mobile: add PartLabels so the app stops hardcoding part IDs

2 files changed, 76 insertions, 0 deletions

diff --git a/mobile/mobile.go b/mobile/mobile.go
index e79e748..d863463 100644
--- a/mobile/mobile.go
+++ b/mobile/mobile.go
@@ -184,6 +184,37 @@ func Days(start string, count int, form, lang string) string {
 	return string(b)
 }
 
+// partLabel is one section's machine ID and its human label.
+type partLabel struct {
+	Part  string `json:"part"`
+	Label string `json:"label"`
+}
+
+// PartLabels returns the form's section IDs and their labels in lang, in display
+// order, as a JSON array. The app builds its reading filters from this instead
+// of hardcoding part IDs -- which is how it came to ship seven 1962 checkboxes
+// the engine never emits.
+//
+// An array, not an object: JSON object key order is not guaranteed and the app
+// renders these in order.
+func PartLabels(form, lang string) string {
+	ids := readings.PartIDs(lectByForm(form))
+	ui := i18n.Get(lang)
+	out := make([]partLabel, 0, len(ids))
+	for _, id := range ids {
+		label := ui.PartLabel[id]
+		if label == "" {
+			label = id
+		}
+		out = append(out, partLabel{Part: id, Label: label})
+	}
+	b, err := json.Marshal(out)
+	if err != nil {
+		return "[]"
+	}
+	return string(b)
+}
+
 // Ping is a trivial JNI smoke test: it returns "pong" so the app can confirm the
 // native engine loaded before issuing a real query.
 func Ping() string { return "pong" }
diff --git a/mobile/mobile_test.go b/mobile/mobile_test.go
index 57e835a..1a115f3 100644
--- a/mobile/mobile_test.go
+++ b/mobile/mobile_test.go
@@ -123,3 +123,48 @@ func BenchmarkDaysWeek(b *testing.B) {
 		Days("2026-07-27", 7, "of", "pl")
 	}
 }
+
+// This is the assertion that would have caught the app's dead 1962 checkboxes:
+// it listed nine part IDs where the engine emits two.
+func TestPartLabelsMatchesWhatTheEngineEmits(t *testing.T) {
+	var ef []map[string]any
+	if err := json.Unmarshal([]byte(PartLabels("ef", "pl")), &ef); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+	if len(ef) != 2 {
+		t.Fatalf("ef: got %d labels, want 2: %v", len(ef), ef)
+	}
+	if ef[0]["part"] != "epistola" || ef[0]["label"] != "Lekcja" {
+		t.Errorf("ef[0] = %v, want epistola/Lekcja", ef[0])
+	}
+	if ef[1]["part"] != "evangelium" || ef[1]["label"] != "Ewangelia" {
+		t.Errorf("ef[1] = %v, want evangelium/Ewangelia", ef[1])
+	}
+
+	var of []map[string]any
+	if err := json.Unmarshal([]byte(PartLabels("of", "pl")), &of); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+	if len(of) != 5 {
+		t.Fatalf("of: got %d labels, want 5: %v", len(of), of)
+	}
+	// aklamacja was missing from the app's hardcoded list.
+	var seen []string
+	for _, e := range of {
+		seen = append(seen, e["part"].(string))
+	}
+	want := []string{"pierwsze_czytanie", "psalm", "drugie_czytanie", "aklamacja", "ewangelia"}
+	for i := range want {
+		if seen[i] != want[i] {
+			t.Errorf("of order = %v, want %v", seen, want)
+			break
+		}
+	}
+}
+
+func TestPartLabelsUnknownForm(t *testing.T) {
+	// An unknown form is treated as the modern one, matching lectByForm.
+	if got := PartLabels("nonsense", "en"); got == "[]" {
+		t.Error("unknown form should fall back to the modern lectionary, not empty")
+	}
+}