FEAT: Discovery Video Service Subscription

discovery/internal/consumers/catalogue.go

@@ -0,0 +1,110 @@
+// Package consumers holds the queue-driven half of the service: work that
+// arrives on a queue rather than as an HTTP request. It is to SQS what
+// internal/handlers is to HTTP — it decodes a message, calls repositories, and
+// decides what the message's fate is — so the same seams apply, and no SQL
+// lives here.
+package consumers
+
+import (
+	"context"
+	"encoding/json"
+	"log"
+	"strings"
+	"thamanyah/discovery/internal/db/repositories"
+	"thamanyah/discovery/internal/models"
+	"thamanyah/discovery/internal/services"
+	"time"
+)
+
+// receiveBackoff is how long the loop waits after a failed receive, so a queue
+// that is unreachable produces a slow trickle of log lines rather than a spin.
+const receiveBackoff = 5 * time.Second
+
+// announcement is what cms publishes to the catalogue topic when a video
+// becomes ready. It is cms's published contract, mirrored here rather than
+// imported: the two services share no code, and this struct is exactly the
+// coupling between them — so a field renamed on one side has to be renamed
+// here too, deliberately.
+//
+// The subscription delivers raw, so this is the whole message body; there is
+// no SNS envelope to unwrap.
+type announcement struct {
+	VideoID     string   `json:"videoId"`
+	Title       string   `json:"title"`
+	PlaybackURL string   `json:"playbackUrl"`
+	Categories  []string `json:"categories"`
+}
+
+// CatalogueEvents consumes the announcements cms publishes.
+type CatalogueEvents struct{}
+
+// Run consumes announcements until ctx is cancelled. It is meant to be run in
+// its own goroutine for the lifetime of the process.
+func (c CatalogueEvents) Run(ctx context.Context) {
+	log.Println("catalogue announcements consumer started")
+
+	for {
+		if ctx.Err() != nil {
+			log.Println("catalogue announcements consumer stopped")
+			return
+		}
+
+		messages, err := services.SQSClient.ReceiveMessages(ctx)
+		if err != nil {
+			if ctx.Err() != nil {
+				log.Println("catalogue announcements consumer stopped")
+				return
+			}
+			log.Printf("Something Went Wrong Receiving Announcements: %s", err)
+			time.Sleep(receiveBackoff)
+			continue
+		}
+
+		for _, message := range messages {
+			if !c.handleAnnouncement(ctx, message.Body) {
+				// Left on the queue on purpose: it becomes visible again when
+				// the visibility timeout expires, and reaches the dead-letter
+				// queue if it keeps failing.
+				continue
+			}
+
+			if err := services.SQSClient.DeleteMessage(ctx, message.ReceiptHandle); err != nil {
+				log.Printf("Something Went Wrong Acknowledging An Announcement: %s", err)
+			}
+		}
+	}
+}
+
+// handleAnnouncement processes one message and reports whether it is finished
+// with — that is, whether it should be deleted from the queue. It returns
+// false only when a retry could plausibly succeed. Anything a retry cannot fix
+// (a body that will never parse, an announcement naming no video) is finished
+// with, however little it accomplished: leaving it on the queue would only
+// stall the announcements behind it.
+func (c CatalogueEvents) handleAnnouncement(ctx context.Context, body string) bool {
+	var announced announcement
+	if err := json.Unmarshal([]byte(body), &announced); err != nil {
+		log.Printf("Discarding An Announcement That Is Not JSON: %s", err)
+		return true
+	}
+
+	if strings.TrimSpace(announced.VideoID) == "" {
+		log.Printf("Discarding An Announcement That Names No Video")
+		return true
+	}
+
+	if err := repositories.VideoRepo.SaveVideo(ctx, models.Video{
+		ID:          announced.VideoID,
+		Title:       announced.Title,
+		PlaybackURL: announced.PlaybackURL,
+		Categories:  announced.Categories,
+	}); err != nil {
+		// Worth another attempt: the save is an upsert, so a redelivery
+		// re-runs it harmlessly.
+		log.Printf("Something Went Wrong Saving An Announced Video: video=%q: %s", announced.VideoID, err)
+		return false
+	}
+
+	log.Printf("Catalogued An Announced Video: video=%q title=%q", announced.VideoID, announced.Title)
+	return true
+}