wip(ui): diff virtualization (#12693)

packages/ui/src/pierre/virtualizer.ts

@@ -0,0 +1,76 @@
+import { type VirtualFileMetrics, Virtualizer } from "@pierre/diffs"
+
+type Target = {
+  key: Document | HTMLElement
+  root: Document | HTMLElement
+  content: HTMLElement | undefined
+}
+
+type Entry = {
+  virtualizer: Virtualizer
+  refs: number
+}
+
+const cache = new WeakMap<Document | HTMLElement, Entry>()
+
+export const virtualMetrics: Partial<VirtualFileMetrics> = {
+  lineHeight: 24,
+  hunkSeparatorHeight: 24,
+  fileGap: 0,
+}
+
+function target(container: HTMLElement): Target | undefined {
+  if (typeof document === "undefined") return
+
+  const root = container.closest("[data-component='session-review']")
+  if (root instanceof HTMLElement) {
+    const content = root.querySelector("[data-slot='session-review-container']")
+    return {
+      key: root,
+      root,
+      content: content instanceof HTMLElement ? content : undefined,
+    }
+  }
+
+  return {
+    key: document,
+    root: document,
+    content: undefined,
+  }
+}
+
+export function acquireVirtualizer(container: HTMLElement) {
+  const resolved = target(container)
+  if (!resolved) return
+
+  let entry = cache.get(resolved.key)
+  if (!entry) {
+    const virtualizer = new Virtualizer()
+    virtualizer.setup(resolved.root, resolved.content)
+    entry = {
+      virtualizer,
+      refs: 0,
+    }
+    cache.set(resolved.key, entry)
+  }
+
+  entry.refs += 1
+  let done = false
+
+  return {
+    virtualizer: entry.virtualizer,
+    release() {
+      if (done) return
+      done = true
+
+      const current = cache.get(resolved.key)
+      if (!current) return
+
+      current.refs -= 1
+      if (current.refs > 0) return
+
+      current.virtualizer.cleanUp()
+      cache.delete(resolved.key)
+    },
+  }
+}