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refactor(e5): deferred review-tail (frontend) — Carousel reuse + shared scroll core

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The last of the deep-review deferred reuse items:

- extract the scroll-affordance machinery (watch the scroller AND its swappable/
  lazily-growing children, diff two edge booleans) that useScrollFade (vertical) and
  Carousel's useHScroll (horizontal) each hand-duplicated into one shared
  lib/useScrollEdges(axis); both hooks now just map start/end to their own shape.

- migrate PlexInfo's two remaining hand-rolled `flex overflow-x-auto` strips — the
  cast row and the collection strips — to the S1 <Carousel> primitive, so they get the
  edge fade + hover/focus scroll buttons (only on the clipped side) for free, matching
  the Discover rails / CastStrip / RelatedStrip.

Pure refactor, no behaviour change. Gate green (tsc, vitest 351, eslint, prettier,
knip). Browser-verified on a movie info page: cast row + collection strip render as
Carousels with the edge fade and the right-scroll button on the clipped cast row.
This commit is contained in:
peter
2026-08-21 06:16:15 +02:00
parent 13fb2b4e61
commit 8f6714e678
4 changed files with 90 additions and 101 deletions
Download Patch File Download Diff File Expand all files Collapse all files
frontend/src/components/Carousel.tsx
+8 -39
View File
@@ -1,7 +1,8 @@
import { useCallback, useEffect, useState, type ReactNode } from "react";
import { useCallback, type ReactNode } from "react";
import { ChevronLeft, ChevronRight } from "lucide-react";
import { useTranslation } from "react-i18next";
import clsx from "clsx";
import { useScrollEdges } from "../lib/useScrollEdges";
// Shared horizontal rail — the one place the app's "row of cards you scroll sideways" lives, replacing
// the hand-rolled `flex gap overflow-x-auto` strips (Cast / Related / collections) and the future
@@ -19,50 +20,18 @@ function scrollBehavior(): ScrollBehavior {
return reduce ? "auto" : "smooth";
}
// Horizontal scroll-affordance: tracks whether the scroller is clipped on the left / right so the rail
// can show a button + fade only where there's more to see. The X-axis twin of useScrollFade — same
// node-state callback ref (re-runs on attach) and same watch-the-children discipline (a rail whose
// cards load in later grows scrollWidth without ever firing a scroll event), and it also hands back the
// element so the buttons can scroll it.
// Horizontal scroll-affordance: whether the scroller is clipped on the left / right, so the rail shows
// a button + fade only where there's more to see. The X-axis face of the shared `useScrollEdges` core
// (the same watch-the-scroller-and-its-children discipline as the vertical `useScrollFade`), plus the
// element itself so the paging buttons can scroll it.
function useHScroll(): {
ref: (node: HTMLElement | null) => void;
el: HTMLElement | null;
left: boolean;
right: boolean;
} {
const [el, setEl] = useState<HTMLElement | null>(null);
const [edge, setEdge] = useState({ left: false, right: false });
useEffect(() => {
if (!el) return;
const update = () => {
const left = el.scrollLeft > 1;
const right = el.scrollLeft + el.clientWidth < el.scrollWidth - 1;
setEdge((prev) => (prev.left === left && prev.right === right ? prev : { left, right }));
};
update();
el.addEventListener("scroll", update, { passive: true });
const ro = new ResizeObserver(update);
ro.observe(el);
for (const child of Array.from(el.children)) ro.observe(child);
const mo = new MutationObserver((records) => {
for (const rec of records) {
for (const node of Array.from(rec.addedNodes))
if (node instanceof Element) ro.observe(node);
for (const node of Array.from(rec.removedNodes))
if (node instanceof Element) ro.unobserve(node);
}
update();
});
mo.observe(el, { childList: true });
return () => {
el.removeEventListener("scroll", update);
ro.disconnect();
mo.disconnect();
};
}, [el]);
return { ref: setEl, el, left: edge.left, right: edge.right };
const { ref, el, start, end } = useScrollEdges("x");
return { ref, el, left: start, right: end };
}
const FADE_PX = 28;
frontend/src/components/PlexInfo.tsx
+5 -4
View File
@@ -15,6 +15,7 @@ import {
useDetailPrefs,
} from "../lib/plexDetailUi";
import { usePref } from "../lib/usePref";
import { Carousel } from "./Carousel";
import PlexCollectionEditor from "./PlexCollectionEditor";
import PlexPlaylistAdd from "./PlexPlaylistAdd";
@@ -614,7 +615,7 @@ export default function PlexInfo({
<h2 className={`mb-2 text-sm font-semibold ${overlay ? "text-white/80" : ""}`}>
{t("plex.info.cast")}
</h2>
<div className="flex gap-3 overflow-x-auto pb-2">
<Carousel ariaLabel={t("plex.info.cast")} gap="gap-3">
{cast.map((c, i) => {
const clickable = !!(onOpenPerson || onFilter);
const inner = (
@@ -669,7 +670,7 @@ export default function PlexInfo({
</div>
);
})}
</div>
</Carousel>
</div>
)}
@@ -694,7 +695,7 @@ export default function PlexInfo({
</button>
)}
</div>
<div className="flex gap-3 overflow-x-auto pb-2">
<Carousel ariaLabel={col.title} gap="gap-3">
{col.items.map((m) => (
<button
key={m.id}
@@ -739,7 +740,7 @@ export default function PlexInfo({
{m.year ? <div className="text-2xs text-muted">{m.year}</div> : null}
</button>
))}
</div>
</Carousel>
</div>
))}
</div>
frontend/src/lib/useScrollEdges.ts
+62
View File
@@ -0,0 +1,62 @@
import { useEffect, useState } from "react";
// The shared scroll-affordance core behind `useScrollFade` (vertical edge fade) and the Carousel's
// `useHScroll` (horizontal scroll buttons). Both need the exact same machinery — track whether a
// scroller is clipped at the START and END of ONE axis, watching the scroller AND its children so the
// edges re-evaluate even when no `scroll` event fires (a rail whose cards load in later grows
// scrollWidth/scrollHeight silently; a Suspense fallback gets SWAPPED for the real content). This is
// that machinery, parameterised by axis; the two hooks just map `start`/`end` to their own shape.
//
// Uses a node-state callback ref (not useRef) so the effect (re)runs whenever the element attaches —
// e.g. a SidePanel that mounts collapsed and only renders its scroll body once expanded still wires up.
// `start`/`end` = there is more content before / after the visible window ("y": top/bottom, "x":
// left/right). The boolean-diff bail-out matters: `scroll` fires per frame and the page scroller's hook
// sits above the whole tree, so returning a new object each frame would re-render everything.
export function useScrollEdges(axis: "x" | "y"): {
ref: (node: HTMLElement | null) => void;
el: HTMLElement | null;
start: boolean;
end: boolean;
} {
const [el, setEl] = useState<HTMLElement | null>(null);
const [edge, setEdge] = useState({ start: false, end: false });
useEffect(() => {
if (!el) return;
const update = () => {
const pos = axis === "x" ? el.scrollLeft : el.scrollTop;
const client = axis === "x" ? el.clientWidth : el.clientHeight;
const scroll = axis === "x" ? el.scrollWidth : el.scrollHeight;
const start = pos > 1;
const end = pos + client < scroll - 1;
setEdge((prev) => (prev.start === start && prev.end === end ? prev : { start, end }));
};
update();
el.addEventListener("scroll", update, { passive: true });
// Watch the scroller AND its content: content that grows/shrinks/decrypts/filters changes neither
// the scroller's own box nor its scroll offset, so without the children nothing re-evaluates.
const ro = new ResizeObserver(update);
ro.observe(el);
for (const child of Array.from(el.children)) ro.observe(child);
// Children get SWAPPED (a lazy page replacing its Suspense fallback), and a ResizeObserver holding a
// detached node simply never fires again — so follow the child list, observing/unobserving exactly
// the nodes named in each record (O(1) per change, not a re-observe of a long list on every append).
const mo = new MutationObserver((records) => {
for (const rec of records) {
for (const node of Array.from(rec.addedNodes))
if (node instanceof Element) ro.observe(node);
for (const node of Array.from(rec.removedNodes))
if (node instanceof Element) ro.unobserve(node);
}
update();
});
mo.observe(el, { childList: true });
return () => {
el.removeEventListener("scroll", update);
ro.disconnect();
mo.disconnect();
};
}, [el, axis]);
return { ref: setEl, el, start: edge.start, end: edge.end };
}
frontend/src/lib/useScrollFade.ts
+15 -58
View File
@@ -1,15 +1,15 @@
import { useEffect, useState, type CSSProperties } from "react";
import { type CSSProperties } from "react";
import { useScrollEdges } from "./useScrollEdges";
// Scroll-affordance for a scroll container (typically one whose native scrollbar is hidden with
// `.no-scrollbar`, but the page scroller keeps its bar and takes the fade anyway):
// fades the top/bottom edge of the content to hint there's more to scroll, but only on the edge
// that's actually clipped (no fade at a boundary, none when it all fits). Returns a callback ref
// to attach to the scroller and the mask `style` to spread onto it. Uses a node-state callback
// ref (not useRef) so the effect (re)runs whenever the element attaches — e.g. a SidePanel that
// mounts collapsed and only renders its scroll body once expanded still wires up correctly.
// `fadeTop` gates the top edge only. Pass false when the scroller's top is a sticky element (a
// table's sticky header): fading there would eat into the header instead of hinting at content, and
// the header would visibly change as the fade turns on with the first scroll.
// Vertical scroll-affordance for a scroll container (typically one whose native scrollbar is hidden
// with `.no-scrollbar`, but the page scroller keeps its bar and takes the fade anyway): fades the
// top/bottom edge of the content to hint there's more to scroll, but only on the edge that's actually
// clipped (no fade at a boundary, none when it all fits). Returns a callback ref to attach to the
// scroller and the mask `style` to spread onto it. The scroller-and-children watching machinery lives
// in the shared `useScrollEdges` (the horizontal twin, Carousel's `useHScroll`, uses the same core).
// `fadeTop` gates the top edge only. Pass false when the scroller's top is a sticky element (a table's
// sticky header): fading there would eat into the header instead of hinting at content, and the header
// would visibly change as the fade turns on with the first scroll.
export function useScrollFade(
fadePx = 20,
fadeTop = true,
@@ -17,52 +17,9 @@ export function useScrollFade(
ref: (node: HTMLElement | null) => void;
style: CSSProperties;
} {
const [el, setEl] = useState<HTMLElement | null>(null);
const [fade, setFade] = useState({ up: false, down: false });
useEffect(() => {
if (!el) return;
// Bail out when neither edge changed: `scroll` fires per frame, and the page scroller's
// hook sits above the whole page tree, so a new object here would re-render on every frame
// of every scroll. The two booleans only flip at the ends of the range.
const update = () => {
const up = el.scrollTop > 1;
const down = el.scrollTop + el.clientHeight < el.scrollHeight - 1;
setFade((prev) => (prev.up === up && prev.down === down ? prev : { up, down }));
};
update();
el.addEventListener("scroll", update, { passive: true });
// Watch the scroller AND its content. Content that grows or shrinks — a lazy page loading in,
// a thread's messages decrypting, a list being filtered — changes neither the scroller's own
// box nor its scrollTop, so without the children nothing would re-evaluate the edges.
const ro = new ResizeObserver(update);
ro.observe(el);
for (const child of Array.from(el.children)) ro.observe(child);
// Children get SWAPPED, and a ResizeObserver holding a detached node simply never fires
// again. Measured: the Plex page opened with no bottom fade over a 3119px list, because the
// node observed at mount was the Suspense fallback the real page then replaced. (Same
// lazy-page race that broke BackToTop.) So follow the child list: the records name exactly
// which nodes arrived and left, which keeps this O(1) per change rather than re-observing
// every child of a long list on each append.
const mo = new MutationObserver((records) => {
for (const rec of records) {
for (const node of Array.from(rec.addedNodes))
if (node instanceof Element) ro.observe(node);
for (const node of Array.from(rec.removedNodes))
if (node instanceof Element) ro.unobserve(node);
}
update();
});
mo.observe(el, { childList: true });
return () => {
el.removeEventListener("scroll", update);
ro.disconnect();
mo.disconnect();
};
}, [el]);
const mask = `linear-gradient(to bottom, transparent, #000 ${fade.up && fadeTop ? fadePx : 0}px, #000 calc(100% - ${
fade.down ? fadePx : 0
const { ref, start, end } = useScrollEdges("y");
const mask = `linear-gradient(to bottom, transparent, #000 ${start && fadeTop ? fadePx : 0}px, #000 calc(100% - ${
end ? fadePx : 0
}px), transparent)`;
return { ref: setEl, style: { maskImage: mask, WebkitMaskImage: mask } };
return { ref, style: { maskImage: mask, WebkitMaskImage: mask } };
}