license_checker.ex

defmodule AlchemyWeb.LicenseChecker do
  @moduledoc """
  At a constant interval, confirm that all connected users have a license.  If not then
  send a message to their channel telling the client to kick them out.
  """
  use GenServer
  alias Alchemy.Licensing

  # The interval between checks
  @interval 1000

  def start_link(opts) do
    GenServer.start_link(__MODULE__, opts)
  end

  def init(_args) do
    schedule_check_licenses()

    {:ok, %{}}
  end

  defp schedule_check_licenses() do
    self() |> Process.send_after(:check_licenses, @interval)
  end

  @doc """
  Check the licenses for all connected users.  If any users don't have a license slot, send a message to their channel
  to tell them so.
  """
  defp check_licenses() do
    # Get all connected user channels
    channel_pids_and_tokens = Registry.lookup(Registry.UserChannels, "users")

    # Get the pids of all channels that no longer have a license
    expired_channel_pids =
      Enum.zip(
        # PIDs
        channel_pids_and_tokens |> Enum.map(&elem(&1, 0)),

        # License details
        channel_pids_and_tokens
        |> Enum.map(&elem(&1, 1))
        |> Licensing.acquire_license_slots()
      )
      |> Enum.filter(fn {_, %Licensing.LicenseDetails{has_license_slot: has_license_slot}} ->
        has_license_slot === false
      end)
      |> Enum.map(&elem(&1, 0))

    # Send a message to each expired channel so they can disconnect their clients
    expired_channel_pids
    |> Enum.each(&send(&1, :license_expired))
  end

  def handle_info(:check_licenses, state) do
    check_licenses()
    schedule_check_licenses()
    {:noreply, state}
  end
end

DISREGARD THIS. IT IS INCORRECT

There is a lot of unnecessary iteration here.

The logic can be summarized as:

defp check_licenses() do
  # Get all connected user channels
  Registry.UserChannels
  |> Registry.lookup("users")
  |> Enum.each(fn {pid, token} -> notify_pid_if_expired(pid, token) end)
end

defp notify_pid_if_expired(pid, token) do
  token
  |> Licensing.acquire_license_slots()
  |> case do
    %Licensing.LicenseDetails{has_license_slot: false} ->
      send(pid, :license_expired)
    _ -> 
      :ok
  end
end

defmodule AlchemyWeb.LicenseChecker do
  @moduledoc """
  At a constant interval, confirm that all connected users have a license.  If not then
  send a message to their channel telling the client to kick them out.
  """
  use GenServer
  alias Alchemy.Licensing

  # The interval between checks
  @interval 1000

  def start_link(opts) do
    GenServer.start_link(__MODULE__, opts)
  end

  def init(_args) do
    schedule_check_licenses()

    {:ok, %{}}
  end

  defp schedule_check_licenses() do
    self() |> Process.send_after(:check_licenses, @interval)
  end

  @doc """
  Check the licenses for all connected users.  If any users don't have a license slot, send a message to their channel
  to tell them so.
  """
  defp check_licenses() do
    Registry.UserChannels
    |> Registry.dispatch("users", fn channel_pids_and_tokens ->
      # Get the pids of all channels that no longer have a license
      expired_channel_pids =
        Enum.zip(
          # PIDs
          channel_pids_and_tokens |> Enum.map(&elem(&1, 0)),

          # License details
          channel_pids_and_tokens
          |> Enum.map(&elem(&1, 1))
          |> Licensing.acquire_license_slots()
        )
        |> Enum.filter(fn {_, %Licensing.LicenseDetails{has_license_slot: has_license_slot}} ->
          has_license_slot === false
        end)
        |> Enum.map(&elem(&1, 0))

      # Send a message to each expired channel so they can disconnect their clients
      expired_channel_pids
      |> Enum.each(&send(&1, :license_expired))
    end)
  end

  def handle_info(:check_licenses, state) do
    check_licenses()
    schedule_check_licenses()
    {:noreply, state}
  end
end