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VirtualItem,
defaultRangeExtractor,
useWindowVirtualizer,
} from "@tanstack/react-virtual";
import {
ReactElement,
useEffect,
useLayoutEffect,
useMemo,
useRef,
useState,
} from "react";
import { useTranslation } from "react-i18next";
import { Link } from "react-router";
import { groupBy, sortBy } from "remeda";
import styled from "styled-components";
import { config } from "shared/config";
import {
ProgramItem,
ProgramItemSignupStrategy,
UserSignup,
} from "shared/types/models/programItem";
import { SignupQuestion } from "shared/types/models/settings";
import { RaisedCard } from "client/components/RaisedCard";
import { getLotterySignups } from "client/utils/getUpcomingProgramItems";
import { useAppSelector } from "client/utils/hooks";
import { registerScrollToTopOverride } from "client/utils/scrollToTop";
import { useTimeNow } from "client/utils/useTimeNow";
import { selectProgramTypeForTexts } from "client/views/admin/adminSlice";
import { ProgramItemListTitle } from "client/views/all-program-items/components/ProgramItemListTitle";
import { getActiveStickyHeaderIndex } from "client/views/all-program-items/programListUtils";
import { selectGroupMembers } from "client/views/group/groupSlice";
import { getIsInGroup } from "client/views/group/groupUtils";
import {
selectDirectSignups,
selectLotterySignups,
} from "client/views/my-program-items/myProgramItemsSlice";
import { ProgramItemEntry } from "client/views/program-item/ProgramItemEntry";
interface Props {
programItems: readonly ProgramItem[];
// Program item to briefly highlight (and scroll to) — the one the user just
// came back from, or null
highlightedProgramItemId: string | null;
}
// The grouped list is flattened into a single sequence of rows (a start-time
// header followed by its program items) so it can be window-virtualized
type VirtualRow =
| { kind: "header"; startTime: string }
| { kind: "item"; programItem: ProgramItem };
// Initial row-height guesses; the virtualizer measures the real heights on
// mount. Keep these close to the real median row heights: every estimated-vs-
// actual mismatch on a row's first measurement is compensated with a scroll
// correction, and large corrections show up as visible jumps when scrolling
// through rows that were skipped past unmeasured (e.g. after a fast fling)
const HEADER_ESTIMATED_HEIGHT = 92;
const ITEM_ESTIMATED_HEIGHT = 350;
// One shared value for every program item nobody has signed up to, so those
// rows keep getting the same reference and the memoized row can bail out
const NO_SIGNUPS: UserSignup[] = [];
// The window scroll offset and measured row sizes when the list unmounts, so
// returning to it (e.g. via the browser back button after viewing a program
// item) restores the exact scroll position — the clicked card comes back where
// it was. Module-scoped so it survives navigation within the SPA session
let savedScrollState: {
offset: number;
measurementsCache: VirtualItem[];
} | null = null;
export const AllProgramItemsList = ({
programItems,
highlightedProgramItemId,
}: Props): ReactElement => {
// Opted out of the React Compiler: the virtualizer hook returns one instance
// that stays referentially stable while its measurements mutate inside it, so
// the row offsets and total size read from it during render are external
// mutable state the compiler cannot see change. Memoized, rows keep the
// offsets they were first rendered with and end up overlapping each other
"use no memo";
const { t, i18n } = useTranslation();
const signups = useAppSelector(
(state) => state.allProgramItems.directSignups,
);
const lotterySignups = useAppSelector(selectLotterySignups);
const directSignups = useAppSelector(selectDirectSignups);
const programTypeForTexts = useAppSelector(selectProgramTypeForTexts);
const groupMembers = useAppSelector(selectGroupMembers);
const isGroupCreator = useAppSelector((state) => state.group.isGroupCreator);
const groupCode = useAppSelector((state) => state.group.groupCode);
const username = useAppSelector((state) => state.login.username);
const timeNow = useTimeNow();
const loggedIn = useAppSelector((state) => state.login.loggedIn);
const userGroup = useAppSelector((state) => state.login.userGroup);
const isInGroup = getIsInGroup(groupCode);
const signupQuestions = useAppSelector(
(state) => state.admin.signupQuestions,
);
// Index sign-ups by program item id so each row is an O(1) lookup instead of
// scanning the full sign-ups array (which made the list render O(n^2)).
// Memoized by hand because the opt-out above also stops the compiler from
// memoizing anything else here, and this component re-renders on every clock
// tick and every scroll-driven virtualizer update
const signupsByProgramItemId = useMemo(
() =>
new Map(signups.map((signup) => [signup.programItemId, signup.users])),
[signups],
);
// Index the first public sign-up question per program item id
const publicSignupQuestionByProgramItemId = useMemo(() => {
const byProgramItemId = new Map<string, SignupQuestion>();
for (const signupQuestion of signupQuestions) {
if (
!signupQuestion.private &&
!byProgramItemId.has(signupQuestion.programItemId)
) {
byProgramItemId.set(signupQuestion.programItemId, signupQuestion);
}
}
return byProgramItemId;
}, [signupQuestions]);
const ownOrGroupCreatorLotterySignups = useMemo(
() =>
getLotterySignups({
lotterySignups,
isGroupCreator,
groupMembers,
isInGroup,
showAllProgramItems: true,
timeNow,
}),
[lotterySignups, isGroupCreator, groupMembers, isInGroup, timeNow],
);
// Flatten the grouped list once per program-item set (stable across scroll and
// language changes so it stays out of the scroll render path)
const { rows, stickyHeaderIndexes } = useMemo(() => {
const sortedProgramItems = sortBy(
programItems,
(programItem) => programItem.startTime,
(programItem) => programItem.title.toLowerCase(),
);
const programItemsByStartTime = groupBy(
sortedProgramItems,
(programItem) => programItem.startTime,
);
const nextRows: VirtualRow[] = [];
const nextStickyHeaderIndexes: number[] = [];
for (const [startTime, programItemsForStartTime] of Object.entries(
programItemsByStartTime,
)) {
nextStickyHeaderIndexes.push(nextRows.length);
nextRows.push({ kind: "header", startTime });
for (const programItem of programItemsForStartTime) {
nextRows.push({ kind: "item", programItem });
}
}
return { rows: nextRows, stickyHeaderIndexes: nextStickyHeaderIndexes };
}, [programItems]);
// The page itself scrolls (no inner scroll container), so virtualize against
// the window. scrollMargin is the list's offset from the top of the document
const listRef = useRef<HTMLDivElement>(null);
const [scrollMargin, setScrollMargin] = useState(0);
useLayoutEffect(() => {
const element = listRef.current;
if (!element) {
return;
}
// Keep the list's document offset current: content above it (the filter
// card) can change height, which would otherwise misalign every row
const updateScrollMargin = (): void => {
const nextScrollMargin =
element.getBoundingClientRect().top + window.scrollY;
setScrollMargin((previous) =>
previous === nextScrollMargin ? previous : nextScrollMargin,
);
};
updateScrollMargin();
const resizeObserver = new ResizeObserver(updateScrollMargin);
resizeObserver.observe(document.body);
window.addEventListener("resize", updateScrollMargin);
return () => {
resizeObserver.disconnect();
window.removeEventListener("resize", updateScrollMargin);
};
}, []);
// When a row's measured height differs from its estimate, the virtualizer
// corrects the scroll position so on-screen content doesn't shift. It issues
// the correction as an absolute scrollTo based on its cached scroll offset,
// which lags the live position by up to a frame while the user is scrolling —
// an absolute target would yank the page back by that lag (a visible jump).
// Apply only the not-yet-applied part of the correction as a relative
// scrollBy instead, which is immune to the stale base offset
const appliedAdjustmentsRef = useRef(0);
useEffect(() => {
// The virtualizer zeroes its cumulative adjustments on every scroll event;
// mirror that so the applied tally stays in sync with it
const resetAppliedAdjustments = (): void => {
appliedAdjustmentsRef.current = 0;
};
window.addEventListener("scroll", resetAppliedAdjustments, {
passive: true,
});
return () => {
window.removeEventListener("scroll", resetAppliedAdjustments);
};
}, []);
const virtualizer = useWindowVirtualizer({
count: rows.length,
scrollToFn: (offset, { adjustments, behavior }) => {
// No adjustments: a navigation scroll (scrollToOffset/scrollToIndex)
// where the absolute target is the intent — pass it through
if (adjustments === undefined) {
window.scrollTo({ top: offset, behavior });
return;
}
const delta = adjustments - appliedAdjustmentsRef.current;
appliedAdjustmentsRef.current = adjustments;
window.scrollBy({ top: delta, behavior });
},
// Seeding the virtualizer with the previous visit's measured row sizes
// lets the saved pixel offset land on the same rows instead of drifting on
// height estimates. Only read when the virtualizer instance is created
initialMeasurementsCache: savedScrollState?.measurementsCache,
estimateSize: (index) =>
rows[index].kind === "header"
? HEADER_ESTIMATED_HEIGHT
: ITEM_ESTIMATED_HEIGHT,
// Rows are measured when they mount, and a mismatch against the estimate
// is fixed with a scroll correction — visible as a jump if the row is
// already on screen. Overscan is the buffer that lets rows mount and
// measure while still off-screen, so it needs to cover a realistic
// per-frame wheel/fling scroll distance
overscan: 10,
scrollMargin,
getItemKey: (index) => {
const row = rows[index];
return row.kind === "header"
? `header-${row.startTime}`
: row.programItem.programItemId;
},
// Always render the active sticky header, even when it's scrolled out of the
// measured range, so it can stay pinned to the top
rangeExtractor: (range) =>
[
...new Set([
getActiveStickyHeaderIndex(stickyHeaderIndexes, range.startIndex),
...defaultRangeExtractor(range),
]),
].sort((a, b) => a - b),
});
const activeStickyHeaderIndex = getActiveStickyHeaderIndex(
stickyHeaderIndexes,
virtualizer.range?.startIndex ?? 0,
);
// Remember the scroll offset and row measurements on unmount so the exact
// position can be restored on return (e.g. via the back button). Runs as a
// layout-effect cleanup to capture the position before the next route
// resets the window scroll. Neither direct offset source is reliable here
// on WebKit: window.scrollY has already been pulled down by scroll
// anchoring when the commit removed content above the list (and may be
// clamped against the shrinking document), and the virtualizer's last
// observed offset misses its own row-measurement compensation scroll while
// the scroll event for it is still undelivered (WebKit dispatches scroll
// events for programmatic scrolls asynchronously — under load only after
// the navigation). The virtualizer tracks that undelivered compensation in
// scrollAdjustments (cleared once the event arrives), so its intended
// offset is scrollOffset + scrollAdjustments. The field is private, so
// read it defensively — if it disappears in an upgrade, only the
// undelivered-event case regresses
useLayoutEffect(() => {
return () => {
const pendingAdjustments =
(virtualizer as unknown as { scrollAdjustments?: number })
.scrollAdjustments ?? 0;
savedScrollState = {
offset:
(virtualizer.scrollOffset ?? window.scrollY) + pendingAdjustments,
measurementsCache: virtualizer.takeSnapshot(),
};
};
}, [virtualizer]);
// On mount, restore the previous scroll position (e.g. returning via the back
// button). The just-viewed item comes back exactly where it was and is
// highlighted there. Guarded to run only once, when the list first has rows
const hasRestoredScrollRef = useRef(false);
useEffect(() => {
if (hasRestoredScrollRef.current || rows.length === 0) {
return;
}
hasRestoredScrollRef.current = true;
if (!savedScrollState || savedScrollState.offset <= 0) {
return;
}
const targetOffset = savedScrollState.offset;
// The document keeps growing for a few frames after mount as rows are
// measured and the scroll margin settles, so a single scrollTo can clamp
// short (the document isn't tall enough yet) and stick there. Re-apply
// across frames until the offset holds — WebKit most often lands short on
// the first frame. Stop once the document stops growing (scrollY no longer
// climbs) so an unreachable target doesn't keep yanking the user for the
// full frame budget, e.g. when the list is now shorter than the saved offset
const MAX_RESTORE_FRAMES = 30;
const MAX_STALLED_FRAMES = 3;
let attempts = 0;
let stalledFrames = 0;
let previousScrollY = -1;
let rafId = 0;
const restore = (): void => {
window.scrollTo(0, targetOffset);
attempts += 1;
const scrollY = Math.round(window.scrollY);
stalledFrames = scrollY > previousScrollY ? 0 : stalledFrames + 1;
previousScrollY = scrollY;
Iif (
scrollY < Math.round(targetOffset) &&
stalledFrames < MAX_STALLED_FRAMES &&
attempts < MAX_RESTORE_FRAMES
) {
rafId = requestAnimationFrame(restore);
}
};
rafId = requestAnimationFrame(restore);
return () => cancelAnimationFrame(rafId);
}, [rows]);
// Make scroll-to-top go through the virtualizer so the smooth scroll isn't
// cancelled by row-measurement adjustments (see client/src/utils/scrollToTop.ts)
useEffect(() => {
return registerScrollToTopOverride(() => {
virtualizer.scrollToOffset(0, { behavior: "smooth" });
});
}, [virtualizer]);
const { programGuideUrlFi, programGuideUrlEn } = config.event();
const programGuideUrl =
i18n.language === "fi" ? programGuideUrlFi : programGuideUrlEn;
if (rows.length === 0) {
return (
<RaisedCard>
<Container>
<NoProgramItemsText>
{t("noProgramItemsAvailable", {
PROGRAM_TYPE: t(
`programTypePartitivePlural.${programTypeForTexts}`,
),
})}
</NoProgramItemsText>
<SecondNoProgramItemsText>
{t("checkProgramGuide")}{" "}
{programGuideUrl ? (
<Link to={programGuideUrl} target="_blank">
{t("programGuide")}
</Link>
) : (
t("programGuide")
)}
.
</SecondNoProgramItemsText>
</Container>
</RaisedCard>
);
}
return (
<div ref={listRef}>
<VirtualContainer style={{ height: virtualizer.getTotalSize() }}>
{virtualizer.getVirtualItems().map((virtualItem) => {
const row = rows[virtualItem.index];
const isActiveStickyHeader =
row.kind === "header" &&
virtualItem.index === activeStickyHeaderIndex;
return (
<VirtualRowWrapper
key={virtualItem.key}
data-index={virtualItem.index}
ref={virtualizer.measureElement}
$sticky={isActiveStickyHeader}
style={
isActiveStickyHeader
? undefined
: {
transform: `translateY(${virtualItem.start - scrollMargin}px)`,
}
}
>
{row.kind === "header" ? (
<ProgramItemListTitle startTime={row.startTime} />
) : (
<ProgramItemEntry
isAlwaysExpanded={false}
isRecentlyViewed={
row.programItem.programItemId === highlightedProgramItemId
}
programItem={row.programItem}
signups={
signupsByProgramItemId.get(row.programItem.programItemId) ??
NO_SIGNUPS
}
signupStrategy={
row.programItem.signupStrategy ??
ProgramItemSignupStrategy.DIRECT
}
lotterySignups={ownOrGroupCreatorLotterySignups}
directSignups={directSignups}
username={username}
loggedIn={loggedIn}
userGroup={userGroup}
publicSignupQuestion={publicSignupQuestionByProgramItemId.get(
row.programItem.programItemId,
)}
/>
)}
</VirtualRowWrapper>
);
})}
</VirtualContainer>
</div>
);
};
const VirtualContainer = styled.div`
position: relative;
width: 100%;
`;
const VirtualRowWrapper = styled.div<{ $sticky: boolean }>`
left: 0;
width: 100%;
/* Contain the child card's vertical margins so the virtualizer measures the
row's real footprint (margins are otherwise excluded from measurement) */
display: flow-root;
/* The active group header is pinned to the top of the viewport; all other
rows are absolutely positioned by the virtualizer via an inline transform.
The header's own 20px top margin is contained by flow-root, so the pin is
lifted by that amount to keep the header flush with the viewport top */
${(props) =>
props.$sticky
? `position: sticky; top: -20px; z-index: 2;`
: `position: absolute; top: 0;`}
`;
const Container = styled.div`
display: flex;
flex-direction: column;
`;
const NoProgramItemsText = styled.span`
color: ${(props) => props.theme.textSecondary};
font-size: ${(props) => props.theme.fontSizeLarge};
`;
const SecondNoProgramItemsText = styled(NoProgramItemsText)`
padding-top: 8px;
`;
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