Hey,

I got a list of structs which I need to convert to a map (or similar useful data structure) that I can then further use to create some Prometheus metrics.

Here is what I got. The code is quite dirty in my opinion and maybe there is a smarter way to do it. I wrote it last night at 1am just to get it done, don’t judge me

Input data:

trackers = [
  %{
    pause: true,
    pause_timeout_in_ms: 72276156,
    position: %{"lat" => 11, "lng" => 1},
    response: nil,
    timeout_in_ms: 309722,
    user_id: "5cb6fb2c2071c963d21c517f"
  },
  %{
    pause: false,
    pause_timeout_in_ms: false,
    position: %{"lat" => 11, "lng" => 1},
    response: %{
      "status" => "ok",
      "vehicle_position" => %{"vehicle" => %{"tracking" => nil}}
    },
    timeout_in_ms: 1747683,
    user_id: "5cb6fb2d2071c963d21c5180"
  }
]

Then I do the following:

trackers
    |> Enum.map(
         fn x ->
           state = case x[:pause] do
             true -> "paused"
             false -> "active"
           end
           health = case x[:response] do
             nil -> "unhealthy"
             _ -> "healthy"
           end
           %{state: state, health: health}
         end
       )
    |> Enum.reduce(
         %{
           "active" => %{
             "healthy" => 0,
             "unhealthy" => 0
           },
           "paused" => %{
             "healthy" => 0,
             "unhealthy" => 0
           }
         },
         fn (x, acc) ->
           put_in(acc[x[:state]][x[:health]], get_in(acc, [x[:state], x[:health]]) + 1)
         end
       )

(Ignore the inline functions, gonna clean it up after the implementation is set)

Which gives me the following output:

%{
  "active" => %{"healthy" => 1, "unhealthy" => 0},
  "paused" => %{"healthy" => 0, "unhealthy" => 1}
}

Which I then use the following way:

series = for {state, health} <- extract_labeled_data(trackers), # extract_labeled_data is the cove above
    {health, value} <- health do
  {[state: state, health: health], value}
end

Prometheus.Model.gauge_metrics(series)

To generate Prometheus metrics like:

app_gateway_tracking_sessions_count{state="active",health="healthy"} 1
app_gateway_tracking_sessions_count{state="active",health="unhealthy"} 0
app_gateway_tracking_sessions_count{state="paused",health="healthy"} 0
app_gateway_tracking_sessions_count{state="paused",health="unhealthy"} 1

I am sure there are some things that can be improved to get from the input data to the final metrics.