Implement invitation codes

app/models/invite_code.rb

@@ -0,0 +1,25 @@
+class InviteCode < ApplicationRecord
+  before_validation :generate_token, on: :create
+
+  class << self
+    def claim!(token)
+      if invite_code = find_by(token: token&.downcase)
+        invite_code.destroy!
+        true
+      end
+    end
+
+    def generate!
+      create!.token
+    end
+  end
+
+  private
+
+  def generate_token
+    loop do
+      self.token = SecureRandom.hex(4)
+      break token unless self.class.exists?(token: token)
+    end
+  end
+end