Reuse document indexes in D&D normalization

internal/modules/dnd/chunk/scenes/chunker.go

@@ -156,28 +156,25 @@ func planFromResponse(doc *source.SourceDocument, response chunkResponse) (sourc
 		return source.ChunkPlan{}, fmt.Errorf("scenes must not be empty")
 	}
 
-	unitIndexes := make(map[int]int, len(doc.Units))
-	for i, unit := range doc.Units {
-		unitIndexes[unit.ID] = i
-	}
+	index := source.NewDocumentIndex(doc)
 
 	ranges := make([]source.ChunkRange, 0, len(response.Scenes))
 	previousEnd := -1
 	for i, scene := range response.Scenes {
-		startUnitID, err := shared.ResolveUnitID(doc, "start_unit_id", scene.StartUnitID)
+		startUnitID, err := shared.ResolveUnitID(index, "start_unit_id", scene.StartUnitID)
 		if err != nil {
 			return source.ChunkPlan{}, fmt.Errorf("scene[%d] %w", i, err)
 		}
-		endUnitID, err := shared.ResolveUnitID(doc, "end_unit_id", scene.EndUnitID)
+		endUnitID, err := shared.ResolveUnitID(index, "end_unit_id", scene.EndUnitID)
 		if err != nil {
 			return source.ChunkPlan{}, fmt.Errorf("scene[%d] %w", i, err)
 		}
 
-		startIndex, ok := unitIndexes[startUnitID]
+		startIndex, ok := index.Position(startUnitID)
 		if !ok {
 			return source.ChunkPlan{}, fmt.Errorf("scene[%d] start_unit_id %d was not found", i, startUnitID)
 		}
-		endIndex, ok := unitIndexes[endUnitID]
+		endIndex, ok := index.Position(endUnitID)
 		if !ok {
 			return source.ChunkPlan{}, fmt.Errorf("scene[%d] end_unit_id %d was not found", i, endUnitID)
 		}