feat(calendar): ordered-stack layer merge (override/suppress/add)

2 files changed, 86 insertions, 0 deletions

diff --git a/internal/calendar/merge.go b/internal/calendar/merge.go
new file mode 100644
index 0000000..ce8fe8f
--- /dev/null
+++ b/internal/calendar/merge.go
@@ -0,0 +1,52 @@
+package calendar
+
+// mergeLayers folds an ordered layer stack into one raw celebration set. Later
+// layers override earlier ones field-by-field; a slug with Fields["suppress"]
+// == "true" is removed; variant sub-sections merge per variant.
+func mergeLayers(layers []Layer) map[string]RawCelebration {
+	out := map[string]RawCelebration{}
+	for _, layer := range layers {
+		for slug, rc := range layer.Cels {
+			if rc.Fields["suppress"] == "true" {
+				delete(out, slug)
+				continue
+			}
+			cur, ok := out[slug]
+			if !ok {
+				cur = RawCelebration{Fields: map[string]string{}, Variants: map[string]map[string]string{}}
+			} else {
+				cur = cloneRaw(cur)
+			}
+			for k, v := range rc.Fields {
+				cur.Fields[k] = v
+			}
+			for variant, fields := range rc.Variants {
+				if cur.Variants[variant] == nil {
+					cur.Variants[variant] = map[string]string{}
+				}
+				for k, v := range fields {
+					cur.Variants[variant][k] = v
+				}
+			}
+			cur.Fields["layer"] = layer.ID // provenance: last writer
+			out[slug] = cur
+		}
+	}
+	return out
+}
+
+func cloneRaw(rc RawCelebration) RawCelebration {
+	nf := make(map[string]string, len(rc.Fields))
+	for k, v := range rc.Fields {
+		nf[k] = v
+	}
+	nv := make(map[string]map[string]string, len(rc.Variants))
+	for variant, fields := range rc.Variants {
+		m := make(map[string]string, len(fields))
+		for k, v := range fields {
+			m[k] = v
+		}
+		nv[variant] = m
+	}
+	return RawCelebration{Fields: nf, Variants: nv}
+}
diff --git a/internal/calendar/merge_test.go b/internal/calendar/merge_test.go
new file mode 100644
index 0000000..168c56f
--- /dev/null
+++ b/internal/calendar/merge_test.go
@@ -0,0 +1,34 @@
+package calendar
+
+import "testing"
+
+func raw(fields map[string]string) RawCelebration {
+	return RawCelebration{Fields: fields, Variants: map[string]map[string]string{}}
+}
+
+func TestMergeLayers(t *testing.T) {
+	base := Layer{ID: "universal", Cels: map[string]RawCelebration{
+		"assumption": raw(map[string]string{"rank": "solemnity", "colour": "white", "name.en": "Assumption"}),
+		"st-x":       raw(map[string]string{"rank": "optional", "date": "01-02"}),
+		"drop-me":    raw(map[string]string{"rank": "memorial", "date": "03-03"}),
+	}}
+	local := Layer{ID: "krakow", Cels: map[string]RawCelebration{
+		"st-x":    raw(map[string]string{"rank": "feast"}),                      // elevate; keep date
+		"drop-me": raw(map[string]string{"suppress": "true"}),                   // remove
+		"st-new":  raw(map[string]string{"rank": "solemnity", "date": "05-08"}), // add
+	}}
+	got := mergeLayers([]Layer{base, local})
+
+	if got["st-x"].Fields["rank"] != "feast" || got["st-x"].Fields["date"] != "01-02" {
+		t.Errorf("st-x merge = %+v", got["st-x"].Fields)
+	}
+	if _, ok := got["drop-me"]; ok {
+		t.Error("drop-me should be suppressed")
+	}
+	if got["st-new"].Fields["date"] != "05-08" {
+		t.Error("st-new should be added")
+	}
+	if got["assumption"].Fields["name.en"] != "Assumption" {
+		t.Error("untouched base entry lost")
+	}
+}