defmodule Localiser.Localisation.Sensor.Manager do
  @moduledoc """
  GenServer that subscribes to the "sensors" PubSub topic and manages
  Sensor.Server lifecycle for a specific floor.

  - {:sensor_enrolled, sensor, room}   → start Sensor.Server if not already running
  - {:sensor_unenrolled, sensor_id}    → terminate the Sensor.Server for this floor
  """

  use GenServer

  alias Localiser.Localisation.Sensor

  def start_link(floor) do
    GenServer.start_link(__MODULE__, floor.id, name: via(floor.id))
  end

  def via(floor_id) do
    {:via, Registry, {Localiser.Registry, {:sensor_manager, floor_id}}}
  end

  @impl true
  def init(floor_id) do
    Phoenix.PubSub.subscribe(Localiser.PubSub, "sensors")
    {:ok, %{floor_id: floor_id}}
  end

  # Sensor placed (or moved) onto this floor's layout.
  @impl true
  def handle_info({:sensor_enrolled, sensor, %{floor_id: floor_id} = room}, %{floor_id: floor_id} = state) do
    case Registry.lookup(Localiser.Registry, {:sensor, sensor.sensor_id}) do
      [] -> Sensor.Supervisor.start_sensor_server(floor_id, sensor, room)
      _ -> :ok  # Sensor.Server is already running and handles position via its own PubSub sub
    end

    {:noreply, state}
  end

  # Sensor removed from layout — stop the server for this floor if it's running.
  def handle_info({:sensor_unenrolled, sensor_id}, %{floor_id: floor_id} = state) do
    case Registry.lookup(Localiser.Registry, {:sensor, sensor_id}) do
      [{pid, _}] ->
        DynamicSupervisor.terminate_child(Sensor.Supervisor.via(floor_id), pid)

      [] ->
        :ok
    end

    {:noreply, state}
  end

  # Ignore all other PubSub broadcasts (sensor announced, calibration_complete, etc.)
  def handle_info(_msg, state), do: {:noreply, state}
end