user upgrades: upgrade to new Stripe checkout system.

This upgrades from the legacy version of Stripe's checkout system to the
new version:

> The legacy version of Checkout presented customers with a modal dialog
> that collected card information, and returned a token or a source to
> your website. In contrast, the new version of Checkout is a smart
> payment page hosted by Stripe that creates payments or subscriptions. It
> supports Apple Pay, Dynamic 3D Secure, and many other features.

Basic overview of the new system:

* We send the user to a checkout page on Stripe.
* Stripe collects payment and sends us a webhook notification when the
  order is complete.
* We receive the webhook notification and upgrade the user.

Docs:

* https://stripe.com/docs/payments/checkout
* https://stripe.com/docs/payments/checkout/migration#client-products
* https://stripe.com/docs/payments/handling-payment-events
* https://stripe.com/docs/payments/checkout/fulfill-orders

app/controllers/user_upgrades_controller.rb

@@ -1,11 +1,12 @@
 class UserUpgradesController < ApplicationController
   helper_method :user
-  skip_before_action :verify_authenticity_token, only: [:create]
+  respond_to :js, :html
 
   def create
-    if params[:stripeToken]
+    @user_upgrade = UserUpgrade.new(recipient: user, purchaser: CurrentUser.user, level: params[:level].to_i)
-      create_stripe
+    @checkout = @user_upgrade.create_checkout
-    end
+
+    respond_with(@user_upgrade)
   end
 
   def new
@@ -22,38 +23,4 @@ class UserUpgradesController < ApplicationController
       CurrentUser.user
     end
   end
-
-  private
-
-  def create_stripe
-    @user = user
-
-    if params[:desc] == "Upgrade to Gold"
-      level = User::Levels::GOLD
-      cost = UserUpgrade.gold_price
-    elsif params[:desc] == "Upgrade to Platinum"
-      level = User::Levels::PLATINUM
-      cost = UserUpgrade.platinum_price
-    elsif params[:desc] == "Upgrade Gold to Platinum" && @user.level == User::Levels::GOLD
-      level = User::Levels::PLATINUM
-      cost = UserUpgrade.upgrade_price
-    else
-      raise "Invalid desc"
-    end
-
-    begin
-      charge = Stripe::Charge.create(amount: cost, currency: "usd", source: params[:stripeToken], description: params[:desc])
-      @user.promote_to!(level, User.system, is_upgrade: true)
-      flash[:success] = true
-    rescue Stripe::StripeError => e
-      DanbooruLogger.log(e)
-      flash[:error] = e.message
-    end
-
-    if @user == CurrentUser.user
-      redirect_to user_upgrade_path
-    else
-      redirect_to user_upgrade_path(user_id: params[:user_id])
-    end
-  end
 end

app/controllers/webhooks_controller.rb

@@ -0,0 +1,13 @@
+class WebhooksController < ApplicationController
+  skip_forgery_protection only: :receive
+  rescue_with Stripe::SignatureVerificationError, status: 400
+
+  def receive
+    if params[:source] == "stripe"
+      UserUpgrade.receive_webhook(request)
+      head 200
+    else
+      head 400
+    end
+  end
+end

app/helpers/user_upgrades_helper.rb

@@ -1,24 +1,4 @@
 module UserUpgradesHelper
-  def stripe_button(desc, cost, user)
-    html = %{
-      <form action="#{user_upgrade_path}" method="POST" class="stripe">
-        <input type="hidden" name="authenticity_token" value="#{form_authenticity_token}">
-        #{hidden_field_tag(:desc, desc)}
-        #{hidden_field_tag(:user_id, user.id)}
-        <script
-          src="https://checkout.stripe.com/checkout.js" class="stripe-button"
-          data-key="#{Danbooru.config.stripe_publishable_key}"
-          data-name="#{Danbooru.config.canonical_app_name}"
-          data-description="#{desc}"
-          data-label="#{desc}"
-          data-amount="#{cost}">
-        </script>
-      </form>
-    }
-
-    raw(html)
-  end
-
   def cents_to_usd(cents)
     number_to_currency(cents / 100, precision: 0)
   end

app/logical/user_upgrade.rb

@@ -1,13 +1,145 @@
 class UserUpgrade
+  attr_reader :recipient, :purchaser, :level
+
+  def self.stripe_publishable_key
+    Danbooru.config.stripe_publishable_key
+  end
+
+  def self.stripe_webhook_secret
+    Danbooru.config.stripe_webhook_secret
+  end
+
   def self.gold_price
     2000
   end
 
   def self.platinum_price
-    4000
+    2 * gold_price
   end
 
-  def self.upgrade_price
+  def self.gold_to_platinum_price
-    2000
+    platinum_price - gold_price
+  end
+
+  def initialize(recipient:, purchaser:, level:)
+    @recipient, @purchaser, @level = recipient, purchaser, level.to_i
+  end
+
+  def upgrade_type
+    if level == User::Levels::GOLD && recipient.level == User::Levels::MEMBER
+      :gold_upgrade
+    elsif level == User::Levels::PLATINUM && recipient.level == User::Levels::MEMBER
+      :platinum_upgrade
+    elsif level == User::Levels::PLATINUM && recipient.level == User::Levels::GOLD
+      :gold_to_platinum_upgrade
+    else
+      raise ArgumentError, "Invalid upgrade"
+    end
+  end
+
+  def upgrade_price
+    case upgrade_type
+    when :gold_upgrade
+      UserUpgrade.gold_price
+    when :platinum_upgrade
+      UserUpgrade.platinum_price
+    when :gold_to_platinum_upgrade
+      UserUpgrade.gold_to_platinum_price
+    end
+  end
+
+  def upgrade_description
+    case upgrade_type
+    when :gold_upgrade
+      "Upgrade to Gold"
+    when :platinum_upgrade
+      "Upgrade to Platinum"
+    when :gold_to_platinum_upgrade
+      "Upgrade Gold to Platinum"
+    end
+  end
+
+  def is_gift?
+    recipient != purchaser
+  end
+
+  def process_upgrade!
+    recipient.with_lock do
+      upgrade_recipient!
+    end
+  end
+
+  def upgrade_recipient!
+    recipient.promote_to!(level, User.system, is_upgrade: true)
+  end
+
+  concerning :StripeMethods do
+    def create_checkout
+      Stripe::Checkout::Session.create(
+        mode: "payment",
+        success_url: Routes.user_upgrade_url(user_id: recipient.id),
+        cancel_url: Routes.new_user_upgrade_url(user_id: recipient.id),
+        client_reference_id: "user_#{purchaser.id}",
+        customer_email: recipient.email_address&.address,
+        payment_method_types: ["card"],
+        line_items: [{
+          price_data: {
+            unit_amount: upgrade_price,
+            currency: "usd",
+            product_data: {
+              name: upgrade_description,
+            },
+          },
+          quantity: 1,
+        }],
+        metadata: {
+          purchaser_id: purchaser.id,
+          recipient_id: recipient.id,
+          purchaser_name: purchaser.name,
+          recipient_name: recipient.name,
+          upgrade_type: upgrade_type,
+          is_gift: is_gift?,
+          level: level,
+        },
+      )
+    end
+
+    class_methods do
+      def register_webhook
+        webhook = Stripe::WebhookEndpoint.create({
+          url: Routes.webhook_user_upgrade_url(source: "stripe"),
+          enabled_events: [
+            "payment_intent.created",
+            "payment_intent.payment_failed",
+            "checkout.session.completed",
+          ],
+        })
+
+        webhook.secret
+      end
+
+      def receive_webhook(request)
+        event = build_event(request)
+
+        if event.type == "checkout.session.completed"
+          checkout_session_completed(event)
+        end
+      end
+
+      def build_event(request)
+        payload = request.body.read
+        signature = request.headers["Stripe-Signature"]
+        Stripe::Webhook.construct_event(payload, signature, stripe_webhook_secret)
+      end
+
+      def checkout_session_completed(event)
+        recipient = User.find(event.data.object.metadata.recipient_id)
+        purchaser = User.find(event.data.object.metadata.purchaser_id)
+        level = event.data.object.metadata.level
+
+        user_upgrade = UserUpgrade.new(recipient: recipient, purchaser: purchaser, level: level)
+        user_upgrade.process_upgrade!
+      end
+    end
   end
 end

app/views/user_upgrades/_stripe_payment.html.erb

@@ -1,10 +0,0 @@
-<div class="section">
-  <p>You can pay with a credit or debit card. Safebooru uses <a href="https://www.stripe.com">Stripe</a> as a payment intermediary so none of your personal information will be stored on the site.</p>
-
-  <% if user.level < User::Levels::GOLD %>
-    <%= stripe_button("Upgrade to Gold", UserUpgrade.gold_price, user) %>
-    <%= stripe_button("Upgrade to Platinum", UserUpgrade.platinum_price, user) %>
-  <% elsif user.level < User::Levels::PLATINUM %>
-    <%= stripe_button("Upgrade Gold to Platinum", UserUpgrade.upgrade_price, user) %>
-  <% end %>
-</div>

app/views/user_upgrades/_stripe_payment_safebooru.html.erb

@@ -1,3 +0,0 @@
-<div class="section">
-  <p>You can pay with a credit or debit card on <%= link_to "Safebooru", new_user_upgrade_url(host: "safebooru.donmai.us", protocol: "https") %>. Your account will then also be upgraded on Danbooru. You can login to Safebooru with the same username and password you use on Danbooru.</p>
-</div>

app/views/user_upgrades/create.js.erb

@@ -0,0 +1,2 @@
+var stripe = Stripe("<%= j UserUpgrade.stripe_publishable_key %>");
+stripe.redirectToCheckout({ sessionId: "<%= j @checkout.id %>" });

app/views/user_upgrades/new.html.erb

@@ -1,5 +1,6 @@
 <% page_title "Account Upgrade" %>
-<% meta_description "Upgrade to a Gold or Platinum account on #{Danbooru.config.app_name}." %>
+<% meta_description "Upgrade to a Gold or Platinum account." %>
+<script src="https://js.stripe.com/v3/"></script>
 
 <%= render "users/secondary_links" %>
 
@@ -96,9 +97,24 @@
       <% if CurrentUser.is_anonymous? %>
         <p><%= link_to "Sign up", new_user_path %> or <%= link_to "login", login_path(url: new_user_upgrade_path) %> first to upgrade your account.</p>
       <% elsif CurrentUser.safe_mode? %>
-        <%= render "stripe_payment" %>
+        <div class="section">
+          <p>You can pay with a credit or debit card. Safebooru uses <a href="https://www.stripe.com">Stripe</a>
+          as a payment intermediary so none of your personal information will be stored on the site.</p>
+
+          <% if user.level < User::Levels::GOLD %>
+            <p><%= button_to "Upgrade to Gold", user_upgrade_path(user_id: user.id, level: User::Levels::GOLD), remote: true, disable_with: "Redirecting..." %></p>
+            <p><%= button_to "Upgrade to Platinum", user_upgrade_path(user_id: user.id, level: User::Levels::PLATINUM), remote: true, disable_with: "Redirecting..." %></p>
+          <% elsif user.level < User::Levels::PLATINUM %>
+            <p><%= button_to "Upgrade Gold to Platinum", user_upgrade_path(user_id: user.id, level: User::Levels::PLATINUM), remote: true, disable_with: "Redirecting..." %></p>
+          <% end %>
+        </div>
       <% else %>
-        <%= render "stripe_payment_safebooru" %>
+        <div class="section">
+          <p>You can pay with a credit or debit card on
+          <%= link_to "Safebooru", new_user_upgrade_url(user_id: user.id, host: "safebooru.donmai.us", protocol: "https") %>.
+          Your account will then also be upgraded on Danbooru. You can login to
+          Safebooru with the same username and password you use on Danbooru.</p>
+        </div>
       <% end %>
     <% end %>
   </div>

config/danbooru_default_config.rb

@@ -359,6 +359,9 @@ module Danbooru
     def stripe_publishable_key
     end
 
+    def stripe_webhook_secret
+    end
+
     def twitter_api_key
     end
 

config/initializers/stripe.rb

@@ -1 +1,2 @@
 Stripe.api_key = Danbooru.config.stripe_secret_key
+Stripe.api_version = "2020-08-27"

config/routes.rb

@@ -257,6 +257,9 @@ Rails.application.routes.draw do
   resource :user_upgrade, :only => [:new, :create, :show]
   resources :user_feedbacks, except: [:destroy]
   resources :user_name_change_requests, only: [:new, :create, :show, :index]
+  resources :webhooks do
+    post :receive, on: :collection
+  end
   resources :wiki_pages, id: /.+?(?=\.json|\.xml|\.html)|.+/ do
     put :revert, on: :member
     get :search, on: :collection

test/fixtures/stripe-webhooks/checkout.session.completed.json

@@ -0,0 +1,55 @@
+{
+  "id": "evt_000",
+  "object": "event",
+  "api_version": "2020-08-27",
+  "created": 1608705740,
+  "data": {
+    "object": {
+      "id": "cs_test_000",
+      "object": "checkout.session",
+      "allow_promotion_codes": null,
+      "amount_subtotal": 2000,
+      "amount_total": 2000,
+      "billing_address_collection": null,
+      "cancel_url": "http://localhost/user_upgrade/new",
+      "client_reference_id": "user_12345",
+      "currency": "usd",
+      "customer": "cus_000",
+      "customer_email": null,
+      "livemode": false,
+      "locale": null,
+      "metadata": {
+        "purchaser_id": "12345",
+        "recipient_id": "12345",
+        "purchaser_name": "user_12345",
+        "recipient_name": "user_12345",
+        "upgrade_type": "gold_upgrade",
+        "is_gift": "false",
+        "level": "30"
+      },
+      "mode": "payment",
+      "payment_intent": "pi_000",
+      "payment_method_types": [
+        "card"
+      ],
+      "payment_status": "paid",
+      "setup_intent": null,
+      "shipping": null,
+      "shipping_address_collection": null,
+      "submit_type": null,
+      "subscription": null,
+      "success_url": "http://localhost/user_upgrade?user_id=12345",
+      "total_details": {
+        "amount_discount": 0,
+        "amount_tax": 0
+      }
+    }
+  },
+  "livemode": false,
+  "pending_webhooks": 3,
+  "request": {
+    "id": null,
+    "idempotency_key": null
+  },
+  "type": "checkout.session.completed"
+}

test/fixtures/stripe-webhooks/payment_intent.created.json

@@ -0,0 +1,67 @@
+{
+  "id": "evt_000",
+  "object": "event",
+  "api_version": "2020-08-27",
+  "created": 1608705945,
+  "data": {
+    "object": {
+      "id": "pi_000",
+      "object": "payment_intent",
+      "amount": 2000,
+      "amount_capturable": 0,
+      "amount_received": 0,
+      "application": null,
+      "application_fee_amount": null,
+      "canceled_at": null,
+      "cancellation_reason": null,
+      "capture_method": "automatic",
+      "charges": {
+        "object": "list",
+        "data": [],
+        "has_more": false,
+        "total_count": 0,
+        "url": "/v1/charges?payment_intent=pi_000"
+      },
+      "client_secret": "pi_000",
+      "confirmation_method": "automatic",
+      "created": 1608705945,
+      "currency": "usd",
+      "customer": null,
+      "description": null,
+      "invoice": null,
+      "last_payment_error": null,
+      "livemode": false,
+      "metadata": {},
+      "next_action": null,
+      "on_behalf_of": null,
+      "payment_method": null,
+      "payment_method_options": {
+        "card": {
+          "installments": null,
+          "network": null,
+          "request_three_d_secure": "automatic"
+        }
+      },
+      "payment_method_types": [
+        "card"
+      ],
+      "receipt_email": null,
+      "review": null,
+      "setup_future_usage": null,
+      "shipping": null,
+      "source": null,
+      "statement_descriptor": null,
+      "statement_descriptor_suffix": null,
+      "status": "requires_payment_method",
+      "transfer_data": null,
+      "transfer_group": null
+    }
+  },
+  "livemode": false,
+  "pending_webhooks": 3,
+  "request": {
+    "id": "req_000",
+    "idempotency_key": null
+  },
+  "type": "payment_intent.created"
+}

test/functional/user_upgrades_controller_test.rb

@@ -1,14 +1,6 @@
 require 'test_helper'
 
 class UserUpgradesControllerTest < ActionDispatch::IntegrationTest
-  setup do
-    StripeMock.start
-  end
-
-  teardown do
-    StripeMock.stop
-  end
-
   context "The user upgrades controller" do
     context "new action" do
       should "render" do
@@ -25,103 +17,24 @@ class UserUpgradesControllerTest < ActionDispatch::IntegrationTest
     end
 
     context "create action" do
-      setup do
+      mock_stripe!
-        @user = create(:user)
-        @token = StripeMock.generate_card_token
-      end
 
-      context "a self upgrade" do
+      context "for a self upgrade to Gold" do
-        should "upgrade a Member to Gold" do
+        should "redirect the user to the Stripe checkout page" do
-          post_auth user_upgrade_path, @user, params: { stripeToken: @token, desc: "Upgrade to Gold" }
+          user = create(:member_user)
-
+          post_auth user_upgrade_path(user_id: user.id), user, params: { level: User::Levels::GOLD }, xhr: true
-          assert_redirected_to user_upgrade_path
-          assert_equal(true, @user.reload.is_gold?)
-        end
-
-        should "upgrade a Member to Platinum" do
-          post_auth user_upgrade_path, @user, params: { stripeToken: @token, desc: "Upgrade to Platinum" }
-
-          assert_redirected_to user_upgrade_path
-          assert_equal(true, @user.reload.is_platinum?)
-        end
-
-        should "upgrade a Gold user to Platinum" do
-          @user.update!(level: User::Levels::GOLD)
-          post_auth user_upgrade_path, @user, params: { stripeToken: @token, desc: "Upgrade Gold to Platinum" }
-
-          assert_redirected_to user_upgrade_path
-          assert_equal(true, @user.reload.is_platinum?)
-        end
-
-        should "log an account upgrade modaction" do
-          assert_difference("ModAction.user_account_upgrade.count") do
-            post_auth user_upgrade_path, @user, params: { stripeToken: @token, desc: "Upgrade to Gold" }
-          end
-        end
-
-        should "send the user a dmail" do
-          assert_difference("@user.dmails.received.count") do
-            post_auth user_upgrade_path, @user, params: { stripeToken: @token, desc: "Upgrade to Gold" }
-          end
-        end
-      end
-
-      context "a gifted upgrade" do
-        should "upgrade the user to Gold" do
-          @other_user = create(:user)
-          post_auth user_upgrade_path, @user, params: { stripeToken: @token, desc: "Upgrade to Gold", user_id: @other_user.id }
-
-          assert_redirected_to user_upgrade_path(user_id: @other_user.id)
-          assert_equal(true, @other_user.reload.is_gold?)
-          assert_equal(false, @user.reload.is_gold?)
-        end
-      end
-
-      context "an upgrade for a user above Platinum level" do
-        should "not demote the user" do
-          @builder = create(:builder_user)
-          post_auth user_upgrade_path, @user, params: { stripeToken: @token, desc: "Upgrade to Gold", user_id: @builder.id }
-
-          assert_response 403
-          assert_equal(true, @builder.reload.is_builder?)
-        end
-      end
-
-      context "an upgrade with a missing Stripe token" do
-        should "not upgrade the user" do
-          post_auth user_upgrade_path, @user, params: { desc: "Upgrade to Gold" }
 
           assert_response :success
-          assert_equal(true, @user.reload.is_member?)
         end
       end
 
-      context "an upgrade with an invalid Stripe token" do
+      context "for a gifted upgrade to Gold" do
-        should "not upgrade the user" do
+        should "redirect the user to the Stripe checkout page" do
-          post_auth user_upgrade_path, @user, params: { stripeToken: "garbage", desc: "Upgrade to Gold" }
+          recipient = create(:member_user)
+          purchaser = create(:member_user)
+          post_auth user_upgrade_path(user_id: recipient.id), purchaser, params: { level: User::Levels::GOLD }, xhr: true
 
-          assert_redirected_to user_upgrade_path
+          assert_response :success
-          assert_equal(true, @user.reload.is_member?)
-        end
-      end
-
-      context "an upgrade with an credit card that is declined" do
-        should "not upgrade the user" do
-          StripeMock.prepare_card_error(:card_declined)
-          post_auth user_upgrade_path, @user, params: { stripeToken: @token, desc: "Upgrade to Gold" }
-
-          assert_redirected_to user_upgrade_path
-          assert_equal(true, @user.reload.is_member?)
-        end
-      end
-
-      context "an upgrade with an credit card that is expired" do
-        should "not upgrade the user" do
-          StripeMock.prepare_card_error(:expired_card)
-          post_auth user_upgrade_path, @user, params: { stripeToken: @token, desc: "Upgrade to Gold" }
-
-          assert_redirected_to user_upgrade_path
-          assert_equal(true, @user.reload.is_member?)
         end
       end
     end

test/functional/webhooks_controller_test.rb

@@ -0,0 +1,167 @@
+require 'test_helper'
+
+class WebhooksControllerTest < ActionDispatch::IntegrationTest
+  mock_stripe!
+
+  def post_webhook(*args, **metadata)
+    event = StripeMock.mock_webhook_event(*args, metadata: metadata)
+    signature = generate_stripe_signature(event)
+    headers = { "Stripe-Signature": signature }
+
+    post receive_webhooks_path(source: "stripe"), headers: headers, params: event, as: :json
+  end
+
+  # https://github.com/stripe-ruby-mock/stripe-ruby-mock/issues/467#issuecomment-634674913
+  # https://stripe.com/docs/webhooks/signatures
+  def generate_stripe_signature(event)
+    time = Time.now
+    secret = UserUpgrade.stripe_webhook_secret
+    signature = Stripe::Webhook::Signature.compute_signature(time, event.to_json, secret)
+    Stripe::Webhook::Signature.generate_header(time, signature, scheme: Stripe::Webhook::Signature::EXPECTED_SCHEME)
+  end
+
+  context "The webhooks controller" do
+    context "receive action" do
+      context "for a request from an unrecognized source" do
+        should "fail" do
+          post receive_webhooks_path(source: "blah")
+          assert_response 400
+        end
+      end
+
+      context "for a Stripe webhook" do
+        context "with a missing signature" do
+          should "fail" do
+            event = StripeMock.mock_webhook_event("payment_intent.created")
+            post receive_webhooks_path(source: "stripe"), params: event, as: :json
+
+            assert_response 400
+          end
+        end
+
+        context "with an invalid signature" do
+          should "fail" do
+            event = StripeMock.mock_webhook_event("payment_intent.created")
+            headers = { "Stripe-Signature": "blah" }
+            post receive_webhooks_path(source: "stripe"), headers: headers, params: event, as: :json
+
+            assert_response 400
+          end
+        end
+
+        context "for a payment_intent.created event" do
+          should "work" do
+            post_webhook("payment_intent.created")
+
+            assert_response 200
+          end
+        end
+
+        context "for a checkout.session.completed event" do
+          context "for a self upgrade" do
+            context "of a Member to Gold" do
+              should "upgrade the user" do
+                @user = create(:member_user)
+
+                post_webhook("checkout.session.completed", {
+                  recipient_id: @user.id,
+                  purchaser_id: @user.id,
+                  upgrade_type: "gold_upgrade",
+                  level: User::Levels::GOLD,
+                })
+
+                assert_response 200
+                assert_equal(User::Levels::GOLD, @user.reload.level)
+              end
+            end
+
+            context "of a Member to Platinum" do
+              should "upgrade the user" do
+                @user = create(:member_user)
+
+                post_webhook("checkout.session.completed", {
+                  recipient_id: @user.id,
+                  purchaser_id: @user.id,
+                  upgrade_type: "platinum_upgrade",
+                  level: User::Levels::PLATINUM,
+                })
+
+                assert_response 200
+                assert_equal(User::Levels::PLATINUM, @user.reload.level)
+              end
+            end
+
+            context "of a Gold user to Platinum" do
+              should "upgrade the user" do
+                @user = create(:gold_user)
+
+                post_webhook("checkout.session.completed", {
+                  recipient_id: @user.id,
+                  purchaser_id: @user.id,
+                  upgrade_type: "gold_to_platinum_upgrade",
+                  level: User::Levels::PLATINUM,
+                })
+
+                assert_response 200
+                assert_equal(User::Levels::PLATINUM, @user.reload.level)
+              end
+            end
+          end
+
+          context "for a gifted upgrade" do
+            context "of a Member to Gold" do
+              should "upgrade the user" do
+                @recipient = create(:member_user)
+                @purchaser = create(:member_user)
+
+                post_webhook("checkout.session.completed", {
+                  recipient_id: @recipient.id,
+                  purchaser_id: @purchaser.id,
+                  upgrade_type: "gold_upgrade",
+                  level: User::Levels::GOLD,
+                })
+
+                assert_response 200
+                assert_equal(User::Levels::GOLD, @recipient.reload.level)
+              end
+            end
+
+            context "of a Member to Platinum" do
+              should "upgrade the user" do
+                @recipient = create(:member_user)
+                @purchaser = create(:member_user)
+
+                post_webhook("checkout.session.completed", {
+                  recipient_id: @recipient.id,
+                  purchaser_id: @purchaser.id,
+                  upgrade_type: "platinum_upgrade",
+                  level: User::Levels::PLATINUM,
+                })
+
+                assert_response 200
+                assert_equal(User::Levels::PLATINUM, @recipient.reload.level)
+              end
+            end
+
+            context "of a Gold user to Platinum" do
+              should "upgrade the user" do
+                @recipient = create(:gold_user)
+                @purchaser = create(:member_user)
+
+                post_webhook("checkout.session.completed", {
+                  recipient_id: @recipient.id,
+                  purchaser_id: @purchaser.id,
+                  upgrade_type: "gold_to_platinum_upgrade",
+                  level: User::Levels::PLATINUM,
+                })
+
+                assert_response 200
+                assert_equal(User::Levels::PLATINUM, @recipient.reload.level)
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

test/test_helper.rb

@@ -26,6 +26,7 @@ class ActiveSupport::TestCase
   include DownloadTestHelper
   include IqdbTestHelper
   include UploadTestHelper
+  extend StripeTestHelper
 
   mock_post_version_service!
   mock_pool_version_service!

test/test_helpers/stripe_test_helper.rb

@@ -0,0 +1,13 @@
+StripeMock.webhook_fixture_path = "test/fixtures/stripe-webhooks"
+
+module StripeTestHelper
+  def mock_stripe!
+    setup do
+      StripeMock.start
+    end
+
+    teardown do
+      StripeMock.stop
+    end
+  end
+end

test/unit/user_upgrade_test.rb

@@ -0,0 +1,41 @@
+require 'test_helper'
+
+class UserUpgradeTest < ActiveSupport::TestCase
+  context "UserUpgrade:" do
+    context "the #process_upgrade! method" do
+      setup do
+        @user = create(:user)
+        @user_upgrade = UserUpgrade.new(recipient: @user, purchaser: @user, level: User::Levels::GOLD)
+      end
+
+      should "update the user's level" do
+        @user_upgrade.process_upgrade!
+        assert_equal(User::Levels::GOLD, @user.reload.level)
+      end
+
+      should "log an account upgrade modaction" do
+        assert_difference("ModAction.user_account_upgrade.count") do
+          @user_upgrade.process_upgrade!
+        end
+      end
+
+      should "send the user a dmail" do
+        assert_difference("@user.dmails.received.count") do
+          @user_upgrade.process_upgrade!
+        end
+      end
+
+      context "for an upgrade for a user above Platinum level" do
+        should "not demote the user" do
+          @user.update!(level: User::Levels::BUILDER)
+
+          assert_raise(User::PrivilegeError) do
+            @user_upgrade.process_upgrade!
+          end
+
+          assert_equal(true, @user.reload.is_builder?)
+        end
+      end
+    end
+  end
+end