Agent - Phoenix Presence - WebSocket

agent_channel.ex

defmodule MyAppWeb.AgentChannel do
  use Phoenix.Channel
  alias MyApp.Presence

  @doc """
  Used by backend agent
  """
  def join("agent:" <> _agent_topic, _message, socket) do
    send(self(), :after_agent_joined)
    {:ok, socket}
  end

  def handle_info(:after_agent_joined, socket) do
    agent = socket.assigns.agent

    {:ok, _} = Presence.track(socket, "agent_status:#{agent.id}", %{})

    {:noreply, socket}
  end
end

agents.ex

defmodule MyApp.Agents do
  @moduledoc """
  The Agents context.
  """
  alias MyApp.Presence

  @doc """
  Returns true if agent is registered under Phoenix Presence.
  """
  def online?(nil), do: false
  def online?(agent_id) do
    agent = get_agent!(agent_id)
    topic = "agent:#{agent.topic}"
    case Presence.get_by_key(topic, "agent_status:#{agent.id}") do
      [] -> false
      %{metas: _metas} ->
        # The _metas would contain a list of connections in the channel,
        # having a phx reference to each of them, suggesting we have an agent live.
        # but the metas as such currently is of no use.
        true
    end
  end
end