Breadcrumbs for React

'use client';

import { useRef } from 'react';
import { cn, useInView, useTexts } from '@/lib/kit';
import { Icon, type IconName } from '@/components/ui/icon';
import { DropdownMenu } from '@/components/ui/dropdown-menu';

const TEXTS = { en: { label: 'Breadcrumb', more: 'Show hidden pages', back: 'Back to' }, de: { label: 'Brotkrumen', more: 'Ausgeblendete Seiten zeigen', back: 'Zurück zu' } };

/* The trail lays itself out from the start, one step after another, when it scrolls into view */
const STYLES =
  '.kitfx-bc-in>li,.kitfx-bc-in>.kitfx-bc-back{animation:kitfx-bc-in .55s var(--ease-kit) both;animation-delay:calc(var(--i,0) * 45ms)}' +
  '@keyframes kitfx-bc-in{from{opacity:0;transform:translateX(-8px)}}' +
  '@media (prefers-reduced-motion:reduce){.kitfx-bc-in>li,.kitfx-bc-in>.kitfx-bc-back{animation:none}}';

/* A line that grows from the start under a link on hover and focus */
const UNDERLINE =
  'relative after:pointer-events-none after:absolute after:inset-x-0 after:-bottom-0.5 after:h-px after:origin-left after:scale-x-0 after:rounded-full after:bg-current after:opacity-60 after:transition-transform after:duration-300 after:ease-[var(--ease-kit)] hover:after:scale-x-100 focus-visible:after:scale-x-100 motion-reduce:after:transition-none';

export interface Crumb {
  label: string;
  href?: string;
  icon?: IconName;
}

export interface BreadcrumbsProps {
  items: Crumb[];
  separator?: 'chevron' | 'slash' | 'dot';
  /** contained: on a quiet pill-shaped surface */
  variant?: 'default' | 'contained';
  /** Collapse the middle into a menu when there are more items */
  maxItems?: number;
  /** On phones show only a back link to the parent page. Default true. */
  backOnMobile?: boolean;
  labels?: Partial<(typeof TEXTS)['en']>;
  className?: string;
}

function Sep({ kind }: { kind: NonNullable<BreadcrumbsProps['separator']> }) {
  if (kind === 'slash') return <span aria-hidden className="select-none text-border-strong">/</span>;
  if (kind === 'dot') return <span aria-hidden className="size-[3px] rounded-full bg-border-strong" />;
  return <Icon name="chevron-right" size={14} className="text-subtle-foreground" />;
}

/**
 * Where the page sits in the site. The last item is the current page (aria-current).
 *   <Breadcrumbs items={[{ label: 'Home', href: '/', icon: 'home' }, { label: 'Docs', href: '/docs' }, { label: 'Tabs' }]} />
 */
export function Breadcrumbs({ items, separator = 'chevron', variant = 'default', maxItems, backOnMobile = true, labels, className }: BreadcrumbsProps) {
  const t = useTexts(TEXTS, labels);
  const collapse = maxItems !== undefined && items.length > maxItems && maxItems >= 3;
  const head = collapse ? items.slice(0, 1) : items;
  const hidden = collapse ? items.slice(1, items.length - (maxItems! - 2)) : [];
  const tail = collapse ? items.slice(items.length - (maxItems! - 2)) : [];
  const parent = items.length > 1 ? items[items.length - 2] : undefined;
  const [ref, inView] = useInView<HTMLElement>();
  const waited = useRef(false);
  if (!inView) waited.current = true;
  const entering = inView && waited.current;
  let order = 0;

  const crumb = (c: Crumb, last: boolean) => (
    <li key={c.label} className="flex min-w-0 items-center" style={{ '--i': order++ } as React.CSSProperties}>
      {last || !c.href ? (
        <span aria-current={last ? 'page' : undefined} className={cn('flex min-w-0 items-center gap-1.5 truncate', last ? 'font-medium text-foreground' : 'text-muted-foreground')}>
          {c.icon && <Icon name={c.icon} size={15} />}
          <span className="truncate">{c.label}</span>
        </span>
      ) : (
        <a href={c.href} className={cn('flex min-w-0 items-center gap-1.5 rounded-md text-muted-foreground transition-colors hover:text-foreground', UNDERLINE)}>
          {c.icon && <Icon name={c.icon} size={15} />}
          <span className={cn('truncate', c.icon && c === items[0] && 'max-sm:sr-only')}>{c.label}</span>
        </a>
      )}
    </li>
  );
  const sep = (k: string) => (
    <li key={k} role="presentation" aria-hidden className="flex items-center" style={{ '--i': order++ } as React.CSSProperties}>
      <Sep kind={separator} />
    </li>
  );

  const list: React.ReactNode[] = [];
  head.forEach((c, i) => {
    if (i) list.push(sep(`s${i}`));
    list.push(crumb(c, !collapse && i === items.length - 1));
  });
  if (collapse) {
    list.push(sep('sh'));
    list.push(
      <li key="more" className="flex items-center" style={{ '--i': order++ } as React.CSSProperties}>
        <DropdownMenu
          items={hidden.map((h) => ({ label: h.label, icon: h.icon, href: h.href }))}
          trigger={
            <button type="button" aria-label={t.more} className="group/more grid h-7 w-8 place-items-center rounded-md text-muted-foreground transition-colors hover:bg-accent hover:text-foreground aria-expanded:bg-accent aria-expanded:text-foreground">
              <Icon name="more-horizontal" size={16} className="transition-transform duration-300 ease-[cubic-bezier(0.34,1.56,0.64,1)] group-hover/more:scale-110 group-aria-expanded/more:scale-90 motion-reduce:transition-none" />
            </button>
          }
        />
      </li>,
    );
    tail.forEach((c, i) => {
      list.push(sep(`st${i}`));
      list.push(crumb(c, i === tail.length - 1));
    });
  }

  return (
    <nav ref={ref} aria-label={t.label} className={cn('min-w-0 text-sm', className)}>
      <style href="kitfx-bc" precedence="default">
        {STYLES}
      </style>
      <ol
        className={cn(
          'flex min-w-0 flex-wrap items-center gap-x-2 gap-y-1',
          !inView && 'opacity-0',
          entering && 'kitfx-bc-in',
          variant === 'contained' && 'inline-flex rounded-full border border-border bg-surface px-3.5 py-1.5 shadow-[var(--highlight)]',
          backOnMobile && parent && 'max-sm:hidden',
        )}
      >
        {list}
      </ol>
      {backOnMobile && parent && (
        <a href={parent.href} className={cn('group/back inline-flex min-h-11 items-center gap-1.5 font-medium text-muted-foreground transition-[color,opacity,translate] duration-500 ease-[var(--ease-kit)] hover:text-foreground sm:hidden', !inView && '-translate-x-2 opacity-0')}>
          <Icon name="chevron-left" size={16} className="transition-transform duration-200 ease-[var(--ease-kit)] group-hover/back:-translate-x-0.5 motion-reduce:transition-none" />
          <span className="sr-only">{t.back} </span>
          {parent.label}
        </a>
      )}
    </nav>
  );
}