feat: Implement Publisher

shared/plugin/implementation/publisher/publisher.go

@@ -0,0 +1,95 @@
+package publisher
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"log"
+	"strings"
+
+	"cloud.google.com/go/pubsub"
+	"google.golang.org/api/option"
+)
+
+// Config holds the Pub/Sub configuration.
+type Config struct {
+	ProjectID string
+	TopicID   string
+}
+
+// Publisher is a concrete implementation of a Google Cloud Pub/Sub publisher.
+type Publisher struct {
+	client *pubsub.Client
+	topic  *pubsub.Topic
+	config *Config
+}
+
+var (
+	ErrProjectMissing = errors.New("missing required field 'Project'")
+	ErrTopicMissing   = errors.New("missing required field 'Topic'")
+	ErrEmptyConfig    = errors.New("empty config")
+)
+
+
+func validate(cfg *Config) error {
+	if cfg == nil {
+		return ErrEmptyConfig
+	}
+	if strings.TrimSpace(cfg.ProjectID) == "" {
+		return ErrProjectMissing
+	}
+	if strings.TrimSpace(cfg.TopicID) == "" {
+		return ErrTopicMissing
+	}
+	return nil
+}
+
+// New initializes a new Publisher instance.
+// It creates a real pubsub.Client and then calls NewWithClient.
+func New(ctx context.Context, config *Config, opts ...option.ClientOption) (*Publisher, error) {
+	if err := validate(config); err != nil {
+		return nil, err
+	}
+	client, err := pubsub.NewClient(ctx, config.ProjectID, opts...)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create pubsub client: %w", err)
+	}
+
+	topic := client.Topic(config.TopicID)
+	exists, err := topic.Exists(ctx)
+	if err != nil {
+		_ = client.Close()
+		return nil, fmt.Errorf("failed to check topic existence: %w", err)
+	}
+	if !exists {
+		_ = client.Close()
+		return nil, fmt.Errorf("topic %s does not exist", config.TopicID)
+	}
+	return &Publisher{
+		client: client,
+		topic:  topic,
+		config: config,
+	}, nil
+}
+
+
+// Publish sends a message to Google Cloud Pub/Sub.
+func (p *Publisher) Publish(ctx context.Context, msg []byte) error {
+	pubsubMsg := &pubsub.Message{
+		Data: msg,
+	}
+
+	result := p.topic.Publish(ctx, pubsubMsg)
+	id, err := result.Get(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to publish message: %w", err)
+	}
+
+	log.Printf("Published message with ID: %s\n", id)
+	return nil
+}
+
+// Close closes the underlying Pub/Sub client.
+func (p *Publisher) Close() error {
+	return p.client.Close()
+}