initial Apply

3 files changed, 70 insertions, 10 deletions

diff --git a/examples/examples.go b/examples/examples.go
index b350576..9c42ce6 100644
--- a/examples/examples.go
+++ b/examples/examples.go
@@ -3,6 +3,7 @@ package examples
 import (
 	"os"
 
+	"codeberg.org/snonux/gonf/internal/resource"
 	"codeberg.org/snonux/gonf/internal/resource/dir"
 	"codeberg.org/snonux/gonf/internal/resource/file"
 	"codeberg.org/snonux/gonf/internal/resource/link"
@@ -69,5 +70,7 @@ func Run() error {
 	_ = os.Link("/tmp/gonf_hello.txt", "/tmp/gonf_stale_hardlink")
 	link.Have("/tmp/gonf_stale_hardlink", IsAbsent())
 
+	resource.Apply()
+
 	return nil
 }
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()
+}
diff --git a/internal/resource/resource_test.go b/internal/resource/resource_test.go
index 947f0ac..8741f2a 100644
--- a/internal/resource/resource_test.go
+++ b/internal/resource/resource_test.go
@@ -6,7 +6,7 @@ import (
 
 func TestResourceID(t *testing.T) {
 	resetRepository()
-	res := Register("File", "/tmp/foo.txt")
+	res := Register("File", "/tmp/foo.txt", &mockApplier{})
 	expected := "File[/tmp/foo.txt]"
 	if res.ID() != expected {
 		t.Errorf("expected ID %s, got %s", expected, res.ID())
@@ -15,7 +15,7 @@ func TestResourceID(t *testing.T) {
 
 func TestResourceString(t *testing.T) {
 	resetRepository()
-	res := Register("File", "/tmp/foo.txt")
+	res := Register("File", "/tmp/foo.txt", &mockApplier{})
 	expected := "File[/tmp/foo.txt]"
 	if res.String() != expected {
 		t.Errorf("expected String %s, got %s", expected, res.String())
@@ -26,7 +26,7 @@ func TestNew(t *testing.T) {
 	resetRepository()
 	type_ := "File"
 	name := "/tmp/foo.txt"
-	res := Register(type_, name)
+	res := Register(type_, name, &mockApplier{})
 
 	if res.Type != type_ {
 		t.Errorf("expected type %s, got %s", type_, res.Type)
@@ -42,7 +42,7 @@ func TestNew(t *testing.T) {
 func TestRepositoryRegister(t *testing.T) {
 	resetRepository()
 	repo := getRepository()
-	res := Register("File", "/tmp/foo.txt")
+	res := Register("File", "/tmp/foo.txt", &mockApplier{})
 
 	// First registration already happened in New()
 	// But we can try to register again via the repository directly
@@ -51,8 +51,12 @@ func TestRepositoryRegister(t *testing.T) {
 	}
 
 	// Registration of a different resource should succeed
-	res2 := Register("File", "/tmp/bar.txt")
+	res2 := Register("File", "/tmp/bar.txt", &mockApplier{})
 	if err := repo.register(res2); err == nil {
 		t.Error("expected error when registering the same resource twice, got nil")
 	}
 }
+
+type mockApplier struct{}
+
+func (m *mockApplier) Apply() error { return nil }