dkubb/axiom-types

# encoding: utf-8

module Axiom
  module Types

    # A module that adds class and instance level options
    module Options

      # Raised when the method is already used
      class ReservedMethodError < ArgumentError; end

      # Defines which options are valid for a given attribute class
      #
      # @example
      #   class MyTypes < Axiom::Types::Object
      #     accept_options :foo, :bar
      #   end
      #
      # @return [self]
      #
      # @api public
      def accept_options(*new_options)
        (new_options - accepted_options).each do |new_option|
          assert_method_available(new_option)
          define_option_method(new_option)
          setup_option(new_option)
        end
        self
      end

    protected

      # Set up the option in the current class and descendants
      #
      # @param [Symbol] new_option
      #   new option to be added
      #
      # @return [self]
      #
      # @api private
      def setup_option(new_option)
        instance_variable_set(:"@#{new_option}", nil)
        accepted_options << new_option
        descendants.each do |descendant|
          descendant.send(__method__, new_option)
        end
        self
      end

    private

      # Adds descendant to descendants array and inherits default options
      #
      # @param [Class] descendant
      #
      # @return [undefined]
      #
      # @api private
      def inherited(descendant)
        super
        options.each do |option, value|
          descendant.setup_option(option).public_send(option, value)
        end
      end

      # Returns default options hash for a given attribute class
      #
      # @example
      #   Axiom::Types::String.options
      #   # => {:primitive => String}
      #
      # @return [Hash]
      #   a hash of default option values
      #
      # @api private
      def options
        accepted_options.each_with_object({}) do |name, options|
          options[name] = public_send(name)
        end
      end

      # Returns an array of valid options
      #
      # @example
      #   Axiom::Types::String.accepted_options
      #   # => [:primitive, :accessor, :reader, :writer]
      #
      # @return [Array]
      #   the array of valid option names
      #
      # @api private
      def accepted_options
        @accepted_options ||= []
      end

      # Assert that the option is not already defined
      #
      # @param [Symbol] name
      #
      # @return [undefined]
      #
      # @raise [ReservedMethodError]
      #   raised when the method is already defined
      #
      # @api private
      def assert_method_available(name)
        return unless respond_to?(name)
        fail(
          ReservedMethodError,
          "method named `#{name.inspect}` is already defined"
        )
      end

      # Adds a reader/writer method for the give option name
      #
      # @param [#to_s] name
      #
      # @return [undefined]
      #
      # @api private
      def define_option_method(name)
        ivar = :"@#{name}"
        define_singleton_method(name) do |*args|
          return instance_variable_get(ivar) if args.empty?
          instance_variable_set(ivar, *args)
          self
        end
      end

    end # module Options
  end # module Types
end # module Axiom