export const API_BASE = process.env.NEXT_PUBLIC_API_URL || '';

// Auth rides on the Better Auth httpOnly session cookie. With API_BASE unset
// (same-origin via Next rewrites) 'same-origin' sends it; a cross-origin
// API_BASE needs 'include' plus CORS credentials on the backend.
const CREDENTIALS: RequestCredentials = API_BASE ? 'include' : 'same-origin';

export interface ApiError {
  error: string;
}

export async function fetchApi<T>(
  endpoint: string,
  options: RequestInit = {}
): Promise<T> {
  const headers: HeadersInit = {
    'Content-Type': 'application/json',
    ...options.headers,
  };

  const res = await fetch(`${API_BASE}${endpoint}`, {
    credentials: CREDENTIALS,
    ...options,
    headers,
  });

  if (!res.ok) {
    const errorData = await res.json().catch(() => ({ error: 'Request failed' }));
    const errorMessage = typeof errorData.error === 'string'
      ? errorData.error
      : (errorData.message || JSON.stringify(errorData) || 'Request failed');
    const error = new Error(errorMessage);
    // Preserve structured error info (e.g. code: 'EVENT_OVER_CAPACITY') so
    // callers can react beyond the message text.
    (error as any).code = errorData.code;
    (error as any).data = errorData;
    throw error;
  }

  return res.json();
}

/**
 * Fetch a file download (CSV/blob) with auth, returning the blob and the
 * filename parsed from the Content-Disposition header.
 */
export async function fetchBlob(
  endpoint: string,
  fallbackFilename: string
): Promise<{ blob: Blob; filename: string }> {
  const res = await fetch(`${API_BASE}${endpoint}`, { credentials: CREDENTIALS });
  if (!res.ok) {
    const errorData = await res.json().catch(() => ({ error: 'Export failed' }));
    throw new Error(errorData.error || 'Export failed');
  }

  const disposition = res.headers.get('Content-Disposition') || '';
  const filenameMatch = disposition.match(/filename="?([^"]+)"?/);
  const filename = filenameMatch ? filenameMatch[1] : fallbackFilename;
  const blob = await res.blob();
  return { blob, filename };
}