Timeline for React

'use client';

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

export type TimelineVariant = 'default' | 'alternate' | 'horizontal' | 'compact';
export type TimelineStatus = 'done' | 'current' | 'upcoming';

export interface TimelineItem {
  title: React.ReactNode;
  description?: React.ReactNode;
  /** Visible time or date, e.g. "Today, 09:12" or "2019" */
  time?: React.ReactNode;
  /** Machine readable date for <time>, e.g. "2026-10-19T09:12" */
  dateTime?: string;
  icon?: IconName;
  /** done and current fill the line up to that point */
  status?: TimelineStatus;
  /** Extra content under the text: an image, a quote, buttons */
  media?: React.ReactNode;
  /** Small label next to the title, e.g. a badge */
  meta?: React.ReactNode;
}

export interface TimelineProps {
  items: TimelineItem[];
  /**
   * default: line on the left with markers. alternate: center line, items left and right
   * (left line on phones). horizontal: a row from lg on, vertical below. compact: dense log with time column.
   */
  variant?: TimelineVariant;
  /** Accessible name of the list */
  label?: string;
  labels?: Partial<(typeof TEXTS)['en']>;
  className?: string;
}

const TEXTS = {
  en: { done: 'Done', current: 'In progress', upcoming: 'Upcoming' },
  de: { done: 'Erledigt', current: 'Läuft', upcoming: 'Geplant' },
};

/*
 * The line fills as you read: each segment follows the scroll position, each
 * point lights up when the line reaches it, each entry rises when it comes into
 * view. The horizontal tracker fills step by step once it is in view.
 * The server renders everything finished, the script only dims what is still ahead.
 */
const STYLES =
  '.kitfx-tl-mark{transition:opacity .45s var(--ease-kit),scale .55s cubic-bezier(.34,1.56,.64,1),filter .45s var(--ease-kit)}' +
  '.kitfx-tl-item[data-lit="0"] .kitfx-tl-mark{opacity:.45;scale:.82;filter:grayscale(1)}' +
  '.kitfx-tl-item[data-lit="1"] .kitfx-tl-mark{animation:kitfx-tl-glow 1s var(--ease-kit)}' +
  '@keyframes kitfx-tl-glow{0%{box-shadow:0 0 0 0 color-mix(in oklab,var(--primary) 45%,transparent)}100%{box-shadow:0 0 0 12px color-mix(in oklab,var(--primary) 0%,transparent)}}' +
  '.kitfx-tl-body{transition:opacity .7s var(--ease-kit),translate .7s var(--ease-kit)}' +
  '.kitfx-tl-item[data-seen="0"] .kitfx-tl-body{opacity:0;translate:0 12px}' +
  '.kitfx-tl-fill{transform-origin:top}' +
  '.kitfx-tl-step .kitfx-tl-fill{transition:transform .5s cubic-bezier(.45,0,.25,1)}' +
  '.kitfx-tl-step[data-fill="0"] .kitfx-tl-fill{transform:scaleY(0)}' +
  '@media (min-width:64rem){.kitfx-tl-row .kitfx-tl-fill{transform-origin:left}.kitfx-tl-step[data-fill="0"] .kitfx-tl-row .kitfx-tl-fill,.kitfx-tl-row.kitfx-tl-step[data-fill="0"] .kitfx-tl-fill{transform:scaleX(0)}}' +
  '@media (prefers-reduced-motion:reduce){.kitfx-tl-mark,.kitfx-tl-body,.kitfx-tl-step .kitfx-tl-fill{transition:none}.kitfx-tl-item .kitfx-tl-mark{animation:none}}';

const clamp01 = (v: number) => Math.min(1, Math.max(0, v));

/** Follows the scroll: fills segments, lights points, shows entries. Writes to the DOM directly, no React render per frame. */
function useScrollTrack(ref: React.RefObject<HTMLOListElement | null>) {
  useEffect(() => {
    const list = ref.current;
    if (!list || prefersReducedMotion()) return;
    let frame = 0;
    const update = () => {
      frame = 0;
      const vh = window.innerHeight;
      // The reading line sits at 62 % of the screen and moves down near the end of the page, so the last entries light up too
      const remaining = document.documentElement.scrollHeight - (window.scrollY + vh);
      const anchor = vh * (0.62 + 0.4 * clamp01(1 - remaining / (vh * 0.5)));
      list.querySelectorAll<HTMLElement>('[data-tl-item]').forEach((item) => {
        const mark = item.querySelector<HTMLElement>('[data-tl-mark]');
        const fill = item.querySelector<HTMLElement>('[data-tl-fill]');
        const top = item.getBoundingClientRect().top;
        item.dataset.seen = top < vh * 0.94 ? '1' : '0';
        if (mark) {
          const r = mark.getBoundingClientRect();
          item.dataset.lit = r.top + r.height / 2 < anchor ? '1' : '0';
        }
        if (fill?.parentElement) {
          const s = fill.parentElement.getBoundingClientRect();
          fill.style.transform = `scaleY(${clamp01((anchor - s.top) / (s.height || 1)).toFixed(3)})`;
        }
      });
    };
    const onScroll = () => {
      if (!frame) frame = requestAnimationFrame(update);
    };
    update();
    window.addEventListener('scroll', onScroll, { passive: true });
    window.addEventListener('resize', onScroll);
    return () => {
      cancelAnimationFrame(frame);
      window.removeEventListener('scroll', onScroll);
      window.removeEventListener('resize', onScroll);
    };
  }, [ref]);
}

/** For the tracker: once in view, the steps light up and the line fills from one to the next */
function useStepTrack(ref: React.RefObject<HTMLOListElement | null>) {
  useEffect(() => {
    const list = ref.current;
    if (!list || prefersReducedMotion()) return;
    if (list.getBoundingClientRect().top < window.innerHeight * 0.85) return;
    const items = Array.from(list.querySelectorAll<HTMLElement>('[data-tl-item]'));
    items.forEach((it) => {
      it.dataset.lit = '0';
      it.dataset.seen = '0';
      it.dataset.fill = '0';
    });
    const timers: number[] = [];
    const io = new IntersectionObserver(
      ([e]) => {
        if (!e?.isIntersecting) return;
        io.disconnect();
        items.forEach((it, i) => {
          timers.push(window.setTimeout(() => (it.dataset.seen = '1'), i * 90));
          timers.push(window.setTimeout(() => (it.dataset.lit = '1'), 200 + i * 520));
          timers.push(window.setTimeout(() => (it.dataset.fill = '1'), 260 + i * 520));
        });
      },
      { rootMargin: '0px 0px -15% 0px' },
    );
    io.observe(list);
    return () => {
      io.disconnect();
      timers.forEach((t) => window.clearTimeout(t));
    };
  }, [ref]);
}

function Marker({ item, small }: { item: TimelineItem; small?: boolean }) {
  const st = item.status;
  if (small) {
    return (
      <span
        data-tl-mark
        className={cn(
          'kitfx-tl-mark relative z-[1] block size-2.5 rounded-full',
          st === 'upcoming' ? 'bg-background shadow-[inset_0_0_0_1.5px_var(--border-strong)]' : st === 'current' ? 'bg-primary shadow-[0_0_0_4px_color-mix(in_oklab,var(--primary)_18%,transparent)]' : 'bg-[color-mix(in_oklab,var(--foreground)_35%,var(--background))]',
        )}
      />
    );
  }
  return (
    <span
      data-tl-mark
      className={cn(
        'kitfx-tl-mark relative z-[1] grid size-8 place-items-center rounded-full',
        st === 'done' && 'bg-primary text-primary-foreground',
        st === 'current' && 'bg-background text-foreground shadow-[inset_0_0_0_1.5px_var(--primary),0_0_0_4px_color-mix(in_oklab,var(--primary)_14%,transparent)]',
        (st === 'upcoming' || !st) && 'border border-border-strong bg-card text-muted-foreground shadow-[var(--shadow-sm)]',
      )}
    >
      {st === 'done' && !item.icon ? <Icon name="check" size={15} strokeWidth={2.2} /> : item.icon ? <Icon name={item.icon} size={15} /> : <span className={cn('size-2 rounded-full', st === 'current' ? 'bg-primary' : 'bg-border-strong')} />}
    </span>
  );
}

function When({ item, className }: { item: TimelineItem; className?: string }) {
  if (!item.time) return null;
  return item.dateTime ? (
    <time dateTime={item.dateTime} className={cn('text-[13px] tabular-nums text-muted-foreground', className)}>
      {item.time}
    </time>
  ) : (
    <span className={cn('text-[13px] tabular-nums text-muted-foreground', className)}>{item.time}</span>
  );
}

function Title({ item, className }: { item: TimelineItem; className?: string }) {
  return (
    <div className={cn('flex flex-wrap items-center gap-x-2.5 gap-y-1', className)}>
      <h3 className={cn('text-[15px] font-semibold tracking-[-0.01em]', item.status === 'upcoming' ? 'text-muted-foreground' : 'text-foreground')}>{item.title}</h3>
      {item.meta}
    </div>
  );
}

/**
 * Line from the bottom of one marker to the top of the next. Done steps and entries without a status
 * get a fill that follows the reader, the rest of the way stays a quiet line.
 */
function Line({ item, className }: { item: TimelineItem; className: string }) {
  const fills = item.status === 'done' || !item.status;
  return (
    <span aria-hidden className={cn('overflow-hidden bg-border-strong', className)}>
      {fills && <span data-tl-fill className={cn('kitfx-tl-fill block size-full', item.status === 'done' ? 'bg-primary' : 'bg-[color-mix(in_oklab,var(--primary)_70%,var(--foreground))]')} />}
    </span>
  );
}

/** Events in order: activity feeds, histories, order tracking and changelogs. */
export function Timeline({ items, variant = 'default', label, labels, className }: TimelineProps) {
  const t = useTexts(TEXTS, labels);
  const sr = (item: TimelineItem) => item.status && <span className="sr-only">, {t[item.status]}</span>;
  const last = items.length - 1;
  const ref = useRef<HTMLOListElement>(null);
  const horizontal = variant === 'horizontal';
  // Both hooks run, only the one for this variant does anything
  useScrollTrack(horizontal ? { current: null } : ref);
  useStepTrack(horizontal ? ref : { current: null });
  const style = (
    <style href="kitfx-tl" precedence="default">
      {STYLES}
    </style>
  );

  if (variant === 'compact') {
    return (
      <ol ref={ref} aria-label={label} className={cn('relative', className)}>
        {style}
        {items.map((item, i) => (
          <li key={i} data-tl-item className="kitfx-tl-item relative grid grid-cols-[1rem_1fr] gap-x-4 pb-7 last:pb-0 sm:grid-cols-[7.5rem_1rem_1fr]">
            <When item={item} className="kitfx-tl-body col-start-2 row-start-1 mb-1 sm:col-start-1 sm:mb-0 sm:pt-px sm:text-right" />
            <span className="relative col-start-1 row-span-3 row-start-1 flex justify-center pt-1.5 sm:col-start-2">
              <Marker item={item} small />
              {i < last && <Line item={item} className="absolute bottom-[-1.75rem] left-1/2 top-4 w-px -translate-x-1/2" />}
            </span>
            <div className="kitfx-tl-body col-start-2 min-w-0 sm:col-start-3 sm:row-start-1">
              <Title item={item} className="[&_h3]:text-sm" />
              {item.description && <div className="mt-1 text-pretty text-sm text-muted-foreground">{item.description}</div>}
              {item.media && <div className="mt-3">{item.media}</div>}
              {sr(item)}
            </div>
          </li>
        ))}
      </ol>
    );
  }

  if (horizontal) {
    return (
      <ol ref={ref} aria-label={label} className={cn('relative lg:flex', className)}>
        {style}
        {items.map((item, i) => (
          <li key={i} data-tl-item className="kitfx-tl-item kitfx-tl-step kitfx-tl-row relative flex gap-4 pb-8 last:pb-0 lg:flex-1 lg:flex-col lg:gap-5 lg:pb-0 lg:pr-6">
            <span className="relative flex shrink-0 flex-col items-center lg:flex-row">
              <Marker item={item} />
              {i < last && <Line item={item} className="absolute bottom-[-2rem] left-1/2 top-8 w-px -translate-x-1/2 lg:bottom-auto lg:left-8 lg:right-[-1.5rem] lg:top-1/2 lg:h-px lg:w-auto lg:translate-x-0" />}
            </span>
            <div className="kitfx-tl-body min-w-0 pt-1 lg:pt-0">
              <When item={item} className="mb-1 block" />
              <Title item={item} />
              {item.description && <div className="mt-1.5 text-pretty text-sm text-muted-foreground">{item.description}</div>}
              {item.media && <div className="mt-3">{item.media}</div>}
              {sr(item)}
            </div>
          </li>
        ))}
      </ol>
    );
  }

  if (variant === 'alternate') {
    return (
      <ol ref={ref} aria-label={label} className={cn('relative', className)}>
        {style}
        {items.map((item, i) => {
          const right = i % 2 === 1;
          return (
            <li key={i} data-tl-item className="kitfx-tl-item relative grid grid-cols-[2rem_1fr] gap-x-5 pb-12 last:pb-0 lg:grid-cols-[1fr_2rem_1fr] lg:gap-x-10">
              <span className="relative col-start-1 row-start-1 flex justify-center lg:col-start-2">
                <Marker item={item} />
                {i < last && <Line item={item} className="absolute bottom-[-3rem] left-1/2 top-8 w-px -translate-x-1/2" />}
              </span>
              {item.time && (
                <Reveal effect="fade" className={cn('row-start-1 hidden lg:block', right ? 'lg:col-start-1 lg:text-right' : 'lg:col-start-3')}>
                  <When item={item} className="block text-[1.75rem] font-semibold leading-8 tracking-[-0.03em] text-[color-mix(in_oklab,var(--primary)_70%,var(--muted-foreground))]" />
                </Reveal>
              )}
              <Reveal className={cn('col-start-2 row-start-1 min-w-0 pt-1', right ? 'lg:col-start-3' : 'lg:col-start-1 lg:text-right')}>
                <When item={item} className="mb-1 block font-medium text-[color-mix(in_oklab,var(--primary)_75%,var(--muted-foreground))] lg:hidden" />
                <Title item={item} className={cn(!right && 'lg:justify-end')} />
                {item.description && <div className={cn('mt-2 text-pretty text-sm leading-relaxed text-muted-foreground', !right && 'lg:ml-auto', 'max-w-[30rem]')}>{item.description}</div>}
                {item.media && <div className={cn('mt-4 max-w-[30rem] overflow-hidden rounded-lg', !right && 'lg:ml-auto')} data-clip-ok>{item.media}</div>}
                {sr(item)}
              </Reveal>
            </li>
          );
        })}
      </ol>
    );
  }

  return (
    <ol ref={ref} aria-label={label} className={cn('relative', className)}>
      {style}
      {items.map((item, i) => (
        <li key={i} data-tl-item className="kitfx-tl-item relative grid grid-cols-[2rem_1fr] gap-x-4 pb-8 last:pb-0">
          <span className="relative flex justify-center">
            <Marker item={item} />
            {i < last && <Line item={item} className="absolute bottom-[-2rem] left-1/2 top-8 w-px -translate-x-1/2" />}
          </span>
          <div className="kitfx-tl-body min-w-0 pt-1">
            <div className="flex flex-wrap items-baseline justify-between gap-x-4 gap-y-1">
              <Title item={item} />
              <When item={item} />
            </div>
            {item.description && <div className="mt-1 text-pretty text-sm text-muted-foreground">{item.description}</div>}
            {item.media && <div className="mt-3">{item.media}</div>}
            {sr(item)}
          </div>
        </li>
      ))}
    </ol>
  );
}