useFetch — Generic Data Fetching Hook

import { useState, useEffect, useCallback } from 'react';

interface UseFetchResult<T> {
  data: T | null;
  error: string | null;
  loading: boolean;
  refetch: () => void;
}

export function useFetch<T>(url: string): UseFetchResult<T> {
  const [data, setData] = useState<T | null>(null);
  const [error, setError] = useState<string | null>(null);
  const [loading, setLoading] = useState(true);

  const fetchData = useCallback(() => {
    let cancelled = false;
    setLoading(true);
    setError(null);

    fetch(url)
      .then((res) => {
        if (!res.ok) throw new Error(`HTTP ${res.status}`);
        return res.json();
      })
      .then((json) => {
        if (!cancelled) setData(json as T);
      })
      .catch((err) => {
        if (!cancelled) setError(err.message);
      })
      .finally(() => {
        if (!cancelled) setLoading(false);
      });

    return () => { cancelled = true; };
  }, [url]);

  useEffect(() => {
    const cleanup = fetchData();
    return cleanup;
  }, [fetchData]);

  return { data, error, loading, refetch: fetchData };
}

// Usage:
// const { data, loading, error } = useFetch<User[]>('/api/users');