fulfillment.rb

class AcceptableQuantityValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
      return if value.nil?
      order = Order.find(record[:order_id])
      currently_fulfilled = order.total_fulfilled

      if record.new_record?
        valid_fulfillment = order.quantity - currently_fulfilled
      else
        valid_fulfillment = order.quantity - (currently_fulfilled - record.quantity_was)
      end

      record.errors[attribute] << "cannot total more than #{valid_fulfillment}" if value > valid_fulfillment
  end
end


class FulfillmentReceived < ActiveModel::Validator
  def validate(record)
      record.errors[:base] << "Cannot modify a received fulfillment" if record.received_was == true
  end
end


class Fulfillment < ActiveRecord::Base
  validates_with FulfillmentReceived

  attr_accessible :quantity, :ship_date, :tracking_number

  belongs_to :order

  validates :quantity, :presence => true,
                       :numericality => {:only_integer => true, :greater_than => 0},
                       :acceptable_quantity => true

  validates :ship_date, :presence => true,
                        :format => {:with => /^\d{4}-\d{2}-\d{2}$/}


  def received!
    return if self.received?
    self.received = true
    self.save!
  end
end