module PriceFields
  module ClassMethods
    def prices(*price_columns) # We assume "price_columns" to finish with "cents"
      price_columns.each do |price_name|
        col_name    = "#{price_name}_cents".to_sym
        var_name    = "#{price_name}_price".to_sym
        method_name = "#{var_name}_with_cast=".to_sym

        self.composed_of var_name, :class_name => "Money", :mapping => [col_name, :cents]

        define_method method_name do |value|
          case value
          when String
            self.send("#{var_name}_without_cast=", Money.new(price_string_to_cents(value)))
          else
            self.send("#{var_name}_without_cast=", value)
          end
        end
        self.alias_method_chain "#{var_name}=".to_sym, :cast
      end
    end
  end

  module InstanceMethods
    def price_string_to_cents(value)
      (BigDecimal(value) * 100).to_i
    end
  end

  def self.included(receiver)
    receiver.extend         ClassMethods
    receiver.send :include, InstanceMethods
  end
end