defmodule CPSolver.Search.VariableSelector.Action do
  @moduledoc """
  Action (activity-based) varaible selector
  (https://www.gecode.org/doc-latest/MPG.pdf, p.8.5.3)
  """
  alias CPSolver.Space
  alias CPSolver.Shared
  alias CPSolver.Variable.Interface
  alias CPSolver.Utils

  def select(variables, data, action_mode) when action_mode in [:action_min, :action_max, :action_size_min, :action_size_max] do
    select_impl(variables, data, action_mode)
    |> Enum.map(fn {var, _action} -> var end)
  end

  defp select_impl(variables, data, :action_min) do
    Utils.minimals(
      variable_actions(variables, Space.get_shared(data)),
      fn {_var, action} -> action end
    )
  end

  defp select_impl(variables, data, :action_max) do
    Utils.maximals(
      variable_actions(variables, Space.get_shared(data)),
      fn {_var, action} -> action end
    )
  end

  defp select_impl(variables, data, :action_size_min) do
    Utils.minimals(
      variable_actions(variables, Space.get_shared(data)),
      fn {var, action} -> action / Interface.size(var) end
    )
  end

  defp select_impl(variables, data, :action_size_max) do
    Utils.maximals(
      variable_actions(variables, Space.get_shared(data)),
      fn {var, action} ->
        action / Interface.size(var) end
    )
  end

  @doc """
  Initialize Action data
  """
  def initialize(space_data, decay) do
    shared = Space.get_shared(space_data)
    Shared.get_auxillary(shared, :action) ||
    (
    action_table = Shared.create_shared_ets_table(shared)
    Shared.put_auxillary(shared, :action, %{propagator_actions: action_table, decay: decay})
    )
  end

  @doc """
  Compute actions of variables in one pass
  """
  def variable_actions(variables, shared) do
    action_data = Shared.get_auxillary(shared, :action)
    global_failure_count = Shared.get_failure_count(shared)

    if action_data && global_failure_count do
      %{variable_actions: action_table, decay: decay} = action_data


      Enum.zip(variables, 
      :ets.select(action_table, for(var <- variables, do: {{Interface.id(var), :_}, [], [:"$_"]})))
  else
    Enum.map(variables, fn var -> {var, 1} end)
  end

  end


end