# Order state machine

Orders flow through a state machine, which is defined in the Spree::Order::Checkout module. It begins with a cart state and ends with at a complete state.

There are six order states by default:

1. cart
2. address
3. delivery
4. payment
5. confirm
6. complete

If you go through the checkout provided in the solidus_frontend gem, you can see that there is a clearly defined step for each of these states during checkout.

The payment state is optional and it's only triggered if payment_required? returns true.

The complete state is triggered in one of two ways:

1. No payment is required on the order. (The total equals 0.)
2. Payment is required on the order, and at least the order total has been received as payment.

# State criteria

Each order state has criteria that must be met before the state can change. For example, before the state can change from cart to address, line items must be present on the order. Then, to change from address to delivery, the user must have a default address assigned.

Once an order meets the criteria to go to the next state, you can call next on the order object to transition into the next state. For example, in the solidus_frontend gem, the Spree::CheckoutController defines a transition_forward method that always calls next unless the order can be completed:

# /frontend/app/controllers/spree/checkout_controller.rb
def transition_forward
  if @order.can_complete?
    @order.complete
  else
    @order.next
  end
end

If next returns false, then the order does not meet the criteria and does not transition to the next state.

# Payments and shipments have their own state machines

Note that a Spree::Order with the state complete does not mean that the payment has been processed or the order shipments have been shipped. See also the values of the payment_state and shipment_state attributes.