Limit number of active notifications

app/src/main/java/org/tasks/Notifier.java

@@ -2,7 +2,10 @@ package org.tasks;
 
 import static android.content.Intent.FLAG_ACTIVITY_MULTIPLE_TASK;
 import static android.content.Intent.FLAG_ACTIVITY_NEW_TASK;
+import static com.google.common.collect.Iterables.skip;
+import static com.google.common.collect.Lists.newArrayList;
 import static com.google.common.collect.Lists.transform;
+import static org.tasks.notifications.NotificationManager.MAX_NOTIFICATIONS;
 import static org.tasks.time.DateTimeUtils.currentTimeMillis;
 
 import android.app.PendingIntent;
@@ -145,6 +148,10 @@ public class Notifier {
       Timber.d("Triggering %s", notifications);
     }
 
+    if (notifications.size() > MAX_NOTIFICATIONS) {
+      notifications = newArrayList(skip(notifications, notifications.size() - MAX_NOTIFICATIONS));
+    }
+
     notificationManager.notifyTasks(notifications, alert, ringNonstop, ringFiveTimes);
 
     if (alert

app/src/main/java/org/tasks/notifications/NotificationLimiter.java

@@ -0,0 +1,43 @@
+package org.tasks.notifications;
+
+import java.util.ArrayList;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Queue;
+
+class NotificationLimiter {
+
+  private final Queue<Long> queue = new LinkedList<>();
+  private final int maxSize;
+  private boolean summary = false;
+
+  NotificationLimiter(int maxSize) {
+    this.maxSize = maxSize;
+  }
+
+  synchronized List<Long> add(long id) {
+    if (id == NotificationManager.SUMMARY_NOTIFICATION_ID) {
+      summary = true;
+    } else {
+      remove(id);
+      queue.add(id);
+    }
+    List<Long> evicted = new ArrayList<>();
+    for (int i = 0 ; i < size() - maxSize ; i++) {
+      evicted.add(queue.remove());
+    }
+    return evicted;
+  }
+
+  synchronized void remove(long id) {
+    if (id == NotificationManager.SUMMARY_NOTIFICATION_ID) {
+      summary = false;
+    } else {
+      queue.remove(id);
+    }
+  }
+
+  private int size() {
+    return queue.size() + (summary ? 1 : 0);
+  }
+}

app/src/main/java/org/tasks/notifications/NotificationManager.java

@@ -58,10 +58,11 @@ public class NotificationManager {
   public static final String NOTIFICATION_CHANNEL_DEFAULT = "notifications";
   public static final String NOTIFICATION_CHANNEL_TASKER = "notifications_tasker";
   public static final String NOTIFICATION_CHANNEL_TIMERS = "notifications_timers";
+  public static final int MAX_NOTIFICATIONS = 40;
   static final String EXTRA_NOTIFICATION_ID = "extra_notification_id";
+  static final int SUMMARY_NOTIFICATION_ID = 0;
   private static final String GROUP_KEY = "tasks";
-  private static final int SUMMARY_NOTIFICATION_ID = 0;
-  private static final int NOTIFICATIONS_PER_SECOND = 5;
+  private static final int NOTIFICATIONS_PER_SECOND = 4;
   private final NotificationManagerCompat notificationManagerCompat;
   private final LocationDao locationDao;
   private final NotificationDao notificationDao;
@@ -70,6 +71,7 @@ public class NotificationManager {
   private final Preferences preferences;
   private final CheckBoxes checkBoxes;
   private final Throttle throttle = new Throttle(NOTIFICATIONS_PER_SECOND);
+  private final NotificationLimiter queue = new NotificationLimiter(MAX_NOTIFICATIONS);
 
   @Inject
   public NotificationManager(
@@ -114,6 +116,7 @@ public class NotificationManager {
 
   public void cancel(long id) {
     notificationManagerCompat.cancel((int) id);
+    queue.remove(id);
     Completable.fromAction(
             () -> {
               if (id == SUMMARY_NOTIFICATION_ID) {
@@ -132,11 +135,12 @@ public class NotificationManager {
   }
 
   public void cancel(List<Long> ids) {
+    for (Long id : ids) {
+      notificationManagerCompat.cancel(id.intValue());
+      queue.remove(id);
+    }
     Completable.fromAction(
             () -> {
-              for (Long id : ids) {
-                notificationManagerCompat.cancel(id.intValue());
-              }
               if (notificationDao.deleteAll(ids) > 0) {
                 notifyTasks(Collections.emptyList(), false, false, false);
               }
@@ -255,6 +259,12 @@ public class NotificationManager {
     notification.deleteIntent =
         PendingIntent.getBroadcast(
             context, (int) notificationId, deleteIntent, PendingIntent.FLAG_UPDATE_CURRENT);
+
+    List<Long> evicted = queue.add(notificationId);
+    if (evicted.size() > 0) {
+      cancel(evicted);
+    }
+
     for (int i = 0; i < ringTimes; i++) {
       throttle.run(() -> notificationManagerCompat.notify((int) notificationId, notification));
     }