module LocalTime
  
  def self.included(base)
    base.extend ClassMethods
  end
  
  module ClassMethods
    
    def local_time(*args)
      options = args.last.is_a?(Hash) ? args.shift : {}
      
      args.each do |field|
        class_eval do
          
          define_method "local_#{field}".to_sym do
            utc_time = read_attribute(field)
            
            if utc_time.is_a?(Time) && tz = TzinfoTimezone[send(options[:timezone] || :timezone) || '']
              tz.utc_to_local(utc_time)
            else
              utc_time
            end
          end
          
          define_method "local_#{field}=".to_sym do |val|
            if val.is_a?(Time) && tz = TzinfoTimezone[send(options[:timezone] || :timezone) || '']
              utc_time = tz.local_to_utc(val)
            else
              utc_time = val
            end
            
            write_attribute field, utc_time
          end
          
        end
      end
      
    end
  end
end

ActiveRecord::Base.class_eval do
  include LocalTime
end