function isLoopbackHostname(hostname: string) {
  return hostname === 'localhost' || hostname === '127.0.0.1';
}

function normalizeBaseUrl(baseUrl: string) {
  return baseUrl.replace(/\/+$/, '');
}

function resolveApiBaseUrl() {
  const configuredBaseUrl = (import.meta.env.VITE_API_BASE_URL ?? '').trim();

  if (typeof window === 'undefined') {
    return normalizeBaseUrl(configuredBaseUrl);
  }

  const fallbackBaseUrl = `${window.location.protocol}//${window.location.hostname}:4000/api`;

  if (!configuredBaseUrl) {
    return fallbackBaseUrl;
  }

  try {
    const configuredUrl = new URL(configuredBaseUrl);

    if (isLoopbackHostname(configuredUrl.hostname) && !isLoopbackHostname(window.location.hostname)) {
      configuredUrl.hostname = window.location.hostname;
      return normalizeBaseUrl(configuredUrl.toString());
    }

    return normalizeBaseUrl(configuredUrl.toString());
  } catch {
    return normalizeBaseUrl(configuredBaseUrl);
  }
}

const apiBaseUrl = resolveApiBaseUrl();

export const hasApiConfig = Boolean(apiBaseUrl);

export async function apiRequest<T>(path: string, init?: RequestInit): Promise<T> {
  if (!apiBaseUrl) {
    throw new Error('VITE_API_BASE_URL is not configured.');
  }

  let response: Response;

  try {
    response = await fetch(`${apiBaseUrl}${path}`, {
      credentials: 'include',
      headers: {
        'Content-Type': 'application/json',
        ...(init?.headers ?? {}),
      },
      ...init,
    });
  } catch (error) {
    throw new Error(
      `Failed to reach the local API at ${apiBaseUrl}. Check that the API server is running and that VITE_API_BASE_URL matches the host you opened in the browser.`,
      { cause: error },
    );
  }

  const contentType = response.headers.get('content-type') || '';
  const payload = contentType.includes('application/json') ? ((await response.json()) as unknown) : null;

  if (!response.ok) {
    const message = payload && typeof payload === 'object' && 'error' in payload ? String(payload.error) : 'Request failed.';
    throw new Error(message);
  }

  return payload as T;
}