defmodule Localiser.MQTT.Router do
  @moduledoc """
  Module responsible for routing incoming MQTT messages to the appropriate handlers.
  """

  use GenServer
  require Logger

  alias Localiser.Domain.Sensors

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

  def route(topic, payload) do
    GenServer.cast(__MODULE__, {:route, topic, payload})
  end

  # GenServer Callbacks

  @impl true
  def init(_opts) do
    {:ok, %{}}
  end

  @impl true
  def handle_cast({:route, topic, payload}, state) do
    case parse_topic(topic) do
      {:rssi, sensor_id} ->
        handle_rssi(sensor_id, payload)

      {:announce, sensor_id} ->
        handle_announce(sensor_id)

      {:error, :invalid_topic} ->
        Logger.debug("[MQTT.Router] Received message with invalid topic: #{topic}")
    end

    {:noreply, state}
  end

  # Private helper functions

  defp parse_topic(topic) do
    # Example topic: "localiser/sensor/device123/rssi"
    case String.split(topic, "/") do
      ["localiser", "sensor", sensor_id, "rssi"] -> {:rssi, sensor_id}
      ["localiser", "sensor", sensor_id, "announce"] -> {:announce, sensor_id}
      _ -> {:error, :invalid_topic}
    end
  end

  defp handle_rssi(sensor_id, payload) do
    with {:ok, %{"tag_id" => tag_id, "rssi" => rssi}} <-
           Jason.decode(payload) do

      reading = %{
        sensor_id: sensor_id,
        tag_id: tag_id,
        rssi: rssi,
        timestamp: DateTime.utc_now()
      }

      Localiser.MQTT.Telemetry.count_reading()
      Localiser.RSSI.Buffer.push(reading)

    else
      {:error, reason} ->
        Logger.error("[MQTT.Router] Bad payload from #{sensor_id}: #{inspect(reason)}")
        Localiser.MQTT.Telemetry.count_error()
    end
  end

  defp handle_announce(sensor_id) do
    case Sensors.upsert_announced(sensor_id) do
      {:ok, _sensor} ->
        Logger.info("[MQTT.Router] Sensor announced: #{sensor_id}")

      {:error, reason} ->
        Logger.error("[MQTT.Router] Failed to register announced sensor #{sensor_id}: #{inspect(reason)}")
    end
  end
end