Segmented control

'use client';

import { useCallback, useEffect, useLayoutEffect, useRef, useState } from 'react';
import { cn, useLocale } from '@/lib/kit';
import { Icon, type IconName } from '@/components/ui/icon';

/*
 * Segmented control: one value out of two to six, as a single track with a
 * thumb that glides to the choice. More than the plain segmented toggle:
 * three surfaces (raised, accent, underline), counts that stay readable on
 * the thumb, options with a second line, an upright form for side panels and
 * a track that fills the width on phones. APG radio group: one tab stop,
 * the arrow keys move and choose, Home and End jump to the ends.
 *
 * Without JavaScript the chosen segment carries the surface itself, so the
 * server render already shows the choice.
 */

const useIsoLayoutEffect = typeof window === 'undefined' ? useEffect : useLayoutEffect;

export type SegmentedSize = 'sm' | 'md' | 'lg';
export type SegmentedAppearance = 'surface' | 'solid' | 'underline';

export interface SegmentOption {
  value: string;
  label: string;
  icon?: IconName;
  /** Small number after the label, e.g. unread items */
  count?: number;
  /** Show only the icon, the label becomes the accessible name */
  iconOnly?: boolean;
  /** Second line, for upright controls */
  description?: string;
  disabled?: boolean;
}

export interface SegmentedControlProps {
  options: SegmentOption[];
  value?: string;
  defaultValue?: string;
  onValueChange?: (value: string) => void;
  /** Accessible name of the group, e.g. "View" */
  label: string;
  size?: SegmentedSize;
  /** surface: raised thumb on a quiet track. solid: thumb in the accent color. underline: a line slides under the choice. */
  appearance?: SegmentedAppearance;
  orientation?: 'horizontal' | 'vertical';
  /** Fill the width. mobile: only below 640 px, the segments share the width equally there. */
  stretch?: boolean | 'mobile';
  /** id of the panel the control switches, for aria-controls */
  controls?: string;
  className?: string;
}

const SIZE: Record<SegmentedSize, { track: string; item: string; square: string; icon: number; text: string; pad: string }> = {
  sm: { track: 'rounded-lg p-[3px]', item: 'min-h-[30px] gap-1.5 rounded-[6px] px-2.5 max-sm:min-h-[38px]', square: 'w-[30px] px-0 max-sm:w-[38px]', icon: 15, text: 'text-[13px]', pad: '[--pad:3px]' },
  md: { track: 'rounded-[10px] p-1', item: 'min-h-9 gap-2 rounded-[7px] px-3.5', square: 'w-9 px-0', icon: 16, text: 'text-sm', pad: '[--pad:4px]' },
  lg: { track: 'rounded-xl p-1', item: 'min-h-11 gap-2 rounded-[9px] px-4', square: 'w-11 px-0', icon: 18, text: 'text-[15px]', pad: '[--pad:4px]' },
};

interface Thumb {
  x: number;
  y: number;
  w: number;
  h: number;
  animate: boolean;
}

/** A choice of one value from a few, with a gliding thumb. Radio group semantics, arrow keys move and choose. */
export function SegmentedControl({
  options,
  value,
  defaultValue,
  onValueChange,
  label,
  size = 'md',
  appearance = 'surface',
  orientation = 'horizontal',
  stretch,
  controls,
  className,
}: SegmentedControlProps) {
  const locale = useLocale();
  const [inner, setInner] = useState(defaultValue ?? options.find((o) => !o.disabled)?.value ?? '');
  const current = value ?? inner;
  const trackRef = useRef<HTMLDivElement>(null);
  const [thumb, setThumb] = useState<Thumb | null>(null);
  const vertical = orientation === 'vertical';
  const underline = appearance === 'underline';
  const s = SIZE[size];

  const choose = (v: string) => {
    if (value === undefined) setInner(v);
    onValueChange?.(v);
  };

  const measure = useCallback(
    (animate: boolean) => {
      const el = trackRef.current?.querySelector<HTMLElement>(`[data-value="${CSS.escape(current)}"]`);
      if (!el) return setThumb(null);
      setThumb({ x: el.offsetLeft, y: el.offsetTop, w: el.offsetWidth, h: el.offsetHeight, animate });
    },
    [current],
  );
  const first = useRef(true);
  useIsoLayoutEffect(() => {
    measure(!first.current);
    first.current = false;
  }, [measure]);
  useEffect(() => {
    const track = trackRef.current;
    if (!track) return;
    const ro = new ResizeObserver(() => measure(false));
    ro.observe(track);
    // Late web fonts change the widths once more
    document.fonts?.ready.then(() => measure(false));
    return () => ro.disconnect();
  }, [measure]);

  const onKeyDown = (e: React.KeyboardEvent) => {
    const keys = ['ArrowRight', 'ArrowLeft', 'ArrowDown', 'ArrowUp', 'Home', 'End'];
    if (!keys.includes(e.key)) return;
    e.preventDefault();
    const enabled = options.map((o, i) => (o.disabled ? -1 : i)).filter((i) => i >= 0);
    if (!enabled.length) return;
    const pos = Math.max(0, enabled.indexOf(options.findIndex((o) => o.value === current)));
    const forward = e.key === 'ArrowRight' || e.key === 'ArrowDown';
    const next = e.key === 'Home' ? enabled[0] : e.key === 'End' ? enabled[enabled.length - 1] : enabled[(pos + (forward ? 1 : -1) + enabled.length) % enabled.length];
    choose(options[next].value);
    trackRef.current?.querySelectorAll<HTMLButtonElement>('[role="radio"]')[next]?.focus();
  };

  const nf = new Intl.NumberFormat(locale === 'de' ? 'de-DE' : 'en-US');
  const ready = thumb !== null;
  const full = stretch === true;
  const phoneFull = stretch === 'mobile';

  return (
    <div
      ref={trackRef}
      role="radiogroup"
      aria-label={label}
      aria-orientation={vertical ? 'vertical' : undefined}
      onKeyDown={onKeyDown}
      className={cn(
        'relative isolate max-w-full',
        vertical ? 'flex flex-col items-stretch' : 'inline-flex items-stretch',
        !vertical && full && 'flex w-full',
        !vertical && phoneFull && 'max-sm:flex max-sm:w-full',
        underline
          ? cn(vertical ? 'gap-0.5 border-s border-border ps-0' : 'gap-1 border-b border-border')
          : cn('bg-muted shadow-[inset_0_0_0_1px_var(--border)]', s.track, vertical && 'gap-0.5'),
        s.pad,
        className,
      )}
    >
      {ready && (
        <span
          aria-hidden
          className={cn(
            'pointer-events-none absolute left-0 top-0 -z-10',
            appearance === 'surface' && 'rounded-[inherit] bg-background shadow-[0_0_0_1px_var(--border),var(--shadow-sm)] dark:bg-[color-mix(in_oklab,var(--foreground)_11%,var(--background))]',
            appearance === 'solid' && 'bg-primary shadow-[inset_0_1px_0_rgb(255_255_255/0.18),var(--shadow-sm)]',
            appearance === 'underline' && 'bg-primary',
            !underline && (size === 'sm' ? 'rounded-[6px]' : size === 'md' ? 'rounded-[7px]' : 'rounded-[9px]'),
            thumb.animate && 'transition-[translate,width,height] duration-[420ms] ease-[cubic-bezier(0.3,1.25,0.5,1)] motion-reduce:transition-none',
          )}
          style={
            underline
              ? vertical
                ? { translate: `-1px ${thumb.y}px`, width: 2, height: thumb.h }
                : { translate: `${thumb.x}px ${thumb.y + thumb.h - 1}px`, width: thumb.w, height: 2 }
              : { translate: `${thumb.x}px ${thumb.y}px`, width: thumb.w, height: thumb.h }
          }
        />
      )}
      {options.map((o) => {
        const on = o.value === current;
        const iconOnly = o.iconOnly && o.icon;
        const onSolid = appearance === 'solid' && on;
        return (
          <button
            key={o.value}
            type="button"
            role="radio"
            aria-checked={on}
            aria-label={iconOnly ? o.label : undefined}
            aria-controls={controls}
            title={iconOnly ? o.label : undefined}
            data-value={o.value}
            disabled={o.disabled}
            tabIndex={on ? 0 : -1}
            onClick={() => choose(o.value)}
            className={cn(
              'relative inline-flex cursor-pointer select-none items-center whitespace-nowrap font-medium outline-none transition-[color,scale,background-color] duration-200 ease-[var(--ease-kit)] active:scale-[0.97] active:duration-100 disabled:pointer-events-none disabled:opacity-45 motion-reduce:active:scale-100',
              'focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-solid focus-visible:outline-ring',
              s.item,
              s.text,
              // The track padding counts toward the finger target: 36 px segment plus 4 px above and below
              !underline && 'after:absolute after:inset-x-0 after:-inset-y-1 after:content-[""]',
              vertical ? 'justify-start text-start' : 'justify-center',
              iconOnly && !vertical && s.square,
              !vertical && (full || phoneFull) && (full ? 'flex-1' : 'max-sm:flex-1'),
              underline && (vertical ? 'min-h-11 rounded-none ps-4 max-sm:min-h-11' : 'min-h-11 rounded-none px-3 pb-px max-sm:min-h-11'),
              on ? (onSolid ? 'text-primary-foreground' : 'text-foreground') : 'text-muted-foreground hover:text-foreground',
              !on && !underline && 'hover:bg-[color-mix(in_oklab,var(--foreground)_4%,transparent)]',
              // Until the thumb is measured (server render, no JavaScript) the chosen segment carries the surface itself
              on && !ready && appearance === 'surface' && 'bg-background shadow-[0_0_0_1px_var(--border),var(--shadow-sm)]',
              on && !ready && appearance === 'solid' && 'bg-primary',
              on && !ready && underline && (vertical ? 'shadow-[inset_2px_0_0_var(--primary)]' : 'shadow-[inset_0_-2px_0_var(--primary)]'),
              o.description && vertical && 'py-2.5',
            )}
          >
            {o.icon && <Icon name={o.icon} size={s.icon} className={cn('shrink-0', !on && !onSolid && 'opacity-80', o.description && vertical && 'self-start mt-0.5')} />}
            {!iconOnly &&
              (o.description && vertical ? (
                <span className="min-w-0 flex-1 whitespace-normal">
                  <span className="block leading-5">{o.label}</span>
                  <span className={cn('mt-0.5 block text-[12px] font-normal leading-4', onSolid ? 'text-primary-foreground/80' : 'text-muted-foreground')}>{o.description}</span>
                </span>
              ) : (
                <span className={cn(vertical && 'flex-1')}>{o.label}</span>
              ))}
            {o.count !== undefined && (
              <span
                className={cn(
                  'inline-grid h-5 min-w-5 shrink-0 place-items-center rounded-md px-1.5 text-[11px] font-semibold tabular-nums leading-none transition-[background-color,color] duration-200',
                  onSolid
                    ? 'bg-[color-mix(in_oklab,var(--primary-foreground)_22%,transparent)] text-primary-foreground'
                    : on
                      ? 'bg-[color-mix(in_oklab,var(--primary)_16%,transparent)] text-[color-mix(in_oklab,var(--primary)_80%,var(--foreground))]'
                      : 'bg-[color-mix(in_oklab,var(--foreground)_8%,transparent)] text-muted-foreground',
                )}
              >
                {nf.format(o.count)}
              </span>
            )}
          </button>
        );
      })}
    </div>
  );
}