1 files changed, 58 insertions, 5 deletions

diff --git a/internal/resource/repository.go b/internal/resource/repository.go
index 8cb88b3..69617d4 100644
--- a/internal/resource/repository.go
+++ b/internal/resource/repository.go
@@ -11,11 +11,11 @@ var (
 	once sync.Once
 )
 
-func getRepository() repository {
+func getRepository() *repository {
 	once.Do(func() {
 		repo = newRepository()
 	})
-	return repo
+	return &repo
 }
 
 func resetRepository() {
@@ -24,17 +24,16 @@ func resetRepository() {
 
 type repository struct {
 	registered map[string]Resource
-	mu         *sync.Mutex
+	mu         sync.Mutex
 }
 
 func newRepository() repository {
 	return repository{
 		registered: make(map[string]Resource),
-		mu:         new(sync.Mutex),
 	}
 }
 
-func (r repository) register(res Resource) error {
+func (r *repository) register(res Resource) error {
 	r.mu.Lock()
 	defer r.mu.Unlock()
 
@@ -47,3 +46,57 @@ func (r repository) register(res Resource) error {
 
 	return nil
 }
+
+func (r *repository) apply() error {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	visited := make(map[string]bool)
+	visiting := make(map[string]bool)
+	var order []Resource
+
+	var visit func(id string) error
+	visit = func(id string) error {
+		if visiting[id] {
+			return fmt.Errorf("circular dependency detected involving %s", id)
+		}
+		if visited[id] {
+			return nil
+		}
+
+		res, ok := r.registered[id]
+		if !ok {
+			return fmt.Errorf("resource %s is depended upon but not registered", id)
+		}
+
+		visiting[id] = true
+		for depID := range res.dependsOn {
+			if err := visit(depID); err != nil {
+				return err
+			}
+		}
+		delete(visiting, id)
+		visited[id] = true
+		order = append(order, res)
+		return nil
+	}
+
+	for id := range r.registered {
+		if err := visit(id); err != nil {
+			return err
+		}
+	}
+
+	for _, res := range order {
+		log.Printf("Applying resource %v", res)
+		if err := res.Apply.Apply(); err != nil {
+			return fmt.Errorf("failed to apply %v: %w", res, err)
+		}
+	}
+
+	return nil
+}
+
+func Apply() error {
+	return getRepository().apply()
+}