feat(app): better diff/code comments (#14621)

Co-authored-by: adamelmore <2363879+adamdottv@users.noreply.github.com>
Co-authored-by: David Hill <iamdavidhill@gmail.com>

packages/ui/src/pierre/file-selection.ts

@@ -0,0 +1,85 @@
+import { type SelectedLineRange } from "@pierre/diffs"
+import { toRange } from "./selection-bridge"
+
+export function findElement(node: Node | null): HTMLElement | undefined {
+  if (!node) return
+  if (node instanceof HTMLElement) return node
+  return node.parentElement ?? undefined
+}
+
+export function findFileLineNumber(node: Node | null): number | undefined {
+  const el = findElement(node)
+  if (!el) return
+
+  const line = el.closest("[data-line]")
+  if (!(line instanceof HTMLElement)) return
+
+  const value = parseInt(line.dataset.line ?? "", 10)
+  if (Number.isNaN(value)) return
+  return value
+}
+
+export function findDiffLineNumber(node: Node | null): number | undefined {
+  const el = findElement(node)
+  if (!el) return
+
+  const line = el.closest("[data-line], [data-alt-line]")
+  if (!(line instanceof HTMLElement)) return
+
+  const primary = parseInt(line.dataset.line ?? "", 10)
+  if (!Number.isNaN(primary)) return primary
+
+  const alt = parseInt(line.dataset.altLine ?? "", 10)
+  if (!Number.isNaN(alt)) return alt
+}
+
+export function findCodeSelectionSide(node: Node | null): SelectedLineRange["side"] {
+  const el = findElement(node)
+  if (!el) return
+
+  const code = el.closest("[data-code]")
+  if (!(code instanceof HTMLElement)) return
+  if (code.hasAttribute("data-deletions")) return "deletions"
+  return "additions"
+}
+
+export function readShadowLineSelection(opts: {
+  root: ShadowRoot
+  lineForNode: (node: Node | null) => number | undefined
+  sideForNode?: (node: Node | null) => SelectedLineRange["side"]
+  preserveTextSelection?: boolean
+}) {
+  const selection =
+    (opts.root as unknown as { getSelection?: () => Selection | null }).getSelection?.() ?? window.getSelection()
+  if (!selection || selection.isCollapsed) return
+
+  const domRange =
+    (
+      selection as unknown as {
+        getComposedRanges?: (options?: { shadowRoots?: ShadowRoot[] }) => StaticRange[]
+      }
+    ).getComposedRanges?.({ shadowRoots: [opts.root] })?.[0] ??
+    (selection.rangeCount > 0 ? selection.getRangeAt(0) : undefined)
+
+  const startNode = domRange?.startContainer ?? selection.anchorNode
+  const endNode = domRange?.endContainer ?? selection.focusNode
+  if (!startNode || !endNode) return
+  if (!opts.root.contains(startNode) || !opts.root.contains(endNode)) return
+
+  const start = opts.lineForNode(startNode)
+  const end = opts.lineForNode(endNode)
+  if (start === undefined || end === undefined) return
+
+  const startSide = opts.sideForNode?.(startNode)
+  const endSide = opts.sideForNode?.(endNode)
+  const side = startSide ?? endSide
+
+  const range: SelectedLineRange = { start, end }
+  if (side) range.side = side
+  if (endSide && side && endSide !== side) range.endSide = endSide
+
+  return {
+    range,
+    text: opts.preserveTextSelection && domRange ? toRange(domRange).cloneRange() : undefined,
+  }
+}