gcppubsub: update readme

Author: agungdwiprasetyo

worker/gcppubsub/README.md

@@ -1,6 +1,9 @@
 # Google Cloud Platform PubSub
 
-## Add to your `candi` service
+## Install this plugin in your `candi` service
+
+### Add in service.go
+
 ```go
 package service
 
@@ -30,3 +33,81 @@ func NewService(cfg *config.Config) factory.ServiceFactory {
 }
 ...
 ```
+
+### Register in module.go
+
+```go
+package examplemodule
+
+import (
+	"example.service/internal/modules/examplemodule/delivery/workerhandler"
+
+    "github.com/agungdwiprasetyo/candi-plugin/worker/gcppubsub"
+
+	"pkg.agungdp.dev/candi/codebase/factory/dependency"
+	"pkg.agungdp.dev/candi/codebase/factory/types"
+	"pkg.agungdp.dev/candi/codebase/interfaces"
+)
+
+type Module struct {
+	// ...another delivery handler
+	workerHandlers map[types.Worker]interfaces.WorkerHandler
+}
+
+func NewModules(deps dependency.Dependency) *Module {
+	return &Module{
+		workerHandlers: map[types.Worker]interfaces.WorkerHandler{
+			// ...another worker handler
+			// ...
+			gcppubsub.GoogleCloudPubSub: workerhandler.NewGCPPubSubHandler(usecaseUOW.User(), deps.GetValidator()),
+		},
+	}
+}
+
+// ...another method
+```
+
+### Create delivery handler
+
+```go
+package workerhandler
+
+import (
+	"context"
+	"encoding/json"
+	
+	"example.service/internal/modules/examplemodule/delivery/workerhandler"
+
+	"pkg.agungdp.dev/candi/codebase/factory/types"
+	"pkg.agungdp.dev/candi/tracer"
+)
+
+// GCPPubSubHandler struct
+type GCPPubSubHandler struct {
+	uc        usecase.Usecase
+	validator interfaces.Validator
+}
+
+// NewGCPPubSubHandler constructor
+func NewGCPPubSubHandler(uc usecase.Usecase, validator interfaces.Validator) *GCPPubSubHandler {
+	return &GCPPubSubHandler{
+		uc:        uc,
+		validator: validator,
+	}
+}
+
+// MountHandlers mount handler group
+func (h *GCPPubSubHandler) MountHandlers(group *types.WorkerHandlerGroup) {
+	group.Add("example-topic", h.handleTopic) // consume topic "example-topic"
+}
+
+func (h *GCPPubSubHandler) handleTopic(ctx context.Context, message []byte) error {
+	trace := tracer.StartTrace(ctx, "DeliveryGCPPubSub:HandleTopic")
+	defer trace.Finish()
+	ctx = trace.Context()
+
+	log.Printf("message consumed. message: %s\n", message)
+	// call usecase
+	return nil
+}
+```