Happy Place - 2

example.ex

defmodule Example
  @pubsub ExampleApp.PubSub
  
  @spec websocket_connections([non_neg_integer]) :: non_neg_integer
  def websocket_connections([_ | _] = shards) do
    shards
    |> Enum.map(&Phoenix.PubSub.Local.local_name(@pubsub, &1))
    |> Enum.reduce(0, fn name, acc ->
      with pid   when is_pid(pid)    <- Process.whereis(name),
           info  when is_list(info)  <- Process.info(pid, [:monitors])[:monitors],
           procs when is_list(procs) <- info |> Enum.map(&(elem(&1, 1))) do
        acc + length(procs)
      else
        _ -> acc
      end
    end)
  end
end