.SDK_INT < 31) {
      ContextCompat.startForegroundService(context, intent)
    } else {
      try {
        ContextCompat.startForegroundService(context, intent)
      } catch (e: IllegalStateException) {
        if (e is ForegroundServiceStartNotAllowedException) {
          Log.e(TAG, "Unable to start foreground service", e)
          throw UnableToStartException(e)
        } else {
          throw e
        }
      }
    }
  }

  /**
   * Literally just a wrapper around [ContextCompat.startForegroundService], but with a name to make the caller understand that this method could throw.
   */
  @JvmStatic
  fun startOrThrow(context: Context, intent: Intent) {
    ContextCompat.startForegroundService(context, intent)
  }

  /**
   * Does its best to start a foreground service, including possibly blocking and waiting until we are able to.
   * However, it is always possible that the attempt will fail, so be sure to handle the [UnableToStartException].
   *
   * @param timeout The maximum time you're willing to wait to create the conditions for a foreground service to start.
   */
  @JvmOverloads
  @JvmStatic
  @Throws(UnableToStartException::class)
  fun startWhenCapable(context: Context, intent: Intent, timeout: Long = DEFAULT_TIMEOUT) {
    try {
      start(context, intent)
    } catch (e: UnableToStartException) {
      Log.w(TAG, "Failed to start normally. Blocking and then trying again.")
      blockUntilCapable(context, timeout)
      start(context, intent)
    }
  }

  /**
   * Identical to [startWhenCapable], except in this case we just throw if we're unable to start the service. Should only be used if there's no good way
   * to gracefully handle the exception (or if you know for sure it won't get thrown).
   *
   * @param timeout The maximum time you're willing to wait to create the conditions for a foreground service to start.
   */
  @JvmOverloads
  @JvmStatic
  fun startWhenCapableOrThrow(context: Context, intent: Intent, timeout: Long = DEFAULT_TIMEOUT) {
    try {
      startWhenCapable(context, intent, timeout)
    } catch (e: UnableToStartException) {
      throw IllegalStateException(e)
    }
  }

  /**
   * Does its best to start a foreground service with your task name, including possibly blocking and waiting until we are able to.
   * However, it is always possible that the attempt will fail, so always handle the [UnableToStartException].
   */
  @Throws(UnableToStartException::class)
  @JvmStatic
  fun startGenericTaskWhenCapable(context: Context, task: String): NotificationController {
    blockUntilCapable(context)
    return GenericForegroundService.startForegroundTask(context, task)
  }

  /**
   * Waits until we're capable of starting a foreground service.
   * @return True if you should expect to be able to start a foreground service, otherwise false. Please note that this isn't *guaranteed*, just what we believe
   *         given the information we have.
   */
  private fun blockUntilCapable(context: Context, timeout: Long = DEFAULT_TIMEOUT): Boolean {
    val alarmManager = ServiceUtil.getAlarmManager(context)

    if (Build.VERSION.SDK_INT < 31 || ApplicationDependencies.getAppForegroundObserver().isForegrounded) {
      return true
    }

    if (!alarmManager.canScheduleExactAlarms()) {
      return false
    }

    val latch: CountDownLatch? = updateMutex.withLock {
      if (activeLatch == null) {
        if (alarmManager.canScheduleExactAlarms()) {
          activeLatch = CountDownLatch(1)
          val pendingIntent = PendingIntent.getBroadcast(context, 0, Intent(context, Receiver::class.java), PendingIntentFlags.mutable())
          alarmManager.setExact(AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime() + 1000, pendingIntent)
        } else {
          Log.w(TAG, "Unable to schedule alarm")
        }
      }
      activeLatch
    }

    if (latch != null) {
      try {
        if (!latch.await(timeout, TimeUnit.MILLISECONDS)) {
          Log.w(TAG, "Time ran out waiting for foreground")
          return false
        }
      } catch (e: InterruptedException) {
        Log.w(TAG, "Interrupted while waiting for foreground")
      }
    }

    return true
  }

  class Receiver : BroadcastReceiver() {
    override fun onReceive(context: Context?, intent: Intent?) {
      updateMutex.withLock {
        activeLatch?.countDown()
        activeLatch = null
      }
    }
  }
}

class UnableToStartException(cause: Throwable) : Exception(cause)