defmodule Liaison do

  @doc """
  Get all current strategies defined in configuration
  """
  @spec get_strategies() :: list(list())
  def get_strategies() do
    Application.get_env(:liaison, :strategies)
  end

  @doc """
  Change the strategies employed and persist them to the environment
  """
  @spec set_strategies(any) :: :ok
  def set_strategies(strategies) do
    # set the new application settings
    Application.put_env(:liaison, :strategies, strategies)

    # create a map by Module (these are the new settings)
    strategies = strategy_by_module(strategies)

    Enum.each(strategies, &apply_strategy/1)
  end

  # def set_strategy(strat_config) do

  # end

  # def set_strategy(module, strat_config) do

  # end

  @doc """
  Returns info about the monitors currently running
  """
  @spec get_monitors() :: list(tuple)
  def get_monitors() do
    Supervisor.which_children(Liaison.Supervisor)
    |> Enum.reject(&(elem(&1, 1) == :undefined))
  end

  defp get_monitored_modules() do
    Enum.map(get_monitors(), &elem(&1, 0))
  end


  # --------------------- helpers ---------------------
  defp strategy_by_module(strategies) do
    Enum.reduce(strategies, [], fn config, acc ->
      [{config[:strategy], config} | acc]
    end)
  end

  defp apply_strategy({module, strat_config}) do
    started_monitors = get_monitored_modules()
    case Enum.member?(started_monitors, module) do
      true ->
        apply(module, :update_strategy, strat_config)

      false ->
        Liaison.Application.add_child(strat_config)
    end
  end
end