step3/api/QuestionsApi/Models/CreditModels.cs

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

namespace QuestionsApi.Models;

public static class CreditEconomy
{
    public const int RollingEarningLimit = 20;
    public static readonly TimeSpan EarningWindow = TimeSpan.FromHours(24);
    public const string ExamTokenSku = "exam_token_1";
    public const string QBankResetTokenSku = "qbank_reset_1";
    public const int ExamTokenPrice = 100;
    public const int QBankResetTokenPrice = 300;

    public static readonly IReadOnlyList<RzStoreProduct> Products =
    [
        new()
        {
            Sku = ExamTokenSku,
            Name = "Exam Simulation Token",
            Description = "Starts one new full exam simulation.",
            CoinPrice = ExamTokenPrice,
            Grant = RzStoreGrant.ExamToken
        },
        new()
        {
            Sku = QBankResetTokenSku,
            Name = "QBank Reset Token",
            Description = "Makes every QBank question eligible again without erasing progress.",
            CoinPrice = QBankResetTokenPrice,
            Grant = RzStoreGrant.QBankResetToken
        }
    ];

    public static RzStoreProduct? FindProduct(string sku) =>
        Products.FirstOrDefault(value => value.Sku.Equals(sku, StringComparison.Ordinal));
}

public static class SlotMachineEconomy
{
    public const int SpinCost = 0; // TODO: restore to 50 once testing is done
    public const int RollingSpinLimit = 200;
    public static readonly TimeSpan SpinWindow = TimeSpan.FromHours(24);

    public static readonly IReadOnlyList<SpinReward> Rewards =
    [
        new() { Key = "jackpot", Label = "10,000 RZ Coins", Description = "Jackpot!", Grant = RzStoreGrant.Coins, CoinAmount = 10000, Probability = 0.005 },
        new() { Key = "epic", Label = "2,000 RZ Coins", Description = "Epic Reward", Grant = RzStoreGrant.Coins, CoinAmount = 2000, Probability = 0.02 },
        new() { Key = "great", Label = "500 RZ Coins", Description = "Great Reward", Grant = RzStoreGrant.Coins, CoinAmount = 500, Probability = 0.10 },
        new() { Key = "exam_token", Label = "Exam Simulation Token", Description = "Starts one new full exam simulation.", Grant = RzStoreGrant.ExamToken, Probability = 0.15 },
        new() { Key = "qbank_reset", Label = "QBank Reset Token", Description = "Makes every QBank question eligible again.", Grant = RzStoreGrant.QBankResetToken, Probability = 0.20 },
        new() { Key = "nice", Label = "100 RZ Coins", Description = "Nice!", Grant = RzStoreGrant.Coins, CoinAmount = 100, Probability = 0.30 },
        new() { Key = "good_luck", Label = "50 RZ Coins", Description = "Good luck!", Grant = RzStoreGrant.Coins, CoinAmount = 50, Probability = 0.225 },
    ];

    public static SpinReward RollReward(double roll)
    {
        var cumulative = 0.0;
        foreach (var reward in Rewards)
        {
            cumulative += reward.Probability;
            if (roll < cumulative) return reward;
        }
        return Rewards[^1];
    }

    public static SpinReward? FindReward(string key) =>
        Rewards.FirstOrDefault(value => value.Key.Equals(key, StringComparison.Ordinal));
}

public enum RzStoreGrant { ExamToken, QBankResetToken, Coins }

public sealed class SpinReward
{
    public string Key { get; set; } = "";
    public string Label { get; set; } = "";
    public string Description { get; set; } = "";
    public RzStoreGrant Grant { get; set; }
    public int CoinAmount { get; set; }
    public double Probability { get; set; }
}

public sealed class RzStoreProduct
{
    public string Sku { get; set; } = "";
    public string Name { get; set; } = "";
    public string Description { get; set; } = "";
    public int CoinPrice { get; set; }
    public RzStoreGrant Grant { get; set; }
}

public sealed class CreditEvent
{
    public string OperationId { get; set; } = "";
    public DateTime CreatedUtc { get; set; }
}

public sealed class CreditPurchaseEvent
{
    public string OperationId { get; set; } = "";
    public string Sku { get; set; } = "";
    public int CoinCost { get; set; }
    public DateTime CreatedUtc { get; set; }
}

public sealed class SpinEvent
{
    public string OperationId { get; set; } = "";
    public string RewardKey { get; set; } = "";
    public int CoinsWon { get; set; }
    public DateTime CreatedUtc { get; set; }
}

public sealed class UserCreditAccount
{
    [BsonId]
    [BsonRepresentation(BsonType.ObjectId)]
    public string? Id { get; set; }
    public string UserId { get; set; } = "";
    public int Credits { get; set; }
    public int ExamTokens { get; set; }
    public int QBankResetTokens { get; set; }
    public int BankCycle { get; set; }
    public bool InitialExamGrantApplied { get; set; }
    public List<CreditEvent> RecentEarnings { get; set; } = [];
    public List<CreditPurchaseEvent> Purchases { get; set; } = [];
    public List<SpinEvent> Spins { get; set; } = [];
    public List<CreditEvent> RecentSpins { get; set; } = [];
    public List<string> AppliedOperations { get; set; } = [];
    public DateTime UpdatedUtc { get; set; } = DateTime.UtcNow;
}

public sealed class CreditStatusResponse
{
    public int Credits { get; set; }
    public int EarnedInRollingWindow { get; set; }
    public int RemainingEarningCapacity { get; set; }
    public int RollingWindowHours { get; set; } = 24;
    public int ExamTokens { get; set; }
    public int QBankResetTokens { get; set; }
    public int BankCycle { get; set; }
    public IReadOnlyList<RzStoreProduct> Products { get; set; } = CreditEconomy.Products;
}

public sealed class CreditPurchaseRequest
{
    public string Sku { get; set; } = "";
    public string OperationId { get; set; } = "";
}

public sealed class QBankResetRequest
{
    public string Confirmation { get; set; } = "";
    public string OperationId { get; set; } = "";
}

public sealed class SpinRequest
{
    public string OperationId { get; set; } = "";
}

public enum CreditOperationResult { Succeeded, InsufficientCredits, InsufficientTokens, OperationConflict, RateLimited }

public sealed class CreditOperationResponse
{
    public CreditOperationResult Result { get; set; }
    public CreditStatusResponse Status { get; set; } = new();
}

public sealed class SpinConfigResponse
{
    public int SpinCost { get; set; } = SlotMachineEconomy.SpinCost;
    public IReadOnlyList<SpinReward> Rewards { get; set; } = SlotMachineEconomy.Rewards;
}

public sealed class SpinResponse
{
    public CreditOperationResult Result { get; set; }
    public string RewardKey { get; set; } = "";
    public string RewardLabel { get; set; } = "";
    public int CoinsWon { get; set; }
    public CreditStatusResponse Status { get; set; } = new();
}