feat: no apply on empty plan (#21)

* feat(runner): skip storing plan binary and sum if no diff is found

* fix(runner): runner should save lastPlanDate even if there's no change

runner/runner.go

@@ -90,11 +90,20 @@ func (r *Runner) init() error {
 
 func (r *Runner) plan() {
 	log.Print("Launching terraform plan")
-	_, err := r.terraform.Plan(context.Background(), tfexec.Out(PlanArtifact))
+	diff, err := r.terraform.Plan(context.Background(), tfexec.Out(PlanArtifact))
 	if err != nil {
 		log.Printf("Terraform plan errored: %s", err)
 		return
 	}
+	log.Printf("Setting last plan date cache at key %s", r.config.Runner.Layer.PlanDate)
+	err = r.cache.Set(r.config.Runner.Layer.PlanDate, []byte(strconv.FormatInt(time.Now().Unix(), 10)), 3600)
+	if err != nil {
+		log.Fatalf("Could not put plan date in cache: %s", err)
+	}
+	if !diff {
+		log.Printf("Terraform plan diff empty, no subsequent apply should be launched")
+		return
+	}
 	plan, err := os.ReadFile(fmt.Sprintf("%s/%s", r.terraform.WorkingDir(), PlanArtifact))
 	if err != nil {
 		log.Fatalf("Could not read plan output: %s", err)
@@ -112,11 +121,6 @@ func (r *Runner) plan() {
 	if err != nil {
 		log.Fatalf("Could not put plan checksum in cache: %s", err)
 	}
-	log.Printf("Setting last plan date cache at key %s", r.config.Runner.Layer.PlanDate)
-	err = r.cache.Set(r.config.Runner.Layer.PlanDate, []byte(strconv.FormatInt(time.Now().Unix(), 10)), 3600)
-	if err != nil {
-		log.Fatalf("Could not put plan date in cache: %s", err)
-	}
 }
 
 func (r *Runner) apply() {