shipment_decorator.rb

Spree::Shipment.class_eval do
  audited associated_with: :order
  has_associated_audits



  def transfer_to_shipment(variant, quantity, shipment_to_transfer_to)
    quantity_already_shipment_to_transfer_to = shipment_to_transfer_to.manifest.find{|mi| mi.line_item.variant == variant}.try(:quantity) || 0

    if (quantity <= 0 || self == shipment_to_transfer_to)
      raise ArgumentError
    end

    transaction do
      order.contents.remove(variant, quantity,self)
      #making the currrency nil here avoids more drastic changes
      order.contents.add(variant, quantity,nil,shipment_to_transfer_to)
      refresh_rates
      save!
      shipment_to_transfer_to.refresh_rates
      shipment_to_transfer_to.save!
    end
  end

end