pkg/apis/nfd: helpers for handling templates in Rule names

Implement a private helper type (nameTemplateHelper) for handling
(executing and caching) of templated names. DeepCopy methods are
manually implemented as controller-gen is not able to help with that.

pkg/apis/nfd/v1alpha1/rule.go

@@ -17,7 +17,9 @@ limitations under the License.
 package v1alpha1
 
 import (
+	"bytes"
 	"strings"
+	"text/template"
 
 	"fmt"
 
@@ -98,3 +100,64 @@ func (m *FeatureMatcher) match(features map[string]*feature.DomainFeatures) (boo
 	}
 	return true, nil
 }
+
+type templateHelper struct {
+	template *template.Template
+}
+
+func newTemplateHelper(name string) (*templateHelper, error) {
+	tmpl, err := template.New("").Option("missingkey=error").Parse(name)
+	if err != nil {
+		return nil, fmt.Errorf("invalid template: %w", err)
+	}
+	return &templateHelper{template: tmpl}, nil
+}
+
+// DeepCopy is a stub to augment the auto-generated code
+func (in *templateHelper) DeepCopy() *templateHelper {
+	if in == nil {
+		return nil
+	}
+	out := new(templateHelper)
+	in.DeepCopyInto(out)
+	return out
+}
+
+// DeepCopyInto is a stub to augment the auto-generated code
+func (in *templateHelper) DeepCopyInto(out *templateHelper) {
+	// HACK: just re-use the template
+	out.template = in.template
+}
+
+func (h *templateHelper) execute(data interface{}) (string, error) {
+	var tmp bytes.Buffer
+	if err := h.template.Execute(&tmp, data); err != nil {
+		return "", err
+	}
+	return tmp.String(), nil
+}
+
+// expandMap is a helper for expanding a template in to a map of strings. Data
+// after executing the template is expexted to be key=value pairs separated by
+// newlines.
+func (h *templateHelper) expandMap(data interface{}) (map[string]string, error) {
+	expanded, err := h.execute(data)
+	if err != nil {
+		return nil, err
+	}
+
+	// Split out individual key-value pairs
+	out := make(map[string]string)
+	for _, item := range strings.Split(expanded, "\n") {
+		// Remove leading/trailing whitespace and skip empty lines
+		if trimmed := strings.TrimSpace(item); trimmed != "" {
+			split := strings.SplitN(trimmed, "=", 2)
+			if len(split) == 1 {
+				out[split[0]] = ""
+			} else {
+				out[split[0]] = split[1]
+			}
+		}
+	}
+	return out, nil
+}