Text scrub

'use client';

import { useCallback, useRef } from 'react';
import { cn, round } from '@/lib/kit';
import { Eyebrow } from '@/components/ui/section';
import { Button } from '@/components/ui/button';
import { lerp, smooth, span, useLive, useSceneProgress } from '@/components/ui/scroll-scene';

/*
 * Large type that moves with the scroll, as one statement per page. The movement follows the
 * scroll exactly (scrubbed), nothing loops on its own. Words and lines move by transform, the
 * outline fill by clip-path on the text alone.
 *
 * Without JavaScript and with reduced motion the statement stands in its finished, readable form.
 *
 *   lines     three or four giant lines slide against each other, small pictures sit between words
 *   converge  the words of one sentence come together from both sides into the middle
 *   scale     one word fills the window and shrinks to its place, the line below arrives
 *   stack     lines rise out of their own slot one after another, like a page being set
 *   outline   a giant outlined line fills with color from left to right
 */

export type TextScrubVariant = 'lines' | 'converge' | 'scale' | 'stack' | 'outline';

export interface TextScrubProps extends Omit<React.HTMLAttributes<HTMLElement>, 'title'> {
  variant?: TextScrubVariant;
  /** The statement, one entry per line. In a line, `[0]` places picture 0 between the words. */
  lines: string[];
  eyebrow?: string;
  /** Text under the statement */
  description?: string;
  action?: { label: string; href: string };
  /** lines: small pictures placed with [0], [1] … in the lines */
  images?: React.ReactNode[];
}

type Els = Record<string, HTMLElement | null>;
const tf = (el: HTMLElement | null | undefined, t: string) => {
  if (el) el.style.transform = t;
};
const op = (el: HTMLElement | null | undefined, o: number) => {
  if (el) el.style.opacity = String(round(o, 3));
};

const BIG = 'font-semibold leading-[0.95] tracking-[-0.045em] text-foreground';

/** A line with [n] markers turned into small rounded pictures */
function Line({ text, images }: { text: string; images?: React.ReactNode[] }) {
  const parts = text.split(/(\[\d+\])/g).filter(Boolean);
  return (
    <>
      {parts.map((part, i) => {
        const m = part.match(/^\[(\d+)\]$/);
        if (!m) return <span key={i}>{part}</span>;
        const img = images?.[Number(m[1]) % Math.max(1, images.length)];
        return img ? (
          <span key={i} aria-hidden className="mx-[0.12em] inline-block h-[0.78em] w-[1.5em] translate-y-[0.06em] overflow-hidden rounded-full align-baseline [&>*]:size-full">
            {img}
          </span>
        ) : null;
      })}
    </>
  );
}

/** Words of all lines, with their line index, for converge */
const wordsOf = (lines: string[]) => lines.flatMap((l, li) => l.replace(/\[\d+\]/g, '').split(/\s+/).filter(Boolean).map((w) => ({ w, li })));
const plain = (lines: string[]) => lines.map((l) => l.replace(/\[\d+\]/g, '').replace(/\s+/g, ' ').trim()).join(' ');

/* ------------------------------------------------------------------ */

/** Large type that moves with the scroll. */
export function TextScrub({ variant = 'lines', lines, eyebrow, description, action, images, className, ...rest }: TextScrubProps) {
  const live = useLive();
  const els = useRef<Els>({});
  const set = (k: string) => (n: HTMLElement | null) => {
    els.current[k] = n;
  };
  const words = wordsOf(lines);

  const apply = useCallback(
    (p: number) => {
      const e = els.current;
      const w = window.innerWidth;
      if (variant === 'lines') {
        // Each line slides against its neighbour, up to a fifth of the window over the whole pass, half as far on phones
        const f = w < 640 ? 0.5 : 1;
        lines.forEach((_, i) => tf(e[`l${i}`], `translate3d(${round((i % 2 ? 1 : -1) * (p - 0.5) * w * 0.22 * f, 1)}px, 0, 0)`));
      }
      if (variant === 'converge') {
        const k = smooth(span(p, 0.08, 0.62));
        words.forEach((_, i) => {
          const side = i % 2 ? 1 : -1;
          const far = w * (0.35 + ((i * 37) % 23) / 100);
          tf(e[`w${i}`], `translate3d(${round(side * far * (1 - k), 1)}px, ${round((i % 3 - 1) * 40 * (1 - k), 1)}px, 0)`);
          op(e[`w${i}`], lerp(0.12, 1, k));
        });
        const d = smooth(span(p, 0.62, 0.85));
        op(e.after, d);
        tf(e.after, `translate3d(0, ${round(20 * (1 - d), 1)}px, 0)`);
      }
      if (variant === 'scale') {
        const k = smooth(span(p, 0.05, 0.6));
        // The word is set at its start size and scaled down, so it stays sharp all the way
        const start = Number(e.word?.dataset.start) || 4;
        tf(e.word, `translate(-50%, -50%) scale(${round(lerp(1, 1 / start, k), 4)})`);
        const d = smooth(span(p, 0.55, 0.8));
        for (const k2 of ['after', 'after2']) {
          op(e[k2], d);
          tf(e[k2], `translate3d(0, ${round(24 * (1 - d), 1)}px, 0)`);
        }
      }
      if (variant === 'stack') {
        lines.forEach((_, i) => {
          // The first line is in place when the stage pins, so the scene never opens on an empty screen
          const a = i === 0 ? -0.22 : 0.06 + (i * 0.6) / Math.max(1, lines.length);
          const k = smooth(span(p, a, a + 0.22));
          // Glyphs reach above the tight line box, 130 % keeps their tops out of the mask too
          tf(e[`l${i}`], `translate3d(0, ${round((1 - k) * 130, 2)}%, 0)`);
        });
        const d = smooth(span(p, 0.72, 0.9));
        op(e.after, d);
        tf(e.after, `translate3d(0, ${round(20 * (1 - d), 1)}px, 0)`);
      }
      if (variant === 'outline') {
        lines.forEach((_, i) => {
          const a = 0.08 + (i * 0.5) / Math.max(1, lines.length);
          const k = span(p, a, a + 0.5 / Math.max(1, lines.length) + 0.12);
          const el = e[`f${i}`];
          if (el) el.style.clipPath = `inset(0 ${round((1 - k) * 100, 2)}% 0 0)`;
        });
        const d = smooth(span(p, 0.7, 0.9));
        op(e.after, d);
        tf(e.after, `translate3d(0, ${round(20 * (1 - d), 1)}px, 0)`);
      }
    },
    [variant, lines, words],
  );
  const track = useSceneProgress<HTMLDivElement>(live, { mode: variant === 'lines' ? 'pass' : 'pin', self: false, onProgress: apply });

  const after = (description || action) && (
    <div className={cn('mx-auto mt-10 max-w-[34rem] text-center', variant === 'outline' && 'mx-0 mt-0 text-left')}>
      {description && <p className="text-pretty text-lead text-muted-foreground">{description}</p>}
      {action && (
        <div className={cn('mt-7 flex justify-center', variant === 'outline' && 'justify-start')}>
          <div className="max-sm:w-full max-sm:[&>span]:w-full">
            <Button href={action.href} icon="arrow-right" magnetic className="max-sm:w-full">
              {action.label}
            </Button>
          </div>
        </div>
      )}
    </div>
  );
  const eyebrowEl = eyebrow && <Eyebrow className={cn('text-center', variant === 'outline' && 'text-left')}>{eyebrow}</Eyebrow>;

  /* ---------- lines: not pinned, the lines slide while the section passes ---------- */
  // Without JavaScript and with reduced motion the lines do not slide, so they wrap like the finished statement below
  if (variant === 'lines' && live) {
    return (
      <section {...rest} className={cn('relative overflow-hidden py-20 sm:py-28 lg:py-36', className)}>
        <div ref={track}>
          <div className="kit-container">{eyebrowEl}</div>
          <h2 className={cn('text-[clamp(1.75rem,0.2rem+7vw,9rem)]', BIG)}>
            <span className="sr-only">{plain(lines)}</span>
            {lines.map((l, i) => (
              <span key={i} aria-hidden className={cn('block whitespace-nowrap', i % 2 ? 'text-right' : 'text-left')}>
                <span ref={set(`l${i}`)} className={cn('inline-block will-change-transform', i % 2 ? 'pr-[6vw]' : 'pl-[6vw]', i === lines.length - 1 && 'kit-accent-text')}>
                  <Line text={l} images={images} />
                </span>
              </span>
            ))}
          </h2>
          <div className="kit-container">{after}</div>
        </div>
      </section>
    );
  }

  /* ---------- static: finished statement ---------- */
  if (!live) {
    return (
      <section {...rest} className={cn('relative overflow-x-clip py-20 sm:py-28 lg:py-36', className)}>
        <div className="kit-container">
          {eyebrowEl}
          <h2 className={cn('text-balance text-[clamp(2.5rem,1.2rem+5vw,6.5rem)]', variant === 'outline' ? 'text-left' : 'text-center', BIG)}>
            {lines.map((l, i) => (
              <span key={i} className={cn('block', i === lines.length - 1 && variant !== 'outline' && 'kit-accent-text')}>
                {l.replace(/\[\d+\]/g, '')}
              </span>
            ))}
          </h2>
          {after}
        </div>
      </section>
    );
  }

  /* ---------- pinned scenes ---------- */
  return (
    <section {...rest} className={cn('relative overflow-x-clip', className)}>
      <div ref={track} data-clip-ok className="relative" style={{ height: '240svh' }}>
        <div className="sticky top-0 flex h-svh flex-col justify-center overflow-clip">
          <div className="kit-container w-full">
            {eyebrowEl}
            {variant === 'converge' && (
              <h2 className={cn('text-balance text-center text-[clamp(2.5rem,1.2rem+5vw,6.5rem)]', BIG)}>
                <span className="sr-only">{plain(lines)}</span>
                {lines.map((_, li) => (
                  <span key={li} aria-hidden className="block">
                    {words.map((w, i) =>
                      w.li === li ? (
                        <span key={i} ref={set(`w${i}`)} className={cn('mx-[0.12em] inline-block will-change-transform', li === lines.length - 1 && 'kit-accent-text')}>
                          {w.w}
                        </span>
                      ) : null,
                    )}
                  </span>
                ))}
              </h2>
            )}
            {variant === 'scale' && (
              <h2 className={cn('text-center text-[clamp(3rem,1.4rem+7vw,9rem)]', BIG)}>
                {/* The word starts large enough to fill the window and shrinks into the line; the invisible copy holds its place, the sr-only copy is what screen readers get */}
                <span className="sr-only">{lines[0]}</span>
                <span aria-hidden className="relative inline-block">
                  <span className="invisible">{lines[0]}</span>
                  <span ref={set('word')} data-start={4.2} aria-hidden className="kit-accent-text absolute left-1/2 top-1/2 origin-center whitespace-nowrap text-[4.2em] will-change-transform" style={{ transform: 'translate(-50%, -50%)' }}>
                    {lines[0]}
                  </span>
                </span>
                {lines.slice(1).map((l, i) => (
                  <span key={i} ref={i === 0 ? set('after') : undefined} className="mt-2 block text-[0.42em] leading-tight tracking-[-0.03em] text-muted-foreground" style={{ opacity: 0 }}>
                    {l}
                  </span>
                ))}
              </h2>
            )}
            {variant === 'stack' && (
              <h2 className={cn('text-center text-[clamp(2.25rem,1.1rem+4.6vw,6rem)]', BIG)}>
                <span className="sr-only">{plain(lines)}</span>
                {lines.map((l, i) => (
                  <span key={i} aria-hidden className="block overflow-hidden pb-[0.14em]">
                    <span ref={set(`l${i}`)} className={cn('block will-change-transform', i === lines.length - 1 && 'kit-accent-text')}>
                      {l.replace(/\[\d+\]/g, '')}
                    </span>
                  </span>
                ))}
              </h2>
            )}
            {variant === 'outline' && (
              <div className="grid grid-cols-1 gap-10 lg:grid-cols-[minmax(0,1fr)_22rem] lg:items-end lg:gap-16">
              <h2 className={cn('text-[clamp(3.25rem,1rem+9vw,11rem)]', BIG)}>
                <span className="sr-only">{plain(lines)}</span>
                {lines.map((l, i) => (
                  <span key={i} aria-hidden className="relative block whitespace-nowrap">
                    <span className="block text-transparent [-webkit-text-stroke:1.5px_color-mix(in_oklab,var(--foreground)_45%,transparent)]">{l}</span>
                    <span ref={set(`f${i}`)} className={cn('absolute inset-0 block', i === lines.length - 1 ? 'text-primary' : 'text-foreground')} style={{ clipPath: 'inset(0 100% 0 0)' }}>
                      {l}
                    </span>
                  </span>
                ))}
              </h2>
              {after && (
                <div ref={set('after')} className="lg:pb-6" style={{ opacity: 0 }}>
                  {after}
                </div>
              )}
              </div>
            )}
            {variant !== 'scale' && variant !== 'outline' && after && (
              <div ref={set('after')} style={{ opacity: 0 }}>
                {after}
              </div>
            )}
            {variant === 'scale' && after && (
              <div ref={set('after2')} style={{ opacity: 0 }}>
                {after}
              </div>
            )}
          </div>
        </div>
      </div>
    </section>
  );
}