function trimTrailingSlash(value: string) {
  return value.endsWith('/') ? value.slice(0, -1) : value;
}

function isInternalHost(hostname: string) {
  return hostname === 'backend'
    || hostname === 'localhost'
    || hostname === '127.0.0.1'
    || hostname.endsWith('.internal');
}

function parseUrl(url: string) {
  try {
    return new URL(url);
  } catch {
    return null;
  }
}

export function resolveApiBaseURL(configuredBaseURL: string | undefined) {
  const fallbackLocal = 'http://localhost:3001';
  const candidate = configuredBaseURL?.trim() || fallbackLocal;

  if (typeof window === 'undefined') {
    return trimTrailingSlash(candidate);
  }

  const parsed = parseUrl(candidate);

  if (!parsed) {
    return `${window.location.origin}`;
  }

  const browserHost = window.location.hostname;
  const browserIsLocal = browserHost === 'localhost' || browserHost === '127.0.0.1';

  if (!browserIsLocal && isInternalHost(parsed.hostname)) {
    console.warn(
      `[fiscal] NEXT_PUBLIC_API_URL is internal (${parsed.hostname}); falling back to https://api.${browserHost}`
    );
    return trimTrailingSlash(`https://api.${browserHost}`);
  }

  return trimTrailingSlash(parsed.toString());
}