export function generateCustomerNumber(): string {
  const timestamp = Date.now().toString(36).toUpperCase();
  const random = Math.random().toString(36).substring(2, 6).toUpperCase();
  return `K${timestamp}${random}`;
}

export function generateContractNumber(type: string | null | undefined): string {
  // Defensiv: ohne validen Type-String fällt der Prefix auf "CON" zurück.
  // Pentest Runde 12: POST /contracts ohne `type` warf
  // "Cannot read properties of undefined (reading 'substring')".
  const safeType = (typeof type === 'string' && type.length > 0) ? type : 'CON';
  const prefix = safeType.substring(0, 3).toUpperCase();
  const timestamp = Date.now().toString(36).toUpperCase();
  const random = Math.random().toString(36).substring(2, 5).toUpperCase();
  return `${prefix}-${timestamp}${random}`;
}

export function paginate(page: number = 1, limit: number = 20) {
  const skip = (page - 1) * limit;
  return { skip, take: limit };
}

export function buildPaginationResponse(
  page: number,
  limit: number,
  total: number
) {
  return {
    page,
    limit,
    total,
    totalPages: Math.ceil(total / limit),
  };
}