'use client';

import { createContext, useContext, useEffect, useState, ReactNode } from 'react';
import { useQueryClient } from '@tanstack/react-query';
import { io } from 'socket.io-client';
import { API_URL, getAccessToken, refreshAccessToken } from '@/lib/api/client';
import { useSession } from '@/lib/session';

// Server topics mapped to the dashboard queries that show that data
const TOPIC_QUERIES: Record<string, string[][]> = {
  tabs: [['tabs'], ['reminder-candidates']],
  commands: [['commands']],
  'planned-tabs': [['planned-tabs'], ['reminder-candidates']],
  device: [['device']],
  reminders: [['reminder-candidates'], ['reminder-history']],
  users: [['users']],
  stock: [['stock'], ['stock-history']],
};

const RealtimeContext = createContext({ connected: false });

export function RealtimeProvider({ children }: { children: ReactNode }) {
  const queryClient = useQueryClient();
  const { venueId } = useSession();
  const [connected, setConnected] = useState(false);

  useEffect(() => {
    const socket = io(`${new URL(API_URL).origin}/realtime`, {
      // Read on every (re)connect so a refreshed token is used. The venue is only used for a superadmin viewing
      // another venue; everyone else follows their own
      auth: (cb) => cb({ token: getAccessToken(), venueId }),
      transports: ['websocket', 'polling'],
    });

    let hasConnected = false;
    let refreshing = false;
    let rejections = 0;

    socket.on('connect', () => {
      setConnected(true);
      rejections = 0;
      // Changes may have been missed while disconnected
      if (hasConnected) queryClient.invalidateQueries();
      hasConnected = true;
    });

    socket.on('disconnect', () => setConnected(false));

    socket.on('invalidate', ({ topics }: { topics: string[] }) => {
      for (const topic of topics) {
        for (const queryKey of TOPIC_QUERIES[topic] ?? []) {
          queryClient.invalidateQueries({ queryKey });
        }
      }
    });

    // The access token expired: refresh it and reconnect (rejected handshakes are not retried
    // automatically). If refreshing fails, the next API call sends the user to the login page.
    socket.on('connect_error', async (error) => {
      if (error.message !== 'unauthorized' || refreshing || ++rejections > 3) return;
      refreshing = true;
      const token = await refreshAccessToken();
      refreshing = false;
      if (token) socket.connect();
    });

    return () => {
      socket.disconnect();
    };
  }, [queryClient, venueId]);

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

export function useRealtime() {
  return useContext(RealtimeContext);
}

/** Polling interval to use only while live updates are unavailable. */
export function usePollingFallback(intervalMs: number): number | false {
  const { connected } = useRealtime();
  return connected ? false : intervalMs;
}