using subscriber more like a client

trigger/pubsub/pubsub.go

@@ -2,6 +2,7 @@ package pubsub
 
 import (
 	"encoding/json"
+	"fmt"
 	"time"
 
 	"cloud.google.com/go/pubsub"
@@ -17,10 +18,8 @@ import (
 type Subscriber struct {
 	providers map[string]provider.Provider
 
-	project      string
-	topic        string
-	subscription string
-	disableAck   bool
+	project    string
+	disableAck bool
 
 	client *pubsub.Client
 }
@@ -32,24 +31,20 @@ type pubsubImplementer interface {
 }
 
 type Opts struct {
-	Project      string
-	Topic        string
-	Subscription string
-	Providers    map[string]provider.Provider
+	ProjectID string
+	Providers map[string]provider.Provider
 }
 
 func NewSubscriber(opts *Opts) (*Subscriber, error) {
-	client, err := pubsub.NewClient(context.Background(), opts.Project)
+	client, err := pubsub.NewClient(context.Background(), opts.ProjectID)
 	if err != nil {
 		return nil, err
 	}
 
 	return &Subscriber{
-		project:      opts.Project,
-		topic:        opts.Topic,
-		subscription: opts.Subscription,
-		providers:    opts.Providers,
-		client:       client,
+		project:   opts.ProjectID,
+		providers: opts.Providers,
+		client:    client,
 	}, nil
 }
 
@@ -59,12 +54,62 @@ type Message struct {
 	Tag    string `json:"tag,omitempty"`
 }
 
+func (s *Subscriber) ensureTopic(ctx context.Context, id string) error {
+	topic := s.client.Topic(id)
+	exists, err := topic.Exists(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to check whether topic exists, error: %s", err)
+	}
+
+	if exists {
+		log.WithFields(log.Fields{
+			"topic": id,
+		}).Info("trigger.pubsub: topic exists")
+		return nil
+	}
+
+	_, err = s.client.CreateTopic(ctx, id)
+	return err
+}
+
+func (s *Subscriber) ensureSubscription(ctx context.Context, subscriptionID, topicID string) error {
+	sub := s.client.Subscription(subscriptionID)
+	exists, err := sub.Exists(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to check whether subscription exists, error: %s", err)
+	}
+	if exists {
+		log.WithFields(log.Fields{
+			"subscription": subscriptionID,
+			"topic":        topicID,
+		}).Info("trigger.pubsub: subscription exists")
+		return nil
+	}
+
+	_, err = s.client.CreateSubscription(ctx, subscriptionID, pubsub.SubscriptionConfig{
+		Topic:       s.client.Topic(topicID),
+		AckDeadline: 10 * time.Second,
+	})
+	return fmt.Errorf("failed to create subscription %s, error: %s", subscriptionID, err)
+}
+
 // Subscribe - initiate subscriber
-func (s *Subscriber) Subscribe(ctx context.Context) error {
-	sub := s.client.Subscription(s.subscription)
+func (s *Subscriber) Subscribe(ctx context.Context, topic, subscription string) error {
+	// ensuring that topic exists
+	err := s.ensureTopic(ctx, topic)
+	if err != nil {
+		return err
+	}
+
+	err = s.ensureSubscription(ctx, subscription, topic)
+	if err != nil {
+		return err
+	}
+
+	sub := s.client.Subscription(subscription)
 	log.Info("trigger.pubsub: subscribing for events...")
 	// err := sub.Receive(ctx, s.callback)
-	err := sub.Receive(ctx, s.callback)
+	err = sub.Receive(ctx, s.callback)
 	if err != nil {
 		log.WithFields(log.Fields{
 			"error": err,