From bad22e6422877b4e5b3c5aa51ba809fb0aa6a808 Mon Sep 17 00:00:00 2001
From: Max Ignatenko <gelraen.ua@gmail.com>
Date: Thu, 14 Nov 2024 12:44:42 +0000
Subject: [PATCH] fix: s/LastSuccess/LastCompletion/ and use it as orignally
 intended

---
 cmd/plc-mirror/mirror.go | 17 ++++++++---------
 cmd/plc-mirror/serve.go  | 11 +++++++++--
 2 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/cmd/plc-mirror/mirror.go b/cmd/plc-mirror/mirror.go
index 808de96..1666fde 100644
--- a/cmd/plc-mirror/mirror.go
+++ b/cmd/plc-mirror/mirror.go
@@ -36,9 +36,9 @@ type Mirror struct {
 	upstream *url.URL
 	limiter  *rate.Limiter
 
-	mu                   sync.RWMutex
-	lastSuccessTimestamp time.Time
-	lastRecordTimestamp  time.Time
+	mu                      sync.RWMutex
+	lastCompletionTimestamp time.Time
+	lastRecordTimestamp     time.Time
 }
 
 func NewMirror(ctx context.Context, upstream string, db *gorm.DB) (*Mirror, error) {
@@ -78,7 +78,7 @@ func (m *Mirror) run(ctx context.Context) {
 			} else {
 				now := time.Now()
 				m.mu.Lock()
-				m.lastSuccessTimestamp = now
+				m.lastCompletionTimestamp = now
 				m.mu.Unlock()
 			}
 			time.Sleep(10 * time.Second)
@@ -86,10 +86,10 @@ func (m *Mirror) run(ctx context.Context) {
 	}
 }
 
-func (m *Mirror) LastSuccess() time.Time {
+func (m *Mirror) LastCompletion() time.Time {
 	m.mu.RLock()
 	defer m.mu.RUnlock()
-	return m.lastSuccessTimestamp
+	return m.lastCompletionTimestamp
 }
 
 func (m *Mirror) LastRecordTimestamp(ctx context.Context) (time.Time, error) {
@@ -201,12 +201,11 @@ func (m *Mirror) runOnce(ctx context.Context) error {
 			return fmt.Errorf("inserting log entry into database: %w", err)
 		}
 
-		m.mu.Lock()
-		m.lastSuccessTimestamp = time.Now()
 		if !lastTimestamp.IsZero() {
+			m.mu.Lock()
 			m.lastRecordTimestamp = lastTimestamp
+			m.mu.Unlock()
 		}
-		m.mu.Unlock()
 
 		log.Info().Msgf("Got %d log entries. New cursor: %q", len(newEntries), cursor)
 	}
diff --git a/cmd/plc-mirror/serve.go b/cmd/plc-mirror/serve.go
index 520de27..245881d 100644
--- a/cmd/plc-mirror/serve.go
+++ b/cmd/plc-mirror/serve.go
@@ -66,14 +66,21 @@ func (s *Server) serve(ctx context.Context, req *http.Request) convreq.HttpRespo
 		requestLatency.WithLabelValues(fmt.Sprint(c)).Observe(float64(time.Now().Sub(start)) / float64(time.Millisecond))
 	}
 
+	// Check if the mirror is up to date.
 	ts, err := s.mirror.LastRecordTimestamp(ctx)
 	if err != nil {
 		return respond.InternalServerError(err.Error())
 	}
 	delay := time.Since(ts)
 	if delay > s.MaxDelay {
-		updateMetrics(http.StatusServiceUnavailable)
-		return respond.ServiceUnavailable(fmt.Sprintf("mirror is %s behind", delay))
+		// Check LastCompletion and if it's recent enough - that means
+		// that we're actually caught up and there simply aren't any recent
+		// PLC operations.
+		completionDelay := time.Since(s.mirror.LastCompletion())
+		if completionDelay > s.MaxDelay {
+			updateMetrics(http.StatusServiceUnavailable)
+			return respond.ServiceUnavailable(fmt.Sprintf("mirror is %s behind", delay))
+		}
 	}
 	log := zerolog.Ctx(ctx)