tusker_push/lib/tusker_push/apns.ex

defmodule TuskerPush.Apns do
  require OpenTelemetry.Tracer
  require Logger

  @type environment() :: :development | :production

  @spec send(environment(), String.t(), Map.t()) :: :ok | {:error, term()}
  def send(apns_env, apns_device_token, payload) do
    :telemetry.execute([:apns, :push], %{monotonic_time: System.monotonic_time()})

    OpenTelemetry.Tracer.with_span :apns_push, %{attributes: [env: apns_env]} do
      do_send(apns_env, apns_device_token, payload)
    end
  end

  @spec do_send(environment(), String.t(), Map.t()) :: :ok | {:error, term()}
  defp do_send(apns_env, apns_device_token, payload) do
    with {:ok, body} <- Jason.encode(payload, pretty_print: false),
         req <- make_request(apns_env, apns_device_token, body),
         {:ok, resp} <- Finch.request(req, TuskerPush.Finch) do
      handle_response(resp, apns_env, apns_device_token, payload)
    else
      {:error, %Finch.Error{reason: :connection_closed}} ->
        Logger.warning("Apns Finch connection_closed, retrying in 1s")
        OpenTelemetry.Tracer.add_event("Finch connection_closed", [])

        Process.sleep(1000)
        __MODULE__.send(apns_env, apns_device_token, payload)

      {:error, %Finch.Error{reason: :disconnected}} ->
        Logger.warning("Apns Finch disconnected, retrying in 1s")
        OpenTelemetry.Tracer.add_event("Finch disconnected", [])

        Process.sleep(1000)
        __MODULE__.send(apns_env, apns_device_token, payload)

      {:error, %Mint.TransportError{reason: :closed}} ->
        Logger.warning("Apns Mint transport closed, retrying in 1s")
        OpenTelemetry.Tracer.add_event("Mint transport closed", [])

        Process.sleep(1000)
        __MODULE__.send(apns_env, apns_device_token, payload)

      {:error, reason} ->
        {:error, reason}
    end
  end

  @spec make_request(environment(), String.t(), binary()) :: Finch.Request.t()
  defp make_request(apns_env, apns_device_token, body) do
    bundle_id = Application.fetch_env!(:tusker_push, :apns)[:bundle_id]

    headers = [
      {"authorization", "bearer #{TuskerPush.Apns.Token.current()}"},
      {"apns-push-type", "alert"},
      {"apns-bundle-id", bundle_id},
      {"apns-topic", bundle_id},
      {"apns-expiration",
       DateTime.utc_now() |> DateTime.add(1, :day) |> DateTime.to_unix() |> Integer.to_string()}
    ]

    Finch.build(
      :post,
      "https://#{host(apns_env)}/3/device/#{apns_device_token}",
      headers,
      body
    )
  end

  @spec handle_response(Finch.Response.t(), environment(), String.t(), Map.t()) ::
          :ok | {:error, term()}

  defp handle_response(resp, apns_env, apns_device_token, payload) do
    maybe_log_unique_id(resp, apns_env)

    if resp.status in 200..299 do
      :ok
    else
      info =
        case Jason.decode(resp.body) do
          {:ok, data} ->
            inspect(data)

          {:error, _} ->
            resp.body
        end

      case {resp.status, info} do
        {403, %{reason: "ExpiredProviderToken"}} ->
          Logger.warning("Expired provider token, retrying")
          OpenTelemetry.Tracer.add_event("Expired provider token", [])

          __MODULE__.send(apns_env, apns_device_token, payload)

        {410, %{reason: "Unregistered"}} ->
          Logger.warning("Device token unregistered")
          OpenTelemetry.Tracer.set_status(:error, "Unregistered device token")

          {:error, :device_token_unregistered}

        _ ->
          Logger.error("Received #{resp.status} with #{inspect(info)}")

          OpenTelemetry.Tracer.set_attributes(
            response_status: resp.status,
            response_info: inspect(info)
          )

          OpenTelemetry.Tracer.set_status(:error, "Unexpected response")

          {:error, "unexpected status #{resp.status}"}
      end
    end
  end

  @spec maybe_log_unique_id(Finch.Response.t(), :development | :production) :: :ok

  defp maybe_log_unique_id(resp, :development) do
    resp.headers
    |> Enum.find(fn
      {"apns-unique-id", _} -> true
      _ -> false
    end)
    |> case do
      {_, id} ->
        Logger.debug("APNS unique id: #{id}")
        OpenTelemetry.Tracer.add_event("APNS unique ID", unique_id: id)

      _ ->
        nil
    end

    :ok
  end

  defp maybe_log_unique_id(_resp, :production), do: :ok

  @spec host(environment()) :: String.t()

  def host(:development) do
    "api.sandbox.push.apple.com"
  end

  def host(:production) do
    "api.push.apple.com"
  end
end