module Collection
  def self.[](type_parameter)
    Set[type_parameter]
  end

  refine Object do
    def Collection(content)
      content = Array(content)

      raise ArgumentError, "Content can't be empty" if content.empty?

      type_parameter = content[0].class

      set = Set[type_parameter].new

      content.each do |member|
        set.add member
      end

      set
    end
  end

  class Set
    include Enumerable

    attr_reader :type_parameter

    def initialize(type_parameter)
      @type_parameter = type_parameter
    end

    def self.[](type_parameter)
      type_parameter_name = constant_name(type_parameter)

      cls = nil
      unless const_defined?(type_parameter_name)
        cls = define_class(type_parameter)
        set_collection_constant(type_parameter, cls)
      else
        cls = const_get(type_parameter_name)
      end

      cls
    end

    def self.define_class(type_parameter)
      cls = Class.new(self) do
        def initialize; end

        define_method :type_parameter do
          type_parameter
        end
      end

      set_collection_constant(type_parameter, cls)

      cls
    end

    def self.constant_name(constant)
      constant.name.gsub('::', '_')
    end

    def self.set_collection_constant(constant, cls)
      class_name = constant_name(constant)

      unless const_defined?(class_name)
        self.const_set(class_name, cls)
      end

      class_name
    end

    def add(val)
      raise ArgumentError, "#{val.inspect} must be a #{type_parameter.name}" unless val.is_a? type_parameter
      set.add(val)
    end
    alias :<< :add

    def entry?(val=nil, &predicate)
      if !block_given?
        predicate = lambda { |m| m == val }
      end

      entries(&predicate).length > 0
    end

    def entries(&predicate)
      set.select(&predicate)
    end

    def entry(&predicate)
      set.find(&predicate)
    end

    def each(&action)
      set.each(&action)
    end

    def entries?
      !set.empty?
    end

    def empty?
      set.empty?
    end

    def length
      set.length
    end
    alias :size :length
    alias :count :length

    private def set
      @set ||= ::Set.new
    end
  end
end