Toast notifications for React

'use client';

import { useCallback, useEffect, useRef, useState, useSyncExternalStore } from 'react';
import { createPortal } from 'react-dom';
import { cn, prefersReducedMotion, useTexts } from '@/lib/kit';
import { Icon, type IconName } from '@/components/ui/icon';
import { Spinner } from '@/components/ui/loading-button';
import { useMounted } from '@/components/ui/popover';

const TEXTS = { en: { close: 'Dismiss', region: 'Notifications' }, de: { close: 'Ausblenden', region: 'Benachrichtigungen' } };

/* The icon pops in with a small overshoot, the timer line runs down and pauses with the stack */
const CSS =
  '.kitfx-toast-icon{animation:kitfx-toast-icon .5s cubic-bezier(.34,1.56,.64,1) .08s both}@keyframes kitfx-toast-icon{from{opacity:0;transform:scale(.4) rotate(-20deg)}}' +
  '.kitfx-toast-timer{transform-origin:left;animation:kitfx-toast-timer var(--kitfx-toast-d) linear forwards}@keyframes kitfx-toast-timer{to{transform:scaleX(0)}}' +
  '@media (prefers-reduced-motion:reduce){.kitfx-toast-icon{animation:none}.kitfx-toast-timer{display:none}}';

/* Toasts that are on their way out: they stay in the list for their exit animation */
const EXIT_MS = 260;
let leaving = new Set<string>();

export type ToastVariant = 'default' | 'success' | 'error' | 'warning' | 'info' | 'loading';

export interface ToastData {
  id: string;
  title: React.ReactNode;
  description?: React.ReactNode;
  variant?: ToastVariant;
  /** One action, e.g. Undo */
  action?: { label: string; onClick: () => void };
  /** ms until it hides, Infinity keeps it. Errors stay longer by default. */
  duration?: number;
}

/* ------------------------------------------------------------------ */
/* Store                                                               */
/* ------------------------------------------------------------------ */

let items: ToastData[] = [];
const listeners = new Set<() => void>();
const emit = () => listeners.forEach((l) => l());
let counter = 0;

function add(data: Omit<ToastData, 'id'> & { id?: string }) {
  const id = data.id ?? `t${++counter}`;
  if (leaving.has(id)) leaving = new Set([...leaving].filter((x) => x !== id));
  const exists = items.some((x) => x.id === id);
  items = exists ? items.map((x) => (x.id === id ? { ...x, ...data, id } : x)) : [{ ...data, id }, ...items];
  emit();
  return id;
}

type Input = Omit<ToastData, 'id' | 'title' | 'variant'> & { id?: string };

/**
 * Show a toast from anywhere. Needs one <Toaster /> on the page.
 *   toast('Saved')  toast.success('Invoice sent', { description: '…' })
 *   toast.promise(save(), { loading: 'Saving', success: 'Saved', error: 'Could not save' })
 */
export const toast = Object.assign((title: React.ReactNode, opts?: Input) => add({ title, ...opts }), {
  success: (title: React.ReactNode, opts?: Input) => add({ title, variant: 'success', ...opts }),
  error: (title: React.ReactNode, opts?: Input) => add({ title, variant: 'error', ...opts }),
  warning: (title: React.ReactNode, opts?: Input) => add({ title, variant: 'warning', ...opts }),
  info: (title: React.ReactNode, opts?: Input) => add({ title, variant: 'info', ...opts }),
  loading: (title: React.ReactNode, opts?: Input) => add({ title, variant: 'loading', duration: Infinity, ...opts }),
  dismiss: (id?: string) => {
    const ids = id ? [id] : items.map((x) => x.id);
    if (typeof window === 'undefined' || prefersReducedMotion()) {
      items = items.filter((x) => !ids.includes(x.id));
      emit();
      return;
    }
    const fresh = ids.filter((x) => !leaving.has(x) && items.some((i) => i.id === x));
    if (!fresh.length) return;
    leaving = new Set([...leaving, ...fresh]);
    items = [...items];
    emit();
    window.setTimeout(() => {
      items = items.filter((x) => !fresh.includes(x.id));
      leaving = new Set([...leaving].filter((x) => !fresh.includes(x)));
      emit();
    }, EXIT_MS);
  },
  promise: <T,>(p: Promise<T>, msgs: { loading: React.ReactNode; success: React.ReactNode; error: React.ReactNode }) => {
    const id = add({ title: msgs.loading, variant: 'loading', duration: Infinity });
    p.then(
      () => add({ id, title: msgs.success, variant: 'success', duration: 4000 }),
      () => add({ id, title: msgs.error, variant: 'error', duration: 6000 }),
    );
    return p;
  },
});

const subscribe = (l: () => void) => {
  listeners.add(l);
  return () => listeners.delete(l);
};
const snapshot = () => items;
const empty: ToastData[] = [];

/* ------------------------------------------------------------------ */
/* View                                                                */
/* ------------------------------------------------------------------ */

/* Status colors come from the kit tokens. In light mode the icon takes a little
   foreground, so the pale warning yellow still reaches 3:1 on the popover. */
const ICON: Record<Exclude<ToastVariant, 'default' | 'loading'>, { icon: IconName; color: string }> = {
  success: { icon: 'check-circle', color: 'text-success' },
  error: { icon: 'x-circle', color: 'text-destructive' },
  warning: { icon: 'alert', color: 'text-[color-mix(in_oklab,var(--warning)_78%,var(--foreground))] dark:text-warning' },
  info: { icon: 'info', color: 'text-info' },
};

export interface ToastViewProps extends Omit<ToastData, 'id' | 'duration'> {
  onDismiss?: () => void;
  labels?: Partial<(typeof TEXTS)['en']>;
  className?: string;
}

/** The visible toast. Rendered by the Toaster, or alone to show the look. */
export function ToastView({ title, description, variant = 'default', action, onDismiss, labels, className }: ToastViewProps) {
  const t = useTexts(TEXTS, labels);
  const icon = variant !== 'default' && variant !== 'loading' ? ICON[variant] : null;
  return (
    <div
      role={variant === 'error' ? 'alert' : 'status'}
      className={cn(
        'group/toast pointer-events-auto relative flex w-full items-start gap-3 rounded-xl border border-border bg-popover p-4 pe-11 text-popover-foreground shadow-[var(--highlight),var(--shadow-lg)]',
        className,
      )}
    >
      <style href="kitfx-toast" precedence="default">
        {CSS}
      </style>
      {variant === 'loading' && <Spinner size={18} className="mt-px text-muted-foreground" />}
      {icon && <Icon key={variant} name={icon.icon} size={18} className={cn('kitfx-toast-icon mt-px', icon.color)} />}
      <div className="min-w-0 flex-1">
        <p className="text-sm font-medium leading-5 text-foreground">{title}</p>
        {description && <p className="mt-0.5 text-pretty text-[13px] leading-5 text-muted-foreground">{description}</p>}
        {action && (
          <button
            type="button"
            onClick={() => {
              action.onClick();
              onDismiss?.();
            }}
            className="mt-2.5 inline-flex h-7 items-center rounded-md border border-border-strong bg-background px-2.5 text-xs font-medium text-foreground shadow-[var(--shadow-sm)] transition-colors hover:bg-accent"
          >
            {action.label}
          </button>
        )}
      </div>
      {onDismiss && (
        <button
          type="button"
          onClick={onDismiss}
          aria-label={t.close}
          className="group/close absolute end-2.5 top-2.5 grid size-7 place-items-center rounded-md text-subtle-foreground transition-colors hover:bg-accent hover:text-foreground"
        >
          <Icon name="x" size={14} className="transition-transform duration-300 ease-[var(--ease-kit)] group-hover/close:rotate-90 motion-reduce:transition-none" />
        </button>
      )}
    </div>
  );
}

function Timed({ item, paused, onHeight, from, className, style, children }: { item: ToastData; paused: boolean; onHeight: (h: number) => void; from: 'top' | 'bottom'; className?: string; style?: React.CSSProperties; children: React.ReactNode }) {
  const ref = useRef<HTMLDivElement>(null);
  const liRef = useRef<HTMLLIElement>(null);
  const total = item.duration ?? (item.variant === 'error' ? 7000 : 4500);
  const left = useRef(total);
  // Arrives from its edge with a little spring
  useEffect(() => {
    const el = liRef.current;
    if (!el || prefersReducedMotion()) return;
    el.animate([{ opacity: 0, transform: `translateY(${from === 'top' ? -24 : 24}px) scale(0.94)` }, { opacity: 1, transform: 'none' }], { duration: 480, easing: 'cubic-bezier(0.34, 1.3, 0.64, 1)' });
  }, [from]);
  useEffect(() => {
    left.current = item.duration ?? (item.variant === 'error' ? 7000 : 4500);
  }, [item.duration, item.variant, item.title]);
  useEffect(() => {
    if (paused || !Number.isFinite(left.current)) return;
    const start = Date.now();
    const id = window.setTimeout(() => toast.dismiss(item.id), left.current);
    return () => {
      window.clearTimeout(id);
      left.current -= Date.now() - start;
    };
  }, [paused, item.id, item.variant, item.title]);
  useEffect(() => {
    const el = ref.current;
    if (!el) return;
    const ro = new ResizeObserver(() => onHeight(el.offsetHeight));
    ro.observe(el);
    return () => ro.disconnect();
  }, [onHeight]);
  return (
    <li ref={liRef} className={className} style={style}>
      <div ref={ref} className="relative">
        {children}
        {Number.isFinite(total) && (
          <span aria-hidden className="pointer-events-none absolute inset-x-4 bottom-0 h-px overflow-hidden rounded-full">
            <span
              key={`${item.variant}-${String(item.title)}`}
              className="kitfx-toast-timer block h-full bg-[color-mix(in_oklab,var(--foreground)_28%,transparent)]"
              style={{ '--kitfx-toast-d': `${total}ms`, animationPlayState: paused ? 'paused' : 'running' } as React.CSSProperties}
            />
          </span>
        )}
      </div>
    </li>
  );
}

export interface ToasterProps {
  position?: 'bottom-right' | 'bottom-center' | 'top-right' | 'top-center';
  /** How many stay visible in the stack */
  visible?: number;
  labels?: Partial<(typeof TEXTS)['en']>;
}

/**
 * Renders the toasts as a stack that fans out on hover or focus. One per page.
 * Timers pause while the pointer or focus is on the stack.
 */
export function Toaster({ position = 'bottom-right', visible = 3, labels }: ToasterProps) {
  const t = useTexts(TEXTS, labels);
  const list = useSyncExternalStore(subscribe, snapshot, () => empty);
  const mounted = useMounted();
  const [expanded, setExpanded] = useState(false);
  const [heights, setHeights] = useState<Record<string, number>>({});
  const setHeight = useCallback((id: string, h: number) => setHeights((cur) => (cur[id] === h ? cur : { ...cur, [id]: h })), []);
  const top = position.startsWith('top');
  const gap = 10;

  useEffect(() => {
    if (!list.length) setExpanded(false);
  }, [list.length]);

  if (!mounted) return null;
  // Toasts on their way out keep their place until they are gone, the rest stacks behind the front one
  const live = list.filter((x) => !leaving.has(x.id));
  const frontHeight = heights[live[0]?.id ?? list[0]?.id] ?? 72;
  const side = position.endsWith('right') ? 1 : 0;
  let offset = 0;
  let rank = 0;
  return createPortal(
    <section
      aria-label={t.region}
      className={cn(
        'pointer-events-none fixed z-[60] flex w-full flex-col px-4 sm:w-[24rem]',
        top ? 'top-4' : 'bottom-4',
        position.endsWith('right') ? 'sm:end-4' : 'sm:start-1/2 sm:-translate-x-1/2',
        'max-sm:inset-x-0',
      )}
      onPointerEnter={() => setExpanded(true)}
      onPointerLeave={() => setExpanded(false)}
      onFocus={() => setExpanded(true)}
      onBlur={(e) => !e.currentTarget.contains(e.relatedTarget as Node) && setExpanded(false)}
    >
      <ol className="relative" style={{ height: expanded ? live.slice(0, visible).reduce((s, x) => s + (heights[x.id] ?? 72) + gap, -gap) : frontHeight }}>
        {list.map((item) => {
          const out = leaving.has(item.id);
          const i = out ? Math.max(0, rank - 1) : rank++;
          const h = heights[item.id] ?? 72;
          const y = expanded ? (out ? Math.max(0, offset - h - gap) : offset) : i * 10;
          if (!out) offset += h + gap;
          const hidden = i >= visible;
          return (
            <Timed
              key={item.id}
              item={item}
              from={top ? 'top' : 'bottom'}
              paused={expanded}
              onHeight={(hh) => setHeight(item.id, hh)}
              className="absolute inset-x-0 transition-[translate,scale,opacity,transform] duration-300 ease-[var(--ease-kit)] motion-reduce:transition-none"
                style={{
                  [top ? 'top' : 'bottom']: 0,
                  zIndex: out ? list.length + 1 : list.length - rank,
                  translate: `0 ${top ? y : -y}px`,
                  scale: expanded || out ? '1' : String(1 - i * 0.05),
                  opacity: hidden || out ? 0 : 1,
                  transform: out ? (side ? 'translateX(calc(100% + 1rem))' : `translateY(${top ? -16 : 16}px) scale(0.96)`) : undefined,
                  pointerEvents: hidden ? 'none' : undefined,
                  transformOrigin: top ? 'bottom center' : 'top center',
                  height: !expanded && i > 0 ? frontHeight : undefined,
                  overflow: !expanded && i > 0 ? 'hidden' : undefined,
                  borderRadius: 12,
                }}
            >
              <ToastView {...item} labels={labels} onDismiss={() => toast.dismiss(item.id)} />
            </Timed>
          );
        })}
      </ol>
    </section>,
    document.body,
  );
}