import { createContext, useContext, useState, useEffect, useRef, useCallback } from 'react';
import toast from 'react-hot-toast';
import { useAuth } from './AuthContext';
import api from '../services/api';

const NotificationContext = createContext();

export function NotificationProvider({ children }) {
  const { user } = useAuth();
  const [notifications, setNotifications] = useState([]);
  const [unreadCount, setUnreadCount] = useState(0);
  // Track seen IDs to detect genuinely new arrivals and show toasts
  const seenIds = useRef(new Set());
  const initialized = useRef(false);

  const fetch = useCallback(async () => {
    if (!user) return;
    try {
      const res = await api.get('/notifications');
      const incoming = res.data.notifications || [];
      setNotifications(incoming);
      setUnreadCount(res.data.unreadCount || 0);

      // First fetch: just seed the seen-set without toasting
      if (!initialized.current) {
        incoming.forEach(n => seenIds.current.add(n.id));
        initialized.current = true;
        return;
      }

      // Subsequent fetches: toast new unread notifications
      const newItems = incoming.filter(n => !n.read && !seenIds.current.has(n.id));
      newItems.forEach(n => {
        seenIds.current.add(n.id);
        const icon = notificationIcon(n.type);
        toast(`${icon} ${n.title}`, { duration: 5000 });
      });
    } catch {
      /* silent – server may not be reachable */
    }
  }, [user]);

  useEffect(() => {
    if (!user) {
      setNotifications([]);
      setUnreadCount(0);
      seenIds.current = new Set();
      initialized.current = false;
      return;
    }
    fetch();
    const interval = setInterval(fetch, 30_000);
    return () => clearInterval(interval);
  }, [user, fetch]);

  const markRead = async (id) => {
    try {
      await api.post(`/notifications/${id}/read`);
      setNotifications(prev =>
        prev.map(n => (n.id === id ? { ...n, read: 1 } : n)),
      );
      setUnreadCount(prev => Math.max(0, prev - 1));
    } catch { /* silent */ }
  };

  const markAllRead = async () => {
    try {
      await api.post('/notifications/read-all');
      setNotifications(prev => prev.map(n => ({ ...n, read: 1 })));
      setUnreadCount(0);
    } catch { /* silent */ }
  };

  return (
    <NotificationContext.Provider value={{ notifications, unreadCount, markRead, markAllRead, refresh: fetch }}>
      {children}
    </NotificationContext.Provider>
  );
}

export function useNotifications() {
  const ctx = useContext(NotificationContext);
  if (!ctx) throw new Error('useNotifications must be used within NotificationProvider');
  return ctx;
}

function notificationIcon(type) {
  switch (type) {
    case 'room_share_added':       return '🔗';
    case 'room_share_removed':     return '🚫';
    case 'federation_invite_received': return '📩';
    default:                       return '🔔';
  }
}