Accordion for React

'use client';

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

export interface AccordionItem {
  /** Stable id, used for the anchor and defaultOpen */
  value: string;
  title: React.ReactNode;
  content: React.ReactNode;
  icon?: IconName;
  /** Quiet text under the title */
  subtitle?: React.ReactNode;
}

export interface AccordionProps {
  items: AccordionItem[];
  /** single: opening one closes the others (native <details name>). multiple: each on its own. */
  type?: 'single' | 'multiple';
  /** Values open on first render */
  defaultOpen?: string[];
  /** divided: hairlines between rows. cards: separate surfaces. contained: one bordered box. */
  variant?: 'divided' | 'cards' | 'contained';
  /** chevron or plus, the plus turns into a minus */
  marker?: 'chevron' | 'plus';
  /** Heading level of the titles, for a correct outline */
  headingLevel?: 2 | 3 | 4;
  className?: string;
}

/*
 * Open and closed follow [open], except while a row closes: then data-closing turns
 * the marker back at once, while the height still runs. Rows rise one after another
 * when the list scrolls into view.
 */
const STYLES =
  '.kitfx-acc-chev,.kitfx-acc-plus{transition:transform .35s var(--ease-kit),translate .2s var(--ease-kit)}' +
  '.kitfx-acc[open]:not([data-closing]) .kitfx-acc-chev{transform:rotate(180deg)}' +
  '.kitfx-acc[open]:not([data-closing]) .kitfx-acc-plus{transform:scaleY(0)}' +
  '.kitfx-acc-card{transition:border-color .3s,box-shadow .3s,translate .3s var(--ease-kit)}' +
  '.kitfx-acc-card[open]:not([data-closing]){border-color:var(--border-strong);box-shadow:var(--highlight),var(--shadow-md)}' +
  '.kitfx-acc-in>.kitfx-acc{animation:kitfx-acc-in .6s var(--ease-kit) both;animation-delay:calc(var(--i,0) * 70ms)}' +
  '@keyframes kitfx-acc-in{from{opacity:0;transform:translateY(12px)}}' +
  '@media (prefers-reduced-motion:reduce){.kitfx-acc-chev,.kitfx-acc-plus,.kitfx-acc-card{transition:none}.kitfx-acc-in>.kitfx-acc{animation:none}}';

const EASE = 'cubic-bezier(0.2, 0.7, 0.2, 1)';

/**
 * Disclosure rows on native <details>: work without JavaScript, open with Enter and Space, searchable with Ctrl F
 * in browsers that support it. With JavaScript the height opens and closes softly (grid rows 0fr to 1fr),
 * the text fades in and the marker turns.
 *   <Accordion type="single" items={[{ value: 'refund', title: 'Can I get a refund?', content: '…' }]} />
 */
export function Accordion({ items, type = 'single', defaultOpen = [], variant = 'divided', marker = 'chevron', headingLevel = 3, className }: AccordionProps) {
  const group = useId();
  const H = `h${headingLevel}` as 'h3';
  const [ref, inView] = useInView<HTMLDivElement>();
  const hidden = useRef(false);
  if (!inView) hidden.current = true;
  const entering = inView && hidden.current;
  const timers = useRef(new Map<HTMLDetailsElement, number>());

  // The script takes over "one at a time", so the others can close softly instead of snapping shut
  useEffect(() => {
    if (prefersReducedMotion()) return;
    ref.current?.querySelectorAll('details[name]').forEach((d) => d.removeAttribute('name'));
  }, [ref]);
  useEffect(() => {
    const map = timers.current;
    return () => map.forEach((t) => window.clearTimeout(t));
  }, []);

  const body = (d: HTMLDetailsElement) => d.querySelector<HTMLElement>(':scope > [data-acc-body]');

  const shut = (d: HTMLDetailsElement) => {
    const b = body(d);
    if (!b || !d.open || d.dataset.closing !== undefined) return;
    window.clearTimeout(timers.current.get(d));
    d.dataset.closing = '';
    (b.firstElementChild as HTMLElement | null)?.style.setProperty('overflow', 'hidden');
    b.dataset.shut = '';
    timers.current.set(
      d,
      window.setTimeout(() => {
        d.open = false;
        delete d.dataset.closing;
        delete b.dataset.shut;
        (b.firstElementChild as HTMLElement | null)?.style.removeProperty('overflow');
      }, 380),
    );
  };

  const show = (d: HTMLDetailsElement) => {
    const b = body(d);
    if (!b) return;
    window.clearTimeout(timers.current.get(d));
    const inner = b.firstElementChild as HTMLElement | null;
    inner?.style.setProperty('overflow', 'hidden');
    if (!d.open) {
      b.dataset.shut = '';
      d.open = true;
      void b.offsetHeight;
    }
    delete d.dataset.closing;
    delete b.dataset.shut;
    inner?.firstElementChild?.animate([{ opacity: 0, transform: 'translateY(-6px)' }, { opacity: 1, transform: 'none' }], { duration: 380, delay: 60, easing: EASE, fill: 'backwards' });
    timers.current.set(
      d,
      window.setTimeout(() => inner?.style.removeProperty('overflow'), 420),
    );
  };

  const onToggle = (e: React.MouseEvent<HTMLElement>) => {
    if (prefersReducedMotion()) return;
    const d = e.currentTarget.parentElement as HTMLDetailsElement;
    e.preventDefault();
    if (d.open && d.dataset.closing === undefined) {
      shut(d);
      return;
    }
    if (type === 'single') ref.current?.querySelectorAll<HTMLDetailsElement>(':scope > details[open]').forEach((o) => o !== d && shut(o));
    show(d);
  };

  return (
    <div
      ref={ref}
      className={cn(
        'w-full',
        variant === 'divided' && 'divide-y divide-border border-y border-border',
        variant === 'cards' && 'grid gap-3',
        variant === 'contained' && 'divide-y divide-border overflow-hidden rounded-xl border border-border bg-card shadow-[var(--highlight),var(--shadow-sm)]',
        !inView && '[&>details]:opacity-0',
        entering && 'kitfx-acc-in',
        className,
      )}
    >
      <style href="kitfx-acc" precedence="default">
        {STYLES}
      </style>
      {items.map((it, i) => (
        <details
          key={it.value}
          id={it.value}
          name={type === 'single' ? group : undefined}
          open={defaultOpen.includes(it.value) || undefined}
          style={{ '--i': i } as React.CSSProperties}
          className={cn('kitfx-acc group/acc', variant === 'cards' && 'kitfx-acc-card rounded-xl border border-border bg-card shadow-[var(--highlight),var(--shadow-sm)] hover:-translate-y-px motion-reduce:hover:translate-y-0')}
        >
          <summary
            onClick={onToggle}
            className={cn(
              'flex min-h-14 cursor-pointer list-none items-center gap-4 py-4 text-left outline-none [&::-webkit-details-marker]:hidden',
              'rounded-lg focus-visible:ring-2 focus-visible:ring-ring',
              variant !== 'divided' && 'px-5',
              variant === 'divided' && 'hover:text-foreground',
            )}
          >
            {it.icon && (
              <span className="grid size-9 shrink-0 place-items-center rounded-lg border border-border bg-surface text-muted-foreground transition-[color,scale] duration-300 ease-[cubic-bezier(0.34,1.56,0.64,1)] group-open/acc:text-foreground group-hover/acc:scale-105 motion-reduce:transition-none">
                <Icon name={it.icon} size={17} />
              </span>
            )}
            <span className="min-w-0 flex-1">
              <H className="text-pretty text-[15px] font-medium leading-snug text-foreground">{it.title}</H>
              {it.subtitle && <span className="mt-0.5 block text-[13px] text-muted-foreground">{it.subtitle}</span>}
            </span>
            {marker === 'chevron' ? (
              <span className="grid shrink-0 place-items-center text-muted-foreground transition-[translate] duration-200 group-hover/acc:translate-y-0.5 motion-reduce:transition-none">
                <Icon name="chevron-down" size={18} className="kitfx-acc-chev" />
              </span>
            ) : (
              <span aria-hidden className="relative grid size-7 shrink-0 place-items-center rounded-full border border-border text-muted-foreground transition-[color,border-color,rotate] duration-300 ease-[var(--ease-kit)] group-open/acc:border-border-strong group-open/acc:text-foreground group-hover/acc:rotate-90 group-open/acc:group-hover/acc:rotate-0 motion-reduce:transition-none">
                <span className="absolute h-[1.5px] w-3 rounded-full bg-current" />
                <span className="kitfx-acc-plus absolute h-3 w-[1.5px] rounded-full bg-current" />
              </span>
            )}
          </summary>
          <div data-acc-body className="grid grid-rows-[1fr] transition-[grid-template-rows] duration-[380ms] ease-[var(--ease-kit)] data-[shut]:grid-rows-[0fr] motion-reduce:transition-none">
            <div className="min-h-0">
              <div className={cn('pb-5 text-pretty text-sm leading-relaxed text-muted-foreground', variant !== 'divided' && 'px-5', it.icon && (variant === 'divided' ? 'ps-[52px]' : 'ps-[72px]'), marker === 'plus' ? 'pe-12' : 'pe-10')}>
                {it.content}
              </div>
            </div>
          </div>
        </details>
      ))}
    </div>
  );
}