feat: ensure a MR is only processed once at a time; in case of many w…

…ebhook events firing

cmd/shared.go

@@ -28,6 +28,8 @@ func getClient(ctx context.Context) (scm.Client, error) {
 }
 
 func ProcessMR(ctx context.Context, client scm.Client, cfg *config.Config, event any) (err error) {
+	defer state.LockForProcessing(ctx)()
+
 	// Write the config to context so we can pull it out later
 	ctx = config.WithConfig(ctx, cfg)
 

pkg/state/mutex.go

@@ -0,0 +1,18 @@
+package state
+
+import (
+	"context"
+	"sync"
+)
+
+var processingMutex sync.Map // Zero value is empty and ready for use
+
+func LockForProcessing(ctx context.Context) func() {
+	key := Provider(ctx) + "/" + ProjectID(ctx) + "/" + MergeRequestID(ctx)
+
+	value, _ := processingMutex.LoadOrStore(key, &sync.Mutex{})
+	mtx := value.(*sync.Mutex) //nolint
+	mtx.Lock()
+
+	return func() { mtx.Unlock() }
+}