params_decorator.rb

# encoding: utf-8

# This helper makes hash keys accessable via simple methods.
# This behaviour allows to treat hash elements as object
# properties that can also be overriden
#
# When set_params_hash is not called, then by default this
# code will look for a params method on the object
#
# class TestingClass
#   include ParamsDecorator
#   set_params_hash :params
#
#   def initialize
#     @params = { 'arman' => :yellow, 'danny' => 'green', 'smith' => false }
#   end
# end
#
# TestClass.new.arman_param # => :yellow
# TestClass.new.danny_param # => 'green'
# TestClass.new.smith_param # => false
#
# or
#
# class TestingClass
#   include ParamsDecorator
#   set_params_hash :some_method
#
#   def some_method
#     @params = { 'arman' => :yellow, 'danny' => 'green' }
#   end
# end
#
# TestClass.new.arman_param # => :yellow
# TestClass.new.danny_param # => 'green'
#
# or
#
# TestClass.new.smith_param # => false
# class TestingClass
#   include ParamsDecorator
#
#   def initialize
#     @params = { 'arman' => :yellow }
#   end
#
#   def arman_param
#     'arman is overriden'
#   end
# end
#
# TestClass.new.arman_param # => 'arman is overriden'

module ParamsDecorator
  def self.included(base)
    base.extend const_get("ClassMethods") if const_defined?("ClassMethods")
  end

  module ClassMethods
    private

    def set_params_hash(hash_name)
      define_method('__params_hash') do
        @__params_hash ||= if respond_to?(hash_name)
                             send(hash_name)
                           elsif instance_variable_defined?(:"@#{hash_name}")
                             instance_variable_get(:"@#{hash_name}")
                           else
                             super
                           end
      end
    end
  end

  private

  def method_missing(missing_method)
    method_name = missing_method.to_s

    if method_name.end_with?('_param')
      key = method_name[0..(method_name.size - ('_param'.size + 1))]
      __params_hash[key] if __params_hash.has_key?(key)
    else
      super
    end
  end

  def __params_hash
    @__params_hash ||= if self.respond_to?(:params)
      params
    else
      Hash.new
    end
  end
end