added an alarm cronjob

server/backend/cron/alarm.go

@@ -1,7 +1,64 @@
 package cron
 
-//lint:ignore U1000 stub
+import (
+	"github.com/TUM-Dev/Campus-Backend/server/model"
+	log "github.com/sirupsen/logrus"
+	"gorm.io/gorm"
+)
+
 func (c *CronService) alarmCron() error {
-	// TODO: implement
+	return notifyAllUsers(c.db, sendGCMNotification)
+}
+
+func sendGCMNotification(*[]model.Device) error {
+	log.Trace("sendGCMNotification")
+	return nil
+}
+
+func notifyAllUsers(db *gorm.DB, callbacks ...func(*[]model.Device) error) error {
+	var pendingNotifications []model.Notification
+	if err := db.
+		Joins("notification_confirmation").
+		Where("notification_confirmation.sent = ?", false).
+		Group("notification").
+		Find(&pendingNotifications).Error; err != nil {
+		log.WithError(err).Error("failed to get pending notifications from the db")
+		return err
+	}
+	for _, pending := range pendingNotifications {
+		// Get a few targets
+		var targets []model.Device
+		if err := db.
+			Distinct("device").
+			Where("notification = ?", pending.Notification).
+			Where("gcmStatus IS NULL").
+			Where("gcmToken IS NOT NULL").
+			Joins("notification_confirmation").
+			Where("notification_confirmation.sent = ?", false).
+			Limit(998).
+			Find(&targets).
+			Error; err != nil {
+			log.WithError(err).Error("failed to get devices which should receive the notification")
+			continue
+		}
+		if len(targets) > 0 {
+			for _, callback := range callbacks {
+				if err := callback(&targets); err != nil {
+					log.WithError(err).Error("callback failed")
+					continue
+				}
+			}
+			// mark as sent for these targets
+			if err := db.
+				Model(&model.NotificationConfirmation{}).
+				Where("notification = ?", pending.Notification).
+				Where("device IN ?", targets).
+				Update("sent", true).
+				Error; err != nil {
+				log.WithError(err).Error("failed to update notification_confirmation")
+				continue
+			}
+		}
+	}
 	return nil
 }