user upgrades: add UserUpgrade model.

Add a model to store the status of user upgrades.

* Store the upgrade purchaser and the upgrade receiver (these are
  different for a gifted upgrade, the same for a self upgrade).
* Store the upgrade type: gold, platinum, or gold-to-platinum upgrades.
* Store the upgrade status:
** pending: User is still on the Stripe checkout page, no payment
   received yet.
** processing: User has completed checkout, but the checkout status in
   Stripe is still 'unpaid'.
** complete: We've received notification from Stripe that the payment
   has gone through and the user has been upgraded.
* Store the Stripe checkout ID, to cross-reference the upgrade record on
  Danbooru with the checkout record on Stripe.

This is the upgrade flow:

* When the user clicks the upgrade button on the upgrade page, we call
  POST /user_upgrades and create a pending UserUpgrade.
* We redirect the user to the checkout page on Stripe.
* When the user completes checkout on Stripe, Stripe sends us a webhook
  notification at POST /webhooks/receive.
* When we receive the webhook, we check the payment status, and if it's
  paid we mark the UserUpgrade as complete and upgrade the user.
* After Stripe sees that we have successfully processed the webhook,
  they redirect the user to the /user_upgrades/:id page, where we show
  the user their upgrade receipt.

app/controllers/user_upgrades_controller.rb

@@ -3,8 +3,8 @@ class UserUpgradesController < ApplicationController
   respond_to :js, :html
 
   def create
-    @user_upgrade = UserUpgrade.new(recipient: user, purchaser: CurrentUser.user, level: params[:level].to_i)
-    @checkout = @user_upgrade.create_checkout
+    @user_upgrade = authorize UserUpgrade.create(recipient: user, purchaser: CurrentUser.user, status: "pending", upgrade_type: params[:upgrade_type])
+    @checkout = @user_upgrade.create_checkout!
 
     respond_with(@user_upgrade)
   end
@@ -13,7 +13,8 @@ class UserUpgradesController < ApplicationController
   end
 
   def show
-    authorize User, :upgrade?
+    @user_upgrade = authorize UserUpgrade.find(params[:id])
+    respond_with(@user_upgrade)
   end
 
   def user

app/models/user.rb

@@ -99,6 +99,8 @@ class User < ApplicationRecord
   has_many :post_votes
   has_many :post_versions, foreign_key: :updater_id
   has_many :bans, -> {order("bans.id desc")}
+  has_many :received_upgrades, class_name: "UserUpgrade", foreign_key: :recipient_id, dependent: :destroy
+  has_many :purchased_upgrades, class_name: "UserUpgrade", foreign_key: :purchaser_id, dependent: :destroy
   has_one :recent_ban, -> {order("bans.id desc")}, :class_name => "Ban"
 
   has_one :api_key

app/models/user_upgrade.rb

@@ -1,5 +1,18 @@
-class UserUpgrade
-  attr_reader :recipient, :purchaser, :level
+class UserUpgrade < ApplicationRecord
+  belongs_to :recipient, class_name: "User"
+  belongs_to :purchaser, class_name: "User"
+
+  enum upgrade_type: {
+    gold: 0,
+    platinum: 10,
+    gold_to_platinum: 20
+  }, _suffix: "upgrade"
+
+  enum status: {
+    pending: 0,
+    processing: 10,
+    complete: 20
+  }
 
   def self.stripe_publishable_key
     Danbooru.config.stripe_publishable_key
@@ -21,51 +34,63 @@ class UserUpgrade
     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
+  def level
+    case upgrade_type
+    when "gold"
+      User::Levels::GOLD
+    when "platinum"
+      User::Levels::PLATINUM
+    when "gold_to_platinum"
+      User::Levels::PLATINUM
     else
-      raise ArgumentError, "Invalid upgrade"
+      raise NotImplementedError
     end
   end
 
   def upgrade_price
     case upgrade_type
-    when :gold_upgrade
+    when "gold"
       UserUpgrade.gold_price
-    when :platinum_upgrade
+    when "platinum"
       UserUpgrade.platinum_price
-    when :gold_to_platinum_upgrade
+    when "gold_to_platinum"
       UserUpgrade.gold_to_platinum_price
+    else
+      raise NotImplementedError
     end
   end
 
   def upgrade_description
     case upgrade_type
-    when :gold_upgrade
+    when "gold"
       "Upgrade to Gold"
-    when :platinum_upgrade
+    when "platinum"
       "Upgrade to Platinum"
-    when :gold_to_platinum_upgrade
+    when "gold_to_platinum"
       "Upgrade Gold to Platinum"
+    else
+      raise NotImplementedError
     end
   end
 
+  def level_string
+    User.level_string(level)
+  end
+
   def is_gift?
     recipient != purchaser
   end
 
-  def process_upgrade!
+  def process_upgrade!(payment_status)
     recipient.with_lock do
-      upgrade_recipient!
+      return if status == "complete"
+
+      if payment_status == "paid"
+        upgrade_recipient!
+        update!(status: :complete)
+      else
+        update!(status: :processing)
+      end
     end
   end
 
@@ -74,12 +99,12 @@ class UserUpgrade
   end
 
   concerning :StripeMethods do
-    def create_checkout
-      Stripe::Checkout::Session.create(
+    def create_checkout!
+      checkout = Stripe::Checkout::Session.create(
         mode: "payment",
-        success_url: Routes.user_upgrade_url(user_id: recipient.id),
+        success_url: Routes.user_upgrade_url(self),
         cancel_url: Routes.new_user_upgrade_url(user_id: recipient.id),
-        client_reference_id: "user_#{purchaser.id}",
+        client_reference_id: "user_upgrade_#{id}",
         customer_email: recipient.email_address&.address,
         payment_method_types: ["card"],
         line_items: [{
@@ -93,6 +118,7 @@ class UserUpgrade
           quantity: 1,
         }],
         metadata: {
+          user_upgrade_id: id,
           purchaser_id: purchaser.id,
           recipient_id: recipient.id,
           purchaser_name: purchaser.name,
@@ -102,6 +128,9 @@ class UserUpgrade
           level: level,
         },
       )
+
+      update!(stripe_id: checkout.id)
+      checkout
     end
 
     class_methods do
@@ -122,7 +151,7 @@ class UserUpgrade
         event = build_event(request)
 
         if event.type == "checkout.session.completed"
-          checkout_session_completed(event)
+          checkout_session_completed(event.data.object)
         end
       end
 
@@ -132,13 +161,9 @@ class UserUpgrade
         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!
+      def checkout_session_completed(checkout)
+        user_upgrade = UserUpgrade.find(checkout.metadata.user_upgrade_id)
+        user_upgrade.process_upgrade!(checkout.payment_status)
       end
     end
   end

app/policies/user_upgrade_policy.rb

@@ -0,0 +1,9 @@
+class UserUpgradePolicy < ApplicationPolicy
+  def create?
+    user.is_member?
+  end
+
+  def show?
+    record.recipient == user || record.purchaser == user || user.is_owner?
+  end
+end

app/views/user_upgrades/new.html.erb

@@ -101,11 +101,11 @@
           <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>
+          <% if user.level == User::Levels::MEMBER %>
+            <p><%= button_to "Upgrade to Gold", user_upgrades_path(user_id: user.id, upgrade_type: "gold"), remote: true, disable_with: "Redirecting..." %></p>
+            <p><%= button_to "Upgrade to Platinum", user_upgrades_path(user_id: user.id, upgrade_type: "platinum"), remote: true, disable_with: "Redirecting..." %></p>
+          <% elsif user.level == User::Levels::GOLD %>
+            <p><%= button_to "Upgrade Gold to Platinum", user_upgrades_path(user_id: user.id, upgrade_type: "gold_to_platinum"), remote: true, disable_with: "Redirecting..." %></p>
           <% end %>
         </div>
       <% else %>

app/views/user_upgrades/show.html.erb

@@ -1,22 +1,47 @@
-<% page_title "Account Upgraded" %>
+<% page_title "User Upgrade Status" %>
 <%= render "users/secondary_links" %>
 
 <div id="c-user-upgrades">
   <div id="a-show">
-    <% if flash[:success] %>
-      <h1>Congratulations!</h1>
+    <h1>User Upgrade</h1>
 
-      <% if user != CurrentUser.user %>
-        <p><%= user.name %> is now a <%= user.level_string %> user. Thanks for supporting the site!</p>
+    <p>
+      <ul>
+        <li>
+          <strong>Purchased</strong>
+          <%= time_ago_in_words_tagged @user_upgrade.updated_at %>
+          by <%= link_to_user @user_upgrade.purchaser %>
+          <% if @user_upgrade.is_gift? %>
+            for <%= link_to_user @user_upgrade.recipient %>
+          <% end %>
+        </li>
+        <li>
+          <strong>Upgrade Type</strong>
+          <%= @user_upgrade.upgrade_type.humanize %>
+        </li>
+        <li>
+          <strong>Status</strong>
+          <%= @user_upgrade.status.humanize %>
+        </li>
+      </ul>
+    </p>
+
+    <% if @user_upgrade.status == "complete" %>
+      <% if @user_upgrade.is_gift? && CurrentUser.user == @user_upgrade.recipient %>
+        <p><%= link_to_user @user_upgrade.purchaser %> has upgraded your account to <%= @user_upgrade.level_string %>. Enjoy your new account!</p>
+      <% elsif @user_upgrade.is_gift? && CurrentUser.user == @user_upgrade.purchaser %>
+        <p><%= link_to_user @user_upgrade.recipient %> is now a <%= @user_upgrade.level_string %> user. Thanks for supporting the site!</p>
       <% else %>
-        <p>You are now a <%= user.level_string %> user. Thanks for supporting the site!</p>
+        <p>You are now a <%= @user_upgrade.level_string %> user. Thanks for supporting the site!</p>
       <% end %>
 
-      <p><%= link_to "Go back to #{Danbooru.config.canonical_app_name}", "https://danbooru.donmai.us" %> to start using your new account.</p>
-    <% elsif flash[:error] %>
-      <h1>An error occurred!</h1>
-      <p><%= flash[:error] %></p>
-      <p><%= link_to "Try again", new_user_upgrade_path %></p>
+      <p><%= link_to "Go back to #{Danbooru.config.canonical_app_name}", "https://danbooru.donmai.us" %> to continue using the site.</p>
+    <% else %>
+      <%= content_for :html_header do %>
+        <meta http-equiv="refresh" content="5">
+      <% end %>
+
+      <p>This order is still being processed. You will be notified as soon as the order is complete.</p>
     <% end %>
   </div>
 </div>