1 files changed, 23 insertions, 0 deletions
diff --git a/web/src/components/grid/selection.ts b/web/src/components/grid/selection.ts
new file mode 100644
index 0000000..a24bbf5
--- /dev/null
+++ b/web/src/components/grid/selection.ts
@@ -0,0 +1,23 @@
+import { CellRef, cellRefEquals } from "../../types";
+
+export type CellRange = [start: CellRef, end: CellRef];
+
+export interface GridSelection {
+  activeCellRef: CellRef;
+  range?: CellRange;
+}
+
+export function extendSelection(
+  selection: GridSelection | undefined,
+  cellRef: CellRef,
+): GridSelection {
+  if (!selection || cellRefEquals(selection.activeCellRef, cellRef)) {
+    return { activeCellRef: cellRef };
+  }
+
+  if (selection.range) {
+    return { ...selection, range: [selection.range[0], cellRef] };
+  }
+
+  return { ...selection, range: [selection.activeCellRef, cellRef] };
+}