import { useEffect, useRef } from 'react';
import { useQueryClient } from '@tanstack/react-query';
import api from '@/lib/api';
import { useSettings } from './useSettings';

/**
 * Prefetches main page data in the background after the app unlocks.
 * Ensures cache is warm before the user navigates to each tab,
 * eliminating the skeleton flash on first visit.
 */
export function usePrefetch(enabled: boolean) {
  const queryClient = useQueryClient();
  const { settings } = useSettings();
  const hasPrefetched = useRef(false);
  const prevEnabled = useRef(false);

  // Reset on re-lock so subsequent unlocks refresh stale data (W-02)
  useEffect(() => {
    if (prevEnabled.current && !enabled) {
      hasPrefetched.current = false;
    }
    prevEnabled.current = enabled;
  }, [enabled]);

  useEffect(() => {
    // Wait for settings to load so upcoming_days is accurate (S-05)
    if (!enabled || hasPrefetched.current || !settings) return;
    hasPrefetched.current = true;

    const now = new Date();
    const clientDate = `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, '0')}-${String(now.getDate()).padStart(2, '0')}`;
    const days = settings.upcoming_days || 7;

    // Prefetch all main page queries (no-op if already cached and fresh)
    queryClient.prefetchQuery({
      queryKey: ['dashboard'],
      queryFn: () => api.get(`/dashboard?client_date=${clientDate}`).then(r => r.data),
      staleTime: 60_000,
    });

    queryClient.prefetchQuery({
      queryKey: ['upcoming', days],
      queryFn: () => api.get(`/upcoming?days=${days}&client_date=${clientDate}`).then(r => r.data),
      staleTime: 60_000,
    });

    queryClient.prefetchQuery({
      queryKey: ['todos'],
      queryFn: () => api.get('/todos').then(r => r.data),
    });

    queryClient.prefetchQuery({
      queryKey: ['reminders'],
      queryFn: () => api.get('/reminders').then(r => r.data),
    });

    queryClient.prefetchQuery({
      queryKey: ['projects'],
      queryFn: () => api.get('/projects').then(r => r.data),
    });

    queryClient.prefetchQuery({
      queryKey: ['people'],
      queryFn: () => api.get('/people').then(r => r.data),
    });

    queryClient.prefetchQuery({
      queryKey: ['locations'],
      queryFn: () => api.get('/locations').then(r => r.data),
    });
  }, [enabled, queryClient, settings]);
}