defmodule Reactivity do
  alias Reactivity.Signal.Source
  alias Reactivity.Signal.Derived
  alias Reactivity.Registry

  
  @doc """
  Lift takes a regular function (a -> b) and lifts into a signal processing
  method. (signal a -> signal b).
  """
  def lift(f) do
    lifted = fn(signal) ->
               # Create the intermediate node.
               {:ok, ds} = Derived.new(f, nil)
                        case signal do
                          {:signal, :source, s} ->
                            Source.add_child(s, ds)
                          {:signal, :derived, s} ->
                            Derived.add_child(s, ds)
                        end
               {:ok, ds}
             end
    lifted
  end

  
  @doc """
  Applies a lifted function on a signal, effectively subscribing to it.
  """
  def apply(signal, f) do
    {:ok, new_signal} = f.(signal)
    new_signal
  end

  
  @doc """
  Convenience function to lift and immediatly apply a function to a signal.
  """
  def liftapp(signal, f) do
    lifted = lift(f)
    Reactivity.apply(signal, lifted)
  end


  @doc """
  Using a keyword to get a signal from the global environment.
  """
  def source(name) do
    {:ok, signal} = Registry.get_source(name)
    signal
  end
end