feat(thread-stats): show board page number in post stats via cache-first lookup

src/hooks/use-post-page-number.ts

@@ -0,0 +1,55 @@
+import { useMemo } from 'react';
+import { useFeed } from '@plebbit/plebbit-react-hooks';
+import useFeedsStore from '@plebbit/plebbit-react-hooks/dist/stores/feeds';
+import { useDirectoryByAddress } from './use-directories';
+import { useBoardFeedPageSize } from './use-board-feed-page-size';
+import { findPostPageInFeed, findPostPageInLoadedBoardFeeds, type FeedsOptionsLike, type LoadedFeedsLike } from '../lib/utils/post-page-resolution';
+
+export interface UsePostPageNumberOptions {
+  subplebbitAddress: string | undefined;
+  postCid: string | undefined;
+  /** When false, page segment is excluded (e.g. pending-post view). When true, resolve and show page. */
+  enabled?: boolean;
+}
+
+/**
+ * Resolve the board pagination page (1-based) for a post in a thread view.
+ * Uses cache-first lookup from feeds store, then preloads via useFeed if miss.
+ * Preload depth is capped to board pagination window (10 pages via paginationFeedPostsPerPage).
+ *
+ * @returns 1-based page number, or undefined when unresolved (render as "?")
+ */
+export function usePostPageNumber({ subplebbitAddress, postCid, enabled = true }: UsePostPageNumberOptions): number | undefined {
+  const community = useDirectoryByAddress(subplebbitAddress);
+  const { guiPostsPerPage, paginationFeedPostsPerPage } = useBoardFeedPageSize(community);
+
+  const canResolve = Boolean(enabled && subplebbitAddress && postCid && guiPostsPerPage > 0);
+
+  // Cache-first: selector returns only computed page to minimize rerenders
+  const cachedPage = useFeedsStore((state) => {
+    if (!canResolve) return undefined;
+    return findPostPageInLoadedBoardFeeds(state.feedsOptions as FeedsOptionsLike, state.loadedFeeds as LoadedFeedsLike, subplebbitAddress!, postCid!, guiPostsPerPage);
+  });
+
+  // Preload when cache miss and enabled (10 GUI pages)
+  const preloadOptions = useMemo(
+    () =>
+      canResolve
+        ? {
+            subplebbitAddresses: [subplebbitAddress!],
+            sortType: 'active' as const,
+            postsPerPage: paginationFeedPostsPerPage,
+          }
+        : undefined,
+    [canResolve, subplebbitAddress, paginationFeedPostsPerPage],
+  );
+
+  const { feed: preloadFeed } = useFeed(preloadOptions);
+
+  const preloadedPage = useMemo(() => {
+    if (!canResolve || !preloadFeed?.length) return undefined;
+    return findPostPageInFeed(preloadFeed, postCid!, guiPostsPerPage);
+  }, [canResolve, postCid, preloadFeed, guiPostsPerPage]);
+
+  return cachedPage ?? preloadedPage;
+}