snapshot of https://github.com/shadcn-ui/ui.git (main, 2026-09-15; blobs > 131072B omitted)

packages/react/src/message-scroller/stores.ts

@@ -0,0 +1,97 @@
+import { EMPTY_MESSAGE_SCROLLER_VISIBILITY_STATE } from "./types"
+import type {
+  MessageScrollerScrollable,
+  MessageScrollerStore,
+  MessageScrollerVisibilityState,
+  MessageScrollerVisibilityStore,
+} from "./types"
+
+// Generic useSyncExternalStore backing: a stable snapshot (referentially equal
+// while isEqual holds, so subscribers only re-render on real transitions) plus
+// optional reference-counting via the subscribe-time lifecycle callbacks.
+function createExternalStore<T>(
+  initialSnapshot: T,
+  isEqual: (a: T, b: T) => boolean
+) {
+  let snapshot = initialSnapshot
+  const listeners = new Set<() => void>()
+
+  return {
+    getSnapshot: () => snapshot,
+    hasListeners: () => listeners.size > 0,
+    setSnapshot: (nextSnapshot: T) => {
+      if (isEqual(snapshot, nextSnapshot)) {
+        return
+      }
+
+      snapshot = nextSnapshot
+      listeners.forEach((listener) => listener())
+    },
+    subscribe: (
+      listener: () => void,
+      onFirstSubscribe?: () => void,
+      onLastUnsubscribe?: () => void
+    ) => {
+      const wasEmpty = listeners.size === 0
+
+      listeners.add(listener)
+
+      if (wasEmpty) {
+        onFirstSubscribe?.()
+      }
+
+      return () => {
+        listeners.delete(listener)
+
+        if (listeners.size === 0) {
+          onLastUnsubscribe?.()
+        }
+      }
+    },
+  }
+}
+
+function createMessageScrollerStore<T>(
+  initialSnapshot: T,
+  isEqual: (a: T, b: T) => boolean
+): MessageScrollerStore<T> {
+  return createExternalStore(initialSnapshot, isEqual)
+}
+
+function createMessageScrollerVisibilityStore(): MessageScrollerVisibilityStore {
+  return createExternalStore(
+    EMPTY_MESSAGE_SCROLLER_VISIBILITY_STATE,
+    areVisibilityStatesEqual
+  )
+}
+
+function areScrollStatesEqual(
+  current: MessageScrollerScrollable,
+  next: MessageScrollerScrollable
+) {
+  return current.start === next.start && current.end === next.end
+}
+
+function areVisibilityStatesEqual(
+  current: MessageScrollerVisibilityState,
+  next: MessageScrollerVisibilityState
+) {
+  if (current.currentAnchorId !== next.currentAnchorId) {
+    return false
+  }
+
+  if (current.visibleMessageIds.length !== next.visibleMessageIds.length) {
+    return false
+  }
+
+  return current.visibleMessageIds.every(
+    (messageId, index) => messageId === next.visibleMessageIds[index]
+  )
+}
+
+export {
+  areScrollStatesEqual,
+  areVisibilityStatesEqual,
+  createMessageScrollerStore,
+  createMessageScrollerVisibilityStore,
+}