Fix linked-comment scrolling

I think this the best solution so far, at the expense of a slight delay in scrolling if the network call stalls.

- Added "fetching by ID" state so that we don't need to use the ugly N-retries method.
- `scrollIntoView` doesn't work if the element is already in the viewport, and the `scrollBy` adjustment doesn't take into account the y-position restoration that we perform on certain type of pages. Use `window.scrollTo` instead and taking into account current scroll position.

flow-typed/Comment.js

@@ -43,6 +43,7 @@ declare type CommentsState = {
   linkedCommentAncestors: { [string]: Array<string> }, // {"linkedCommentId": ["parentId", "grandParentId", ...]}
   pinnedCommentsById: {}, // ClaimId -> array of pinned comment IDs
   isLoading: boolean,
+  isLoadingById: boolean,
   isLoadingByParentId: { [string]: boolean },
   myComments: ?Set<string>,
   isFetchingReacts: boolean,

ui/component/commentsList/index.js

@@ -9,6 +9,7 @@ import {
   makeSelectTopLevelCommentsForUri,
   makeSelectTopLevelTotalPagesForUri,
   selectIsFetchingComments,
+  selectIsFetchingCommentsById,
   selectIsFetchingReacts,
   makeSelectTotalCommentsCountForUri,
   selectOthersReactsById,
@@ -33,6 +34,7 @@ const select = (state, props) => {
     claim: makeSelectClaimForUri(props.uri)(state),
     claimIsMine: makeSelectClaimIsMine(props.uri)(state),
     isFetchingComments: selectIsFetchingComments(state),
+    isFetchingCommentsById: selectIsFetchingCommentsById(state),
     isFetchingReacts: selectIsFetchingReacts(state),
     fetchingChannels: selectFetchingMyChannels(state),
     settingsByChannelId: selectSettingsByChannelId(state),

ui/component/commentsList/view.jsx

@@ -14,14 +14,12 @@ import usePersistedState from 'effects/use-persisted-state';
 import { ENABLE_COMMENT_REACTIONS } from 'config';
 import Empty from 'component/common/empty';
 import debounce from 'util/debounce';
+import useFetched from 'effects/use-fetched';
 import { useIsMobile, useIsMediumScreen } from 'effects/use-screensize';
 import { getChannelIdFromClaim } from 'util/claim';
 
 const DEBOUNCE_SCROLL_HANDLER_MS = 200;
 
-// "3" due to 2 separate fetches needed + 1 buffer just in case.
-const MAX_LINKED_COMMENT_SCROLL_ATTEMPTS = 3;
-
 function scaleToDevicePixelRatio(value) {
   const devicePixelRatio = window.devicePixelRatio || 1.0;
   if (devicePixelRatio < 1.0) {
@@ -44,6 +42,7 @@ type Props = {
   claimIsMine: boolean,
   myChannels: ?Array<ChannelClaim>,
   isFetchingComments: boolean,
+  isFetchingCommentsById: boolean,
   isFetchingReacts: boolean,
   linkedCommentId?: string,
   totalComments: number,
@@ -69,6 +68,7 @@ function CommentList(props: Props) {
     claimIsMine,
     myChannels,
     isFetchingComments,
+    isFetchingCommentsById,
     isFetchingReacts,
     linkedCommentId,
     totalComments,
@@ -83,15 +83,15 @@ function CommentList(props: Props) {
   const DEFAULT_SORT = ENABLE_COMMENT_REACTIONS ? SORT_BY.POPULARITY : SORT_BY.NEWEST;
   const [sort, setSort] = usePersistedState('comment-sort-by', DEFAULT_SORT);
   const [page, setPage] = React.useState(0);
-  const [lcScrollAttempts, setLcScrollAttempts] = React.useState(
-    linkedCommentId ? 0 : MAX_LINKED_COMMENT_SCROLL_ATTEMPTS
-  );
   const isMobile = useIsMobile();
   const isMediumScreen = useIsMediumScreen();
   const [expandedComments, setExpandedComments] = React.useState(!isMobile && !isMediumScreen);
   const totalFetchedComments = allCommentIds ? allCommentIds.length : 0;
   const channelId = getChannelIdFromClaim(claim);
   const channelSettings = channelId ? settingsByChannelId[channelId] : undefined;
+  const fetchedCommentsOnce = useFetched(isFetchingComments);
+  const fetchedReactsOnce = useFetched(isFetchingReacts);
+  const fetchedLinkedComment = useFetched(isFetchingCommentsById);
 
   // Display comments immediately if not fetching reactions
   // If not, wait to show comments until reactions are fetched
@@ -203,19 +203,19 @@ function CommentList(props: Props) {
 
   // Scroll to linked-comment
   useEffect(() => {
-    if (lcScrollAttempts < MAX_LINKED_COMMENT_SCROLL_ATTEMPTS && readyToDisplayComments && !isFetchingComments) {
+    if (fetchedLinkedComment && fetchedCommentsOnce && fetchedReactsOnce) {
       const elems = document.getElementsByClassName(COMMENT_HIGHLIGHTED);
       if (elems.length > 0) {
-        setLcScrollAttempts(MAX_LINKED_COMMENT_SCROLL_ATTEMPTS);
+        const ROUGH_HEADER_HEIGHT = 125; // @see: --header-height
         const linkedComment = elems[0];
-        linkedComment.scrollIntoView({ block: 'start' });
-        window.scrollBy(0, -125);
-      } else {
-        setLcScrollAttempts(lcScrollAttempts + 1);
+        window.scrollTo({
+          top: linkedComment.getBoundingClientRect().top + window.scrollY - ROUGH_HEADER_HEIGHT,
+          left: 0,
+          behavior: 'smooth',
+        });
       }
     }
-    // eslint-disable-next-line react-hooks/exhaustive-deps
-  }, [readyToDisplayComments, isFetchingComments]); // We just want to respond to these, nothing else.
+  }, [fetchedLinkedComment, fetchedCommentsOnce, fetchedReactsOnce]);
 
   // Infinite scroll
   useEffect(() => {

ui/constants/action_types.js

@@ -253,6 +253,7 @@ export const COMMENT_LIST_STARTED = 'COMMENT_LIST_STARTED';
 export const COMMENT_LIST_COMPLETED = 'COMMENT_LIST_COMPLETED';
 export const COMMENT_LIST_FAILED = 'COMMENT_LIST_FAILED';
 export const COMMENT_LIST_RESET = 'COMMENT_LIST_RESET';
+export const COMMENT_BY_ID_STARTED = 'COMMENT_BY_ID_STARTED';
 export const COMMENT_BY_ID_COMPLETED = 'COMMENT_BY_ID_COMPLETED';
 export const COMMENT_CREATE_STARTED = 'COMMENT_CREATE_STARTED';
 export const COMMENT_CREATE_COMPLETED = 'COMMENT_CREATE_COMPLETED';

ui/redux/actions/comments.js

@@ -203,6 +203,10 @@ export function doCommentList(
 
 export function doCommentById(commentId: string, toastIfNotFound: boolean = true) {
   return (dispatch: Dispatch, getState: GetState) => {
+    dispatch({
+      type: ACTIONS.COMMENT_BY_ID_STARTED,
+    });
+
     return Comments.comment_by_id({ comment_id: commentId, with_ancestors: true })
       .then((result: CommentByIdResponse) => {
         const { item, items, ancestors } = result;

ui/redux/reducers/comments.js

@@ -21,6 +21,7 @@ const defaultState: CommentsState = {
   superChatsByUri: {},
   pinnedCommentsById: {}, // ClaimId -> array of pinned comment IDs
   isLoading: false,
+  isLoadingById: false,
   isLoadingByParentId: {},
   isCommenting: false,
   myComments: undefined,
@@ -335,6 +336,8 @@ export default handleActions(
       };
     },
 
+    [ACTIONS.COMMENT_BY_ID_STARTED]: (state) => ({ ...state, isLoadingById: true }),
+
     [ACTIONS.COMMENT_BY_ID_COMPLETED]: (state: CommentsState, action: any) => {
       const { comment, ancestors } = action.data;
       const claimId = comment.claim_id;
@@ -375,6 +378,7 @@ export default handleActions(
 
       return {
         ...state,
+        isLoadingById: false,
         topLevelCommentsById,
         topLevelTotalCommentsById,
         topLevelTotalPagesById,

ui/redux/selectors/comments.js

@@ -9,6 +9,7 @@ const selectState = (state) => state.comments || {};
 
 export const selectCommentsById = createSelector(selectState, (state) => state.commentById || {});
 export const selectIsFetchingComments = createSelector(selectState, (state) => state.isLoading);
+export const selectIsFetchingCommentsById = createSelector(selectState, (state) => state.isLoadingById);
 export const selectIsFetchingCommentsByParentId = createSelector(selectState, (state) => state.isLoadingByParentId);
 export const selectIsPostingComment = createSelector(selectState, (state) => state.isCommenting);
 export const selectIsFetchingReacts = createSelector(selectState, (state) => state.isFetchingReacts);