Preview Rail

// Shared motion tokens. Easing curves mirror the CSS custom properties in
// globals.css; springs are the canonical physics used across components.
// Strong custom variants — defaults like `ease-in`/`ease-out` feel weak.

export const EASE_OUT = [0.16, 1, 0.3, 1] as const;
export const EASE_IN_OUT = [0.77, 0, 0.175, 1] as const;
export const EASE_DRAWER = [0.32, 0.72, 0, 1] as const;

/** CSS string form of EASE_OUT for inline style transitions. */
export const EASE_OUT_CSS = "cubic-bezier(0.16, 1, 0.3, 1)";

/** Press feedback on buttons and other tappable surfaces. */
export const SPRING_PRESS = {
  type: "spring",
  stiffness: 500,
  damping: 30,
  mass: 0.6,
} as const;

/** Content swaps — label/icon slots trading places inside a control. */
export const SPRING_SWAP = {
  type: "spring",
  stiffness: 460,
  damping: 30,
  mass: 0.55,
} as const;

/** Overlay panel entrances — modals and sheets summoned by pointer. */
export const SPRING_PANEL = {
  type: "spring",
  stiffness: 420,
  damping: 40,
  mass: 0.5,
} as const;

/** Shared-layout glides — pills, indicators and panels morphing between positions. */
export const SPRING_LAYOUT = {
  type: "spring",
  stiffness: 360,
  damping: 32,
  mass: 0.6,
} as const;

/** Cursor-follow physics for decorative mouse tracking (magnetic, tilt, dock). */
export const SPRING_MOUSE = {
  stiffness: 200,
  damping: 15,
  mass: 0.3,
} as const;

/** Dragged handles and fills (sliders) — critically damped `useSpring` config,
 * so the value follows the pointer butterily and never rebounds off an end. */
export const SPRING_GLIDE = {
  stiffness: 700,
  damping: 50,
  mass: 0.5,
} as const;

"use client";

import { type RefObject, useEffect } from "react";

/**
 * What the dismissing gesture does to the control it landed on.
 *
 * `"pass-through"` is the platform norm (native popover light-dismiss): the
 * tap closes the overlay *and* activates whatever was under it. Use
 * `"consume"` where the open overlay sits over or beside controls that would
 * be costly to trigger by accident — the dismissal then swallows the
 * activation too, so the gesture only closes.
 */
export type DismissBehavior = "pass-through" | "consume";

export interface DismissOptions {
  /** Default `"pass-through"`. */
  behavior?: DismissBehavior;
  /** Dismiss on Escape as well. Default true. */
  escape?: boolean;
  /** Return true for an outside target that should *not* dismiss. Must be stable. */
  ignore?: (target: Element) => boolean;
}

/**
 * What every currently open dismiss scope counts as inside itself. A consumed
 * dismissal reads this to tell a stray gesture from one that belongs to an
 * overlay in front of it: overlays have no shared z-order to consult, but the
 * one the gesture landed in has said as much by registering it.
 */
const openScopes = new Set<(target: Element) => boolean>();

function claimedByAnotherScope(
  self: (target: Element) => boolean,
  target: Element,
) {
  for (const scope of openScopes) {
    if (scope !== self && scope(target)) return true;
  }
  return false;
}

// preventDefault on pointerdown does not suppress the click that follows, so
// consuming a gesture means swallowing that click itself. The swallower
// deliberately outlives the effect that installed it — the dismissal it
// belongs to has already unmounted or re-rendered by the time the click lands.
// It releases on that click, or on the next gesture if the pointer is dragged
// away and no click ever arrives, so it can never eat a later one. A keydown
// releases it too: a gesture that ends with neither a click nor a cancel would
// otherwise leave it armed, and the click Enter synthesizes on some focused
// control is not the one this dismissal was owed.
function consumeActivation(source: Event) {
  const swallow = (event: MouseEvent) => {
    event.preventDefault();
    event.stopPropagation();
    release();
  };
  const restart = (event: Event) => {
    if (event !== source) release();
  };
  const release = () => {
    window.removeEventListener("click", swallow, true);
    window.removeEventListener("pointerdown", restart, true);
    window.removeEventListener("pointercancel", restart, true);
    window.removeEventListener("keydown", release, true);
  };
  window.addEventListener("click", swallow, true);
  window.addEventListener("pointerdown", restart, true);
  window.addEventListener("pointercancel", restart, true);
  window.addEventListener("keydown", release, true);
}

/**
 * Close an open overlay on Escape or a pointerdown outside `ref`. Pass `null`
 * for `ref` when what counts as inside isn't one element, and say so with
 * `ignore` instead.
 *
 * The pointerdown listener is capture-phase: a bubble-phase one is blinded by
 * any handler in between that stops propagation, and an overlay cannot know
 * what it is layered over. `onDismiss` and `ignore` must be stable (wrap in
 * useCallback) so the listeners aren't re-bound every render while open.
 */
export function useDismiss(
  open: boolean,
  onDismiss: () => void,
  ref: RefObject<HTMLElement | null> | null,
  {
    behavior = "pass-through",
    escape: dismissOnEscape = true,
    ignore,
  }: DismissOptions = {},
) {
  useEffect(() => {
    if (!open) return;
    const inside = (target: Element) =>
      Boolean(ref?.current?.contains(target)) || Boolean(ignore?.(target));
    const onKey = (event: KeyboardEvent) => {
      if (dismissOnEscape && event.key === "Escape") onDismiss();
    };
    const onPointer = (event: PointerEvent) => {
      const target = event.target as Element | null;
      if (!target || inside(target)) return;
      // Outside this overlay, but inside one that is also open: the gesture is
      // that overlay's to answer, and swallowing its click from behind would
      // cost the user the control they actually aimed at.
      if (behavior === "consume" && !claimedByAnotherScope(inside, target)) {
        consumeActivation(event);
      }
      onDismiss();
    };
    openScopes.add(inside);
    window.addEventListener("keydown", onKey);
    window.addEventListener("pointerdown", onPointer, true);
    return () => {
      openScopes.delete(inside);
      window.removeEventListener("keydown", onKey);
      window.removeEventListener("pointerdown", onPointer, true);
    };
  }, [open, onDismiss, ref, behavior, dismissOnEscape, ignore]);
}

"use client";

import { useMemo, useRef } from "react";
import { isHoveringPointer } from "@/lib/touch";

interface BoundaryEvent {
  pointerId: number;
  pointerType: string;
  buttons: number;
}

export interface HoverGesture {
  /** True when this enter starts a hover: the pointer arrived resting, not pressing. */
  enter: (event: BoundaryEvent) => boolean;
  /** True when this leave ends a hover that entered as one. */
  leave: (event: BoundaryEvent) => boolean;
}

/**
 * Pairs a surface's enter with its leave, per pointer.
 *
 * `isHoveringPointer` answers the question the *enter* asks — is this pointer
 * resting on the surface or pressing it — and both boundary cases go wrong if
 * the leave is asked the same question again:
 *
 * - A pen with no hover never rests. It arrives in contact, taps, and the spec
 *   then requires its boundary events after `pointerup`, so the leave carries
 *   `buttons: 0` and reads as a mouse gliding off. Hover teardown then undid
 *   the tap — the panel the pen had just opened closed under it.
 * - A mouse pressed on the surface and dragged off leaves with `buttons: 1`.
 *   Skipping teardown there strands the surface open: the release happens
 *   outside, and no second leave ever comes.
 *
 * So the state a hover holds is released by the pointer that took it, whatever
 * the buttons say at the boundary, and a pointer that arrived in contact never
 * took it in the first place. Contact is the exception tracked here, not
 * hover: a leave from a pointer this surface never saw enter — mounted under
 * the cursor, say — still counts, since the alternative is state with no way
 * out.
 */
export function useHoverGesture(): HoverGesture {
  const contact = useRef(new Set<number>());

  return useMemo(
    () => ({
      enter: (event) => {
        if (isHoveringPointer(event)) {
          contact.current.delete(event.pointerId);
          return true;
        }
        contact.current.add(event.pointerId);
        return false;
      },
      leave: (event) => {
        const arrivedInContact = contact.current.delete(event.pointerId);
        return !arrivedInContact && event.pointerType !== "touch";
      },
    }),
    [],
  );
}

"use client";

import { useMemo, useRef } from "react";

/** What a pointerdown recorded, read back by the click that ends its gesture. */
export interface TapRecord<S> {
  /** Which input started the gesture. */
  pointerType: string;
  /** What the surface was showing when it started. */
  state: S;
}

export interface TapGesture<S> {
  /** Record the gesture a pointerdown starts, with the state it starts in. */
  start: (event: { pointerType: string }, state: S) => void;
  /** Read the record and clear it. `null` when no pointer is behind this click. */
  take: () => TapRecord<S> | null;
  /** Drop the record: this gesture will never spend it on a click. */
  drop: () => void;
}

/**
 * The pointer gesture behind a click, recorded where the click cannot report
 * it. A `click` carries no `pointerType` in the engines that matter, so the
 * `pointerdown` before it is the only thing that says which input activated
 * the control — and whether one did at all, since keyboard activation
 * synthesizes a click with no pointer behind it.
 *
 * State goes in with the record because a click reports that no better: a
 * browser that focuses a control on contact can open the very panel the tap
 * was meant to open, and reading "is it open" at click time then undoes it.
 * What the gesture started against is what it acts on.
 *
 * The record is spent by one click and dropped by everything else, because a
 * record that outlives its gesture is worse than none:
 *
 * - A scroll or an OS gesture takes the touch away — `pointercancel`, no click
 *   ever — and the finger would sit in the record until some later click.
 * - That later click is often `Enter` on a keyboard, which arrives with no
 *   pointerdown of its own and would inherit the abandoned finger. A keydown
 *   is the start of a keyboard activation and never part of a tap, so it drops
 *   the record too.
 *
 * Both ends have to be wired by the surface: `drop` on `onPointerCancel` and
 * on `onKeyDown`.
 */
export function useTapGesture<S>(): TapGesture<S> {
  const record = useRef<TapRecord<S> | null>(null);

  return useMemo(
    () => ({
      start: (event, state) => {
        record.current = { pointerType: event.pointerType, state };
      },
      take: () => {
        const spent = record.current;
        record.current = null;
        return spent;
      },
      drop: () => {
        record.current = null;
      },
    }),
    [],
  );
}

import { clsx, type ClassValue } from "clsx"
import { twMerge } from "tailwind-merge"

export function cn(...inputs: ClassValue[]) {
  return twMerge(clsx(inputs))
}

// Shared touch primitives. iOS and iPadOS run their own gestures on top of the
// page — the long-press selection callout and the selection it drags in with
// it — and they win: once the platform claims a touch it cancels ours
// mid-gesture, so a press-and-hold or a drag simply dies. Surfaces that own
// their gesture have to opt out.
//
// What the two classes below cover, precisely:
// - `-webkit-touch-callout: none` stops iOS's long-press callout. WebKit-only:
//   it is not a property other engines have, so it is inert everywhere else.
// - `user-select: none` stops the long-press selection on every engine,
//   Android included, and stops a drag from painting a selection under the
//   cursor. It is inherited, so it reaches every descendant — which is why the
//   two classes differ only in whether they apply it unconditionally.
// What neither covers:
// - Chrome for Android's long-press menu on a link or an image. No CSS
//   suppresses it; a gesture surface that wraps one needs its own
//   `onContextMenu` with `preventDefault()`.
// - The native drag of an `<img>` or `<a>` descendant. `-webkit-user-drag` is
//   not inherited and plain divs and buttons are not drag sources, so setting
//   it on the surface does nothing — the child itself needs `draggable={false}`.

/**
 * Classes for a surface that *is* the control: a thumb, a drum, a stage, a
 * handle, a hold button. Selection is suppressed on every input, because a
 * drag that highlights the control's own label is wrong on a mouse too.
 * Compose with `touch-none` when the surface also owns the scroll axis — leave
 * it off when the page must still scroll from there.
 */
export const TOUCH_GESTURE_CLASS = "select-none [-webkit-touch-callout:none]";

/**
 * The same opt-out for a gesture surface that wraps content the consumer owns:
 * a scroller, a context-menu trigger, a sheet header, a list row. Selection is
 * suppressed only where the platform runs its own press gestures — a coarse
 * pointer — so a mouse user can still select and copy that content. If the
 * gesture itself would paint a selection under the cursor, add `select-none`
 * for the duration of the gesture rather than reaching for
 * `TOUCH_GESTURE_CLASS`.
 *
 * `pointer: coarse` describes the *primary* pointer and nothing else, so a
 * hybrid machine reads it wrong in both directions: a tablet with a mouse
 * plugged in keeps touch as primary and loses mouse selection, and a laptop
 * with a touchscreen keeps the mouse as primary and leaves selection live
 * under a finger. No media query can answer per interaction — the query is
 * about the device, and the question is about the gesture in progress. The
 * default stays here because it is right on the machines that are one thing or
 * the other, and losing a selection is a nuisance; where the miss costs a
 * *gesture* instead, the surface pairs it with `holdSelection` on the press.
 */
export const TOUCH_GESTURE_CONTENT_CLASS =
  "[-webkit-touch-callout:none] pointer-coarse:select-none";

/**
 * Grow a small control's *hit area* to at least 44×44px (WCAG 2.5.5, Apple
 * HIG) on a coarse pointer, without changing what it looks like or the space
 * it takes in layout. An invisible `::after` box, centered on the control and
 * `max(100%, 2.75rem)` on each axis, catches the taps: a 32px icon button
 * reaches 6px past each edge, a wide 40px button only grows vertically, and a
 * control already 44px or larger is left as it is. Hit-testing a pseudo
 * element lands on its owner, so handlers, focus and `:active` all behave.
 *
 * Mouse and trackpad rendering is untouched — nothing here applies outside
 * `pointer: coarse`. Requirements on the element it goes on:
 * - It must be the containing block: add `relative` (and keep it mergeable, so
 *   a consumer's `absolute` still wins through `cn`).
 * - It must not clip itself (`overflow-hidden`), or the overhang is clipped
 *   away along with its hit area.
 * - It must render children: `<input>` and other void elements have no
 *   `::after`. Put it on the wrapper or label instead.
 * - It must not already use `::after` for something visible.
 *
 * Centered 44px means two 32px buttons with a 4px gap overlap by 8px; the
 * later one wins that strip, which still ends well short of the earlier
 * button's visual center. Below a ~32px pitch the later neighbour starts
 * eating into that center — use `TOUCH_TARGET_Y_CLASS` for such dense rows.
 *
 * The overhang is real geometry: inside a scroll container it counts as
 * scrollable overflow, so a control flush against a scroller's edge can add a
 * few pixels of scroll on touch screens. Give such a scroller a little padding
 * on that side.
 */
export const TOUCH_TARGET_CLASS =
  "pointer-coarse:after:absolute pointer-coarse:after:top-1/2 pointer-coarse:after:left-1/2 pointer-coarse:after:size-[max(100%,2.75rem)] pointer-coarse:after:-translate-x-1/2 pointer-coarse:after:-translate-y-1/2 pointer-coarse:after:content-['']";

/**
 * `TOUCH_TARGET_CLASS` on the vertical axis only, for controls packed tighter
 * than ~32px apart in a row (pagination dots, dense swatches), where growing
 * sideways would hand most of each control to its neighbour. Same rules.
 */
export const TOUCH_TARGET_Y_CLASS =
  "pointer-coarse:after:absolute pointer-coarse:after:inset-x-0 pointer-coarse:after:top-1/2 pointer-coarse:after:h-[max(100%,2.75rem)] pointer-coarse:after:-translate-y-1/2 pointer-coarse:after:content-['']";

/**
 * Suppress selection on `element` for as long as a gesture is running on it,
 * whatever the primary pointer of the machine happens to be. Returns the
 * release. Inline, so it wins over the class above and is gone again the
 * moment the gesture ends.
 *
 * For the press gestures a native selection would otherwise steal — a
 * long-press that opens a menu. Elsewhere prefer the classes: a surface that
 * takes selection away for the whole session is a surface whose text nobody
 * can copy.
 */
export function holdSelection(element: HTMLElement) {
  element.style.setProperty("user-select", "none");
  element.style.setProperty("-webkit-user-select", "none");
  return () => {
    element.style.removeProperty("user-select");
    element.style.removeProperty("-webkit-user-select");
  };
}

/**
 * Pointer capture, best effort. WebKit throws `NotFoundError` when the pointer
 * is already gone by the time the handler runs — routine on iOS, where the
 * system can claim the touch first — and an uncaught throw takes the rest of
 * the handler, the gesture included, down with it. Touch pointers carry
 * implicit capture anyway, so losing it is never fatal.
 */
export function capturePointer(element: Element, pointerId: number) {
  try {
    element.setPointerCapture(pointerId);
  } catch {
    // Pointer is no longer active — implicit capture still applies on touch.
  }
}

/** Release a capture taken with `capturePointer`, ignoring a stale pointer. */
export function releasePointer(element: Element, pointerId: number) {
  try {
    if (element.hasPointerCapture(pointerId)) {
      element.releasePointerCapture(pointerId);
    }
  } catch {
    // Capture was already dropped by the browser.
  }
}

/**
 * Whether this event came from a pointer that is *hovering*: not a touch, and
 * not currently pressed. Which input the user is holding right now is not
 * something a device capability can answer — a touchscreen laptop hovers and
 * taps, and iPadOS reports a fine hovering pointer for a finger — so both
 * paths stay live and each handler branches on the event it was given.
 *
 * A pen resting on the glass is making contact, not hovering: `buttons` is the
 * tell, and it sends a pen tap down the same route a finger takes.
 *
 * This answers what an *enter* asks. A leave is the other half of a pair and
 * has to be read against the enter that started it — `useHoverGesture` in
 * `lib/hooks/use-hover-gesture` does that, and hover surfaces should use it
 * rather than asking this question twice.
 */
export const isHoveringPointer = (event: {
  pointerType: string;
  buttons: number;
}) => event.pointerType !== "touch" && event.buttons === 0;

"use client";
// karaui.kamisama-v0.my.id/components/motion/preview-rail

import { AnimatePresence, motion, useReducedMotion } from "motion/react";
import {
  type MouseEvent,
  type PointerEvent,
  type ReactNode,
  useCallback,
  useId,
  useRef,
  useState,
} from "react";
import { EASE_OUT, SPRING_LAYOUT } from "@/lib/ease";
import { useDismiss } from "@/lib/hooks/use-dismiss";
import { useHoverGesture } from "@/lib/hooks/use-hover-gesture";
import { useTapGesture } from "@/lib/hooks/use-tap-gesture";
import { cn } from "@/lib/utils";

export interface PreviewRailItem {
  id: string;
  label: string;
  ariaLabel?: string;
  description?: ReactNode;
  href?: string;
  target?: "_blank" | "_self" | "_parent" | "_top";
  rel?: string;
}

export interface PreviewRailProps {
  items: PreviewRailItem[];
  label?: string;
  orientation?: "vertical" | "horizontal";
  activeId?: string;
  defaultActiveId?: string;
  onActiveChange?: (id: string) => void;
  onItemSelect?: (item: PreviewRailItem) => void;
  renderPreview?: (item: PreviewRailItem) => ReactNode;
  showPreview?: boolean;
  previewSide?: "before" | "after";
  highlightActive?: boolean;
  itemSize?: number;
  children?: ReactNode;
  className?: string;
  railClassName?: string;
  previewContainerClassName?: string;
  previewClassName?: string;
}

function DefaultPreview({ item }: { item: PreviewRailItem }) {
  return (
    <div
      data-slot="preview-rail-card"
      className="rounded-2xl border border-border bg-card p-4 shadow-sm"
    >
      <p
        data-slot="preview-rail-title"
        className="font-medium text-card-foreground"
      >
        {item.label}
      </p>
      {item.description ? (
        <div
          data-slot="preview-rail-description"
          className="mt-1 text-sm leading-6 text-muted-foreground"
        >
          {item.description}
        </div>
      ) : null}
    </div>
  );
}

export function PreviewRail({
  items,
  label = "Section navigation",
  orientation = "vertical",
  activeId,
  defaultActiveId,
  onActiveChange,
  onItemSelect,
  renderPreview,
  showPreview = true,
  previewSide = "after",
  highlightActive = false,
  itemSize = 24,
  children,
  className,
  railClassName,
  previewContainerClassName,
  previewClassName,
}: PreviewRailProps) {
  const uid = useId();
  const reduce = useReducedMotion();
  const rootRef = useRef<HTMLDivElement>(null);
  const [internalActiveId, setInternalActiveId] = useState(
    defaultActiveId ?? items[0]?.id ?? "",
  );
  const [hoveredId, setHoveredId] = useState<string | null>(null);
  // A finger cannot hover, so a tap lights the tick instead. Kept apart from
  // the hovered one: they end in different ways, and a stray mouse move must
  // not clear a tick the keyboard or a tap chose.
  const [pinnedId, setPinnedId] = useState<string | null>(null);
  const [focusedId, setFocusedId] = useState<string | null>(null);
  // A click carries no pointerType, so the pointerdown before it is what says
  // whether the activation was a tap. Keyboard activation has none at all.
  const tap = useTapGesture<boolean>();
  const hover = useHoverGesture();

  const clearPinned = useCallback(() => setPinnedId(null), []);

  // The next tap outside the rail stands in for the pointer leaving it. The
  // card is a preview, so that tap passes through to whatever it landed on.
  useDismiss(pinnedId !== null, clearPinned, rootRef);

  const requestedActiveId = activeId ?? internalActiveId;
  const selectedId = items.some((item) => item.id === requestedActiveId)
    ? requestedActiveId
    : (items[0]?.id ?? "");
  const displayedId = hoveredId ?? pinnedId ?? focusedId ?? "";
  const highlightedId = displayedId || (highlightActive ? selectedId : "");
  const displayedIndex = items.findIndex((item) => item.id === highlightedId);
  const rowTemplate = items.length
    ? `repeat(${items.length}, ${itemSize}px)`
    : undefined;
  const isHorizontal = orientation === "horizontal";

  const selectItem = (id: string) => {
    if (activeId === undefined) setInternalActiveId(id);
    onActiveChange?.(id);
  };

  return (
    <motion.div
      layoutRoot
      ref={rootRef}
      onBlur={(event) => {
        // Both tick sources leave with the focus: a tap does not always land
        // focus, but when it does, tabbing away must not strand the card.
        if (!event.currentTarget.contains(event.relatedTarget)) {
          setFocusedId(null);
          setPinnedId(null);
        }
      }}
      className={cn(
        "isolate relative flex w-full overflow-visible",
        isHorizontal
          ? "min-h-64 flex-col items-center justify-center"
          : "min-h-80",
        className,
      )}
    >
      <nav
        aria-label={label}
        onPointerLeave={(event) => {
          // A touch pointer leaves on lift, which would clear the tick the tap
          // just chose — that one is cleared by the outside tap instead.
          if (hover.leave(event)) setHoveredId(null);
        }}
        style={
          isHorizontal
            ? { gridTemplateColumns: rowTemplate }
            : { gridTemplateRows: rowTemplate }
        }
        className={cn(
          "relative z-10 grid shrink-0",
          isHorizontal
            ? "h-12 w-fit max-w-full self-center justify-center"
            : "w-12 content-center",
          railClassName,
        )}
      >
        {items.map((item, index) => {
          const selected = item.id === selectedId;
          const highlighted = item.id === highlightedId;
          const distance =
            displayedIndex < 0 ? Number.POSITIVE_INFINITY : Math.abs(index - displayedIndex);
          const scale = highlighted
            ? 1
            : distance === 1
              ? 0.68
              : distance === 2
                ? 0.44
                : 0.25;

          const itemContent = (
            <>
              <motion.span
                data-slot="preview-rail-tick"
                aria-hidden="true"
                animate={isHorizontal ? { scaleY: scale } : { scaleX: scale }}
                transition={reduce ? { duration: 0 } : SPRING_LAYOUT}
                className={cn(
                  "block bg-current",
                  isHorizontal
                    ? "h-12 w-0.5 origin-bottom"
                    : "h-0.5 w-12 origin-left",
                  highlighted ? "text-foreground" : undefined,
                )}
              />
            </>
          );

          const sharedClassName = cn(
            "relative flex text-muted-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 focus-visible:ring-offset-background",
            isHorizontal
              ? "h-12 w-6 items-end justify-center"
              : "h-6 w-12 items-center",
          );
          const sharedStyle = isHorizontal
            ? { width: itemSize }
            : { height: itemSize };
          const handlePointerEnter = (event: PointerEvent<HTMLElement>) => {
            if (hover.enter(event)) setHoveredId(item.id);
          };
          const handlePointerDown = (event: PointerEvent<HTMLElement>) => {
            tap.start(event, pinnedId === item.id);
            setFocusedId(null);
          };
          // A gesture the platform takes away sends no click, and a key press
          // starts an activation that never had a pointer behind it: either
          // one leaves a record the next click would read as a tap of its own.
          const dropGesture = () => tap.drop();
          const handleFocus = (currentTarget: HTMLElement) => {
            if (currentTarget.matches(":focus-visible")) {
              setFocusedId(item.id);
            }
          };
          const handleSelect = (event: MouseEvent<HTMLElement>) => {
            const gesture = tap.take();
            const tapped =
              gesture !== null && gesture.pointerType !== "mouse";

            if (tapped) {
              // A link would otherwise show its preview and leave the page in
              // the same tap, so the card is never read: the first tap lights
              // the tick, the second follows the link.
              if (item.href && !gesture.state) {
                event.preventDefault();
                setPinnedId(item.id);
                return;
              }
              setPinnedId(item.id);
            }

            selectItem(item.id);
            onItemSelect?.(item);
          };

          return item.href ? (
            <a
              key={item.id}
              data-slot="preview-rail-item"
              href={item.href}
              target={item.target}
              rel={
                item.rel ??
                (item.target === "_blank" ? "noreferrer noopener" : undefined)
              }
              aria-label={item.ariaLabel ?? item.label}
              aria-current={selected ? "page" : undefined}
              onPointerEnter={handlePointerEnter}
              onPointerDown={handlePointerDown}
              onPointerCancel={dropGesture}
              onKeyDown={dropGesture}
              onFocus={(event) => handleFocus(event.currentTarget)}
              onClick={handleSelect}
              style={sharedStyle}
              className={sharedClassName}
            >
              {itemContent}
            </a>
          ) : (
            <button
              key={item.id}
              data-slot="preview-rail-item"
              type="button"
              aria-label={item.ariaLabel ?? item.label}
              aria-current={selected ? "location" : undefined}
              onPointerEnter={handlePointerEnter}
              onPointerDown={handlePointerDown}
              onPointerCancel={dropGesture}
              onKeyDown={dropGesture}
              onFocus={(event) => handleFocus(event.currentTarget)}
              onClick={handleSelect}
              style={sharedStyle}
              className={sharedClassName}
            >
              {itemContent}
            </button>
          );
        })}
      </nav>

      {showPreview ? (
        <div
          aria-hidden="true"
          style={
            isHorizontal
              ? { gridTemplateColumns: rowTemplate }
              : { gridTemplateRows: rowTemplate }
          }
          className={cn(
            "pointer-events-none absolute z-50 grid",
            isHorizontal
              ? "top-1/2 left-1/2 h-5 w-fit max-w-full -translate-x-1/2 -translate-y-1/2 justify-center"
              : previewSide === "before"
                ? "inset-y-0 right-16 left-4 content-center"
                : "inset-y-0 right-4 left-16 content-center",
            previewContainerClassName,
          )}
        >
          {items.map((item) => (
            <div
              key={item.id}
              style={
                isHorizontal ? { width: itemSize } : { height: itemSize }
              }
              className={cn(
                "relative flex items-center",
                isHorizontal ? "justify-center" : undefined,
              )}
            >
              {item.id === displayedId ? (
                <div
                  className={cn(
                    isHorizontal
                      ? "absolute bottom-12 left-1/2 w-72 -translate-x-1/2"
                      : cn(
                          "w-full max-w-sm",
                          previewSide === "before" && "ml-auto",
                        ),
                    previewClassName,
                  )}
                >
                  <motion.div
                    layoutId={`preview-rail-card-${uid}`}
                    transition={reduce ? { duration: 0 } : SPRING_LAYOUT}
                  >
                    <AnimatePresence mode="wait" initial={false}>
                      <motion.div
                        key={item.id}
                        initial={
                          reduce
                            ? { opacity: 0 }
                            : { opacity: 0, y: 4, filter: "blur(6px)" }
                        }
                        animate={
                          reduce
                            ? { opacity: 1 }
                            : { opacity: 1, y: 0, filter: "blur(0px)" }
                        }
                        exit={
                          reduce
                            ? { opacity: 0 }
                            : {
                                opacity: 0,
                                y: -2,
                                filter: "blur(4px)",
                                transition: {
                                  duration: 0.12,
                                  ease: EASE_OUT,
                                },
                              }
                        }
                        transition={{
                          duration: reduce ? 0 : 0.18,
                          ease: EASE_OUT,
                        }}
                      >
                        {renderPreview ? (
                          renderPreview(item)
                        ) : (
                          <DefaultPreview item={item} />
                        )}
                      </motion.div>
                    </AnimatePresence>
                  </motion.div>
                </div>
              ) : null}
            </div>
          ))}
        </div>
      ) : null}

      {children ? (
        <div className="min-h-0 min-w-0 flex-1">{children}</div>
      ) : null}
    </motion.div>
  );
}