Flip cards in 3D

'use client';

import { useEffect, useState } from 'react';
import { cn, prefersReducedMotion, useTexts } from '@/lib/kit';
import { Eyebrow } from '@/components/ui/section';
import { Button } from '@/components/ui/button';
import { Icon, type IconName } from '@/components/ui/icon';
import { Reveal } from '@/components/ui/reveal';
import { Stagger } from '@/components/ui/motion';
import { ease3d } from '@/components/ui/depth';

/*
 * Cards with a front and a back that turn over in 3D. A card turns on hover (mouse and pen), on a
 * click or tap, and with Enter or Space on its turn button; Escape turns it back. The hidden side is
 * inert, so the keyboard and screen readers only meet the side in view. Both sides share one grid
 * cell, the card is as tall as its taller side and nothing below jumps.
 *
 * With reduced motion the sides cross fade instead of turning. Without JavaScript a hover card still
 * turns on hover, a click card shows its front with the back in the document for screen readers.
 *
 *   team     portraits that turn to a short bio and a contact link
 *   facts    questions that turn to their answer, myth or fact
 *   product  a product picture that turns to its details and a button
 *   stats    numbers that flip upward to what is behind them
 *   gift     one large voucher, the front a design, the back the code and how to redeem it
 *
 *   <FlipCard front={…} back={…} trigger="click" axis="x" label="Revenue" />   a single card
 */

export type FlipCardsVariant = 'team' | 'facts' | 'product' | 'stats' | 'gift';

const TEXTS = {
  en: { turn: 'Turn over', turnBack: 'Turn back', myth: 'Myth', fact: 'Fact', redeem: 'How to redeem', code: 'Code', mail: 'Write an email' },
  de: { turn: 'Umdrehen', turnBack: 'Zurückdrehen', myth: 'Mythos', fact: 'Stimmt', redeem: 'So löst du ein', code: 'Code', mail: 'E-Mail schreiben' },
};

/* ------------------------------------------------------------------ */
/* The single card                                                     */
/* ------------------------------------------------------------------ */

export interface FlipCardProps {
  front: React.ReactNode;
  back: React.ReactNode;
  /** hover turns on mouse over and on click, click only on click. Default hover. */
  trigger?: 'hover' | 'click';
  /** y turns sideways, x flips upward. Default y. */
  axis?: 'x' | 'y';
  /** Name of the card for the turn button, e.g. the person or the question */
  label: string;
  /** Start on the back */
  defaultFlipped?: boolean;
  /** Classes of both faces (radius, border, background) */
  faceClassName?: string;
  className?: string;
  labels?: Partial<(typeof TEXTS)['en']>;
}

const FOCUS = 'focus-visible:outline-2 focus-visible:outline-offset-4 focus-visible:outline-solid focus-visible:outline-primary';

/** A card with two sides that turns over in 3D. */
export function FlipCard({ front, back, trigger = 'hover', axis = 'y', label, defaultFlipped = false, faceClassName, className, labels }: FlipCardProps) {
  const t = useTexts(TEXTS, labels);
  const [flipped, setFlipped] = useState(defaultFlipped);
  const [ready, setReady] = useState(false);
  const [fade, setFade] = useState(false);
  useEffect(() => {
    setReady(true);
    setFade(prefersReducedMotion());
  }, []);
  const rot = axis === 'y' ? 'rotateY' : 'rotateX';
  const hover = trigger === 'hover';
  const enter = (e: React.PointerEvent) => hover && e.pointerType !== 'touch' && setFlipped(true);
  const leave = (e: React.PointerEvent) => hover && e.pointerType !== 'touch' && setFlipped(false);
  const face = cn('relative [grid-area:1/1] [backface-visibility:hidden] [-webkit-backface-visibility:hidden]', faceClassName);
  // Before hydration a hover card turns with CSS alone, afterwards the state leads
  const cssHover = hover && !ready ? 'group-hover/flip:[transform:var(--flip-to)]' : '';

  return (
    <div
      className={cn('group/flip relative [perspective:1400px]', className)}
      onPointerEnter={enter}
      onPointerLeave={leave}
      onKeyDown={(e) => {
        if (e.key === 'Escape' && flipped) setFlipped(false);
      }}
    >
      <div
        className={cn('grid h-full [transform-style:preserve-3d] transition-transform duration-700 motion-reduce:transition-none', cssHover)}
        style={{ transform: !fade && flipped ? `${rot}(180deg)` : undefined, transitionTimingFunction: ease3d, ['--flip-to' as string]: `${rot}(180deg)` }}
      >
        <div className={cn(face, fade ? 'transition-[opacity,visibility] duration-300' : 'transition-[visibility] duration-700', fade && flipped && 'opacity-0', ready && flipped && 'invisible')} inert={ready && flipped ? true : undefined}>
          {front}
          <button type="button" aria-expanded={false} onClick={() => setFlipped(true)} className={cn('absolute inset-0 z-10 cursor-pointer rounded-[inherit]', FOCUS)}>
            <span className="sr-only">
              {t.turn}: {label}
            </span>
          </button>
        </div>
        <div
          className={cn(face, fade ? 'transition-[opacity,visibility] duration-300' : 'transition-[visibility] duration-700', fade && !flipped && 'opacity-0', ready && !flipped && 'invisible')}
          style={fade ? undefined : { transform: `${rot}(180deg)` }}
          inert={ready && !flipped ? true : undefined}
        >
          {back}
          <button
            type="button"
            aria-expanded
            onClick={() => setFlipped(false)}
            className={cn('absolute right-3 top-3 z-10 flex size-11 cursor-pointer items-center justify-center rounded-full text-muted-foreground transition-colors hover:bg-accent hover:text-foreground sm:size-9', FOCUS)}
          >
            <Icon name="rotate-ccw" size={16} />
            <span className="sr-only">
              {t.turnBack}: {label}
            </span>
          </button>
        </div>
      </div>
    </div>
  );
}

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

export interface FlipItem {
  title: string;
  /** team: role; facts: myth or fact as 'myth' | 'fact'; product: price; stats: the number */
  meta?: string;
  /** the text on the back */
  text?: string;
  /** product, gift: points on the back */
  points?: string[];
  icon?: IconName;
  href?: string;
}

export interface FlipCardsProps extends Omit<React.HTMLAttributes<HTMLElement>, 'title'> {
  variant?: FlipCardsVariant;
  eyebrow?: string;
  title?: React.ReactNode;
  description?: string;
  items: FlipItem[];
  /** team: portraits; product: pictures; gift: the design on the front */
  media?: React.ReactNode[];
  /** product, gift: the button on the back */
  action?: { label: string; href?: string };
  /** Override how the cards turn */
  trigger?: 'hover' | 'click';
  labels?: Partial<(typeof TEXTS)['en']>;
}

const CARD = 'rounded-2xl border border-border bg-card shadow-[var(--highlight),var(--shadow-md)]';

function Head({ eyebrow, title, description, center = true }: Pick<FlipCardsProps, 'eyebrow' | 'title' | 'description'> & { center?: boolean }) {
  if (!title) return null;
  return (
    <Reveal className={cn('max-w-[42rem]', center && 'mx-auto text-center')}>
      {eyebrow && <Eyebrow>{eyebrow}</Eyebrow>}
      <h2 className="text-balance text-h2 font-semibold text-foreground">{title}</h2>
      {description && <p className={cn('mt-4 max-w-[36rem] text-pretty text-lead text-muted-foreground', center && 'mx-auto')}>{description}</p>}
    </Reveal>
  );
}

/** A hint in the corner of a front side that it turns */
function TurnHint() {
  return (
    <span aria-hidden className="absolute right-3 top-3 flex size-8 items-center justify-center rounded-full bg-[color-mix(in_oklab,var(--card)_80%,transparent)] text-muted-foreground shadow-[var(--shadow-sm)] backdrop-blur transition-transform duration-500 group-hover/flip:rotate-180">
      <Icon name="rotate-cw" size={14} />
    </span>
  );
}

/** Cards that turn over to show what is on their back. */
export function FlipCards({ variant = 'team', eyebrow, title, description, items, media = [], action, trigger, labels, className, ...rest }: FlipCardsProps) {
  const t = useTexts(TEXTS, labels);
  const pic = (i: number) => (media.length ? media[i % media.length] : null);

  if (variant === 'gift') {
    const it = items[0];
    if (!it) return null;
    return (
      <section {...rest} className={cn('relative overflow-x-clip py-20 sm:py-28', className)}>
        <div className="kit-container grid grid-cols-1 items-center gap-12 md:grid-cols-[minmax(0,0.9fr)_minmax(0,1.1fr)] lg:gap-20">
          <div>
            <Head eyebrow={eyebrow} title={title} description={description} center={false} />
            {action && (
              <div className="mt-8">
                <Button href={action.href} icon="arrow-right" className="max-sm:w-full">
                  {action.label}
                </Button>
              </div>
            )}
          </div>
          <FlipCard
            trigger={trigger ?? 'click'}
            label={it.title}
            labels={labels}
            className="mx-auto w-full max-w-[32rem]"
            faceClassName="rounded-3xl"
            front={
              <div className="relative aspect-[1.586] overflow-hidden rounded-3xl bg-[color-mix(in_oklab,var(--primary)_80%,black)] text-white shadow-[var(--shadow-lg)]">
                <div data-clip-ok className="absolute inset-0 opacity-70 [&>*]:size-full">{pic(0)}</div>
                <span aria-hidden className="absolute inset-0 bg-[linear-gradient(160deg,color-mix(in_oklab,var(--primary)_25%,transparent),color-mix(in_oklab,var(--primary)_55%,black))]" />
                <div className="relative flex h-full flex-col justify-between p-6 sm:p-8">
                  <p className="text-[13px] font-medium uppercase tracking-[0.12em] opacity-85">{eyebrow}</p>
                  <div className="flex items-end justify-between gap-4">
                    <p className="text-[clamp(1.6rem,1.2rem+1.6vw,2.4rem)] font-semibold leading-[1.05] tracking-[-0.03em]">{it.title}</p>
                    {it.meta && <p className="shrink-0 text-[clamp(1.6rem,1.2rem+1.6vw,2.4rem)] font-semibold tabular-nums">{it.meta}</p>}
                  </div>
                </div>
                <TurnHint />
              </div>
            }
            back={
              <div className="flex aspect-[1.586] flex-col rounded-3xl border border-border bg-card p-6 shadow-[var(--highlight),var(--shadow-lg)] sm:p-8">
                <p className="text-[13px] text-muted-foreground">{t.code}</p>
                <p className="mt-1 text-[clamp(1.2rem,1rem+1vw,1.6rem)] font-semibold tracking-[0.14em] text-foreground">{it.text}</p>
                <p className="mt-auto text-[13px] font-medium text-foreground">{t.redeem}</p>
                <ol className="mt-2 grid gap-1 text-[13.5px] text-muted-foreground sm:gap-1.5">
                  {(it.points ?? []).map((p, i) => (
                    <li key={p} className="flex gap-2.5">
                      <span className="flex size-5 shrink-0 items-center justify-center rounded-full bg-[color-mix(in_oklab,var(--primary)_14%,var(--card))] text-[11px] font-semibold text-primary">{i + 1}</span>
                      <span className="min-w-0">{p}</span>
                    </li>
                  ))}
                </ol>
              </div>
            }
          />
        </div>
      </section>
    );
  }

  const cols = variant === 'facts' ? 'sm:grid-cols-2 lg:grid-cols-3' : variant === 'stats' || items.length >= 4 ? 'sm:grid-cols-2 lg:grid-cols-4' : 'sm:grid-cols-2 lg:grid-cols-3';
  const how = trigger ?? (variant === 'facts' || variant === 'stats' ? 'click' : 'hover');

  return (
    <section {...rest} className={cn('relative py-20 sm:py-28', className)}>
      <div className="kit-container">
        <Head eyebrow={eyebrow} title={title} description={description} />
        <Stagger as="ul" className={cn('grid grid-cols-1 gap-5 lg:gap-6', title && 'mt-12 sm:mt-16', cols)}>
          {items.map((it, i) => (
            <li key={i} className="flex">
              {variant === 'team' && (
                <FlipCard
                  trigger={how}
                  label={it.title}
                  labels={labels}
                  className="w-full"
                  faceClassName="rounded-2xl"
                  front={
                    <div className={cn(CARD, 'h-full p-3')}>
                      <div className="aspect-[4/5] overflow-hidden rounded-xl bg-surface [&>*]:size-full">{pic(i)}</div>
                      <div className="px-2 pb-1 pt-4">
                        <h3 className="text-[17px] font-semibold text-foreground">{it.title}</h3>
                        {it.meta && <p className="text-[14px] text-muted-foreground">{it.meta}</p>}
                      </div>
                      <TurnHint />
                    </div>
                  }
                  back={
                    <div className={cn(CARD, 'flex h-full flex-col bg-[color-mix(in_oklab,var(--primary)_7%,var(--card))] p-6')}>
                      <p className="pr-10 text-[17px] font-semibold text-foreground">{it.title}</p>
                      {it.meta && <p className="text-[14px] text-primary">{it.meta}</p>}
                      <p className="mt-4 text-pretty text-[14.5px] leading-relaxed text-muted-foreground">{it.text}</p>
                      {it.href && (
                        <a href={it.href} className={cn('mt-auto inline-flex min-h-11 cursor-pointer items-center gap-2 pt-6 text-[14px] font-medium text-foreground hover:text-primary', FOCUS)}>
                          <Icon name="mail" size={16} />
                          {t.mail}
                        </a>
                      )}
                    </div>
                  }
                />
              )}
              {variant === 'facts' && (
                <FlipCard
                  trigger={how}
                  label={it.title}
                  labels={labels}
                  className="w-full"
                  faceClassName="rounded-2xl"
                  front={
                    <div className={cn(CARD, 'flex h-full min-h-[13rem] flex-col p-6 sm:p-7')}>
                      <span className="flex size-10 items-center justify-center rounded-xl bg-[color-mix(in_oklab,var(--primary)_12%,var(--card))] text-primary">
                        <Icon name={it.icon ?? 'help-circle'} size={19} />
                      </span>
                      <p className="mt-auto pt-6 text-balance text-[18px] font-semibold leading-snug text-foreground">{it.title}</p>
                      <TurnHint />
                    </div>
                  }
                  back={
                    <div className={cn(CARD, 'flex h-full min-h-[13rem] flex-col p-6 sm:p-7', it.meta === 'fact' ? 'bg-[color-mix(in_oklab,var(--success)_9%,var(--card))]' : 'bg-[color-mix(in_oklab,var(--primary)_7%,var(--card))]')}>
                      <span className={cn('inline-flex w-fit items-center gap-1.5 rounded-md px-2 py-1 text-[12.5px] font-semibold', it.meta === 'fact' ? 'bg-[color-mix(in_oklab,var(--success)_16%,var(--card))] text-success-foreground' : 'bg-[color-mix(in_oklab,var(--primary)_14%,var(--card))] text-primary')}>
                        <Icon name={it.meta === 'fact' ? 'check' : 'x'} size={13} />
                        {it.meta === 'fact' ? t.fact : t.myth}
                      </span>
                      <p className="mt-4 text-pretty pr-6 text-[15px] leading-relaxed text-foreground">{it.text}</p>
                    </div>
                  }
                />
              )}
              {variant === 'product' && (
                <FlipCard
                  trigger={how}
                  label={it.title}
                  labels={labels}
                  className="w-full"
                  faceClassName="rounded-2xl"
                  front={
                    <div className={cn(CARD, 'flex h-full flex-col p-3')}>
                      <div className="aspect-square overflow-hidden rounded-xl bg-surface [&>*]:size-full">{pic(i)}</div>
                      <div className="flex items-baseline justify-between gap-3 px-2 pb-2 pt-4">
                        <h3 className="text-[16px] font-semibold text-foreground">{it.title}</h3>
                        {it.meta && <span className="shrink-0 text-[15px] font-semibold tabular-nums text-foreground">{it.meta}</span>}
                      </div>
                      <TurnHint />
                    </div>
                  }
                  back={
                    <div className={cn(CARD, 'flex h-full flex-col p-6')}>
                      <p className="pr-10 text-[16px] font-semibold text-foreground">{it.title}</p>
                      {it.text && <p className="mt-2 text-[14px] leading-relaxed text-muted-foreground">{it.text}</p>}
                      <dl className="mt-5 grid gap-2 border-t border-border pt-4 text-[13.5px]">
                        {(it.points ?? []).map((p) => {
                          const [k, v] = p.split('|');
                          return (
                            <div key={p} className="flex justify-between gap-3">
                              <dt className="text-muted-foreground">{k}</dt>
                              <dd className="text-right font-medium text-foreground">{v}</dd>
                            </div>
                          );
                        })}
                      </dl>
                      <div className="mt-auto pt-6">
                        <Button href={it.href ?? action?.href} size="sm" className="w-full" iconLeft="cart">
                          {action?.label ?? it.title}
                        </Button>
                      </div>
                    </div>
                  }
                />
              )}
              {variant === 'stats' && (
                <FlipCard
                  trigger={how}
                  axis="x"
                  label={it.title}
                  labels={labels}
                  className="w-full"
                  faceClassName="rounded-2xl"
                  front={
                    <div className={cn(CARD, 'flex h-full min-h-[11.5rem] flex-col justify-between p-6')}>
                      <p className="text-[14px] text-muted-foreground">{it.title}</p>
                      <p className="text-[clamp(2.4rem,1.8rem+2vw,3.4rem)] font-semibold leading-none tracking-[-0.045em] tabular-nums text-foreground">{it.meta}</p>
                      <TurnHint />
                    </div>
                  }
                  back={
                    <div className={cn(CARD, 'flex h-full min-h-[11.5rem] flex-col bg-[color-mix(in_oklab,var(--primary)_8%,var(--card))] p-6')}>
                      <p className="flex items-center gap-2 pr-10 text-[14px] font-medium text-primary">
                        <Icon name={it.icon ?? 'info'} size={15} />
                        {it.title}
                      </p>
                      <p className="mt-3 text-pretty text-[14.5px] leading-relaxed text-foreground">{it.text}</p>
                    </div>
                  }
                />
              )}
            </li>
          ))}
        </Stagger>
      </div>
    </section>
  );
}