orcha

defmodule Orcha do
  @type message() :: term()
  @type timestamp() :: pos_integer()

  @opaque t() :: %__MODULE__{
            registry: %{atom() => any()}
          }

  @callback handle_request({module(), message()}, timestamp(), t()) ::
              {{:ok, result :: term()}, t()} | {:error, reason :: term()}

  defstruct registry: %{}

  def initialize(_args \\ []), do: %__MODULE__{}

  def register(%__MODULE__{} = realm, {mod, func, args}) do
    state = apply(mod, func, args)
    put_state(mod, state, realm)
  end

  def request({mod, msg}, timestamp, realm) do
    with {:ok, state} <- Map.fetch(realm.registry, mod) do
      case apply(mod, :handle_request, [msg, {timestamp, realm}, state]) do
        {result, new_state} ->
          new_realm = put_state(mod, new_state, realm)
          {result, new_realm}

        {result, new_state, %__MODULE__{} = new_realm} ->
          new_realm = put_state(mod, new_state, new_realm)
          {result, new_realm}
      end
    else
      :error ->
        raise "Requesting unregistered service: #{inspect(mod)}"
    end
  end

  defp put_state(mod, state, %__MODULE__{} = realm) do
    update_in(realm.registry, &Map.put(&1, mod, state))
  end
end