module PercentBase
  def self.included(base)
    base.extend ClassMethods
  end
 
  module ClassMethods
    def has_percent(attribute_name = :pretty_percent, column = :percent)
      raise(ArgumentError, "Cannot name attribute and column the same") if attribute_name.to_s == column.to_s
 
      class_eval <<-END
        def #{attribute_name}=(value)
          return if value == ''
          self[:#{column}] = value.nil? ? nil : (value.to_s.gsub(/[^\\d\\.]/, '').to_f)/100
        end
 
        def #{attribute_name}
          return nil if self[:#{column}].blank?
          perc = self[:#{column}] * 100
          perc = perc.to_i == perc ? perc.to_i : perc
          perc.to_s + "%"
        end
      END
    end
  end
end
 
ActiveRecord::Base.send :include, PercentBase