Index mapping assembly for composition and overlays

internal/engine/mapping_index.go

@@ -0,0 +1,37 @@
+package engine
+
+import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+
+// mappingIndex keeps ordered document entries and their lookup positions in
+// sync while one composition or overlay is assembled.
+type mappingIndex struct {
+	byNode map[*document.Node]map[string]int
+}
+
+func (m *mappingIndex) entries(node *document.Node) map[string]int {
+	if m.byNode == nil {
+		m.byNode = make(map[*document.Node]map[string]int)
+	}
+	if entries, ok := m.byNode[node]; ok {
+		return entries
+	}
+	entries := make(map[string]int, len(node.Mapping))
+	for index, entry := range node.Mapping {
+		entries[entry.Key] = index
+	}
+	m.byNode[node] = entries
+	return entries
+}
+
+func (m *mappingIndex) find(node *document.Node, key string) int {
+	if index, ok := m.entries(node)[key]; ok {
+		return index
+	}
+	return -1
+}
+
+func (m *mappingIndex) append(node *document.Node, entry document.Entry) {
+	entries := m.entries(node)
+	entries[entry.Key] = len(node.Mapping)
+	node.Mapping = append(node.Mapping, entry)
+}