fix: unblock jikan limiter waits

integrations/jikan/rate/limiter.go

@@ -9,7 +9,7 @@ import (
 
 type Limiter struct {
 	mu          sync.Mutex
-	lastReqTime time.Time
+	nextReqTime time.Time
 	interval    time.Duration
 }
 
@@ -19,24 +19,32 @@ func NewLimiter(interval time.Duration) *Limiter {
 
 // Wait enforces minimum spacing between upstream Jikan requests.
 func (l *Limiter) Wait(ctx context.Context) error {
-	l.mu.Lock()
-	defer l.mu.Unlock()
-
-	now := time.Now()
-	nextAllowed := l.lastReqTime.Add(l.interval)
-	if now.Before(nextAllowed) {
-		timer := time.NewTimer(nextAllowed.Sub(now))
-		defer timer.Stop()
-
-		select {
-		case <-timer.C:
-		case <-ctx.Done():
-			return fmt.Errorf("request canceled while waiting for rate limit: %w", ctx.Err())
-		}
-		l.lastReqTime = time.Now()
+	waitUntil := l.reserve(time.Now())
+	if waitUntil.IsZero() {
 		return nil
 	}
 
-	l.lastReqTime = now
-	return nil
+	timer := time.NewTimer(time.Until(waitUntil))
+	defer timer.Stop()
+
+	select {
+	case <-timer.C:
+		return nil
+	case <-ctx.Done():
+		return fmt.Errorf("request canceled while waiting for rate limit: %w", ctx.Err())
+	}
+}
+
+func (l *Limiter) reserve(now time.Time) time.Time {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+
+	if l.nextReqTime.IsZero() || now.After(l.nextReqTime) {
+		l.nextReqTime = now.Add(l.interval)
+		return time.Time{}
+	}
+
+	waitUntil := l.nextReqTime
+	l.nextReqTime = l.nextReqTime.Add(l.interval)
+	return waitUntil
 }

integrations/jikan/rate/limiter_test.go

@@ -0,0 +1,40 @@
+package rate
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestLimiterDoesNotHoldLockWhileWaiting(t *testing.T) {
+	limiter := NewLimiter(250 * time.Millisecond)
+	if err := limiter.Wait(context.Background()); err != nil {
+		t.Fatalf("initial wait: %v", err)
+	}
+
+	firstCtx, cancelFirst := context.WithCancel(context.Background())
+	defer cancelFirst()
+
+	firstDone := make(chan error, 1)
+	go func() {
+		firstDone <- limiter.Wait(firstCtx)
+	}()
+
+	time.Sleep(20 * time.Millisecond)
+
+	secondCtx, cancelSecond := context.WithTimeout(context.Background(), 30*time.Millisecond)
+	defer cancelSecond()
+
+	startedAt := time.Now()
+	err := limiter.Wait(secondCtx)
+	elapsed := time.Since(startedAt)
+	if err == nil {
+		t.Fatal("second wait succeeded, want context timeout")
+	}
+	if elapsed > 150*time.Millisecond {
+		t.Fatalf("second wait took %s, want it to observe context timeout without waiting behind first caller", elapsed)
+	}
+
+	cancelFirst()
+	<-firstDone
+}