Introduce "zero priced orders" to checkout UI and order state flow

app/controllers/split_checkout_controller.rb

@@ -203,6 +203,7 @@ class SplitCheckoutController < ::BaseController
 
   def validate_payment!
     return true if params.dig(:order, :payments_attributes, 0, :payment_method_id).present?
+    return true if @order.zero_priced_order?
 
     @order.errors.add :payment_method, I18n.t('split_checkout.errors.select_a_payment_method')
   end

app/helpers/checkout_helper.rb

@@ -120,6 +120,8 @@ module CheckoutHelper
   end
 
   def payment_or_shipping_price(method, order)
+    return unless method
+
     price = method.compute_amount(order)
     if price.zero?
       t('checkout_method_free')

app/models/spree/order.rb

@@ -621,6 +621,10 @@ module Spree
       raise Core::GatewayError, Spree.t(:no_pending_payments) if pending_payments.empty?
 
       pending_payments.each do |payment|
+        if payment.amount.zero? && zero_priced_order?
+          payment.update_columns(state: "completed", captured_at: Time.zone.now)
+        end
+
         break if payment_total >= total
 
         yield payment

app/views/split_checkout/_payment.html.haml

@@ -8,28 +8,32 @@
       %div.checkout-title
         = t("split_checkout.step2.payment_method.title")
 
-      - selected_payment_method = @order.payments&.with_state(:checkout)&.first&.payment_method_id
-      - selected_payment_method ||= available_payment_methods[0].id if available_payment_methods.length == 1
-      - available_payment_methods.each do |payment_method|
-        %div.checkout-input.checkout-input-radio
-          = f.radio_button :payment_method_id, payment_method.id,
-            id: "payment_method_#{payment_method.id}",
-            name: "order[payments_attributes][][payment_method_id]",
-            checked: (payment_method.id == selected_payment_method),
-            "data-action": "paymentmethod#selectPaymentMethod",
-            "data-paymentmethod-id": "#{payment_method.id}",
-            "data-paymentmethod-target": "input"
-          = f.label :payment_method_id, "#{payment_method.name}", for: "payment_method_#{payment_method.id}"
-          %em.fees=payment_or_shipping_price(payment_method, @order)
+      - if @order.zero_priced_order?
+        %h3= t(:no_payment_required)
+        = hidden_field_tag "order[payments_attributes][][amount]", 0
+      - else
+        - selected_payment_method = @order.payments&.with_state(:checkout)&.first&.payment_method_id
+        - selected_payment_method ||= available_payment_methods[0].id if available_payment_methods.length == 1
+        - available_payment_methods.each do |payment_method|
+          %div.checkout-input.checkout-input-radio
+            = f.radio_button :payment_method_id, payment_method.id,
+              id: "payment_method_#{payment_method.id}",
+              name: "order[payments_attributes][][payment_method_id]",
+              checked: (payment_method.id == selected_payment_method),
+              "data-action": "paymentmethod#selectPaymentMethod",
+              "data-paymentmethod-id": "#{payment_method.id}",
+              "data-paymentmethod-target": "input"
+            = f.label :payment_method_id, "#{payment_method.name}", for: "payment_method_#{payment_method.id}"
+            %em.fees=payment_or_shipping_price(payment_method, @order)
 
-        .paymentmethod-container{"data-paymentmethod-id": "#{payment_method.id}", style: "display: #{payment_method.id == selected_payment_method ? "block" : "none"}"}
-          - if payment_method.description && !payment_method.description.empty?
-            .paymentmethod-description.panel
-              #{payment_method.description}
-          .paymentmethod-form
-            = render partial: "split_checkout/payment/#{payment_method.method_type}", locals: { payment_method: payment_method, f: f }
+          .paymentmethod-container{"data-paymentmethod-id": "#{payment_method.id}", style: "display: #{payment_method.id == selected_payment_method ? "block" : "none"}"}
+            - if payment_method.description && !payment_method.description.empty?
+              .paymentmethod-description.panel
+                #{payment_method.description}
+            .paymentmethod-form
+              = render partial: "split_checkout/payment/#{payment_method.method_type}", locals: { payment_method: payment_method, f: f }
 
-      = f.error_message_on :payment_method, standalone: true
+        = f.error_message_on :payment_method, standalone: true
 
     %div.checkout-substep
       = t("split_checkout.step2.explaination")

app/views/split_checkout/_summary.html.haml

@@ -54,16 +54,21 @@
         %a.summary-edit{href: main_app.checkout_step_path(:payment)}
           = t("split_checkout.step3.payment_method.edit")
       .two-columns
+        - payment_method = last_payment_method(@order)
         %div
-          - payment_method = last_payment_method(@order)
-          = payment_method&.name
-          %em.fees=payment_or_shipping_price(payment_method, @order)
+          - if payment_method
+            = payment_method.name
+            %em.fees
+              = payment_or_shipping_price(payment_method, @order)
+          - elsif @order.zero_priced_order?
+            %h4= t(:no_payment_required)
+
         - if payment_method&.description.present?
           %div
             .summary-subtitle
               = t("split_checkout.step3.payment_method.instructions")
             %div
-              = last_payment_method(@order)&.description
+              = payment_method&.description
 
 
     %div.checkout-substep