Add Danbooru Winter Sale.

app/models/user.rb

@@ -437,7 +437,9 @@ class User < ApplicationRecord
       end
 
       def tag_query_limit(level)
-        if level >= User::Levels::BUILDER
+        if level >= User::Levels::MEMBER && Danbooru.config.is_promotion?
+          Float::INFINITY
+        elsif level >= User::Levels::BUILDER
           Float::INFINITY
         elsif level == User::Levels::PLATINUM
           12

app/models/user_upgrade.rb

@@ -37,7 +37,11 @@ class UserUpgrade < ApplicationRecord
   end
 
   def self.gold_price
-    2000
+    if Danbooru.config.is_promotion?
+      1500
+    else
+      2000
+    end
   end
 
   def self.platinum_price
@@ -161,6 +165,9 @@ class UserUpgrade < ApplicationRecord
           price: price_id,
           quantity: 1,
         }],
+        discounts: [{
+          coupon: promotion_discount_id,
+        }],
         metadata: {
           user_upgrade_id: id,
           purchaser_id: purchaser.id,
@@ -218,6 +225,12 @@ class UserUpgrade < ApplicationRecord
       !pending?
     end
 
+    def promotion_discount_id
+      if Danbooru.config.is_promotion?
+        Danbooru.config.stripe_promotion_discount_id
+      end
+    end
+
     def upgrade_price_id(currency)
       case [upgrade_type, currency]
       when ["gold", "usd"]