fix(reminders): make sure reminders are only sent once per user

Previously, when a user was creator and assigned to a task, they would get two reminder notifications for the same task. This was caused by Vikunja first fetching all creators and then all assignees and not removing duplicates from that list.

Related: https://community.vikunja.io/t/duplicate-email-reminders/1505/3

pkg/models/task_reminder.go

@@ -171,6 +171,8 @@ func getTasksWithRemindersDueAndTheirUsers(s *xorm.Session, now time.Time) (remi
 		usersPerTask[ur.Task.ID] = append(usersPerTask[ur.Task.ID], ur)
 	}
 
+	seen := make(map[int64]map[int64]bool)
+
 	// Time zone cache per time zone string to avoid parsing the same time zone over and over again
 	tzs := make(map[string]*time.Location)
 	// Figure out which reminders are actually due in the time zone of the users
@@ -178,6 +180,17 @@ func getTasksWithRemindersDueAndTheirUsers(s *xorm.Session, now time.Time) (remi
 
 		for _, u := range usersPerTask[r.TaskID] {
 
+			// This ensures we send each reminder only once to each user
+			if seen[r.TaskID] == nil {
+				seen[r.Ta2skID] = make(map[int64]bool)
+			}
+
+			if _, exists := seen[r.TaskID][u.User.ID]; exists {
+				continue
+			}
+
+			seen[r.TaskID][u.User.ID] = true
+
 			if u.User.Timezone == "" {
 				u.User.Timezone = config.GetTimeZone().String()
 			}

pkg/models/task_reminder_test.go

@@ -30,7 +30,7 @@ func TestReminderGetTasksInTheNextMinute(t *testing.T) {
 		s := db.NewSession()
 		defer s.Close()
 
-		now, err := time.Parse(time.RFC3339Nano, "2018-12-01T01:13:00Z")
+		now, err := time.Parse(time.RFC3339Nano, "2018-12-01T01:12:00Z")
 		assert.NoError(t, err)
 		notifications, err := getTasksWithRemindersDueAndTheirUsers(s, now)
 		assert.NoError(t, err)