/hats: don't list hats unavailable for use

Fix #1160

app/controllers/hats_controller.rb

@@ -14,7 +14,7 @@ class HatsController < ApplicationController
 
     @hat_groups = {}
 
-    Hat.all.includes(:user).each do |h|
+    Hat.active.includes(:user).each do |h|
       @hat_groups[h.hat] ||= []
       @hat_groups[h.hat].push h
     end

app/models/hat.rb

@@ -1,12 +1,14 @@
 class Hat < ApplicationRecord
   belongs_to :user
-  belongs_to :granted_by_user, :class_name => "User", :inverse_of => false
+  belongs_to :granted_by_user, class_name: "User", inverse_of: false
 
   after_create :log_moderation
 
   validates :user, :granted_by_user, :hat, presence: true
   validates :hat, :link, length: { maximum: 255 }
 
+  scope :active, -> { joins(:user).where(doffed_at: nil).merge(User.active) }
+
   def doff_by_user_with_reason(user, reason)
     m = Moderation.new
     m.user_id = self.user_id