defmodule CPSolver.Constraint do
  alias CPSolver.Variable

  @callback propagators(args :: list()) :: [atom()]
  @callback variables(args :: list()) :: [Variable.t()]

  defmacro __using__(_) do
    quote do
      @behaviour CPSolver.Constraint
      def variables(args) do
        args
      end

      defoverridable variables: 1
    end
  end

  def new(constraint_impl, args) do
    %{
      propagators: constraint_impl.propagators(args)
    }
  end

  def constraint_to_propagators({constraint_mod, args}) when is_list(args) do
    constraint_mod.propagators(args)
  end

  def constraint_to_propagators(constraint) when is_tuple(constraint) do
    [constraint_mod | args] = Tuple.to_list(constraint)
    constraint_mod.propagators(args)
  end
end