step3/api/QuestionsApi/Models/UserProfileModels.cs

using MongoDB.Bson;
using MongoDB.Bson.Serialization.Attributes;

namespace QuestionsApi.Models;

public sealed class UserStudyProfile
{
    [BsonId]
    [BsonRepresentation(BsonType.ObjectId)]
    public string? Id { get; set; }
    public string UserId { get; set; } = "";
    public DateTime? TargetExamDate { get; set; }
    public string PreparationStage { get; set; } = "pre_dedicated";
    public int WeeklyGoalHours { get; set; } = 10;
    public string PreferredStudyMode { get; set; } = "mixed";
    public double QuestionTextScale { get; set; } = 1.0;
    public double CcsTextScale { get; set; } = 1.0;
    public int Revision { get; set; }
    public DateTime UpdatedUtc { get; set; } = DateTime.UtcNow;
}

public sealed class UpdateUserStudyProfileRequest
{
    public DateTime? TargetExamDate { get; set; }
    public string PreparationStage { get; set; } = "pre_dedicated";
    public int WeeklyGoalHours { get; set; } = 10;
    public string PreferredStudyMode { get; set; } = "mixed";
}

public sealed class UpdateTextScaleRequest
{
    public double? QuestionTextScale { get; set; }
    public double? CcsTextScale { get; set; }
}

public sealed class DeletedUserTombstone
{
    [BsonId]
    public string UserId { get; set; } = "";
    public DateTime DeletedUtc { get; set; } = DateTime.UtcNow;
}

public static class UserStudyProfileValidator
{
    private static readonly HashSet<string> Stages = ["pre_dedicated", "dedicated", "final_review"];
    private static readonly HashSet<int> Goals = [5, 10, 15, 20, 25];
    private static readonly HashSet<string> Modes = ["mixed", "question_bank", "ccs", "exam_simulation"];

    public static string? Validate(UpdateUserStudyProfileRequest request)
    {
        if (!Stages.Contains(request.PreparationStage)) return "Invalid preparation stage.";
        if (!Goals.Contains(request.WeeklyGoalHours)) return "Weekly goal must be 5, 10, 15, 20, or 25 hours.";
        if (!Modes.Contains(request.PreferredStudyMode)) return "Invalid preferred study mode.";
        if (request.TargetExamDate?.Kind == DateTimeKind.Local)
            request.TargetExamDate = request.TargetExamDate.Value.ToUniversalTime();
        return null;
    }
}

public static class UpdateTextScaleRequestValidator
{
    private const double Min = 0.85;
    private const double Max = 1.35;

    public static string? Validate(UpdateTextScaleRequest request)
    {
        if (request.QuestionTextScale is { } questionScale && (questionScale < Min || questionScale > Max))
            return "Question text scale must be between 0.85 and 1.35.";
        if (request.CcsTextScale is { } ccsScale && (ccsScale < Min || ccsScale > Max))
            return "CCS text scale must be between 0.85 and 1.35.";
        return null;
    }
}