Centralize daypart key canonicalization

internal/forecast/derive_test.go

@@ -658,3 +658,26 @@ func assertTimedValueClose(t *testing.T, name string, got *TimedValue, want floa
 		t.Fatalf("%s = %#v, want %v", name, got, want)
 	}
 }
+
+func TestCanonicalDaypartKey(t *testing.T) {
+	for _, tt := range []struct {
+		name  string
+		value string
+		want  string
+	}{
+		{name: "blank", value: " \t ", want: ""},
+		{name: "casing", value: "MORNING", want: "morning"},
+		{name: "punctuation runs", value: " Morning--Commute / School ", want: "morning_commute_school"},
+		{name: "Unicode", value: "Déjà Vu", want: "déjà_vu"},
+		{name: "letters and digits", value: "Day 1 Outlook", want: "day_1_outlook"},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := CanonicalDaypartKey(tt.value); got != tt.want {
+				t.Fatalf("CanonicalDaypartKey(%q) = %q, want %q", tt.value, got, tt.want)
+			}
+		})
+	}
+	if CanonicalDaypartKey("Morning commute") != CanonicalDaypartKey("MORNING--COMMUTE") {
+		t.Fatal("equivalent configured names must have the same canonical daypart key")
+	}
+}