fix(patches): handle patches that can add optional keys

cluster and subnet are optional, when failure domains are present
we shouldn't generate nutanixmachinetemplate with placeholder values.
when failure domains are not present, we should be able to inject
actual values for cluster and subnet.

Author: thunderboltsid

pkg/handlers/nutanix/mutation/machinedetails/inject.go

@@ -6,6 +6,7 @@ package machinedetails
 import (
 	"context"
 	"errors"
+	"fmt"
 	"slices"
 
 	apiextensionsv1 "k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1"
@@ -88,15 +89,29 @@ func (h *nutanixMachineDetailsPatchHandler) Mutate(
 		&holderRef,
 		h.patchSelector,
 		log,
-		func(obj *capxv1.NutanixMachineTemplate) error {
+		func(machineTemplate *capxv1.NutanixMachineTemplate) error {
+			// First, ensure the required fields exist in the original unstructured object
+			// if they will be set by the mutation
+			if nutanixMachineDetailsVar.Cluster != nil {
+				if err := ensureClusterFieldExists(obj); err != nil {
+					return fmt.Errorf("failed to ensure cluster field exists: %w", err)
+				}
+			}
+			if len(nutanixMachineDetailsVar.Subnets) > 0 {
+				if err := ensureSubnetFieldExists(obj); err != nil {
+					return fmt.Errorf("failed to ensure subnet field exists: %w", err)
+				}
+			}
+
 			log.WithValues(
-				"patchedObjectKind", obj.GetObjectKind().GroupVersionKind().String(),
-				"patchedObjectName", client.ObjectKeyFromObject(obj),
-			).Info("setting Nutanix machine details in worker NutanixMachineTemplate spec")
+				"patchedObjectKind", machineTemplate.GetObjectKind().GroupVersionKind().String(),
+				"patchedObjectName", client.ObjectKeyFromObject(machineTemplate),
+			).Info("setting Nutanix machine details in NutanixMachineTemplate spec")
 
-			spec := obj.Spec.Template.Spec
+			spec := machineTemplate.Spec.Template.Spec
 
 			spec.BootType = nutanixMachineDetailsVar.BootType
+
 			if nutanixMachineDetailsVar.Cluster != nil {
 				spec.Cluster = *nutanixMachineDetailsVar.Cluster
 			}
@@ -125,8 +140,55 @@ func (h *nutanixMachineDetailsPatchHandler) Mutate(
 			spec.GPUs = slices.Clone(nutanixMachineDetailsVar.GPUs)
 			spec.Project = nutanixMachineDetailsVar.Project.DeepCopy()
 
-			obj.Spec.Template.Spec = spec
+			machineTemplate.Spec.Template.Spec = spec
+			log.WithValues(
+				"patchedObjectKind", machineTemplate.GetObjectKind().GroupVersionKind().String(),
+				"patchedObjectName", client.ObjectKeyFromObject(machineTemplate),
+				"patchedObject", machineTemplate,
+			).V(5).Info("Patched Nutanix machine details in NutanixMachineTemplate spec")
 			return nil
 		},
 	)
 }
+
+// ensureClusterFieldExists ensures the cluster field exists in the unstructured object
+func ensureClusterFieldExists(obj *unstructured.Unstructured) error {
+	clusterPath := []string{"spec", "template", "spec", "cluster"}
+	if !hasNestedField(obj.Object, clusterPath) {
+		// Add empty cluster field structure
+		return unstructured.SetNestedMap(obj.Object, map[string]any{
+			"type": "",
+		}, clusterPath...)
+	}
+	return nil
+}
+
+// ensureSubnetFieldExists ensures the subnet field exists in the unstructured object
+func ensureSubnetFieldExists(obj *unstructured.Unstructured) error {
+	subnetPath := []string{"spec", "template", "spec", "subnet"}
+	if !hasNestedField(obj.Object, subnetPath) {
+		// Add empty subnet field
+		return unstructured.SetNestedSlice(obj.Object, []any{}, subnetPath...)
+	}
+	return nil
+}
+
+// hasNestedField checks if a nested field exists in an unstructured object
+func hasNestedField(obj map[string]interface{}, path []string) bool {
+	current := obj
+	for _, key := range path {
+		if current == nil {
+			return false
+		}
+		val, exists := current[key]
+		if !exists {
+			return false
+		}
+		if next, ok := val.(map[string]interface{}); ok {
+			current = next
+		} else {
+			return len(path) == 1
+		}
+	}
+	return true
+}