Exportable module for exporting XML

exportable.rb

##
# Exportable module to help create XML from models.
#
# Author: Joel Parker Henderson (joel@joelparkerhenderson.com)
# License: GPL
#
module Exportable

  ##
  # Get this object's export string, such as an XML element string.
  #
  # Example:
  #
  #     class Item < String
  #       include Exportable
  #     end
  #
  #     a = Item.new("Hello")
  #     a.export 
  #     #=> "<item>Hello</item>"
  #
  # Example using a given key:
  #
  #     a.export("foo")
  #     #=> "<foo>Hello</foo>"
  #
  # Example using a given key and given value:
  #
  #     a.export("foo", "goo")
  #     #=> "<foo>goo</foo>"
  #
  def export(key = export_key, value = export_value)
    "<#{key}>#{value}</#{key}>"
  end

  ##
  # Get this object's export key, such as a XML tag name string.
  #
  # This default implementation returns the class name, adjusted 
  # so the first letter is lowercase as per XML convention.
  #
  # Example:
  #
  #     class Item < String
  #       include Exportable
  #     end
  #
  #     a = Item.new
  #     a.export_key 
  #     #=> "item"
  #
  def export_key
    self.class.name.sub(/^./){$&.downcase}
  end

  ##
  # Get this object's export value, such as an XML tag content string.
  #
  # Example:
  #
  #     class Item < String
  #       include Exportable
  #     end
  #
  #     a = Item.new("Hello")
  #     a.export_value 
  #     #=> "Hello"
  #
  def export_value
    to_s
  end

  ##
  # Export an object as an XML string.
  #
  # This method has cases for four kinds of objects.
  #
  #   * Exportable.
  #   * Enumerable with items, such as an Array.
  #   * Enumerable with pairs, such as a Hash.
  #   * Anything else.
  #
  # Example:
  #
  #     class Item < String
  #       include Exportable
  #     end
  #
  #     class Color < String
  #       include Exportable
  #     end
  #
  #     a = Item.new
  #
  #     # Object is Exportable
  #     obj = Color.new("Red")
  #     a.export_object(obj)
  #     #=> "<color>Red</color>"
  #
  #     # Object is Enumerable with items that are Exportable
  #     obj = [Color.new("Red"), Color.new("Green")]
  #     a.export_object(obj)
  #     #=> "<color>Red</color><color>Green</color>"
  #
  #     # Object is Enumerable with pairs and vaules that are Exportable
  #     obj = {foo: Color.new("Red"), goo: Color.new("Green")}
  #     a.export_object(obj)
  #     #=> "<foo><color>Red</color></foo><goo><color>Green</color></goo>"
  #
  #     # Object is anything else, e.g. a String
  #     obj = "Anything"
  #     a.export_object(obj)
  #     #=> "Anything"
  #
  def export_object(object)
    case object
    when Exportable
      export_object_when_exportable(object)
    when Enumerable
      export_object_when_enumerable(object)
    else
      export_object_when_default(object)
    end
  end

  def export_object_when_exportable(object)
    object.export
  end

  def export_object_when_enumerable(object)
    if object.respond_to?(:each_pair)
      export_object_when_enumerable_with_pairs(object)
    else
      export_object_when_enumerable_with_items(object)
    end
  end

  def export_object_when_enumerable_with_items(object)
    object.map{|x| 
      export_object(x) 
    }.join
  end

  def export_object_when_enumerable_with_pairs(object)
    object.keys.map{|key|
      export(key, export_object(object[key]))
    }.join
  end

  def export_object_when_default(object)
    object.to_s
  end

  ## 
  # Export an instance variable.
  #
  # This implementation calls #export_object on the variable.
  #
  # Example:
  #
  #     class Item
  #       include Exportable
  #       attr_accessor :color
  #     end
  #
  #     a = Item.new
  #     a.color = "Red"
  #     a.export_instance_variable(:@color)
  #     #=> "<color>Red</color>"
  #   
  #     
  def export_instance_variable(variable)
    export(
      variable.to_s.sub(/^@/,''),
      export_object(instance_variable_get(variable))
    )
  end

  ## 
  # Export all the instance variables.
  #
  #     class Item
  #       include Exportable
  #       attr_accessor :color
  #       attr_accessor :size
  #     end
  #
  # This implementation calls #export_instance_variable on each variable.
  #
  # Example:
  #
  #     a = Item.new
  #     a.color = "Red"
  #     a.size = "Large"
  #     a.export_instance_variables
  #     #=> "<color>Red</color><size>Large</size>"
  #   
  #     
  def export_instance_variables
    instance_variables.map{|variable|
      export_instance_variable(variable)
    }.join
  end

  ##
  # Export the result of sending a message to this object.
  #
  # Example:
  #
  #     class Item < String
  #       include Exportable
  #     end
  #
  #     a = Item.new("Hello")
  #     a.export_send("length")
  #     #=> "<length>5</length>"
  #   
  # Example using a key that is different than the message name:
  #
  #     a.export_send("foo", "length")
  #     #=> "<foo>5</foo>"
  #  
  def export_send(key, message_name = nil, *args, &block)
    export(key, __send__(message_name || key, *args, &block))
  end

  ##
  # Export an enumerable.
  #
  # This implementation calls #export on each element.
  #
  #     class Item < String
  #       attr_accessor :colors
  #     end
  #
  #     class Color < String
  #       include Exportable
  #     end
  #
  #     a = Item.new
  #     a.colors = [Color.new("Red"), Color.new("Green")]
  #     a.export_enumerable("colors")
  #     #=> "<colors><color>Red</color><color>Green</color></colors>"
  #
  def export_enumerable(key, enumerable = nil)
    export(key, (enumerable || self.__send__(key)).map(&:export).join)
  end

end