Refactor updating order state

It makes the code a bit easier to read

app/controllers/concerns/checkout_steps.rb

@@ -40,6 +40,10 @@ module CheckoutSteps
     redirect_to_step_based_on_order
   end
 
+  # Checkout step and allowed order state
+  # * step details : order state in cart, address or delivery
+  # * step payment : order state is payment
+  # * step summary : order state is confirmation
   def check_step
     case @order.state
     when "cart", "address", "delivery"
@@ -48,14 +52,4 @@ module CheckoutSteps
       redirect_to checkout_step_path(:payment) if summary_step?
     end
   end
-
-  def update_order_state
-    if @order.state == "confirmation" && payment_step?
-      @order.back_to_payment
-    end
-
-    return unless @order.state.in?(["payment", "confirmation"]) && details_step?
-
-    @order.back_to_address
-  end
 end

app/controllers/split_checkout_controller.rb

@@ -23,10 +23,12 @@ class SplitCheckoutController < ::BaseController
   before_action :hide_ofn_navigation, only: [:edit, :update]
 
   def edit
-    redirect_to_step_based_on_order unless params[:step]
-
-    update_order_state if params[:step]
-    check_step if params[:step]
+    if params[:step].blank?
+      redirect_to_step_based_on_order
+    else
+      update_order_state
+      check_step
+    end
 
     return if available_shipping_methods.any?
 
@@ -128,4 +130,15 @@ class SplitCheckoutController < ::BaseController
   def order_params
     @order_params ||= Checkout::Params.new(@order, params, spree_current_user).call
   end
+
+  # Update order state based on the step we are loading to avoid discrepancy between step and order
+  # state. We need to do this when moving back to a previous checkout step, the update action takes
+  # care of moving the order state forward.
+  def update_order_state
+    return @order.back_to_payment if @order.confirmation? && payment_step?
+
+    return unless @order.after_delivery_state? && details_step?
+
+    @order.back_to_address
+  end
 end

app/models/spree/order.rb

@@ -616,6 +616,10 @@ module Spree
       state.in?(["cart", "address", "delivery"])
     end
 
+    def after_delivery_state?
+      state.in?(["payment", "confirmation"])
+    end
+
     private
 
     def reapply_tax_on_changed_address

spec/controllers/split_checkout_controller_spec.rb

@@ -74,6 +74,7 @@ describe SplitCheckoutController, type: :controller do
           it "updates the order state to payment" do
             get :edit, params: { step: "payment" }
 
+            expect(response.status).to eq 200
             expect(order.reload.state).to eq("payment")
           end
         end
@@ -82,6 +83,7 @@ describe SplitCheckoutController, type: :controller do
           it "updates the order state to address" do
             get :edit, params: { step: "details" }
 
+            expect(response.status).to eq 200
             expect(order.reload.state).to eq("address")
           end
         end
@@ -96,6 +98,7 @@ describe SplitCheckoutController, type: :controller do
           it "updates the order state to address" do
             get :edit, params: { step: "details" }
 
+            expect(response.status).to eq 200
             expect(order.reload.state).to eq("address")
           end
         end