Passive tag monitor process.

• Repeatedly polls for passive targets in range.
• Emits an event when target enters.
• Emits another event when target leaves.

Target presence is tracked by polling nfc_initiator_target_is_present with a short debounce.

Usage

defmodule MyApp.NFC do
  use LibNFC.Presence

  @impl true
  def handle_target_in(target, state) do
    # ...
    {:ok, state}
  end

  @impl true
  def handle_target_out(state) do
    # ...
    {:ok, state}
  end
end

defmodule MyApp.Application do
  def start(_, _) do
    children = [
      ...
      {MyApp.NFC, client_state: :foo}
    ]

    Supervisor.start_link(...)
  end
endcopy