bad_code_example.ex

def register_user(%{organisation_id: org_id, account_type: type}} = user_params) do
  case Enum.all?(["name", "email", "password", "organisation_id"], fn(field) -> user_params[field] end) do
    true ->
      case Repo.get(Organisation, org_id) do
        nil -> {:error, :not_found}
        org ->
          valid =
            case type do
              "basic" -> org.used + 1 > org.capacity
              "pro" -> org.used + 2 > org.capacity
              "elite" ->
                if org.grandfathered do
                  org.used + 1 > org.capacity
                else
                  org.used + 3 > org.capacity
                end
            end

          if valid do
            %User
            |> User.changeset(user_params, organisation)
            |> Repo.insert()
            |> case do
              {:ok, %User{} = user} ->
                case EmailLibary.send("Welcome to OurCompany", user.to, "hello@xyz.com") do
                  :ok -> {:ok, user}
                  error -> error
                end
              error -> error
            end
          else
              {:error, :over_capacity}
          end
      end
    false -> :error
  end
end