Add root namespace method to Key (#208)

Author: dennis-tra

key.go

@@ -150,6 +150,19 @@ func (k Key) BaseNamespace() string {
 	return n[len(n)-1]
 }
 
+// RootNamespace returns the "root" namespace of this key
+//
+//	NewKey("/Comedy/MontyPython/Actor:JohnCleese").RootNamespace()
+//	"Comedy"
+//	NewKey("/").RootNamespace()
+//	""
+//	NewKey("/Comedy:MontyPython").RootNamespace()
+//	"Comedy:MontyPython"
+func (k Key) RootNamespace() string {
+	n := k.Namespaces()
+	return n[0]
+}
+
 // Type returns the "type" of this key (value of last namespace).
 //
 //	NewKey("/Comedy/MontyPython/Actor:JohnCleese").Type()

key_test.go

@@ -204,3 +204,23 @@ func TestKeyUnmarshalJSON(t *testing.T) {
 		}
 	}
 }
+
+func TestKey_RootNamespace(t *testing.T) {
+	tests := []struct {
+		name string
+		key  string
+		want string
+	}{
+		{name: "empty path", key: "/", want: ""},
+		{name: "single namespace", key: "/Comedy", want: "Comedy"},
+		{name: "long path", key: "/Comedy/MontyPython/Actor:JohnCleese", want: "Comedy"},
+		{name: "root + type", key: "/Comedy:MontyPython", want: "Comedy:MontyPython"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := RawKey(tt.key).RootNamespace(); got != tt.want {
+				t.Errorf("RootNamespace() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}