```ruby
class StartRound
  attr_reader :round, :errors

  def initialize(game)
    @game = game
    @round = nil
    @errors = []
  end

  def call
    @game.with_lock do
      validate_round_can_be_started

      if errors.none?
        create_round
        create_tricks!
        deal_cards
      end
    end
  end

  private

  def validate_round_can_be_started
    unless all_existing_rounds_finished?
      add_error("rounds can't be started on games with unfinished rounds")
    end
  end

  def all_existing_rounds_finished?
    @game.rounds.all?(&:finished?)
  end

  def create_round
    @round = @game.rounds.create!(order_in_game: @game.rounds.count + 1,
                                  odd_players_score: 0,
                                  even_players_score: 0)
  end

  def create_tricks!
    Round::NUMBER_OF_TRICKS.times do |n|
      @round.tricks.create!(order_in_round: n + 1)
    end
  end

  def deal_cards
    deck = BuildDeck.new.call
    dealer = DealCards.new(@round, deck)
    dealer.call
  end

  def add_error(message)
    @errors << message
  end
end
```

Refactor AM Validations into service - to be applied across the board
user
```ruby
# TODO apply AM validations pattern to all other services.
class StartRound
  include ActiveModel::Validations
  attr_reader :round

  validate :round_can_be_started

  def initialize(game)
    @game = game
    @round = nil
  end

  def call
    @game.with_lock do

      if valid?
        create_round
        create_tricks!
        deal_cards
      end
    end
  end

  private

  def round_can_be_started
    errors.add(:base, "rounds can't be started on games with unfinished rounds") if rounds_in_progress?
  end

  def rounds_in_progress?
    @game.rounds.any? { |round| !round.finished? }
  end

  # TODO: check if scores are specified anywhere else for round.
  def create_round
    @round = @game.rounds.create!(order_in_game: @game.rounds.count)
  end

  def create_tricks!
    Round::NUMBER_OF_TRICKS.times do |n|
      @round.tricks.create!(order_in_round: n)
    end
  end

  def deal_cards
    deck = BuildDeck.new.call
    DealCards.new(@round, deck).call
  end
end
```
assistant