defmodule BirdyChatWeb.ServerChannel do
  use BirdyChatWeb, :channel

  @impl true
  def join("server:" <> server_id, payload, socket) do
    if authorised?(payload, server_id) do
      {:ok, socket}
    else
      {:error, %{reason: "unauthorised"}}
    end
  end

  @impl true
  def handle_in("new_message", {:binary, message}, socket) do
    result = :erlang.binary_to_term(message, [:safe])

    # TODO: Add validation that this is the right server.
    case BirdyChat.Message.validate(result) do
      {:ok, changeset} ->
        case BirdyChat.MessageWriter.write(changeset.changes) do
          :ok ->
            {:reply, {:ok, {:binary, message}}, socket}
        end
    end
  end

  # Simple token-based authentication. Servers should use the same Phoenix secret key so they will
  # have the basis for generating tokens.
  defp authorised?(%{"token" => token}, server_id) do
    case Phoenix.Token.verify(BirdyChatWeb.Endpoint, "serverAuth", token, max_age: 86400) do
      {:ok, id} -> id == server_id
      {:error, :invalid} -> false
    end
  end
end