Add internal/kctl and internal/config packages with unit tests

internal/kctl/labels.go

@@ -0,0 +1,33 @@
+package kctl
+
+import "sort"
+
+// DistinctLabelValues returns the sorted, unique, non-empty values of the
+// given label key across a set of namespaces (name -> labels map).
+func DistinctLabelValues(namespaces map[string]map[string]string, labelKey string) []string {
+	seen := map[string]bool{}
+	for _, labels := range namespaces {
+		if v, ok := labels[labelKey]; ok && v != "" {
+			seen[v] = true
+		}
+	}
+	result := make([]string, 0, len(seen))
+	for v := range seen {
+		result = append(result, v)
+	}
+	sort.Strings(result)
+	return result
+}
+
+// NamespacesForLabelValue returns the sorted namespace names whose labelKey
+// matches the given value exactly.
+func NamespacesForLabelValue(namespaces map[string]map[string]string, labelKey, value string) []string {
+	result := make([]string, 0)
+	for ns, labels := range namespaces {
+		if labels[labelKey] == value {
+			result = append(result, ns)
+		}
+	}
+	sort.Strings(result)
+	return result
+}