Add events (#777)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/777
Co-authored-by: konrad <konrad@kola-entertainments.de>
Co-committed-by: konrad <konrad@kola-entertainments.de>

pkg/user/listeners.go

@@ -0,0 +1,45 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2021 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public Licensee as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package user
+
+import (
+	"code.vikunja.io/api/pkg/events"
+	"code.vikunja.io/api/pkg/metrics"
+	"code.vikunja.io/api/pkg/modules/keyvalue"
+	"github.com/ThreeDotsLabs/watermill/message"
+)
+
+func RegisterListeners() {
+	events.RegisterListener((&CreatedEvent{}).Name(), &IncreaseUserCounter{})
+}
+
+///////
+// User Events
+
+// IncreaseUserCounter  represents a listener
+type IncreaseUserCounter struct {
+}
+
+// Name defines the name for the IncreaseUserCounter listener
+func (s *IncreaseUserCounter) Name() string {
+	return "increase.user.counter"
+}
+
+// Hanlde is executed when the event IncreaseUserCounter listens on is fired
+func (s *IncreaseUserCounter) Handle(payload message.Payload) (err error) {
+	return keyvalue.IncrBy(metrics.UserCountKey, 1)
+}