event_bus_metrics

defmodule EventBus.Metrics.Web.SSEController do
  @moduledoc """
  Router for sse events
  """

  use Plug.Router

  import EventBus.Metrics.Web.BaseRouter

  alias EventBus.Metrics
  alias SSE.Chunk

  @topic :eb_sse_streamed

  plug(:match)
  plug(:dispatch)

  get "/" do
    data = {@topic, sse_chunk()}
    conn
    |> put_cross_origin_header()
    |> SSE.stream(data)
  end

  match(_, do: send_not_found(conn, "path"))

  defp sse_chunk do
    %Chunk{
      comment: "Streaming event_bus metrics...",
      id: UUID.uuid4(),
      event: "init",
      data: prepare_data(),
      retry: 15_000,
    }
  end

  defp prepare_data do
    case Poison.encode(init_data()) do
      {:ok, data} -> data
      {:error, _} -> nil
    end
  end

  defp init_data do
    [
      Metrics.list_topics(),
      Metrics.list_subscribers(),
      Metrics.list_events()
    ]
  end
end