Scroll selection anchor into view when adding new comment (#21328)

* Scroll selection anchor into view when adding new comment

* check if cursor is near viewport edge

GitOrigin-RevId: 57d4195f7ce1513a56249365b45b3959b4ea813f

services/web/frontend/js/features/source-editor/utils/is-cursor-near-edge.ts

@@ -0,0 +1,23 @@
+import { EditorView } from '@codemirror/view'
+
+const TOP_EDGE_THRESHOLD = 100
+const BOTTOM_EDGE_THRESHOLD = 200
+
+export function isCursorNearViewportEdge(view: EditorView, pos: number) {
+  const cursorCoords = view.coordsAtPos(pos)
+
+  if (!cursorCoords) {
+    return false
+  }
+
+  const scrollInfo = view.scrollDOM.getBoundingClientRect()
+
+  // check if the cursor is near the top of the viewport
+  if (Math.abs(cursorCoords.bottom - scrollInfo.top) <= TOP_EDGE_THRESHOLD) {
+    return true
+  }
+  // check if the cursor is near the bottom of the viewport
+  const viewportHeight = view.scrollDOM.clientHeight
+  const viewportBottom = scrollInfo.top + viewportHeight
+  return Math.abs(cursorCoords.bottom - viewportBottom) <= BOTTOM_EDGE_THRESHOLD
+}