refactor thumbnail fetching, add caching

src/components/catalog-row/catalog-row.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useMemo, useRef, useState } from 'react';
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 import { createPortal } from 'react-dom';
 import { useTranslation } from 'react-i18next';
 import { Link, useLocation, useParams } from 'react-router-dom';
@@ -119,14 +119,18 @@ const CatalogPost = ({ post }: { post: Comment }) => {
   const initialCommentMediaInfo = useMemo(() => getCommentMediaInfo(post), [post]);
   const [commentMediaInfo, setCommentMediaInfo] = useState(initialCommentMediaInfo);
   const hasThumbnail = getHasThumbnail(commentMediaInfo, link);
-  useEffect(() => {
+
+  const fetchThumbnail = useCallback(async () => {
     if (initialCommentMediaInfo?.type === 'webpage' && !initialCommentMediaInfo.thumbnail) {
-      fetchWebpageThumbnailIfNeeded(initialCommentMediaInfo).then(setCommentMediaInfo);
-    } else {
-      setCommentMediaInfo(initialCommentMediaInfo);
+      const newMediaInfo = await fetchWebpageThumbnailIfNeeded(initialCommentMediaInfo);
+      setCommentMediaInfo(newMediaInfo);
     }
   }, [initialCommentMediaInfo]);
 
+  useEffect(() => {
+    fetchThumbnail();
+  }, [fetchThumbnail]);
+
   const { hidden } = useHide({ cid });
 
   const location = useLocation();

src/components/post-desktop/post-desktop.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useMemo, useState } from 'react';
+import { useCallback, useEffect, useMemo, useState } from 'react';
 import { Trans, useTranslation } from 'react-i18next';
 import { Link, useLocation, useParams } from 'react-router-dom';
 import { Comment, useAuthorAvatar, useComment, useEditedComment, useSubplebbit } from '@plebbit/plebbit-react-hooks';
@@ -212,14 +212,18 @@ const PostMedia = ({ post }: PostProps) => {
   // some sites have CORS access, so the thumbnail can be fetched client-side, which is helpful if subplebbit.settings.fetchThumbnailUrls is false
   const initialCommentMediaInfo = useMemo(() => getCommentMediaInfo(post), [post]);
   const [commentMediaInfo, setCommentMediaInfo] = useState(initialCommentMediaInfo);
-  useEffect(() => {
+
+  const fetchThumbnail = useCallback(async () => {
     if (initialCommentMediaInfo?.type === 'webpage' && !initialCommentMediaInfo.thumbnail) {
-      fetchWebpageThumbnailIfNeeded(initialCommentMediaInfo).then(setCommentMediaInfo);
-    } else {
-      setCommentMediaInfo(initialCommentMediaInfo);
+      const newMediaInfo = await fetchWebpageThumbnailIfNeeded(initialCommentMediaInfo);
+      setCommentMediaInfo(newMediaInfo);
     }
   }, [initialCommentMediaInfo]);
 
+  useEffect(() => {
+    fetchThumbnail();
+  }, [fetchThumbnail]);
+
   const { url } = commentMediaInfo || {};
   let type = commentMediaInfo?.type;
   const gifFrameUrl = useFetchGifFirstFrame(url);

src/components/post-mobile/post-mobile.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useMemo, useState } from 'react';
+import { useCallback, useEffect, useMemo, useState } from 'react';
 import { Trans, useTranslation } from 'react-i18next';
 import { Link, useLocation, useParams } from 'react-router-dom';
 import { Comment, useAuthorAvatar, useComment, useEditedComment, useSubplebbit } from '@plebbit/plebbit-react-hooks';
@@ -43,14 +43,18 @@ const PostInfoAndMedia = ({ openReplyModal, post, postReplyCount = 0, roles }: P
   // some sites have CORS access, so the thumbnail can be fetched client-side, which is helpful if subplebbit.settings.fetchThumbnailUrls is false
   const initialCommentMediaInfo = useMemo(() => getCommentMediaInfo(post), [post]);
   const [commentMediaInfo, setCommentMediaInfo] = useState(initialCommentMediaInfo);
-  useEffect(() => {
+
+  const fetchThumbnail = useCallback(async () => {
     if (initialCommentMediaInfo?.type === 'webpage' && !initialCommentMediaInfo.thumbnail) {
-      fetchWebpageThumbnailIfNeeded(initialCommentMediaInfo).then(setCommentMediaInfo);
-    } else {
-      setCommentMediaInfo(initialCommentMediaInfo);
+      const newMediaInfo = await fetchWebpageThumbnailIfNeeded(initialCommentMediaInfo);
+      setCommentMediaInfo(newMediaInfo);
     }
   }, [initialCommentMediaInfo]);
 
+  useEffect(() => {
+    fetchThumbnail();
+  }, [fetchThumbnail]);
+
   const hasThumbnail = getHasThumbnail(commentMediaInfo, link);
   const [showThumbnail, setShowThumbnail] = useState(true);
 

src/lib/utils/media-utils.ts

@@ -135,14 +135,6 @@ const fetchWebpageThumbnail = async (url: string): Promise<string | undefined> =
   }
 };
 
-export const fetchWebpageThumbnailIfNeeded = async (commentMediaInfo: CommentMediaInfo): Promise<CommentMediaInfo> => {
-  if (commentMediaInfo.type === 'webpage' && !commentMediaInfo.thumbnail) {
-    const thumbnail = await fetchWebpageThumbnail(commentMediaInfo.url);
-    return { ...commentMediaInfo, thumbnail };
-  }
-  return commentMediaInfo;
-};
-
 export const getCommentMediaInfo = (comment: Comment): CommentMediaInfo | undefined => {
   if (!comment?.thumbnailUrl && !comment?.link) {
     return;
@@ -192,3 +184,30 @@ export const getMediaDimensions = (commentMediaInfo: CommentMediaInfo | undefine
 
   return '';
 };
+
+export const fetchWebpageThumbnailIfNeeded = async (commentMediaInfo: CommentMediaInfo): Promise<CommentMediaInfo> => {
+  if (commentMediaInfo.type === 'webpage' && !commentMediaInfo.thumbnail) {
+    const cachedThumbnail = getCachedThumbnail(commentMediaInfo.url);
+    if (cachedThumbnail) {
+      return { ...commentMediaInfo, thumbnail: cachedThumbnail };
+    }
+    const thumbnail = await fetchWebpageThumbnail(commentMediaInfo.url);
+    if (thumbnail) {
+      setCachedThumbnail(commentMediaInfo.url, thumbnail);
+    }
+    return { ...commentMediaInfo, thumbnail };
+  }
+  return commentMediaInfo;
+};
+const THUMBNAIL_CACHE_KEY = 'webpageThumbnailCache';
+
+export const getCachedThumbnail = (url: string): string | null => {
+  const cache = JSON.parse(localStorage.getItem(THUMBNAIL_CACHE_KEY) || '{}');
+  return cache[url] || null;
+};
+
+export const setCachedThumbnail = (url: string, thumbnail: string): void => {
+  const cache = JSON.parse(localStorage.getItem(THUMBNAIL_CACHE_KEY) || '{}');
+  cache[url] = thumbnail;
+  localStorage.setItem(THUMBNAIL_CACHE_KEY, JSON.stringify(cache));
+};