import type { DashboardEvent } from '../../../../packages/api-contracts/src/index.js';
import {
  createContext,
  useCallback,
  useContext,
  useEffect,
  useMemo,
  useState,
  type PropsWithChildren,
} from 'react';
import { Link } from 'react-router-dom';
import { z } from 'zod';
import { useDashboardRealtime } from './realtime-provider.js';
import './notifications.css';

export type NotificationTone = 'info' | 'success' | 'warning' | 'error';

export interface NotificationItem {
  id: string;
  title: string;
  message: string;
  occurredAt: string;
  tone: NotificationTone;
  href?: string;
  isRead: boolean;
}

export type NotificationDraft = Omit<NotificationItem, 'isRead'>;

interface NotificationContextValue {
  isOpen: boolean;
  notifications: readonly NotificationItem[];
  toasts: readonly NotificationItem[];
  unreadCount: number;
  clearAll(): void;
  dismissToast(id: string): void;
  setOpen(isOpen: boolean): void;
}

interface RealtimeSubscription {
  subscribe(listener: (event: DashboardEvent) => void): () => void;
}

const STORAGE_KEY = 'reddit-bot.notifications.v1';
const MAX_NOTIFICATIONS = 50;
const NotificationContext = createContext<NotificationContextValue | null>(null);
const StoredNotificationsSchema = z.array(z.strictObject({
  id: z.string(),
  title: z.string(),
  message: z.string(),
  occurredAt: z.string(),
  tone: z.enum(['info', 'success', 'warning', 'error']),
  href: z.string().optional(),
  isRead: z.boolean(),
}));

function notificationStorage(): Storage | undefined {
  try {
    return globalThis.localStorage;
  } catch {
    return undefined;
  }
}

function titleCase(value: string): string {
  return value.charAt(0).toUpperCase() + value.slice(1).replaceAll('-', ' ');
}

export function notificationForEvent(event: DashboardEvent): NotificationDraft | null {
  switch (event.type) {
    case 'reply.received':
      return {
        id: event.id,
        occurredAt: event.occurredAt,
        title: `New reply from u/${event.payload.sender}`,
        message: event.payload.preview?.trim() || 'A new message arrived in this conversation.',
        tone: 'success',
        href: `/conversations/${encodeURIComponent(event.payload.conversationId)}`,
      };
    case 'media.received':
      return {
        id: event.id,
        occurredAt: event.occurredAt,
        title: `Image received from u/${event.payload.sender}`,
        message: event.payload.count > 1
          ? `${event.payload.count} images are attached to this conversation.`
          : 'An image is attached to this conversation.',
        tone: 'success',
        href: `/conversations/${encodeURIComponent(event.payload.conversationId)}`,
      };
    case 'message.sent':
      return null;
    case 'message.failed':
      return {
        id: event.id,
        occurredAt: event.occurredAt,
        title: `Message to u/${event.payload.recipient} failed`,
        message: event.payload.reason,
        tone: 'error',
        href: event.payload.conversationId
          ? `/conversations/${encodeURIComponent(event.payload.conversationId)}`
          : '/operations',
      };
    case 'bot.status.changed':
      if (event.payload.status !== 'stopped') return null;
      return {
        id: event.id,
        occurredAt: event.occurredAt,
        title: `Bot ${event.payload.status}`,
        message: event.payload.reason ?? `The bot is now ${event.payload.status}.`,
        tone: 'warning',
        href: '/operations',
      };
    case 'sync.completed':
      return null;
    case 'sync.failed':
      return {
        id: event.id,
        occurredAt: event.occurredAt,
        title: `${titleCase(event.payload.kind)} sync failed`,
        message: event.payload.reason,
        tone: 'error',
        href: '/operations',
      };
    case 'rate-limit.changed':
      if (!event.payload.limited) return null;
      return {
        id: event.id,
        occurredAt: event.occurredAt,
        title: 'Rate limit reached',
        message: event.payload.reason ?? 'Sending will resume when the limit resets.',
        tone: 'warning',
        href: '/operations',
      };
    case 'reddit.session.changed':
      if (!['expired', 'logged-out', 'error'].includes(event.payload.status)) return null;
      return {
        id: event.id,
        occurredAt: event.occurredAt,
        title: 'Reddit account needs attention',
        message: event.payload.reason ?? (event.payload.username
          ? `The session for u/${event.payload.username} changed to ${event.payload.status}.`
          : `Session status changed to ${event.payload.status}.`),
        tone: 'error',
        href: '/accounts',
      };
    case 'conversation.updated':
    case 'sync.started':
    case 'sync.progress':
    case 'log.created':
      return null;
  }
}

function loadNotifications(): NotificationItem[] {
  const storage = notificationStorage();
  if (!storage) return [];
  try {
    const value: unknown = JSON.parse(storage.getItem(STORAGE_KEY) ?? '[]');
    const parsed = StoredNotificationsSchema.safeParse(value);
    return parsed.success ? parsed.data.slice(0, MAX_NOTIFICATIONS) : [];
  } catch {
    return [];
  }
}

export interface NotificationProviderProps extends PropsWithChildren {
  realtime?: RealtimeSubscription;
}

export function NotificationProvider({ children, realtime: realtimeOverride }: NotificationProviderProps) {
  const dashboardRealtime = useDashboardRealtime();
  const realtime = realtimeOverride ?? dashboardRealtime;
  const [isOpen, setIsOpenState] = useState(false);
  const [notifications, setNotifications] = useState<NotificationItem[]>(loadNotifications);
  const [toasts, setToasts] = useState<NotificationItem[]>([]);

  const dismissToast = useCallback((id: string) => {
    setToasts((current) => current.filter((toast) => toast.id !== id));
  }, []);

  const setOpen = useCallback((nextOpen: boolean) => {
    setIsOpenState(nextOpen);
    if (nextOpen) setNotifications((current) => current.map((item) => ({ ...item, isRead: true })));
  }, []);

  useEffect(() => {
    try {
      notificationStorage()?.setItem(STORAGE_KEY, JSON.stringify(notifications));
    } catch {
      // Storage can be unavailable in private or restricted browser contexts.
    }
  }, [notifications]);

  useEffect(() => {
    if (isOpen && notifications.some((item) => !item.isRead)) {
      setNotifications((current) => current.map((item) => ({ ...item, isRead: true })));
    }
  }, [isOpen, notifications]);

  useEffect(() => realtime.subscribe((event) => {
    const draft = notificationForEvent(event);
    if (!draft) return;
    const item = { ...draft, isRead: false };
    setNotifications((current) => current.some((entry) => entry.id === item.id)
      ? current
      : [item, ...current].slice(0, MAX_NOTIFICATIONS));
    setToasts((current) => current.some((entry) => entry.id === item.id)
      ? current
      : [...current, item]);
  }), [realtime]);

  useEffect(() => {
    function closeOnEscape(event: KeyboardEvent): void {
      if (event.key === 'Escape') setOpen(false);
    }
    globalThis.addEventListener('keydown', closeOnEscape);
    return () => globalThis.removeEventListener('keydown', closeOnEscape);
  }, [setOpen]);

  const value = useMemo<NotificationContextValue>(() => ({
    isOpen,
    notifications,
    toasts,
    unreadCount: notifications.filter((item) => !item.isRead).length,
    clearAll: () => setNotifications([]),
    dismissToast,
    setOpen,
  }), [dismissToast, isOpen, notifications, setOpen, toasts]);

  return <NotificationContext.Provider value={value}>{children}</NotificationContext.Provider>;
}

function useNotifications(): NotificationContextValue {
  const context = useContext(NotificationContext);
  if (!context) throw new Error('Notifications must be used within NotificationProvider');
  return context;
}

function BellIcon() {
  return (
    <svg aria-hidden="true" viewBox="0 0 24 24">
      <path d="M18 8a6 6 0 0 0-12 0c0 7-3 7-3 9h18c0-2-3-2-3-9M10 21h4" />
    </svg>
  );
}

export function NotificationBell({ className = '' }: { className?: string }) {
  const { isOpen, setOpen, unreadCount } = useNotifications();
  return (
    <button
      aria-controls="notification-centre"
      aria-expanded={isOpen}
      aria-label={unreadCount > 0 ? `Notifications, ${unreadCount} unread` : 'Notifications'}
      className={`notification-bell ${className}`.trim()}
      onClick={() => setOpen(!isOpen)}
      type="button"
    >
      <BellIcon />
      {unreadCount > 0 ? <span className="notification-badge">{unreadCount > 99 ? '99+' : unreadCount}</span> : null}
    </button>
  );
}

function formattedTime(value: string): string {
  const date = new Date(value);
  if (Number.isNaN(date.getTime())) return '';
  return new Intl.DateTimeFormat(undefined, { dateStyle: 'medium', timeStyle: 'short' }).format(date);
}

function NotificationContent({ item }: { item: NotificationItem }) {
  return (
    <>
      <span className={`notification-signal ${item.tone}`} aria-hidden="true" />
      <span className="notification-copy">
        <strong>{item.title}</strong>
        <span>{item.message}</span>
        <time dateTime={item.occurredAt}>{formattedTime(item.occurredAt)}</time>
      </span>
    </>
  );
}

export function NotificationViewport() {
  const { clearAll, dismissToast, isOpen, notifications, setOpen, toasts } = useNotifications();
  return (
    <>
      {isOpen ? <button aria-label="Close notifications" className="notification-backdrop" onClick={() => setOpen(false)} type="button" /> : null}
      <aside aria-label="Notifications" className={isOpen ? 'notification-centre is-open' : 'notification-centre'} id="notification-centre">
        <header>
          <div>
            <span className="eyebrow">Activity inbox</span>
            <h2>Notifications</h2>
          </div>
          <button aria-label="Close notification centre" className="notification-close" onClick={() => setOpen(false)} type="button">×</button>
        </header>
        {notifications.length > 0 ? (
          <>
            <ol className="notification-list">
              {notifications.map((item) => (
                <li key={item.id}>
                  {item.href ? (
                    <Link className="notification-entry" onClick={() => setOpen(false)} to={item.href}>
                      <NotificationContent item={item} />
                    </Link>
                  ) : <div className="notification-entry"><NotificationContent item={item} /></div>}
                </li>
              ))}
            </ol>
            <footer><button className="notification-clear" onClick={clearAll} type="button">Clear all</button></footer>
          </>
        ) : (
          <div className="notification-empty">
            <span aria-hidden="true"><BellIcon /></span>
            <strong>All quiet</strong>
            <p>New replies, received images, and important account alerts will appear here.</p>
          </div>
        )}
      </aside>
      <div aria-atomic="false" aria-live="polite" className="toast-stack">
        {toasts.map((toast) => (
          <div className={`notification-toast ${toast.tone}`} key={toast.id} role={toast.tone === 'error' ? 'alert' : 'status'}>
            {toast.href ? (
              <Link onClick={() => dismissToast(toast.id)} to={toast.href}><NotificationContent item={toast} /></Link>
            ) : <div><NotificationContent item={toast} /></div>}
            <button aria-label={`Dismiss ${toast.title}`} onClick={() => dismissToast(toast.id)} type="button">×</button>
          </div>
        ))}
      </div>
    </>
  );
}