Add unsubscribe link to e-mails (#25378)

app/controllers/mail_subscriptions_controller.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class MailSubscriptionsController < ApplicationController
+  layout 'auth'
+
+  skip_before_action :require_functional!
+
+  before_action :set_body_classes
+  before_action :set_user
+  before_action :set_type
+
+  def show; end
+
+  def create
+    @user.settings[email_type_from_param] = false
+    @user.save!
+  end
+
+  private
+
+  def set_user
+    @user = GlobalID::Locator.locate_signed(params[:token], for: 'unsubscribe')
+  end
+
+  def set_body_classes
+    @body_classes = 'lighter'
+  end
+
+  def set_type
+    @type = email_type_from_param
+  end
+
+  def email_type_from_param
+    case params[:type]
+    when 'follow', 'reblog', 'favourite', 'mention', 'follow_request'
+      "notification_emails.#{params[:type]}"
+    else
+      raise ArgumentError
+    end
+  end
+end