Pagination for React

'use client';

import { useLayoutEffect, useRef, useState } from 'react';
import { cn, prefersReducedMotion, useInView, useLocale, useTexts } from '@/lib/kit';
import { Icon } from '@/components/ui/icon';

const TEXTS = {
  en: { label: 'Pagination', prev: 'Previous', next: 'Next', page: 'Page', of: 'of', first: 'First page', last: 'Last page', showing: 'Showing', to: 'to', results: 'results', perPage: 'Rows per page', more: 'Load more', loading: 'Loading', loaded: 'shown', all: 'All shown' },
  de: { label: 'Seitennavigation', prev: 'Zurück', next: 'Weiter', page: 'Seite', of: 'von', first: 'Erste Seite', last: 'Letzte Seite', showing: 'Zeige', to: 'bis', results: 'Ergebnissen', perPage: 'Zeilen pro Seite', more: 'Mehr laden', loading: 'Wird geladen', loaded: 'angezeigt', all: 'Alles angezeigt' },
};
type Texts = (typeof TEXTS)['en'];

/* Entrance when the bar scrolls into view, a number that rolls in when it changes, a pop for "all shown" */
const STYLES =
  '.kitfx-pg-in .kitfx-pg-part{animation:kitfx-pg-in .55s var(--ease-kit) both;animation-delay:calc(var(--i,0) * 40ms)}' +
  '@keyframes kitfx-pg-in{from{opacity:0;transform:translateY(8px)}}' +
  '.kitfx-pg-roll{display:inline-block;animation:kitfx-pg-roll .4s var(--ease-kit) both}@keyframes kitfx-pg-roll{from{opacity:0;transform:translateY(.45em)}}' +
  '.kitfx-pg-pop{animation:kitfx-pg-pop .5s cubic-bezier(.34,1.56,.64,1) both}@keyframes kitfx-pg-pop{from{opacity:0;transform:scale(.6)}}' +
  '.kitfx-pg-spin{animation:kitfx-pg-spin .8s linear infinite}@keyframes kitfx-pg-spin{to{transform:rotate(360deg)}}' +
  '@media (prefers-reduced-motion:reduce){.kitfx-pg-in .kitfx-pg-part,.kitfx-pg-roll,.kitfx-pg-pop{animation:none}.kitfx-pg-spin{animation-duration:2.4s}}';

const SPRING = 'cubic-bezier(0.34, 1.25, 0.64, 1)';
const EASE = 'cubic-bezier(0.2, 0.7, 0.2, 1)';

/** Page numbers with gaps: 1 … 4 5 6 … 12 */
export function pageRange(page: number, total: number, siblings = 1): (number | 'gap')[] {
  const size = siblings * 2 + 5;
  if (total <= size) return Array.from({ length: total }, (_, i) => i + 1);
  const start = Math.max(2, Math.min(page - siblings, total - siblings * 2 - 2));
  const end = Math.min(total - 1, Math.max(page + siblings, siblings * 2 + 3));
  const out: (number | 'gap')[] = [1];
  if (start > 2) out.push('gap');
  for (let i = start; i <= end; i++) out.push(i);
  if (end < total - 1) out.push('gap');
  out.push(total);
  return out;
}

/** Entrance only for elements that were below the fold, so nothing above it blinks on load */
function useEntrance<T extends Element>() {
  const [ref, inView] = useInView<T>();
  const waited = useRef(false);
  if (!inView) waited.current = true;
  return [ref, inView, inView && waited.current] as const;
}

export interface PaginationProps {
  page?: number;
  defaultPage?: number;
  total: number;
  onPageChange?: (page: number) => void;
  /** Build real links for each page, e.g. (p) => `?page=${p}` */
  href?: (page: number) => string;
  /** numbers: buttons for each page. simple: previous and next with "Page 3 of 12". */
  variant?: 'numbers' | 'simple';
  /** Results line on the left, e.g. { from: 21, to: 40, count: 248 } */
  summary?: { from: number; to: number; count: number };
  labels?: Partial<Texts>;
  className?: string;
}

const item = 'relative inline-flex h-10 min-w-10 items-center justify-center rounded-lg px-2 text-sm tabular-nums transition-colors outline-none focus-visible:ring-2 focus-visible:ring-ring';

/**
 * Page navigation. On phones the numbers turn into "3 / 12" between the arrows.
 * The highlight glides to the chosen page, numbers slide to their new places.
 *   <Pagination total={12} defaultPage={5} summary={{ from: 41, to: 50, count: 118 }} />
 */
export function Pagination({ page: pageProp, defaultPage = 1, total, onPageChange, href, variant = 'numbers', summary, labels, className }: PaginationProps) {
  const t = useTexts(TEXTS, labels);
  const locale = useLocale();
  const [inner, setInner] = useState(defaultPage);
  const page = pageProp ?? inner;
  const fmt = (n: number) => n.toLocaleString(locale === 'de' ? 'de-DE' : 'en-US');
  const go = (p: number) => {
    const next = Math.min(total, Math.max(1, p));
    setInner(next);
    onPageChange?.(next);
  };
  const [ref, inView, entering] = useEntrance<HTMLElement>();
  const listRef = useRef<HTMLUListElement>(null);
  const markRef = useRef<HTMLSpanElement>(null);
  const [mark, setMark] = useState<{ x: number; w: number } | null>(null);
  const places = useRef<Map<string, number> | null>(null);
  const range = pageRange(page, total);

  // One highlight for the current page that glides, and numbers that glide to their new place (FLIP)
  useLayoutEffect(() => {
    const list = listRef.current;
    if (!list) return;
    const measure = () => {
      const cur = list.querySelector<HTMLElement>('[aria-current="page"]');
      setMark((m) => {
        if (!cur || !cur.offsetWidth) return null;
        const next = { x: cur.offsetLeft, w: cur.offsetWidth };
        return m && m.x === next.x && m.w === next.w ? m : next;
      });
    };
    measure();
    const ro = new ResizeObserver(measure);
    ro.observe(list);
    return () => ro.disconnect();
  }, [page]);

  const prevMark = useRef(mark);
  useLayoutEffect(() => {
    const el = markRef.current;
    const prev = prevMark.current;
    prevMark.current = mark;
    if (!el || !mark || !prev || prefersReducedMotion() || (prev.x === mark.x && prev.w === mark.w)) return;
    el.animate([{ transform: `translateX(${prev.x}px) scaleX(${prev.w / mark.w})` }, { transform: `translateX(${mark.x}px)` }], { duration: 440, easing: SPRING });
  }, [mark]);

  useLayoutEffect(() => {
    const list = listRef.current;
    if (!list) return;
    const nodes = Array.from(list.querySelectorAll<HTMLElement>(':scope > li[data-key]'));
    const now = new Map(nodes.map((n) => [n.dataset.key!, n.offsetLeft]));
    const before = places.current;
    places.current = now;
    if (!before || prefersReducedMotion()) return;
    nodes.forEach((n) => {
      const was = before.get(n.dataset.key!);
      const x = now.get(n.dataset.key!)!;
      if (was === undefined) n.animate([{ opacity: 0, transform: 'scale(0.7)' }, { opacity: 1, transform: 'none' }], { duration: 320, easing: EASE });
      else if (was !== x) n.animate([{ transform: `translateX(${was - x}px)` }, { transform: 'none' }], { duration: 380, easing: EASE });
    });
  }, [page]);

  const btn = ({ to, label, children, className: cls, current, key }: { to: number; label?: string; children: React.ReactNode; className?: string; current?: boolean; key?: string }) => {
    const disabled = to < 1 || to > total || (to === page && !current);
    const common = cn(item, cls, disabled && 'pointer-events-none opacity-40');
    if (href && !disabled)
      return (
        <a key={key} href={href(to)} aria-label={label} aria-current={current ? 'page' : undefined} onClick={() => go(to)} className={common}>
          {children}
        </a>
      );
    return (
      <button key={key} type="button" aria-label={label} aria-current={current ? 'page' : undefined} disabled={disabled} onClick={() => go(to)} className={common}>
        {children}
      </button>
    );
  };

  const arrows = (side: 'prev' | 'next', withText: boolean) =>
    btn({
      to: side === 'prev' ? page - 1 : page + 1,
      label: withText ? undefined : t[side],
      className: cn('group/arrow gap-1.5 border border-border bg-background text-foreground shadow-[var(--shadow-sm)] transition-[background-color,translate] hover:bg-accent active:translate-y-px', withText && 'px-3 max-sm:px-0 max-sm:min-w-10'),
      children: (
        <>
          {side === 'prev' && <Icon name="chevron-left" size={16} className="transition-transform duration-200 ease-[var(--ease-kit)] group-hover/arrow:-translate-x-0.5 motion-reduce:transition-none" />}
          {withText && <span className="max-sm:sr-only">{t[side]}</span>}
          {side === 'next' && <Icon name="chevron-right" size={16} className="transition-transform duration-200 ease-[var(--ease-kit)] group-hover/arrow:translate-x-0.5 motion-reduce:transition-none" />}
        </>
      ),
    });

  const status = (
    <span className="px-2 text-sm tabular-nums text-muted-foreground" aria-live="polite">
      {t.page}{' '}
      <span key={page} className="kitfx-pg-roll font-medium text-foreground">
        {fmt(page)}
      </span>{' '}
      {t.of} {fmt(total)}
    </span>
  );

  return (
    <nav ref={ref} aria-label={t.label} className={cn('flex w-full flex-wrap items-center gap-x-6 gap-y-3', summary ? 'justify-between' : 'justify-center', !inView && '[&_.kitfx-pg-part]:opacity-0', entering && 'kitfx-pg-in', className)}>
      <style href="kitfx-pg" precedence="default">
        {STYLES}
      </style>
      {summary && (
        <p className="kitfx-pg-part text-sm text-muted-foreground max-sm:hidden">
          {t.showing} <span className="font-medium tabular-nums text-foreground">{fmt(summary.from)}</span> {t.to} <span className="font-medium tabular-nums text-foreground">{fmt(summary.to)}</span> {t.of}{' '}
          <span className="font-medium tabular-nums text-foreground">{fmt(summary.count)}</span> {t.results}
        </p>
      )}
      {variant === 'simple' ? (
        <div className="kitfx-pg-part flex items-center gap-2 max-sm:w-full max-sm:justify-between" style={{ '--i': 1 } as React.CSSProperties}>
          {arrows('prev', true)}
          {status}
          {arrows('next', true)}
        </div>
      ) : (
        <div className="flex items-center gap-1 max-sm:w-full max-sm:justify-between">
          <span className="kitfx-pg-part" style={{ '--i': 1 } as React.CSSProperties}>
            {arrows('prev', true)}
          </span>
          <ul ref={listRef} className="relative isolate flex items-center gap-1 max-sm:hidden">
            {mark && (
              <span
                ref={markRef}
                aria-hidden
                className="pointer-events-none absolute left-0 top-0 -z-10 h-10 origin-left rounded-lg bg-primary shadow-[var(--shadow-sm)]"
                style={{ width: mark.w, transform: `translateX(${mark.x}px)` }}
              />
            )}
            {range.map((p, i) =>
              p === 'gap' ? (
                <li key={`g${i < 3 ? 'a' : 'b'}`} data-key={`g${i < 3 ? 'a' : 'b'}`} aria-hidden className="kitfx-pg-part grid h-10 w-8 place-items-center text-subtle-foreground" style={{ '--i': i + 2 } as React.CSSProperties}>
                  <Icon name="more-horizontal" size={16} />
                </li>
              ) : (
                <li key={p} data-key={p} className="kitfx-pg-part" style={{ '--i': i + 2 } as React.CSSProperties}>
                  {btn({
                    to: p,
                    current: p === page,
                    label: `${t.page} ${p}`,
                    className: p === page ? cn('font-medium text-primary-foreground', !mark && 'bg-primary shadow-[var(--shadow-sm)]') : 'text-muted-foreground hover:bg-accent hover:text-foreground',
                    children: p,
                  })}
                </li>
              ),
            )}
          </ul>
          <span className="sm:hidden">{status}</span>
          <span className="kitfx-pg-part" style={{ '--i': range.length + 2 } as React.CSSProperties}>
            {arrows('next', true)}
          </span>
        </div>
      )}
    </nav>
  );
}

export interface LoadMoreProps {
  shown: number;
  count: number;
  onLoadMore?: () => void;
  loading?: boolean;
  labels?: Partial<Texts>;
  className?: string;
}

/**
 * Progress through a long list and one button for more. For feeds and shops.
 * The bar fills as more arrives, the button turns into a spinner while loading,
 * and the end is marked with a check instead of a missing button.
 */
export function LoadMore({ shown, count, onLoadMore, loading, labels, className }: LoadMoreProps) {
  const t = useTexts(TEXTS, labels);
  const locale = useLocale();
  const fmt = (n: number) => n.toLocaleString(locale === 'de' ? 'de-DE' : 'en-US');
  const share = Math.min(1, Math.max(0, shown / (count || 1)));
  const pct = Math.round(share * 100);
  const [ref, inView, entering] = useEntrance<HTMLDivElement>();
  return (
    <div ref={ref} className={cn('mx-auto grid w-full max-w-[16rem] justify-items-center gap-4 text-center', !inView && '[&_.kitfx-pg-part]:opacity-0', entering && 'kitfx-pg-in', className)}>
      <style href="kitfx-pg" precedence="default">
        {STYLES}
      </style>
      <p className="kitfx-pg-part text-sm text-muted-foreground" aria-live="polite">
        <span key={shown} className="kitfx-pg-roll font-medium tabular-nums text-foreground">
          {fmt(shown)}
        </span>{' '}
        {t.of} {fmt(count)} {t.loaded}
      </p>
      <div className="kitfx-pg-part h-1 w-full overflow-hidden rounded-full bg-track" style={{ '--i': 1 } as React.CSSProperties} role="progressbar" aria-valuenow={pct} aria-valuemin={0} aria-valuemax={100} aria-label={`${fmt(shown)} ${t.of} ${fmt(count)}`}>
        <div
          data-clip-ok
          className="h-full w-full rounded-full bg-foreground transition-transform duration-700 ease-[var(--ease-kit)] motion-reduce:transition-none"
          style={{ transform: `translateX(${inView ? (share - 1) * 100 : -100}%)`, transitionDelay: entering ? '250ms' : undefined }}
        />
      </div>
      {shown < count ? (
        <button
          type="button"
          onClick={onLoadMore}
          disabled={loading}
          aria-busy={loading || undefined}
          style={{ '--i': 2 } as React.CSSProperties}
          className="kitfx-pg-part group/more inline-flex h-11 items-center gap-2 rounded-lg border border-border-strong bg-background px-5 text-sm font-medium text-foreground shadow-[var(--shadow-sm)] transition-[background-color,translate,opacity] duration-200 hover:bg-accent active:translate-y-px disabled:opacity-60"
        >
          <span className="relative grid size-4 place-items-center">
            <Icon name="arrow-down" size={16} className={cn('transition-[opacity,translate] duration-200 ease-[var(--ease-kit)] group-hover/more:translate-y-0.5 motion-reduce:transition-none', loading && 'translate-y-1 opacity-0')} />
            {loading && (
              <svg viewBox="0 0 16 16" className="kitfx-pg-spin absolute size-4" aria-hidden>
                <circle cx="8" cy="8" r="6" fill="none" stroke="currentColor" strokeOpacity="0.2" strokeWidth="2" />
                <path d="M8 2a6 6 0 0 1 6 6" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" />
              </svg>
            )}
          </span>
          {loading ? t.loading : t.more}
        </button>
      ) : (
        <p className="kitfx-pg-pop inline-flex h-11 items-center gap-2 text-sm font-medium text-foreground">
          <span className="grid size-5 place-items-center rounded-full bg-[color-mix(in_oklab,var(--success)_16%,transparent)] text-success-foreground">
            <Icon name="check" size={13} strokeWidth={2.4} />
          </span>
          {t.all}
        </p>
      )}
    </div>
  );
}