policy-service/lib/policy_service/aggregates/policy_id.ex

defmodule PolicyService.Aggregates.PolicyId do
  @derive Jason.Encoder
  defstruct [:org_id, :policy_type, :application_id]

  def new(org_id, policy_type, application_id) do
    %__MODULE__{
      org_id: org_id,
      policy_type: policy_type,
      application_id: application_id
    }
  end

  def parse(string) when is_binary(string) do
    case String.split(string, ":", parts: 3) do
      [org_id, policy_type, application_id] ->
        {:ok,
         %__MODULE__{
           org_id: org_id,
           policy_type: policy_type,
           application_id: application_id
         }}

      _ ->
        {:error, :invalid_policy_id}
    end
  end

  def parse!(string) do
    case parse(string) do
      {:ok, id} -> id
      {:error, reason} -> raise ArgumentError, "invalid policy id #{inspect(string)}: #{reason}"
    end
  end

  defimpl String.Chars do
    def to_string(%PolicyService.Aggregates.PolicyId{
          org_id: org_id,
          policy_type: policy_type,
          application_id: application_id
        }) do
      org_id <> ":" <> policy_type <> ":" <> application_id
    end
  end

  defimpl Commanded.Serialization.JsonDecoder do
    def decode(%{org_id: org_id, policy_type: policy_type, application_id: application_id}) do
      PolicyService.Aggregates.PolicyId.new(org_id, policy_type, application_id)
    end

    def decode(id), do: id
  end
end