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/events/events.go

@@ -0,0 +1,97 @@
+// 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 events
+
+import (
+	"context"
+	"encoding/json"
+	"time"
+
+	"code.vikunja.io/api/pkg/log"
+	vmetrics "code.vikunja.io/api/pkg/metrics"
+	"github.com/ThreeDotsLabs/watermill"
+	"github.com/ThreeDotsLabs/watermill/components/metrics"
+	"github.com/ThreeDotsLabs/watermill/message"
+	"github.com/ThreeDotsLabs/watermill/message/router/middleware"
+	"github.com/ThreeDotsLabs/watermill/pubsub/gochannel"
+)
+
+var pubsub *gochannel.GoChannel
+
+// Event represents the event interface used by all events
+type Event interface {
+	Name() string
+}
+
+// InitEvents sets up everything needed to work with events
+func InitEvents() (err error) {
+	logger := log.NewWatermillLogger()
+
+	router, err := message.NewRouter(
+		message.RouterConfig{},
+		logger,
+	)
+	if err != nil {
+		return err
+	}
+
+	router.AddMiddleware(
+		middleware.Retry{
+			MaxRetries:      5,
+			InitialInterval: time.Millisecond * 100,
+			Logger:          logger,
+			Multiplier:      2,
+		}.Middleware,
+		middleware.Recoverer,
+	)
+
+	metricsBuilder := metrics.NewPrometheusMetricsBuilder(vmetrics.GetRegistry(), "", "")
+	metricsBuilder.AddPrometheusRouterMetrics(router)
+
+	pubsub = gochannel.NewGoChannel(
+		gochannel.Config{
+			OutputChannelBuffer: 1024,
+		},
+		logger,
+	)
+
+	for topic, funcs := range listeners {
+		for _, handler := range funcs {
+			router.AddNoPublisherHandler(topic+"."+handler.Name(), topic, pubsub, func(msg *message.Message) error {
+				return handler.Handle(msg.Payload)
+			})
+		}
+	}
+
+	return router.Run(context.Background())
+}
+
+// Dispatch dispatches an event
+func Dispatch(event Event) error {
+	if isUnderTest {
+		dispatchedTestEvents = append(dispatchedTestEvents, event)
+		return nil
+	}
+
+	content, err := json.Marshal(event)
+	if err != nil {
+		return err
+	}
+
+	msg := message.NewMessage(watermill.NewUUID(), content)
+	return pubsub.Publish(event.Name(), msg)
+}