Add UI for setting up account migration (#5832)

app/controllers/settings/migrations_controller.rb

@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+class Settings::MigrationsController < ApplicationController
+  layout 'admin'
+
+  before_action :authenticate_user!
+
+  def show
+    @migration = Form::Migration.new(account: current_account.moved_to_account)
+  end
+
+  def update
+    @migration = Form::Migration.new(resource_params)
+
+    if @migration.valid?
+      if current_account.moved_to_account_id != @migration.account&.id
+        current_account.update!(moved_to_account: @migration.account)
+        ActivityPub::UpdateDistributionWorker.perform_async(@account.id)
+      end
+
+      redirect_to settings_migration_path
+    else
+      render :show
+    end
+  end
+
+  private
+
+  def resource_params
+    params.require(:migration).permit(:acct)
+  end
+end

app/models/form/migration.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+class Form::Migration
+  include ActiveModel::Validations
+
+  attr_accessor :acct, :account
+
+  validates :acct, presence: true
+
+  def initialize(attrs = {})
+    @account = attrs[:account]
+    @acct    = attrs[:account].acct unless @account.nil?
+    @acct    = attrs[:acct].gsub(/\A@/, '').strip unless attrs[:acct].nil?
+  end
+
+  def valid?
+    return false unless super
+    set_account
+    errors.empty?
+  end
+
+  private
+
+  def set_account
+    self.account = ResolveRemoteAccountService.new.call(acct) if account.nil? && acct.present?
+  end
+end

app/views/settings/migrations/show.html.haml

@@ -0,0 +1,17 @@
+- content_for :page_title do
+  = t('settings.migrate')
+
+= simple_form_for @migration, as: :migration, url: settings_migration_path, html: { method: :put } do |f|
+  - if @migration.account
+    %p.hint= t('migrations.currently_redirecting')
+
+    .fields-group
+      = render partial: 'authorize_follows/card', locals: { account: @migration.account }
+
+  = render 'shared/error_messages', object: @migration
+
+  .fields-group
+    = f.input :acct, placeholder: t('migrations.acct')
+
+  .actions
+    = f.button :button, t('migrations.proceed'), type: :submit, class: 'negative'

app/views/settings/profiles/show.html.haml

@@ -21,3 +21,8 @@
 
   .actions
     = f.button :button, t('generic.save_changes'), type: :submit
+
+%hr/
+
+%h6= t('auth.migrate_account')
+%p.muted-hint= t('auth.migrate_account_html', path: settings_migration_path)