Reuse indexes for D&D citation validation

internal/modules/dnd/shared/citations.go

@@ -7,27 +7,37 @@ import (
 	"gitea.maximumdirect.net/eric/notarius/internal/core/source"
 )
 
+// CitationResolver resolves cited ranges against one source document.
+type CitationResolver struct {
+	doc   *source.SourceDocument
+	index source.DocumentIndex
+}
+
+// NewCitationResolver prepares citation resolution for doc.
+func NewCitationResolver(doc *source.SourceDocument) (*CitationResolver, error) {
+	if doc == nil {
+		return nil, fmt.Errorf("source document must not be nil")
+	}
+	return &CitationResolver{doc: doc, index: source.NewDocumentIndex(doc)}, nil
+}
+
 // CitedText resolves cited source ranges in document order, including each
 // source unit once, and joins the resulting text with newlines.
-func CitedText(doc *source.SourceDocument, refs []source.SourceRef) (string, error) {
-	if doc == nil {
-		return "", fmt.Errorf("source document must not be nil")
-	}
-
-	included := make([]bool, len(doc.Units))
+func (r *CitationResolver) CitedText(refs []source.SourceRef) (string, error) {
+	included := make([]bool, len(r.doc.Units))
 	for _, ref := range refs {
-		if err := source.ValidateRef(doc, ref); err != nil {
+		if err := r.index.ValidateRef(ref); err != nil {
 			return "", fmt.Errorf("resolve cited source range: %w", err)
 		}
-		start, _ := source.UnitIndex(doc, ref.StartUnitID)
-		end, _ := source.UnitIndex(doc, ref.EndUnitID)
+		start, _ := r.index.Position(ref.StartUnitID)
+		end, _ := r.index.Position(ref.EndUnitID)
 		for index := start; index <= end; index++ {
 			included[index] = true
 		}
 	}
 
-	parts := make([]string, 0, len(doc.Units))
-	for index, unit := range doc.Units {
+	parts := make([]string, 0, len(r.doc.Units))
+	for index, unit := range r.doc.Units {
 		if included[index] {
 			parts = append(parts, unit.Text)
 		}