feat: wait for enrolled sensors to announce, factory reset them on deletion

lib/localiser/domain/sensors.ex

@@ -55,6 +55,8 @@ defmodule Localiser.Domain.Sensors do
   end
 
   def delete_sensor(%Sensor{} = sensor) do
+    topic = "localiser/sensor/#{sensor.sensor_id}/cmd"
+    Localiser.MQTT.Connection.publish(topic, Jason.encode!(%{command: "factory_reset"}))
     Repo.delete(sensor)
   end
 
@@ -89,14 +91,45 @@ defmodule Localiser.Domain.Sensors do
 
   # Sensor lifecycle / enrollment helpers
 
+  @enrollment_timeout_ms Application.compile_env(:localiser, :enrollment_timeout_ms, 10_000)
+
+  # Called by the phone app to indicate a sensor is about to come online.
+  # Creates an unconfirmed sensor record and starts a timeout Task.
+  def expect_sensor(sensor_id) do
+    result =
+      %Sensor{}
+      |> Sensor.changeset(%{sensor_id: sensor_id, confirmed: false})
+      |> Repo.insert(
+        on_conflict: [set: [confirmed: false, updated_at: DateTime.utc_now()]],
+        conflict_target: :sensor_id,
+        returning: true
+      )
+
+    case result do
+      {:ok, sensor} ->
+        Phoenix.PubSub.broadcast(Localiser.PubSub, "sensors", {:sensor_expected, sensor})
+        Task.start(fn ->
+          Process.sleep(@enrollment_timeout_ms)
+          fresh = Repo.get_by(Sensor, sensor_id: sensor_id)
+          if fresh && !fresh.confirmed do
+            Phoenix.PubSub.broadcast(Localiser.PubSub, "sensors", {:sensor_enrollment_timeout, sensor_id})
+          end
+        end)
+        {:ok, sensor}
+
+      error ->
+        error
+    end
+  end
+
   # Called when an ESP board self-announces on MQTT. Inserts a new unplaced sensor
-  # record, or bumps updated_at if the sensor_id already exists.
+  # record, or marks it confirmed if the sensor_id already exists.
   def upsert_announced(sensor_id) do
     result =
       %Sensor{}
-      |> Sensor.changeset(%{sensor_id: sensor_id})
+      |> Sensor.changeset(%{sensor_id: sensor_id, confirmed: true})
       |> Repo.insert(
-        on_conflict: [set: [updated_at: DateTime.utc_now()]],
+        on_conflict: [set: [confirmed: true, updated_at: DateTime.utc_now()]],
         conflict_target: :sensor_id,
         returning: true
       )