const GATEWAY_URL = process.env['NEXT_PUBLIC_GATEWAY_URL'] ?? 'http://localhost:14242';

export interface ApiRequestInit extends Omit<RequestInit, 'body'> {
  body?: unknown;
}

export interface ApiError {
  statusCode: number;
  message: string;
}

/**
 * Fetch wrapper for the Mosaic gateway API.
 * Sends credentials (cookies) and JSON body automatically.
 */
export async function api<T>(path: string, init?: ApiRequestInit): Promise<T> {
  const { body, headers: customHeaders, ...rest } = init ?? {};

  const headers: Record<string, string> = {
    Accept: 'application/json',
    ...(customHeaders as Record<string, string>),
  };

  if (body !== undefined) {
    headers['Content-Type'] = 'application/json';
  }

  const res = await fetch(`${GATEWAY_URL}${path}`, {
    credentials: 'include',
    ...rest,
    headers,
    body: body !== undefined ? JSON.stringify(body) : undefined,
  });

  if (!res.ok) {
    const errorBody = (await res.json().catch(() => ({
      statusCode: res.status,
      message: res.statusText,
    }))) as ApiError;
    throw Object.assign(new Error(errorBody.message), {
      statusCode: errorBody.statusCode,
    });
  }

  if (res.status === 204) return undefined as T;
  return (await res.json()) as T;
}