feat(event_producer): implement pubsub adapters

Introduces the `gcppubsubadapters` package to connect the `EventProducer`
domain logic to Google Cloud Pub/Sub.

This includes:
- `EventProducerSubscriberAdapter`: A high-level adapter that routes incoming
  Pub/Sub messages (RefreshSearch, BatchRefresh, ConfigurationChanged) to
  the appropriate `EventProducer` methods.
- `EventProducerPublisherAdapter`: An adapter for publishing `FeatureDiffEvent`
  notifications back to Pub/Sub.
- `RunGroup`: A concurrency utility for managing the lifecycle of multiple
  blocking subscribers.

Author: jcscottiii

lib/gcppubsub/gcppubsubadapters/event_producer.go

@@ -0,0 +1,163 @@
+// Copyright 2025 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package gcppubsubadapters
+
+import (
+	"context"
+	"log/slog"
+
+	"github.com/GoogleChrome/webstatus.dev/lib/event"
+	batchrefreshv1 "github.com/GoogleChrome/webstatus.dev/lib/event/batchrefreshtrigger/v1"
+	featurediffv1 "github.com/GoogleChrome/webstatus.dev/lib/event/featurediff/v1"
+	refreshv1 "github.com/GoogleChrome/webstatus.dev/lib/event/refreshsearchcommand/v1"
+	searchconfigv1 "github.com/GoogleChrome/webstatus.dev/lib/event/searchconfigurationchanged/v1"
+	"github.com/GoogleChrome/webstatus.dev/lib/workertypes"
+)
+
+type EventProducerSearchMessageHandler interface {
+	ProcessSearch(ctx context.Context, searchID string, query string,
+		frequency workertypes.JobFrequency, triggerID string) error
+}
+
+type EventProducerBatchUpdateHandler interface {
+	ProcessBatchUpdate(ctx context.Context, triggerID string, frequency workertypes.JobFrequency) error
+}
+
+type EventSubscriber interface {
+	Subscribe(ctx context.Context, subID string,
+		handler func(ctx context.Context, msgID string, data []byte) error) error
+}
+
+type SubscriberConfig struct {
+	SearchSubscriptionID      string
+	BatchUpdateSubscriptionID string
+}
+
+type EventProducerSubscriberAdapter struct {
+	searchEventHandler EventProducerSearchMessageHandler
+	batchUpdateHandler EventProducerBatchUpdateHandler
+	eventSubscriber    EventSubscriber
+	config             SubscriberConfig
+	searchEventRouter  *event.Router
+	batchUpdateRouter  *event.Router
+}
+
+func NewEventProducerSubscriberAdapter(
+	searchMessageHandler EventProducerSearchMessageHandler,
+	batchUpdateHandler EventProducerBatchUpdateHandler,
+	eventSubscriber EventSubscriber,
+	config SubscriberConfig,
+) *EventProducerSubscriberAdapter {
+	searchEventRouter := event.NewRouter()
+
+	batchUpdateRouter := event.NewRouter()
+
+	ret := &EventProducerSubscriberAdapter{
+		searchEventHandler: searchMessageHandler,
+		batchUpdateHandler: batchUpdateHandler,
+		eventSubscriber:    eventSubscriber,
+		config:             config,
+		searchEventRouter:  searchEventRouter,
+		batchUpdateRouter:  batchUpdateRouter,
+	}
+
+	event.Register(searchEventRouter, ret.processRefreshSearchCommand)
+	event.Register(searchEventRouter, ret.processSearchConfigurationChangedEvent)
+
+	event.Register(batchUpdateRouter, ret.processBatchUpdateCommand)
+
+	return ret
+}
+
+func (a *EventProducerSubscriberAdapter) processRefreshSearchCommand(ctx context.Context,
+	eventID string, event refreshv1.RefreshSearchCommand) error {
+	slog.InfoContext(ctx, "received refresh search command", "eventID", eventID, "event", event)
+
+	return a.searchEventHandler.ProcessSearch(ctx, event.SearchID, event.Query,
+		event.Frequency.ToWorkerTypeJobFrequency(), eventID)
+}
+
+func (a *EventProducerSubscriberAdapter) processSearchConfigurationChangedEvent(ctx context.Context,
+	eventID string, event searchconfigv1.SearchConfigurationChangedEvent) error {
+	slog.InfoContext(ctx, "received search configuration changed event", "eventID", eventID, "event", event)
+
+	return a.searchEventHandler.ProcessSearch(ctx, event.SearchID, event.Query,
+		event.Frequency.ToWorkerTypeJobFrequency(), eventID)
+}
+
+func (a *EventProducerSubscriberAdapter) Subscribe(ctx context.Context) error {
+	return RunGroup(ctx,
+		// Handler 1: Search
+		func(ctx context.Context) error {
+			return a.eventSubscriber.Subscribe(ctx, a.config.SearchSubscriptionID,
+				func(ctx context.Context, msgID string, data []byte) error {
+					return a.searchEventRouter.HandleMessage(ctx, msgID, data)
+				})
+		},
+		// Handler 2: Batch Update
+		func(ctx context.Context) error {
+			return a.eventSubscriber.Subscribe(ctx, a.config.BatchUpdateSubscriptionID,
+				func(ctx context.Context, msgID string, data []byte) error {
+					return a.batchUpdateRouter.HandleMessage(ctx, msgID, data)
+				})
+		},
+	)
+}
+
+func (a *EventProducerSubscriberAdapter) processBatchUpdateCommand(ctx context.Context,
+	eventID string, event batchrefreshv1.BatchRefreshTrigger) error {
+	slog.InfoContext(ctx, "received batch update command", "eventID", eventID, "event", event)
+
+	return a.batchUpdateHandler.ProcessBatchUpdate(ctx, eventID,
+		event.Frequency.ToWorkerTypeJobFrequency())
+}
+
+type EventPublisher interface {
+	Publish(ctx context.Context, topicID string, data []byte) (string, error)
+}
+
+type EventProducerPublisherAdapter struct {
+	eventPublisher EventPublisher
+	topicID        string
+}
+
+func NewEventProducerPublisherAdapter(eventPublisher EventPublisher, topicID string) *EventProducerPublisherAdapter {
+	return &EventProducerPublisherAdapter{
+		eventPublisher: eventPublisher,
+		topicID:        topicID,
+	}
+}
+
+func (a *EventProducerPublisherAdapter) Publish(ctx context.Context,
+	req workertypes.PublishEventRequest) (string, error) {
+	b, err := event.New(featurediffv1.FeatureDiffEvent{
+		EventID:       req.EventID,
+		SearchID:      req.SearchID,
+		Query:         req.Query,
+		Summary:       req.Summary,
+		StateID:       req.StateID,
+		StateBlobPath: req.StateBlobPath,
+		DiffID:        req.DiffID,
+		DiffBlobPath:  req.DiffBlobPath,
+		GeneratedAt:   req.GeneratedAt,
+		Frequency:     featurediffv1.ToJobFrequency(req.Frequency),
+		Reasons:       featurediffv1.ToReasons(req.Reasons),
+	})
+	if err != nil {
+		return "", err
+	}
+
+	return a.eventPublisher.Publish(ctx, a.topicID, b)
+}