require 'facets/functor'

# TODO: Consider Enumerator methods

module Enumerable #:nodoc:

  # Per element meta-functor.
  #
  #   [1,2,3].per + 3             #=> [4,5,6]
  #   [1,2,3].per(:map) + 3       #=> [4,5,6]
  #   [1,2,3].per(:select) > 1    #=> [2,3]
  #
  #   [1,2,3].per.map + 3       #=> [4,5,6]
  #   [1,2,3].per.select > 1    #=> [2,3]
  #
  def per(enum_method=nil, *enum_args)
    if enum_method
      Permeator.new(self, enum_method, *enum_args)
      #Functor.new do |op, *args|
      #  __send__(enum_method, *enum_args){ |x| x.__send__(op, *args) } #, &blk) }
      #end
    else
      @__per__ ||= Functor.new do |enum_method, *enum_args|
        Permeator.new(self, enum_method, *enum_args)
        #Functor.new do |op, *args|
        #  __send__(enum_method, *enum_args){ |x| x.__send__(op, *args) } #, &blk) }
        #end
      end
    end
  end

  # Permeator is a Functor for operating over each element of an Enumearble.
  # (Note: This used to be called an Elementor.)
  #
  # TODO: With Ruby 1.9+ this would not be required, as it can be replaced
  # by a generic Functor, becuase then lambda definitions can pass blocks.
  #
  class Permeator #:nodoc:
    private(*instance_methods.select{|x| x !~ /^__/ })

    def initialize(enum_object, enum_method=nil, *enum_args)
      @enum_object = enum_object
      @enum_method = enum_method || :map
      @enum_args   = enum_args
    end

    def instance_delegate
      @enum_object
    end

    def instance_operator
      @enum_method
    end

    def method_missing(sym, *args, &blk)
      @enum_object.__send__(@enum_method){ |x| x.__send__(sym, *args, &blk) }
    end
  end

end

