Add (back) option to set redirect notice on account without moving followers (#11994)

Fix #11913

app/models/form/redirect.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+class Form::Redirect
+  include ActiveModel::Model
+
+  attr_accessor :account, :target_account, :current_password,
+                :current_username
+
+  attr_reader :acct
+
+  validates :acct, presence: true, domain: { acct: true }
+  validate :validate_target_account
+
+  def valid_with_challenge?(current_user)
+    if current_user.encrypted_password.present?
+      errors.add(:current_password, :invalid) unless current_user.valid_password?(current_password)
+    else
+      errors.add(:current_username, :invalid) unless account.username == current_username
+    end
+
+    return false unless errors.empty?
+
+    set_target_account
+    valid?
+  end
+
+  def acct=(val)
+    @acct = val.to_s.strip.gsub(/\A@/, '')
+  end
+
+  private
+
+  def set_target_account
+    @target_account = ResolveAccountService.new.call(acct)
+  rescue Goldfinger::Error, HTTP::Error, OpenSSL::SSL::SSLError, Mastodon::Error
+    # Validation will take care of it
+  end
+
+  def validate_target_account
+    if target_account.nil?
+      errors.add(:acct, I18n.t('migrations.errors.not_found'))
+    else
+      errors.add(:acct, I18n.t('migrations.errors.already_moved')) if account.moved_to_account_id.present? && account.moved_to_account_id == target_account.id
+      errors.add(:acct, I18n.t('migrations.errors.move_to_self')) if account.id == target_account.id
+    end
+  end
+end