step3/api/QuestionsApi/Services/Flashcards/FlashcardSettingsStore.cs

using MongoDB.Driver;
using QuestionsApi.Models;

namespace QuestionsApi.Services.Flashcards;

public sealed class FlashcardSettingsStore
{
    private readonly IMongoCollection<FlashcardSettings> _settings;

    public FlashcardSettingsStore(MongoDatabaseProvider mongo)
    {
        _settings = mongo.Database.GetCollection<FlashcardSettings>("FlashcardSettings");
        _settings.Indexes.CreateOne(new CreateIndexModel<FlashcardSettings>(
            Builders<FlashcardSettings>.IndexKeys.Ascending(v => v.UserId),
            new CreateIndexOptions { Unique = true, Name = "flashcard_settings_unique_user" }));
    }

    public async Task<FlashcardSettings> GetAsync(string userId) =>
        await _settings.Find(v => v.UserId == userId).FirstOrDefaultAsync()
        ?? new FlashcardSettings { UserId = userId };

    public async Task<FlashcardSettings> UpdateAsync(string userId, UpdateFlashcardSettingsRequest request)
    {
        var now = DateTime.UtcNow;
        return await _settings.FindOneAndUpdateAsync(
            v => v.UserId == userId,
            Builders<FlashcardSettings>.Update
                .Set(v => v.NewCardsPerDay, Math.Clamp(request.NewCardsPerDay, 0, 2000))
                .Set(v => v.ReviewsPerDay, Math.Clamp(request.ReviewsPerDay, 0, 5000))
                .Set(v => v.DesiredRetention, FsrsFlashcardScheduler.DesiredRetention)
                .Set(v => v.UpdatedUtc, now)
                .Inc(v => v.Revision, 1)
                .SetOnInsert(v => v.UserId, userId),
            new FindOneAndUpdateOptions<FlashcardSettings> { IsUpsert = true, ReturnDocument = ReturnDocument.After });
    }
}