sale_filter_form.rb

class SaleFilterForm
  include ActiveModel::Model
  include Virtus.model(nullify_blank: true)

  attribute :from_price, Integer
  attribute :to_price, Integer
  attribute :from_year, Integer
  attribute :to_year, Integer
  
  attribute :with_images, Boolean, default: false

  attribute :model_id, Integer
  attribute :body_type_ids, Array[Integer]
  validates :model_id, numericality: { only_integer: true, greater_than_or_equal_to: 0 }, allow_nil: true  

  validate :check_model_existence

  def fetch
    SalesByFilter.new(self).fetch
  end

  private

  def valid?
    super &&
      YearRange.new(from_year, to_year).valid? &&
      PriceRange.new(from_price, to_price).valid?
  end

  def check_model_existence
    if model_id.present?
      errors.add(:model_id, 'такой модели не существует') unless Model.exists?(model_id)
    end
  end
end

class SalesByFilter
  delegate ':price and etc..', to: :filter_model

  def initlialize(filter_model)
    @filter_model = filter_model
  end
  
  def fetch
    sales_scope.merge(automobiles_scope)
  end

  def sales_scope
    scope = Sale.joins(:automobile)

    if scope_by_price?
      price_range = PriceRange.new(from_price, to_price)
      scope.price_between(price_range)
    end

    scope
  end

  def automobiles_scope
    scope = Automobile.all
    scope = scope.for_model(model_id) if scope_by_model?

    if scope_by_year?
      year_range  = YearRange.new(from_year, to_year)
      scope.year_between(year_range)
    end

    scope.with_images(with_images)
  end

  def scope_by_model?
    model_id.present?
  end

  def scope_by_price?
    from_price.present? || to_price.present?
  end

  def scope_by_year?
    from_year.present? || to_year.present?
  end
end