Message Scroller

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

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

// 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 | SVGElement | 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;
      },
    }),
    [],
  );
}

// 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";

/**
 * 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;

/**
 * Elements that can usually take keyboard focus. The selector cannot see
 * everything focus() checks (an element under `display: none`, say), so a
 * caller that needs certainty tries focus() and checks where it landed.
 */
export const FOCUSABLE_SELECTOR = [
  "a[href]",
  "button:not(:disabled)",
  "input:not(:disabled):not([type='hidden'])",
  "select:not(:disabled)",
  "textarea:not(:disabled)",
  "[tabindex]:not([tabindex='-1'])",
].join(",");

"use client";

import {
  type KeyboardEvent,
  type RefObject,
  useEffect,
  useMemo,
  useRef,
} from "react";
import { useOnOpen } from "@/lib/hooks/use-on-open";
import { useRowCursor } from "@/lib/hooks/use-row-cursor";

export interface ListboxRow {
  id: string;
  label: string;
  disabled?: boolean;
}

// How long typed characters keep building one typeahead query.
const TYPEAHEAD_MS = 500;

/**
 * Keyboard model for a popup listbox whose options are focusable buttons.
 *
 * The active option is resolved during render through `useRowCursor`, so the
 * roving `tabIndex` and the next key press always agree with what is on
 * screen. Opening starts on the selected option, or the first enabled one.
 * Arrow keys, Home and End move between enabled options, and printable
 * characters jump to the next option whose label starts with what was typed.
 * DOM focus follows the active option while the list is open; each option
 * carries its id in `data-listbox-id` so the list can find it.
 */
export function useListbox({
  open,
  rows,
  selected,
  list,
}: {
  open: boolean;
  rows: readonly ListboxRow[];
  selected: string | undefined;
  list: RefObject<HTMLElement | null>;
}) {
  const enabled = useMemo(() => rows.filter((row) => !row.disabled), [rows]);
  const { activeIndex, moveTo, moveActive } = useRowCursor(enabled, "");
  useOnOpen(open, () =>
    moveTo(enabled.some((row) => row.id === selected) ? (selected ?? null) : null),
  );
  const activeId = enabled[activeIndex]?.id;
  const typed = useRef({ text: "", at: 0 });
  // A list rendered open does not take focus from the page on mount; focus
  // follows only once it has been opened, or once focus is already inside.
  const openedOnMount = useRef(open);
  useEffect(() => {
    if (!open) openedOnMount.current = false;
  }, [open]);

  useEffect(() => {
    if (!open || activeId === undefined) return;
    if (
      openedOnMount.current &&
      !list.current?.contains(document.activeElement)
    )
      return;
    const option = Array.from(
      list.current?.querySelectorAll<HTMLElement>("[data-listbox-id]") ?? [],
    ).find((element) => element.dataset.listboxId === activeId);
    option?.focus({ preventScroll: false });
  }, [open, activeId, list]);

  const onKeyDown = (event: KeyboardEvent) => {
    const { key } = event;
    if (key === "ArrowDown" || key === "ArrowUp") {
      event.preventDefault();
      moveActive(key === "ArrowDown" ? 1 : -1);
    } else if (key === "Home" || key === "End") {
      event.preventDefault();
      const row = key === "Home" ? enabled[0] : enabled[enabled.length - 1];
      if (row) moveTo(row.id);
    } else if (
      key.length === 1 &&
      key !== " " &&
      !event.ctrlKey &&
      !event.metaKey &&
      !event.altKey
    ) {
      const now = Date.now();
      const char = key.toLowerCase();
      const text =
        now - typed.current.at < TYPEAHEAD_MS ? typed.current.text + char : char;
      typed.current = { text, at: now };
      // A repeated single letter cycles through the options that start with it.
      const from = text.length === 1 ? activeIndex + 1 : activeIndex;
      for (let step = 0; step < enabled.length; step++) {
        const row = enabled[(from + step) % enabled.length];
        if (row.label.toLowerCase().startsWith(text)) {
          moveTo(row.id);
          break;
        }
      }
    }
  };

  return { activeId, onKeyDown };
}

"use client";

import { useCallback, useState } from "react";
import { getFaviconUrl } from "@/lib/favicon";

/**
 * Resolves a site favicon and drops it once it is known to be unusable, so
 * callers can draw their own glyph instead of a broken image. Plenty of sites
 * answer `/favicon.ico` with a 403 or 404, and `onError` is not enough to catch
 * it: an image the browser starts loading from server-rendered HTML usually
 * fails before React attaches a handler, and that event is never replayed.
 * `decode()` settles on the image's final state instead of relying on an event
 * firing at the right moment.
 */
export function useFavicon(url?: string) {
  const resolved = url ? getFaviconUrl(url) : null;
  const [failedSrc, setFailedSrc] = useState<string | null>(null);
  const src = resolved && resolved !== failedSrc ? resolved : null;

  const ref = useCallback(
    (img: HTMLImageElement | null) => {
      if (!img || !src) return;

      let released = false;
      img.decode().catch(() => {
        if (!released) setFailedSrc(src);
      });

      // The node is going away or the source changed; a late rejection then
      // describes an image we are no longer showing.
      return () => {
        released = true;
      };
    },
    [src],
  );

  return { src, ref };
}

"use client";

import { useEffect, useState } from "react";

/**
 * Returns true only on devices that have a true hover (mouse / trackpad).
 * Touch devices fire phantom `:hover` on tap that sticks until tap-elsewhere
 * — gate hover-only effects (scale lifts, magnetic pulls) behind this.
 */
export function useHoverCapable() {
  const [canHover, setCanHover] = useState(false);

  useEffect(() => {
    if (typeof window === "undefined" || !window.matchMedia) return;
    const mq = window.matchMedia("(hover: hover) and (pointer: fine)");
    const update = () => setCanHover(mq.matches);
    update();
    mq.addEventListener?.("change", update);
    return () => mq.removeEventListener?.("change", update);
  }, []);

  return canHover;
}

"use client";

import { useState } from "react";

/**
 * Runs `start` during the render in which `open` becomes true.
 *
 * Opening a list starts a fresh session — an empty query, the highlight back at
 * the top — and that is a resolution, not a side effect: a passive effect runs
 * after the commit, so the new session would carry the last one's state for a
 * window in which a key press can land.
 *
 * `start` may only set state belonging to the calling component. Anything that
 * reaches outside it — a consumer's callback, a DOM write, moving focus — is a
 * side effect, and React rejects a callback that sets another component's state
 * during this one's render. Put those in an effect keyed to `open`.
 */
export function useOnOpen(open: boolean, start: () => void) {
  const [wasOpen, setWasOpen] = useState(open);
  if (open !== wasOpen) {
    setWasOpen(open);
    if (open) start();
  }
}

"use client";

import { useCallback, useLayoutEffect, useRef, useState } from "react";

/**
 * Where the keyboard or the pointer last moved to: the row's id, stamped with
 * the query it was placed under.
 */
type RowCursor = { id: string; query: string };

/** The cursor's row, or -1 once the query has moved on or the row has left. */
function indexOfCursor(
  rows: readonly { id: string }[],
  query: string,
  cursor: RowCursor | null,
) {
  if (cursor === null || cursor.query !== query) return -1;
  return rows.findIndex((row) => row.id === cursor.id);
}

/**
 * The highlighted row of a list whose rows can change under it.
 *
 * Which row is highlighted is resolved during render, never in a passive
 * effect: a passive effect runs after the commit, so a list that had just
 * changed would carry an `aria-activedescendant` naming a row that has left it,
 * and a key pressed in that window would commit the wrong row or nothing at
 * all.
 *
 * The cursor holds the row's id, not its position. A position alone cannot tell
 * a list that shrank from one that swapped its rows for a different set of the
 * same length, and the second case is the one that silently hands Enter to a
 * row the user never chose. A cursor whose row has left the list returns the
 * highlight to the first row rather than to the nearest surviving one: the row
 * the user aimed at is gone, and the first row is where a new query already
 * puts the highlight.
 *
 * Pass the query the list is filtered by. The cursor is stamped with it and
 * dropped when it changes, so a caller cannot forget to clear it — including a
 * caller whose query arrives as a prop and so never runs its own handler. Rows
 * that come back under a query that has moved on cannot revive it either.
 * `moveTo(null)` is for deliberate resets, such as reopening the list.
 *
 * Both callbacks keep one identity for the life of the component, and read the
 * rows and the query through a ref to do it. A caller will put them in an
 * effect's dependencies — the exhaustive-deps rule makes it — and a `moveTo`
 * rebuilt on every keystroke would re-run that effect on every keystroke.
 */
export function useRowCursor(rows: readonly { id: string }[], query: string) {
  const [cursor, setCursor] = useState<RowCursor | null>(null);
  // Written after commit, not during render: a render React discards or has not
  // finished still runs the component body, and an event handler that read this
  // in that window would stamp the cursor with a query the committed tree does
  // not have.
  const latest = useRef({ rows, query });
  useLayoutEffect(() => {
    latest.current = { rows, query };
  });

  const cursorRow = indexOfCursor(rows, query, cursor);
  // Cleared rather than ignored: React re-runs this render with the cursor
  // already gone, so rows that come back cannot revive a highlight the user has
  // stopped aiming at.
  if (cursor !== null && cursorRow < 0) setCursor(null);

  const moveTo = useCallback(
    (id: string | null) =>
      setCursor(id === null ? null : { id, query: latest.current.query }),
    [],
  );

  const moveActive = useCallback((direction: 1 | -1) => {
    const { rows: live, query: liveQuery } = latest.current;
    const last = live.length - 1;
    if (last < 0) return;
    // Steps from the row the cursor is really on, inside the update, so that
    // two keys landing in one batch move two rows rather than one.
    setCursor((current) => {
      const at = Math.max(indexOfCursor(live, liveQuery, current), 0);
      const next = Math.min(Math.max(at + direction, 0), last);
      return { id: live[next].id, query: liveQuery };
    });
  }, []);

  return { activeIndex: cursorRow < 0 ? 0 : cursorRow, moveTo, moveActive };
}

/** Resolve a website URL to its conventional root favicon location. */
export function getFaviconUrl(value: string) {
  try {
    return new URL("/favicon.ico", value).toString();
  } catch {
    return null;
  }
}

"use client";
// beui.dev/components/agents/message-scroller

import { useReducedMotion } from "motion/react";
import {
  type ComponentPropsWithRef,
  type Ref,
  useCallback,
  useEffect,
  useLayoutEffect,
  useRef,
  useState,
} from "react";
import {
  PreviewRail,
  type PreviewRailItem,
} from "@/components/motion/preview-rail";
import { cn } from "@/lib/utils";

const PREVIEW_TITLE_LENGTH = 56;
const PREVIEW_DESCRIPTION_LENGTH = 88;

function truncateMessageText(text: string, limit: number) {
  if (text.length <= limit) return text;
  const excerpt = text.slice(0, limit);
  const boundary = excerpt.lastIndexOf(" ");
  return `${excerpt.slice(0, boundary > limit * 0.65 ? boundary : limit).trim()}…`;
}

function getMessageText(message: HTMLElement) {
  const surface =
    message.querySelector<HTMLElement>('[data-slot="message-bubble-content"]') ??
    message.querySelector<HTMLElement>('[data-slot="message-content"]') ??
    message;
  return (surface.textContent ?? "").replace(/\s+/g, " ").trim();
}

function getMessagePreview(
  message: HTMLElement,
  assistantResponse?: HTMLElement,
) {
  const text = getMessageText(message);
  if (!text) {
    return { label: "Message", description: undefined };
  }

  if (text.length <= PREVIEW_TITLE_LENGTH) {
    const responseText = assistantResponse
      ? getMessageText(assistantResponse)
      : "";
    return {
      label: text,
      description: responseText
        ? truncateMessageText(responseText, PREVIEW_DESCRIPTION_LENGTH)
        : undefined,
    };
  }

  const titleExcerpt = text.slice(0, PREVIEW_TITLE_LENGTH);
  const titleBoundary = titleExcerpt.lastIndexOf(" ");
  const titleEnd =
    titleBoundary > PREVIEW_TITLE_LENGTH * 0.65
      ? titleBoundary
      : PREVIEW_TITLE_LENGTH;
  const label = `${text.slice(0, titleEnd).trim()}…`;
  const responseText = assistantResponse
    ? getMessageText(assistantResponse)
    : text.slice(titleEnd).trim();
  return {
    label,
    description: responseText
      ? truncateMessageText(responseText, PREVIEW_DESCRIPTION_LENGTH)
      : undefined,
  };
}

export interface MessageScrollerProps extends ComponentPropsWithRef<"div"> {
  /** Keep streamed output pinned while the reader remains near the end. */
  followOutput?: boolean;
  /** Distance from the end that still counts as following the output. */
  followThreshold?: number;
  /** Smoothly follow growing content. */
  smooth?: boolean;
  /** Reports when the reader leaves or returns to the live edge. */
  onFollowChange?: (following: boolean) => void;
  /** Accessible label for the scrollable transcript. */
  label?: string;
  /** Marks the transcript as waiting for more streamed content. */
  busy?: boolean;
  /** Adds a compact rail for navigating between rendered Message rows. */
  navigation?: "rail";
  /** Accessible label for the optional message navigation rail. */
  navigationLabel?: string;
  viewportClassName?: string;
  contentClassName?: string;
  railClassName?: string;
  viewportRef?: Ref<HTMLElement>;
  viewportProps?: Omit<
    ComponentPropsWithRef<"section">,
    "children" | "className" | "ref"
  >;
  contentProps?: Omit<
    ComponentPropsWithRef<"div">,
    "children" | "className" | "ref"
  >;
}

export function MessageScroller({
  followOutput = true,
  followThreshold = 56,
  smooth = true,
  onFollowChange,
  label = "Conversation",
  busy,
  navigation,
  navigationLabel = "Message navigation",
  viewportClassName,
  contentClassName,
  railClassName,
  viewportRef: externalViewportRef,
  viewportProps,
  contentProps,
  className,
  children,
  ...props
}: MessageScrollerProps) {
  const reduce = useReducedMotion() ?? false;
  const viewportRef = useRef<HTMLElement>(null);
  const contentRef = useRef<HTMLDivElement>(null);
  const followingRef = useRef(followOutput);
  const programmaticScrollRef = useRef(false);
  const scrollTimerRef = useRef<number | undefined>(undefined);
  const frameRef = useRef<number | undefined>(undefined);
  const railFrameRef = useRef<number | undefined>(undefined);
  const railIdRef = useRef(new WeakMap<HTMLElement, string>());
  const railIdCounterRef = useRef(0);
  const railTargetsRef = useRef(new Map<string, HTMLElement>());
  const [railItems, setRailItems] = useState<PreviewRailItem[]>([]);
  const [activeRailId, setActiveRailId] = useState("");
  const [railOverflowing, setRailOverflowing] = useState(false);
  const {
    onScroll: onViewportScroll,
    onWheel: onViewportWheel,
    onTouchStart: onViewportTouchStart,
    onKeyDown: onViewportKeyDown,
    ...restViewportProps
  } = viewportProps ?? {};

  const setViewportRef = useCallback(
    (node: HTMLElement | null) => {
      viewportRef.current = node;
      if (typeof externalViewportRef === "function") {
        externalViewportRef(node);
      } else if (externalViewportRef) {
        externalViewportRef.current = node;
      }
    },
    [externalViewportRef],
  );

  const setFollowing = useCallback(
    (next: boolean) => {
      if (followingRef.current === next) return;
      followingRef.current = next;
      onFollowChange?.(next);
    },
    [onFollowChange],
  );

  const updateActiveRailItem = useCallback(() => {
    if (navigation !== "rail") return;
    const viewport = viewportRef.current;
    const targets = [...railTargetsRef.current.entries()];
    if (!viewport || targets.length === 0) return;

    const viewportRect = viewport.getBoundingClientRect();
    if (viewport.scrollTop <= followThreshold) {
      const firstId = targets[0]?.[0] ?? "";
      setActiveRailId((current) => (current === firstId ? current : firstId));
      return;
    }

    const distanceFromEnd =
      viewport.scrollHeight - viewport.scrollTop - viewport.clientHeight;
    if (distanceFromEnd <= followThreshold) {
      const lastId = targets.at(-1)?.[0] ?? "";
      setActiveRailId((current) => (current === lastId ? current : lastId));
      return;
    }

    const viewportCenter = viewportRect.top + viewportRect.height / 2;
    let nearestId = targets[0]?.[0] ?? "";
    let nearestDistance = Number.POSITIVE_INFINITY;

    for (const [id, element] of targets) {
      const rect = element.getBoundingClientRect();
      const messageCenter = rect.top + rect.height / 2;
      const distance = Math.abs(messageCenter - viewportCenter);
      if (distance < nearestDistance) {
        nearestDistance = distance;
        nearestId = id;
      }
    }

    setActiveRailId((current) =>
      current === nearestId ? current : nearestId,
    );
  }, [followThreshold, navigation]);

  const syncRailItems = useCallback(() => {
    if (navigation !== "rail") return;
    const content = contentRef.current;
    const viewport = viewportRef.current;
    if (!content || !viewport) return;

    const messages = Array.from(
      content.querySelectorAll<HTMLElement>('[data-slot="message"]'),
    );
    const targets = new Map<string, HTMLElement>();
    const nextItems = messages.map((message, index) => {
      let id = railIdRef.current.get(message);
      if (!id) {
        railIdCounterRef.current += 1;
        id = `message-rail-${railIdCounterRef.current}`;
        railIdRef.current.set(message, id);
      }
      targets.set(id, message);
      const sender = message.dataset.from ?? "conversation";
      const assistantResponse =
        sender === "user"
          ? messages
              .slice(index + 1)
              .find((candidate) => candidate.dataset.from === "assistant")
          : undefined;
      const preview = getMessagePreview(message, assistantResponse);

      return {
        id,
        label: preview.label,
        description: preview.description,
        ariaLabel: `Go to ${sender} message ${index + 1} of ${messages.length}`,
      };
    });

    railTargetsRef.current = targets;
    setRailItems((current) => {
      const unchanged =
        current.length === nextItems.length &&
        current.every(
          (item, index) =>
            item.id === nextItems[index]?.id &&
            item.label === nextItems[index]?.label &&
            item.description === nextItems[index]?.description &&
            item.ariaLabel === nextItems[index]?.ariaLabel,
        );
      return unchanged ? current : nextItems;
    });
    setRailOverflowing(
      viewport.scrollHeight > viewport.clientHeight + 1 && messages.length > 1,
    );
  }, [navigation]);

  const scheduleRailSync = useCallback(() => {
    if (navigation !== "rail") return;
    if (railFrameRef.current) cancelAnimationFrame(railFrameRef.current);
    railFrameRef.current = requestAnimationFrame(() => {
      syncRailItems();
      updateActiveRailItem();
    });
  }, [navigation, syncRailItems, updateActiveRailItem]);

  const scrollToEnd = useCallback((behavior: ScrollBehavior) => {
    const viewport = viewportRef.current;
    if (!viewport) return;

    programmaticScrollRef.current = true;
    if (typeof viewport.scrollTo === "function") {
      viewport.scrollTo({ top: viewport.scrollHeight, behavior });
    } else {
      viewport.scrollTop = viewport.scrollHeight;
    }
    if (scrollTimerRef.current) window.clearTimeout(scrollTimerRef.current);
    scrollTimerRef.current = window.setTimeout(() => {
      programmaticScrollRef.current = false;
    }, behavior === "smooth" ? 320 : 0);
  }, []);

  const handleScroll = useCallback(() => {
    const viewport = viewportRef.current;
    if (!viewport || programmaticScrollRef.current) return;

    const distance =
      viewport.scrollHeight - viewport.scrollTop - viewport.clientHeight;
    setFollowing(distance <= followThreshold);
    updateActiveRailItem();
  }, [followThreshold, setFollowing, updateActiveRailItem]);

  const leaveLiveEdge = useCallback(() => {
    programmaticScrollRef.current = false;
  }, []);

  useLayoutEffect(() => {
    followingRef.current = followOutput;
    if (!followOutput) return;

    frameRef.current = requestAnimationFrame(() => scrollToEnd("auto"));
    return () => {
      if (frameRef.current) cancelAnimationFrame(frameRef.current);
    };
  }, [followOutput, scrollToEnd]);

  useEffect(() => {
    const content = contentRef.current;
    if (!content || typeof ResizeObserver === "undefined") return;

    const observer = new ResizeObserver(() => {
      scheduleRailSync();
      if (!followOutput || !followingRef.current) return;
      scrollToEnd(reduce || !smooth ? "auto" : "smooth");
    });
    observer.observe(content);

    return () => observer.disconnect();
  }, [followOutput, reduce, scheduleRailSync, scrollToEnd, smooth]);

  useEffect(() => {
    if (navigation !== "rail") {
      railTargetsRef.current.clear();
      setRailItems([]);
      setRailOverflowing(false);
      return;
    }

    const content = contentRef.current;
    const viewport = viewportRef.current;
    if (!content || !viewport) return;

    scheduleRailSync();
    const mutationObserver =
      typeof MutationObserver === "undefined"
        ? null
        : new MutationObserver(scheduleRailSync);
    mutationObserver?.observe(content, {
      childList: true,
      characterData: true,
      subtree: true,
    });

    const resizeObserver =
      typeof ResizeObserver === "undefined"
        ? null
        : new ResizeObserver(scheduleRailSync);
    resizeObserver?.observe(content);
    resizeObserver?.observe(viewport);

    return () => {
      mutationObserver?.disconnect();
      resizeObserver?.disconnect();
    };
  }, [navigation, scheduleRailSync]);

  useEffect(
    () => () => {
      if (scrollTimerRef.current) window.clearTimeout(scrollTimerRef.current);
      if (frameRef.current) cancelAnimationFrame(frameRef.current);
      if (railFrameRef.current) cancelAnimationFrame(railFrameRef.current);
    },
    [],
  );

  const scrollToRailItem = useCallback(
    (item: PreviewRailItem) => {
      const viewport = viewportRef.current;
      const target = railTargetsRef.current.get(item.id);
      if (!viewport || !target) return;

      const lastItem = railItems.at(-1)?.id === item.id;
      setActiveRailId(item.id);
      if (lastItem) {
        setFollowing(true);
        scrollToEnd(reduce || !smooth ? "auto" : "smooth");
        return;
      }

      setFollowing(false);
      programmaticScrollRef.current = true;
      const viewportRect = viewport.getBoundingClientRect();
      const targetRect = target.getBoundingClientRect();
      const top =
        viewport.scrollTop +
        targetRect.top -
        viewportRect.top -
        (viewport.clientHeight - targetRect.height) / 2;
      const behavior = reduce || !smooth ? "auto" : "smooth";

      if (typeof viewport.scrollTo === "function") {
        viewport.scrollTo({ top, behavior });
      } else {
        viewport.scrollTop = top;
      }
      if (scrollTimerRef.current) window.clearTimeout(scrollTimerRef.current);
      scrollTimerRef.current = window.setTimeout(() => {
        programmaticScrollRef.current = false;
      }, behavior === "smooth" ? 320 : 0);
    },
    [railItems, reduce, scrollToEnd, setFollowing, smooth],
  );

  const viewport = (
    <section
      ref={setViewportRef}
      aria-label={label}
      {...restViewportProps}
      onScroll={(event) => {
        handleScroll();
        onViewportScroll?.(event);
      }}
      onWheel={(event) => {
        leaveLiveEdge();
        onViewportWheel?.(event);
      }}
      onTouchStart={(event) => {
        leaveLiveEdge();
        onViewportTouchStart?.(event);
      }}
      onKeyDown={(event) => {
        if (["ArrowUp", "PageUp", "Home"].includes(event.key)) {
          leaveLiveEdge();
        }
        onViewportKeyDown?.(event);
      }}
      className={cn(
        "h-full overflow-y-auto overscroll-contain outline-none [overflow-anchor:none] focus-visible:ring-2 focus-visible:ring-inset focus-visible:ring-ring",
        navigation === "rail"
          ? "[-ms-overflow-style:none] [scrollbar-width:none] [&::-webkit-scrollbar]:hidden"
          : "[scrollbar-gutter:stable]",
        viewportClassName,
        navigation === "rail" && railOverflowing && "pr-10",
      )}
    >
      <div
        ref={contentRef}
        role="log"
        aria-live="polite"
        aria-relevant="additions text"
        aria-busy={busy}
        className={contentClassName}
        {...contentProps}
      >
        {children}
      </div>
    </section>
  );

  return (
    <div
      data-slot="message-scroller"
      className={cn("min-h-0", className)}
      {...props}
    >
      {navigation === "rail" ? (
        <PreviewRail
          items={railOverflowing ? railItems : []}
          label={navigationLabel}
          activeId={activeRailId}
          onItemSelect={scrollToRailItem}
          previewSide="before"
          highlightActive
          itemSize={14}
          className="h-full min-h-0 overflow-hidden"
          previewContainerClassName="right-8 left-3"
          previewClassName="mr-1 w-64 max-w-full [&_[data-slot=preview-rail-card]]:h-20 [&_[data-slot=preview-rail-card]]:overflow-hidden [&_[data-slot=preview-rail-card]]:p-3 [&_[data-slot=preview-rail-title]]:line-clamp-1 [&_[data-slot=preview-rail-title]]:text-xs [&_[data-slot=preview-rail-title]]:leading-4 [&_[data-slot=preview-rail-description]]:line-clamp-2 [&_[data-slot=preview-rail-description]]:text-xs [&_[data-slot=preview-rail-description]]:leading-4"
          railClassName={cn(
            "absolute inset-y-3 right-1 w-7 content-center py-1 [&_[data-slot=preview-rail-item]]:w-7 [&_[data-slot=preview-rail-item]]:justify-end [&_[data-slot=preview-rail-tick]]:h-px [&_[data-slot=preview-rail-tick]]:w-4 [&_[data-slot=preview-rail-tick]]:origin-right",
            railOverflowing
              ? "pointer-events-auto opacity-100"
              : "pointer-events-none opacity-0",
            railClassName,
          )}
        >
          {viewport}
        </PreviewRail>
      ) : (
        viewport
      )}
    </div>
  );
}