feat(json-crdt-extensions): 🎸 improve .points() iteration at offset

Author: streamich

src/json-crdt-extensions/peritext/overlay/Overlay.ts

@@ -203,7 +203,7 @@ export class Overlay<T = string> implements Printable, Stateful {
       return () => (closed ? u : (closed = true, [u, u]));
     }
     let p1: OverlayPoint<T> | undefined;
-    let p2: OverlayPoint<T> | undefined;
+    let p2: OverlayPoint<T> | undefined = after;
     const iterator = this.points0(after);
     return () => {
       const next = iterator();

src/json-crdt-extensions/peritext/overlay/__tests__/Overlay.pairs.spec.ts

@@ -5,7 +5,7 @@ import {MarkerOverlayPoint} from '../MarkerOverlayPoint';
 import {OverlayPoint} from '../OverlayPoint';
 
 const runPairsTests = (setup: () => Kit) => {
-  describe('.pairs()', () => {
+  describe('.pairs() full range', () => {
     test('returns [undef, undef] single pair for an empty overlay', () => {
       const {peritext} = setup();
       const overlay = peritext.overlay;
@@ -133,6 +133,34 @@ const runPairsTests = (setup: () => Kit) => {
       expect(p3.refs.length).toBe(2);
     });
   });
+
+  describe('.pairs() at offset', () => {
+    test('in empty overlay, after caret returns the last edge', () => {
+      const {peritext} = setup();
+      const overlay = peritext.overlay;
+      peritext.editor.cursor.setAt(5);
+      overlay.refresh();
+      const first = overlay.first()!;
+      const pairs = [...overlay.pairs(first)];
+      expect(pairs).toEqual([
+        [first, undefined],
+      ]);
+    });
+
+    test('in empty overlay, after selection start returns the selection and the edge', () => {
+      const {peritext} = setup();
+      const overlay = peritext.overlay;
+      peritext.editor.cursor.setAt(2, 4);
+      overlay.refresh();
+      const p1 = overlay.first()!;
+      const p2 = next(p1)!;
+      const list = [...overlay.pairs(p1)];
+      expect(list).toEqual([
+        [p1, p2],
+        [p2, undefined],
+      ]);
+    });
+  });
 };
 
 describe('numbers "0123456789", no edits', () => {