1 files changed, 52 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}
+}