Ensure one braintree customer per spree user

Ensure that when creating braintree customers we create one per spree
user. To do this, first generate a token with the given customer id if
available. When a braintree customer already exists, rather than create
a new braintree customer, add the payment method to the existing
braintree customer.

app/controllers/solidus_paypal_braintree/client_tokens_controller.rb

@@ -1,11 +1,9 @@
 module SolidusPaypalBraintree
-  class ClientTokensController < Spree::Api::BaseController
-    skip_before_action :authenticate_user
-
+  class ClientTokensController < Spree::BaseController
     before_action :load_gateway
 
     def create
-      render json: { client_token: @gateway.generate_token, payment_method_id: @gateway.id }
+      render json: { client_token: generate_token, payment_method_id: @gateway.id }
     end
 
     private
@@ -18,5 +16,20 @@ def load_gateway
         @gateway = ::SolidusPaypalBraintree::Gateway.where(active: true).merge(store_payment_methods_scope).first!
       end
     end
+
+    def generate_token
+      options = {}
+      options[:customer_id] = customer_id if customer_id.present?
+
+      @gateway.generate_token(options)
+    rescue ::SolidusPaypalBraintree::Gateway::TokenGenerationDisabledError => error
+      Rails.logger.error error
+      nil
+    end
+
+    def customer_id
+      return unless try_spree_current_user&.braintree_customer
+      try_spree_current_user.braintree_customer.braintree_customer_id
+    end
   end
 end

app/models/solidus_paypal_braintree/gateway.rb

@@ -4,6 +4,8 @@ module SolidusPaypalBraintree
   class Gateway < ::Spree::PaymentMethod
     include RequestProtection
 
+    class TokenGenerationDisabledError < StandardError; end
+
     # Error message from Braintree that gets returned by a non voidable transaction
     NON_VOIDABLE_STATUS_ERROR_REGEXP = /can only be voided if status is authorized/
 
@@ -196,18 +198,33 @@ def try_void(payment)
     #
     # @api public
     # @param payment [Spree::Payment]
-    # @return [SolidusPaypalBraintree::Customer]
+    # @return [SolidusPaypalBraintree::Customer, NilClass]
     def create_profile(payment)
       source = payment.source
+      user = source.user
+      source.customer = user&.braintree_customer
+
+      return if source.token.present? || source.nonce.nil?
+
+      if source.customer.present?
+        # Add new payment method to existing customer
+        result = braintree.payment_method.create(
+          braintree_payment_method_params_for(payment)
+        )
+        fail Spree::Core::GatewayError, result.message unless result.success?
 
-      return if source.token.present? || source.customer.present? || source.nonce.nil?
+        source.token = result.payment_method.token
+        source.save!
+
+        return source.customer
+      end
 
       result = braintree.customer.create(customer_profile_params(payment))
       fail Spree::Core::GatewayError, result.message unless result.success?
 
       customer = result.customer
 
-      source.create_customer!(braintree_customer_id: customer.id).tap do
+      source.create_customer!(user_id: user&.id, braintree_customer_id: customer.id).tap do
         if customer.payment_methods.any?
           source.token = customer.payment_methods.last.token
         end
@@ -216,12 +233,16 @@ def create_profile(payment)
       end
     end
 
+    # @raise [TokenGenerationDisabledError]
+    #   If `preferred_token_generation_enabled` is false
+    #
+    # @param options [Hash]
+    #   The options for braintree.
+    #   See: https://developers.braintreepayments.com/reference/request/client-token/generate/ruby
+    #
     # @return [String]
     #   The token that should be used along with the Braintree js-client sdk.
     #
-    #   returns an error message if `preferred_token_generation_enabled` is
-    #   set to false.
-    #
     # @example
     #   <script>
     #     var token = #{Spree::Braintree::Gateway.first!.generate_token}
@@ -235,9 +256,12 @@ def create_profile(payment)
     #       }
     #     );
     #   </script>
-    def generate_token
-      return TOKEN_GENERATION_DISABLED_MESSAGE unless preferred_token_generation_enabled
-      braintree.client_token.generate
+    def generate_token(options = {})
+      unless preferred_token_generation_enabled
+        raise TokenGenerationDisabledError, TOKEN_GENERATION_DISABLED_MESSAGE
+      end
+
+      braintree.client_token.generate(options)
     end
 
     def payment_profiles_supported?
@@ -378,5 +402,16 @@ def customer_profile_params(payment)
 
       params
     end
+
+    def braintree_payment_method_params_for(payment)
+      source = payment.source
+      user = source.user
+
+      params = {}
+      params[:payment_method_nonce] = source.nonce
+      params[:customer_id] = user.braintree_customer.braintree_customer_id
+
+      params
+    end
   end
 end

app/models/spree/user_decorator.rb

@@ -0,0 +1,4 @@
+Spree.user_class.class_eval do
+  has_one :braintree_customer, class_name: 'SolidusPaypalBraintree::Customer',
+                               inverse_of: :user
+end