Idea for refactor acts_as_list

list.rb

before_create :set_default_position
before_save :prepare_new_position
after_save :cleanup_new_position
after_save :cleanup_old_position

def set_default_position
  return if self[position_column]

  bottom_item =
    acts_as_list_class
      .unscope(:select, :where)
      .where(scope_condition)
      .where.not(position_column => nil)
      .reorder(position_column => :desc)
      .limit(1)
      .pluck(position_column)
      .try(:first)

  if bottom_item
    self[position_column] = bottom_item + 1
  else
    self[position_column] = acts_as_list_top
  end

  # Don't halt the callback chain
  true
end

def prepare_new_position
  old_position, new_position = changes[position_column]
  new_position ||= self[position_column]

  scope =
    acts_as_list_class
      .unscope(:select, :where)
      .where(scope_condition)
      .where(self.class.arel_table[position_column].gteq(new_position))

  scope = scope.where(self.class.arel_table[position_column].lt(old_position)) if old_position

  scope.update_all("#{position_column} = (#{position_column} + 1) * -1")
end

def cleanup_new_position
  old_position, new_position = changes[position_column]
  new_position ||= self[position_column]

  acts_as_list_class
    .unscope(:select, :where)
    .where(scope_condition)
    .where(self.class.arel_table[position_column].lt(0))
    .update_all("#{position_column} = #{position_column} * -1")
end

def cleanup_old_position
  old_position, _new_position = saved_changes[position_column]
  old_scope_value, new_scope_value = saved_changes[scope_name.to_s]

  return unless old_scope_value && old_scope_value != new_scope_value

  acts_as_list_class
    .unscope(:select, :where)
    .where(scope_name => old_scope_value)
    .where(self.class.arel_table[position_column].gteq(old_position))
    .update_all("#{position_column} = #{position_column} - 1")
end