/** id type */
type id = integer;

/** @title User */
type user = struct {
    /** unique id of the user */
    id: id,
    name: string?,
    type: enum {"admin", "writer", "reader"},
    SNSs: [string],
};
/**
 * @title Group
 * this expresses a group of users
 */
type group = struct {
  id: id,
  admin: user?,
  members: [user],
  // this is short hand of `string where format = "date-time"`
  created_at: format("date-time"),
};

type password = string where 1 <= length && length <= 128 && it =~ /[a-z0-9!"#$%&'()=~|@]+/;

type error = struct {
  code: string,
  message?: string,
};

type not_found = error & struct {
  code: "not_found",
};