Form layouts

'use client';

import { useEffect, useRef, useState } from 'react';
import { cn, prefersReducedMotion, useInView } from '@/lib/kit';

/*
 * The frame of a form: sections with a title on the side (settings) or on
 * top (contact, application), a responsive grid for fields and a footer for
 * the actions. Fields come from input, select, textarea and friends.
 */

/**
 * Lets the direct children rise one after another once the group scrolls
 * into view (kit-stagger from kit.css). Server-rendered visible, so nothing
 * hides without JavaScript or with reduced motion. After the entrance the
 * delays go, so focus and hover react at once.
 */
function useRise(step = 60) {
  const [ref, inView] = useInView<HTMLDivElement>();
  const [done, setDone] = useState(false);
  useEffect(() => {
    if (!inView) return;
    const t = window.setTimeout(() => setDone(true), step * 8 + 800);
    return () => window.clearTimeout(t);
  }, [inView, step]);
  return { ref, className: cn('kit-stagger', !inView && 'kit-stagger-wait', done && 'kit-stagger-done'), style: { '--kit-step': `${step}ms` } as React.CSSProperties };
}

export interface FormSectionProps {
  title: React.ReactNode;
  description?: React.ReactNode;
  /** side: title in a column on the left from desktop up. top: title above the fields. */
  layout?: 'side' | 'top';
  className?: string;
  children: React.ReactNode;
}

/** A group of fields with a heading. Several sections are divided by hairlines. */
export function FormSection({ title, description, layout = 'top', className, children }: FormSectionProps) {
  const head = useRise(80);
  if (layout === 'side') {
    return (
      <section className={cn('grid gap-x-12 gap-y-6 py-8 first:pt-0 last:pb-0 lg:grid-cols-[minmax(0,17rem)_minmax(0,1fr)] [&+&]:border-t [&+&]:border-border', className)}>
        <div ref={head.ref} className={head.className} style={head.style}>
          <h3 className="text-[15px] font-semibold tracking-[-0.01em] text-foreground">{title}</h3>
          {description && <p className="mt-1.5 max-w-[34ch] text-pretty text-[13.5px] leading-relaxed text-muted-foreground">{description}</p>}
        </div>
        <div className="min-w-0">{children}</div>
      </section>
    );
  }
  return (
    <section className={cn('py-7 first:pt-0 last:pb-0 [&+&]:border-t [&+&]:border-border', className)}>
      <div ref={head.ref} className={head.className} style={head.style}>
        <h3 className="text-[15px] font-semibold tracking-[-0.01em] text-foreground">{title}</h3>
        {description && <p className="mt-1 text-pretty text-[13.5px] leading-relaxed text-muted-foreground">{description}</p>}
      </div>
      <div className="mt-5">{children}</div>
    </section>
  );
}

/** Fields side by side from tablet up. Use span={2} on wide fields (col-span-full). The fields rise one after another as the form scrolls in. */
export function FormGrid({ columns = 2, className, children }: { columns?: 1 | 2 | 3; className?: string; children: React.ReactNode }) {
  const rise = useRise(60);
  return (
    <div ref={rise.ref} style={rise.style} className={cn('grid gap-x-5 gap-y-6', columns === 2 && 'sm:grid-cols-2', columns === 3 && 'sm:grid-cols-2 lg:grid-cols-3', rise.className, className)}>
      {children}
    </div>
  );
}

/** The action row: secondary actions left, the main one right. Stacks with the main action on top on phones. */
export function FormActions({ note, divider = true, className, children }: { note?: React.ReactNode; divider?: boolean; className?: string; children: React.ReactNode }) {
  return (
    // Right after a section its bottom padding is the gap, no extra margin on top
    <div className={cn('mt-8 flex flex-col-reverse gap-4 sm:flex-row sm:items-center sm:justify-between [section+&]:mt-0', divider && 'border-t border-border pt-6', className)}>
      {note ? <p className="text-pretty text-[13px] leading-relaxed text-muted-foreground sm:max-w-[26rem]">{note}</p> : <span className="max-sm:hidden" />}
      <div className="flex flex-col-reverse gap-2.5 sm:flex-row sm:items-center [&>*]:max-sm:w-full">{children}</div>
    </div>
  );
}

/** A summary of all errors on top of a long form, linking to each field. Put it where focus goes after a failed submit. */
export function FormErrorSummary({ title, errors, className }: { title: React.ReactNode; errors: { field: string; message: React.ReactNode }[]; className?: string }) {
  // A new set of errors (after a failed submit) nudges the box once, so the eye finds it
  const ref = useRef<HTMLDivElement>(null);
  const key = errors.map((e) => e.field).join('|');
  const last = useRef(key);
  useEffect(() => {
    if (last.current === key) return;
    last.current = key;
    const el = ref.current;
    if (!el || !key || prefersReducedMotion() || typeof el.animate !== 'function') return;
    el.animate([{ transform: 'translateX(0)' }, { transform: 'translateX(-6px)' }, { transform: 'translateX(5px)' }, { transform: 'translateX(-3px)' }, { transform: 'translateX(0)' }], { duration: 420, easing: 'ease-out' });
  }, [key]);
  if (!errors.length) return null;
  return (
    <div ref={ref} role="alert" tabIndex={-1} className={cn('rounded-xl border border-[color-mix(in_oklab,var(--destructive)_40%,var(--border))] bg-[color-mix(in_oklab,var(--destructive)_6%,var(--card))] p-4', className)}>
      <p className="text-sm font-semibold text-destructive">{title}</p>
      <ul className="mt-2 grid gap-1 text-[13px] text-foreground">
        {errors.map((e) => (
          <li key={e.field} className="flex gap-2 before:mt-[7px] before:size-1 before:shrink-0 before:rounded-full before:bg-destructive before:content-['']">
            <a href={`#${e.field}`} className="underline decoration-[color-mix(in_oklab,var(--destructive)_40%,transparent)] underline-offset-4 hover:decoration-destructive">
              {e.message}
            </a>
          </li>
        ))}
      </ul>
    </div>
  );
}