The Trigger behaviour is used for implementing triggers for poller behaviors such as GrovePi.Sound and GrovePi.Button.

The triggers must implement two callbacks, init/1 and update/2.

Example

The following is the implementation of GrovePi.Button.DefaultTrigger. Processes can subscribe to two events :released and :pressed.

defmodule GrovePi.Button.DefaultTrigger do
  @behaviour GrovePi.Trigger

  defmodule State do
    @moduledoc false
    defstruct value: 0
  end

  def init(_) do
    {:ok, %State{}}
  end

  def update(value, %{value: value} = state) do
    {:ok, state}
  end

  def update(new_value, state) do
    {event(new_value), %{state | value: new_value}}
  end

  defp event(0), do: :released
  defp event(1), do: :pressed
end