// Fired when any API call returns 401 (session expired/absent). App registers it
// to drop to the login screen.
let onUnauthorized: (() => void) | null = null;
export function setUnauthorizedHandler(fn: (() => void) | null): void {
  onUnauthorized = fn;
}

interface ApiOptions extends RequestInit {
  // When true, a 401 body is returned to the caller instead of throwing +
  // firing the logout hook. Used by /login to surface { success, error }.
  allowAuthErrorBody?: boolean;
}

export async function apiFetch<T>(url: string, options?: ApiOptions): Promise<T> {
  const { allowAuthErrorBody, ...init } = options ?? {};
  const res = await fetch(url, init);
  if (!res.ok) {
    if (res.status === 401) {
      if (!allowAuthErrorBody) { onUnauthorized?.(); throw new Error('unauthenticated'); }
      // else fall through and return the { success, error } body
    } else if (res.status === 400 || res.status === 409) {
      // Validation / conflict responses carry a { error, message } body the caller reads.
    } else {
      const text = await res.text().catch(() => res.statusText);
      throw new Error(text || `HTTP ${res.status}`);
    }
  }
  return res.json() as Promise<T>;
}

export function apiGet<T>(url: string): Promise<T> {
  return apiFetch<T>(url);
}

export function apiPost<T>(url: string, body: unknown, options?: ApiOptions): Promise<T> {
  return apiFetch<T>(url, {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(body),
    ...options,
  });
}