# A module that gathers the classes and modules used by element constraints.
module Gecode::Constraints::IntEnum::Element 
  # Describes an expression stub started with an int var enum following with an 
  # array access using an integer variables .
  class ExpressionStub < Gecode::Constraints::Int::CompositeStub
    def constrain_equal(variable, params)
      enum, position, strength = @params.values_at(:lhs, :position, :strength)
      if variable.nil?
        variable = @model.int_var(enum.domain_range)
      end

      @model.add_interaction do
        # The enum can be a constant array.
        enum = enum.to_int_var_array if enum.respond_to? :to_int_var_array
        Gecode::Raw::element(@model.active_space, enum, 
          position.bind, variable.bind, strength)
      end
      return variable
    end
  end
  
  # Methods needed to add support for element constraints to enums.
  module AdditionalEnumMethods
    # This adds the adder for the methods in the modules including it. The 
    # reason for doing it so indirect is that the first #[] won't be defined 
    # before the module that this is mixed into is mixed into an enum.
    def self.included(enum_mod)
      enum_mod.module_eval do
        # Now we enter the module AdditionalEnumMethods is mixed into.
        class << self
          alias_method :pre_element_included, :included
          def included(mod)
            mod.module_eval do
              # Now we enter the module that the module possibly defining #[] 
              # is mixed into.
              if instance_methods.include? '[]'
                alias_method :pre_element_access, :[]
              end
            
              def [](*vars)
                # Hook in an element constraint if a variable is used for array 
                # access.
                if vars.first.kind_of? Gecode::FreeIntVar
                  params = {:lhs => self, :position => vars.first}
                  return Gecode::Constraints::IntEnum::Element::ExpressionStub.new(
                    @model, params)
                else
                  pre_element_access(*vars) if respond_to? :pre_element_access
                end
              end
            end
            pre_element_included(mod)
          end
        end
      end
    end
  end
end

module Gecode::IntEnumMethods
  include Gecode::Constraints::IntEnum::Element::AdditionalEnumMethods
end

module Gecode::FixnumEnumMethods
  include Gecode::Constraints::IntEnum::Element::AdditionalEnumMethods
end