feat: Update variable getter to handle nested fields

pkg/capi/clustertopology/variables/variable.go

@@ -7,19 +7,41 @@ import (
 	"encoding/json"
 
 	apiextensionsv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
+	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"sigs.k8s.io/cluster-api/exp/runtime/topologymutation"
 )
 
 // Get finds and parses variable to given type.
 func Get[T any](
 	variables map[string]apiextensionsv1.JSON,
 	name string,
+	fields ...string,
 ) (value T, found bool, err error) {
 	variable, found, err := topologymutation.GetVariable(variables, name)
 	if err != nil || !found {
 		return value, found, err
 	}
 
-	err = json.Unmarshal(variable.Raw, &value)
+	jsonValue := variable.Raw
+
+	if len(fields) > 0 {
+		var unstr map[string]interface{}
+		err = json.Unmarshal(jsonValue, &unstr)
+		if err != nil {
+			return value, found, err
+		}
+
+		nestedField, found, err := unstructured.NestedFieldCopy(unstr, fields...)
+		if err != nil || !found {
+			return value, found, err
+		}
+
+		jsonValue, err = json.Marshal(nestedField)
+		if err != nil {
+			return value, found, err
+		}
+	}
+
+	err = json.Unmarshal(jsonValue, &value)
 	return value, err == nil, err
 }

pkg/capi/clustertopology/variables/variables_test.go

@@ -51,3 +51,57 @@ func TestGetVariable_ParseError(t *testing.T) {
 	g.Expect(found).To(BeFalse())
 	g.Expect(parsed).To(BeEmpty())
 }
+
+func TestGet_ValidNestedFieldAsStruct(t *testing.T) {
+	g := NewWithT(t)
+
+	type nestedStruct struct {
+		Bar string `json:"bar"`
+	}
+	sampleValue := []byte(`{"foo": {"bar": "baz"}}`)
+	vars := map[string]apiextensionsv1.JSON{
+		"sampleVar": {Raw: sampleValue},
+	}
+	parsed, found, err := variables.Get[nestedStruct](vars, "sampleVar", "foo")
+	g.Expect(err).NotTo(HaveOccurred())
+	g.Expect(found).To(BeTrue())
+	g.Expect(parsed).To(Equal(nestedStruct{
+		Bar: "baz",
+	}))
+}
+
+func TestGet_ValidNestedFieldAsScalar(t *testing.T) {
+	g := NewWithT(t)
+
+	sampleValue := []byte(`{"foo": {"bar": "baz"}}`)
+	vars := map[string]apiextensionsv1.JSON{
+		"sampleVar": {Raw: sampleValue},
+	}
+	parsed, found, err := variables.Get[string](vars, "sampleVar", "foo", "bar")
+	g.Expect(err).NotTo(HaveOccurred())
+	g.Expect(found).To(BeTrue())
+	g.Expect(parsed).To(Equal("baz"))
+}
+
+func TestGet_InvalidNestedFieldType(t *testing.T) {
+	g := NewWithT(t)
+
+	sampleValue := []byte(`{"foo": {"bar": "baz"}}`)
+	vars := map[string]apiextensionsv1.JSON{
+		"sampleVar": {Raw: sampleValue},
+	}
+	_, _, err := variables.Get[int](vars, "sampleVar", "foo", "bar")
+	g.Expect(err).To(HaveOccurred())
+}
+
+func TestGet_MissingNestedField(t *testing.T) {
+	g := NewWithT(t)
+
+	sampleValue := []byte(`{"foo": {"bar": "baz"}}`)
+	vars := map[string]apiextensionsv1.JSON{
+		"sampleVar": {Raw: sampleValue},
+	}
+	_, found, err := variables.Get[string](vars, "sampleVar", "foo", "nonexistent")
+	g.Expect(err).NotTo(HaveOccurred())
+	g.Expect(found).To(BeFalse())
+}