public async Task <List <DeckModel> > GetDecksAsync(Guid userId)
        {
            var deckEntities = await deckRepository.GetUserDecksAsync(userId);

            var decks = deckEntities.ConvertAll(deck => deckMapper.Map(deck));

            foreach (var deck in decks)
            {
                var cards = await cardRepository.GetCardsByDeckAsync(deck.Id);

                GatherStatistics(deck, cards);
            }

            return(decks);
        }