Bottom nav

'use client';

import { useEffect, useId, useRef, useState } from 'react';
import { cn, prefersReducedMotion, useTexts } from '@/lib/kit';
import { Icon, type IconName } from '@/components/ui/icon';

/*
 * The tab bar at the bottom of a phone screen, for web apps and mobile sites.
 *
 *   labels          icons with labels, a soft light glides behind the active icon
 *   center-action   two tabs on each side of a raised main button that opens quick actions
 *   floating        a glass pill above the content, the lens glides to the active tab
 *   hide-on-scroll  a slim bar that slides away while you read down and returns on the way up
 *   with-sheet      four tabs and More, which opens a sheet with every other place
 *
 * position fixed (default) sits at the bottom of the window: full width on
 * phones, a centered floating bar on tablets, hidden from 1024 px where a
 * sidebar or navbar takes over (desktop shows it anyway). position contained
 * sits at the bottom of the nearest positioned parent, for phone mockups.
 *
 * Every tab is at least 44 px tall, the active one carries aria-current, and
 * the light only moves with transform.
 */

export type BottomNavVariant = 'labels' | 'center-action' | 'floating' | 'hide-on-scroll' | 'with-sheet';

export interface BottomNavItem {
  label: string;
  icon: IconName;
  href?: string;
  /** A count, or true for a dot */
  badge?: number | boolean;
  active?: boolean;
}

export interface BottomNavProps {
  variant?: BottomNavVariant;
  items: BottomNavItem[];
  /** center-action: the main button and the quick actions it opens */
  action?: { label: string; icon?: IconName; actions?: { label: string; icon: IconName; href?: string }[] };
  /** with-sheet: the More tab and what its sheet holds */
  more?: { label: string; title?: string; items: { label: string; icon: IconName; href?: string; description?: string }[] };
  /** fixed (default) or contained in the nearest positioned parent */
  position?: 'fixed' | 'contained';
  /** fixed: show on desktops too. Default false. */
  desktop?: boolean;
  /** Start with the quick actions or the sheet open (Studio preview) */
  defaultOpen?: boolean;
  onChange?: (index: number) => void;
  labels?: Partial<(typeof TEXTS)['en']>;
  className?: string;
}

const TEXTS = {
  en: { nav: 'Main', close: 'Close', new: 'new', actions: 'Quick actions' },
  de: { nav: 'Hauptnavigation', close: 'Schließen', new: 'neu', actions: 'Schnellaktionen' },
};
type Texts = (typeof TEXTS)['en'];

const STYLES = `
@keyframes kbn-pop{0%{transform:scale(1)}40%{transform:scale(.86)}100%{transform:scale(1)}}
.kbn-pop{animation:kbn-pop .38s var(--ease-kit)}
@keyframes kbn-up{from{opacity:0;transform:translateY(12px) scale(.96)}}
.kbn-up{animation:kbn-up .42s var(--ease-kit) both;animation-delay:calc(var(--kbn-i,0)*45ms)}
@media (prefers-reduced-motion:reduce){.kbn-pop,.kbn-up{animation:none}}
`;

function BadgeMark({ badge, t }: { badge: BottomNavItem['badge']; t: Texts }) {
  if (!badge) return null;
  if (badge === true) return <span aria-label={t.new} className="absolute -right-0.5 -top-0.5 size-2.5 rounded-full border-2 border-[var(--kbn-bg)] bg-destructive" />;
  return (
    <span className="absolute -right-2.5 -top-1.5 grid h-[18px] min-w-[18px] place-items-center rounded-full border-2 border-[var(--kbn-bg)] bg-destructive px-1 text-[10px] font-semibold tabular-nums leading-none text-destructive-foreground">
      {badge > 99 ? '99+' : badge}
    </span>
  );
}

/** Hides while the page (or a [data-scroll-root] around or beside a contained bar) scrolls down */
function useHideOnScroll(enabled: boolean, root: React.RefObject<HTMLElement | null>) {
  const [hidden, setHidden] = useState(false);
  useEffect(() => {
    if (!enabled || prefersReducedMotion()) return;
    // The page, or a [data-scroll-root] around the bar or next to it
    const box = root.current?.closest<HTMLElement>('[data-scroll-root]') ?? root.current?.parentElement?.querySelector<HTMLElement>(':scope > [data-scroll-root]') ?? null;
    const target: HTMLElement | Window = box ?? window;
    const pos = () => (box ? box.scrollTop : window.scrollY);
    let last = pos();
    let frame = 0;
    const onScroll = () => {
      if (frame) return;
      frame = requestAnimationFrame(() => {
        frame = 0;
        const y = pos();
        const d = y - last;
        if (Math.abs(d) < 6) return;
        setHidden(d > 0 && y > 48);
        last = y;
      });
    };
    target.addEventListener('scroll', onScroll, { passive: true });
    return () => {
      cancelAnimationFrame(frame);
      target.removeEventListener('scroll', onScroll);
    };
  }, [enabled, root]);
  return hidden;
}

/**
 * A tab bar for the bottom of the screen.
 *   <BottomNav items={[{ label: 'Home', icon: 'home', active: true }, { label: 'Search', icon: 'search' }, …]} />
 */
export function BottomNav({ variant = 'labels', items, action, more, position = 'fixed', desktop = false, defaultOpen = false, onChange, labels, className }: BottomNavProps) {
  const t = useTexts(TEXTS, labels);
  const [active, setActive] = useState(() => Math.max(0, items.findIndex((i) => i.active)));
  const [pressed, setPressed] = useState<number | null>(null);
  const [open, setOpen] = useState(defaultOpen);
  const root = useRef<HTMLElement>(null);
  const sheetId = useId();
  const hidden = useHideOnScroll(variant === 'hide-on-scroll', root);
  const contained = position === 'contained';

  useEffect(() => {
    if (!open) return;
    const onKey = (e: KeyboardEvent) => e.key === 'Escape' && setOpen(false);
    window.addEventListener('keydown', onKey);
    return () => window.removeEventListener('keydown', onKey);
  }, [open]);

  const pick = (i: number, e: React.MouseEvent) => {
    const href = items[i]?.href;
    if (!href || href === '#') e.preventDefault();
    setActive(i);
    setPressed(i);
    setOpen(false);
    onChange?.(i);
  };

  // Where the bar sits
  const place = contained
    ? 'absolute inset-x-0 bottom-0'
    : cn('fixed inset-x-0 bottom-0 sm:bottom-4 sm:left-1/2 sm:right-auto sm:w-[min(32rem,calc(100%-2rem))] sm:-translate-x-1/2', !desktop && 'lg:hidden');
  const floating = variant === 'floating';
  const shell = cn(
    'z-40 [--kbn-bg:var(--card)]',
    place,
    floating ? (contained ? 'bottom-7 px-3' : 'max-sm:bottom-3 max-sm:px-3') : '',
  );
  const bar = cn(
    'relative border-border bg-[color-mix(in_oklab,var(--card)_88%,transparent)] backdrop-blur-xl',
    floating ? 'rounded-[1.75rem] border shadow-[var(--highlight),var(--shadow-lg)]' : cn('border-t', !contained && 'sm:rounded-2xl sm:border sm:shadow-[var(--highlight),var(--shadow-lg)]'),
    // A phone mockup has no safe area, its home bar needs the same room
    contained ? (floating ? '' : 'pb-5') : 'pb-[env(safe-area-inset-bottom)]',
  );

  const n = items.length;
  const tab = (it: BottomNavItem, i: number, opts: { slim?: boolean; lens?: boolean } = {}) => {
    const on = i === active;
    return (
      <li key={it.label} className="min-w-0">
        <a
          href={it.href ?? '#'}
          aria-current={on ? 'page' : undefined}
          onClick={(e) => pick(i, e)}
          className={cn(
            'group/tab relative flex w-full flex-col items-center justify-center gap-1 rounded-xl outline-none transition-colors duration-300 focus-visible:outline-solid focus-visible:outline-2 focus-visible:-outline-offset-2 focus-visible:outline-[var(--ring)]',
            opts.slim ? 'h-14' : 'h-16',
            on ? 'text-foreground' : 'text-muted-foreground hover:text-foreground',
          )}
        >
          <span key={pressed === i ? `p${i}` : i} className={cn('relative grid h-8 w-14 place-items-center', pressed === i && 'kbn-pop')}>
            {/* Until the shared light is placed, each active tab lights itself (server, no JS) */}
            <Icon name={it.icon} size={22} strokeWidth={on ? 2 : 1.6} className={cn('relative transition-[color,transform] duration-300', on && !opts.lens && 'text-[color-mix(in_oklab,var(--primary)_82%,var(--foreground))]')} />
            <BadgeMark badge={it.badge} t={t} />
          </span>
          {!opts.slim && <span className={cn('max-w-full truncate px-1 text-[11px] leading-none tracking-[-0.005em]', on ? 'font-semibold' : 'font-medium')}>{it.label}</span>}
          {opts.slim && <span className="sr-only">{it.label}</span>}
          {opts.slim && <span aria-hidden className={cn('absolute bottom-2 size-1 rounded-full bg-primary transition-[opacity,transform] duration-300', on ? 'scale-100 opacity-100' : 'scale-0 opacity-0')} />}
        </a>
      </li>
    );
  };

  /** The light behind the active icon: one element, moved by whole tab widths */
  const light = (count: number, index: number, kind: 'pill' | 'lens') => (
    <span aria-hidden className="pointer-events-none absolute inset-y-0 left-0 flex items-start justify-center transition-transform duration-500 ease-[var(--ease-kit)] motion-reduce:transition-none" style={{ width: `${100 / count}%`, transform: `translateX(${index * 100}%)` }}>
      {kind === 'pill' ? (
        <span className="mt-2 h-8 w-14 rounded-full bg-[color-mix(in_oklab,var(--primary)_16%,transparent)]" />
      ) : (
        <span className="mt-1 h-14 w-[4.5rem] max-w-[calc(100%-4px)] rounded-[1.25rem] bg-[color-mix(in_oklab,var(--foreground)_8%,transparent)] shadow-[var(--highlight)] ring-1 ring-border" />
      )}
    </span>
  );

  const styles = (
    <style href="kit-bottom-nav" precedence="default">
      {STYLES}
    </style>
  );

  /* ---------- center-action ---------- */
  if (variant === 'center-action') {
    const half = Math.ceil(n / 2);
    const left = items.slice(0, half);
    const right = items.slice(half);
    const cols = n + 1;
    const lightIndex = active < half ? active : active + 1;
    return (
      <>
        {styles}
        {open && <div aria-hidden onClick={() => setOpen(false)} className={cn('z-30 bg-scrim kit-rise [--kit-delay:0ms]', contained ? 'absolute inset-0' : 'fixed inset-0')} />}
        <nav ref={root} aria-label={t.nav} className={cn(shell, className)}>
          {open && action?.actions?.length ? (
            <ul id={sheetId} aria-label={t.actions} className="absolute inset-x-0 bottom-full mb-3 flex flex-col items-center gap-2 px-4">
              {action.actions.map((a, i) => (
                <li key={a.label} className="kbn-up" style={{ '--kbn-i': action.actions!.length - 1 - i } as React.CSSProperties}>
                  <a href={a.href ?? '#'} onClick={(e) => { if (!a.href || a.href === '#') e.preventDefault(); setOpen(false); }} className="flex h-12 items-center gap-3 rounded-full border border-border bg-popover pl-2 pr-5 text-[14px] font-medium text-foreground shadow-[var(--highlight),var(--shadow-md)] outline-none transition-transform duration-200 hover:-translate-y-0.5 focus-visible:outline-solid focus-visible:outline-2 focus-visible:outline-[var(--ring)]">
                    <span className="grid size-9 place-items-center rounded-full bg-[color-mix(in_oklab,var(--primary)_14%,transparent)] text-[color-mix(in_oklab,var(--primary)_82%,var(--foreground))]">
                      <Icon name={a.icon} size={18} />
                    </span>
                    {a.label}
                  </a>
                </li>
              ))}
            </ul>
          ) : null}
          <div className={bar}>
            <ul className="relative grid px-1" style={{ gridTemplateColumns: `repeat(${cols}, minmax(0, 1fr))` }}>
              {light(cols, lightIndex, 'pill')}
              {left.map((it, i) => tab(it, i))}
              <li className="relative flex justify-center">
                <button
                  type="button"
                  aria-expanded={action?.actions?.length ? open : undefined}
                  aria-controls={action?.actions?.length ? sheetId : undefined}
                  onClick={() => setOpen((o) => !o)}
                  className="group/fab absolute -top-5 grid size-14 place-items-center rounded-full bg-primary text-primary-foreground shadow-[inset_0_1px_0_rgb(255_255_255/0.22),0_8px_24px_-6px_color-mix(in_oklab,var(--primary)_60%,transparent)] outline-none ring-4 ring-[var(--kbn-bg)] transition-transform duration-300 ease-[var(--ease-kit)] hover:scale-105 focus-visible:outline-solid focus-visible:outline-2 focus-visible:outline-offset-4 focus-visible:outline-[var(--ring)] active:scale-95"
                >
                  <Icon name={action?.icon ?? 'plus'} size={24} strokeWidth={2} className={cn('transition-transform duration-500 ease-[var(--ease-kit)] motion-reduce:transition-none', open && 'rotate-[135deg]')} />
                  <span className="sr-only">{open ? t.close : (action?.label ?? '')}</span>
                </button>
                <span aria-hidden className="mt-auto pb-2.5 text-[11px] font-medium leading-none text-muted-foreground">{action?.label}</span>
              </li>
              {right.map((it, i) => tab(it, i + half))}
            </ul>
          </div>
        </nav>
      </>
    );
  }

  /* ---------- with-sheet ---------- */
  if (variant === 'with-sheet' && more) {
    const cols = n + 1;
    const moreOn = open;
    return (
      <>
        {styles}
        {open && <div aria-hidden onClick={() => setOpen(false)} className={cn('z-30 bg-scrim kit-rise [--kit-delay:0ms]', contained ? 'absolute inset-0' : 'fixed inset-0')} />}
        <nav ref={root} aria-label={t.nav} className={cn(shell, className)}>
          {open && (
            <div id={sheetId} role="dialog" aria-label={more.title ?? more.label} className={cn('absolute inset-x-0 bottom-full mb-0 rounded-t-3xl border border-b-0 border-border bg-popover px-4 pb-4 pt-2 shadow-[var(--shadow-lg)] kbn-up', !contained && 'sm:mb-2 sm:rounded-3xl sm:border-b')}>
              <span aria-hidden className="mx-auto mb-3 block h-1 w-9 rounded-full bg-border-strong" />
              <div className="mb-3 flex items-center justify-between px-1">
                <p className="text-[15px] font-semibold text-foreground">{more.title ?? more.label}</p>
                <button type="button" onClick={() => setOpen(false)} aria-label={t.close} className="-mr-2 grid size-11 place-items-center rounded-full text-muted-foreground hover:bg-accent hover:text-foreground">
                  <Icon name="x" size={18} />
                </button>
              </div>
              <ul className="grid grid-cols-2 gap-2">
                {more.items.map((m, i) => (
                  <li key={m.label} className="kbn-up" style={{ '--kbn-i': i } as React.CSSProperties}>
                    <a href={m.href ?? '#'} onClick={(e) => { if (!m.href || m.href === '#') e.preventDefault(); setOpen(false); }} className="flex min-h-16 flex-col justify-center gap-1 rounded-2xl border border-border bg-surface p-3 outline-none transition-colors hover:bg-accent focus-visible:outline-solid focus-visible:outline-2 focus-visible:outline-[var(--ring)]">
                      <Icon name={m.icon} size={20} className="text-[color-mix(in_oklab,var(--primary)_82%,var(--foreground))]" />
                      <span className="text-[13px] font-medium text-foreground">{m.label}</span>
                      {m.description && <span className="text-[11px] leading-snug text-muted-foreground">{m.description}</span>}
                    </a>
                  </li>
                ))}
              </ul>
            </div>
          )}
          <div className={cn(bar, open && 'rounded-t-none')}>
            <ul className="relative grid px-1" style={{ gridTemplateColumns: `repeat(${cols}, minmax(0, 1fr))` }}>
              {light(cols, moreOn ? n : active, 'pill')}
              {items.map((it, i) => tab(it, i))}
              <li className="min-w-0">
                <button type="button" aria-expanded={open} aria-controls={sheetId} onClick={() => setOpen((o) => !o)} className={cn('relative flex h-16 w-full flex-col items-center justify-center gap-1 rounded-xl outline-none transition-colors focus-visible:outline-solid focus-visible:outline-2 focus-visible:-outline-offset-2 focus-visible:outline-[var(--ring)]', open ? 'text-foreground' : 'text-muted-foreground hover:text-foreground')}>
                  <span className="relative grid h-8 w-14 place-items-center">
                    <Icon name={open ? 'x' : 'grid'} size={22} strokeWidth={open ? 2 : 1.6} className={cn('transition-transform duration-300', open && 'rotate-90 text-[color-mix(in_oklab,var(--primary)_82%,var(--foreground))]')} />
                  </span>
                  <span className={cn('text-[11px] leading-none', open ? 'font-semibold' : 'font-medium')}>{more.label}</span>
                </button>
              </li>
            </ul>
          </div>
        </nav>
      </>
    );
  }

  /* ---------- labels, floating, hide-on-scroll ---------- */
  const slim = variant === 'hide-on-scroll';
  return (
    <>
      {styles}
      <nav
        ref={root}
        aria-label={t.nav}
        className={cn(shell, 'transition-transform duration-500 ease-[var(--ease-kit)] motion-reduce:transition-none', hidden && 'translate-y-[calc(100%+1.5rem)] sm:translate-y-[calc(100%+2rem)]', className)}
      >
        <div className={bar}>
          <ul className={cn('relative grid', floating ? 'px-1.5' : 'px-1')} style={{ gridTemplateColumns: `repeat(${n}, minmax(0, 1fr))` }}>
            {!slim && light(n, active, floating ? 'lens' : 'pill')}
            {items.map((it, i) => tab(it, i, { slim, lens: floating }))}
          </ul>
        </div>
      </nav>
    </>
  );
}