Add freemium access economy and token store

api/QuestionsApi.Tests/AccessCatalogTests.cs

@@ -0,0 +1,30 @@
+using QuestionsApi.Models;
+using Xunit;
+
+namespace QuestionsApi.Tests;
+
+public sealed class AccessCatalogTests
+{
+    [Fact]
+    public void FreeEconomy_HasTheReleaseLimits()
+    {
+        Assert.Equal(20, AccessCatalog.FreeQuestionLimit);
+        Assert.Equal(20, AccessCatalog.CreditEarningLimit);
+        Assert.Equal(100, AccessCatalog.DayPassCreditCost);
+    }
+
+    [Theory]
+    [InlineData("access_day_1", 100, AccessGrant.DayToken)]
+    [InlineData("access_week_1", 500, AccessGrant.WeekToken)]
+    [InlineData("access_month_1", 2000, AccessGrant.MonthToken)]
+    [InlineData("exam_token_1", 199, AccessGrant.ExamToken)]
+    [InlineData("qbank_reset_1", 499, AccessGrant.ResetToken)]
+    public void Products_HaveServerControlledPrices(string sku, long cents, string grant)
+    {
+        var product = AccessCatalog.Products[sku];
+
+        Assert.Equal(cents, product.AmountCents);
+        Assert.Equal("usd", product.Currency);
+        Assert.Equal(grant, product.Grant);
+    }
+}

api/QuestionsApi/Controllers/AccessController.cs

@@ -0,0 +1,71 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using QuestionsApi.Models;
+using QuestionsApi.Services;
+using System.Security.Claims;
+
+namespace QuestionsApi.Controllers;
+
+[ApiController]
+[Route("api/access")]
+[Authorize(Roles = "USER,SUPER")]
+public sealed class AccessController(
+    AccessStore access,
+    ExamSimulationStore simulations,
+    RatingStore ratings,
+    TimeProvider clock) : ControllerBase
+{
+    [HttpGet]
+    public async Task<IActionResult> Get() =>
+        Ok(await access.GetStatusAsync(UserId(), User.IsInRole("SUPER")));
+
+    [HttpPost("redeem-credits")]
+    public async Task<IActionResult> RedeemCredits(RedeemCreditsRequest request)
+    {
+        if (!ValidOperationId(request.OperationId)) return BadRequest("A valid operationId is required.");
+        var status = await access.RedeemCreditsAsync(UserId(), request.OperationId.Trim());
+        return status is null
+            ? Conflict(new { code = "insufficient_credits", message = "100 credits are required to redeem a day pass." })
+            : Ok(status);
+    }
+
+    [HttpPost("activate-token")]
+    public async Task<IActionResult> ActivateToken(ActivateAccessTokenRequest request)
+    {
+        if (!ValidOperationId(request.OperationId)) return BadRequest("A valid operationId is required.");
+        if (request.Token.Trim().ToLowerInvariant() is not ("day" or "week" or "month"))
+            return BadRequest("token must be day, week, or month");
+        var status = await access.ActivateTokenAsync(UserId(), request.OperationId.Trim(), request.Token);
+        return status is null
+            ? Conflict(new { code = "token_unavailable", message = "That access token is not available." })
+            : Ok(status);
+    }
+
+    [HttpPost("qbank-reset")]
+    public async Task<IActionResult> ResetQBank(ResetQBankRequest request)
+    {
+        if (request.Confirmation != "RESET_QBANK") return BadRequest("Type RESET_QBANK to confirm.");
+        if (!ValidOperationId(request.OperationId)) return BadRequest("A valid operationId is required.");
+        if (await simulations.FindActiveAsync(UserId()) is not null)
+            return Conflict(new { code = "active_exam", message = "Finish or abandon the active exam simulation before resetting the QBank." });
+        var cycle = await access.ApplyResetAsync(UserId(), request.OperationId.Trim());
+        if (cycle is null)
+            return Conflict(new { code = "reset_token_unavailable", message = "A QBank reset token is required." });
+        await ratings.ResetUserAsync(UserId(), clock.GetUtcNow().UtcDateTime);
+        return Ok(await access.GetStatusAsync(UserId(), User.IsInRole("SUPER")));
+    }
+
+    [HttpPost("steam-checkouts")]
+    public IActionResult SteamCheckout() => Problem(
+        statusCode: StatusCodes.Status503ServiceUnavailable,
+        title: "Steam Wallet checkout is not configured",
+        detail: "Steam purchases will be enabled after the Steamworks application and product catalog are configured.");
+
+    private string UserId() => User.FindFirstValue(ClaimTypes.NameIdentifier)
+        ?? User.FindFirstValue(ClaimTypes.Name)
+        ?? User.Identity?.Name
+        ?? throw new UnauthorizedAccessException();
+
+    private static bool ValidOperationId(string value) =>
+        !string.IsNullOrWhiteSpace(value) && value.Trim().Length <= 100;
+}

api/QuestionsApi/Controllers/AccessPurchasesController.cs

@@ -0,0 +1,106 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using QuestionsApi.Models;
+using QuestionsApi.Services;
+using Stripe;
+using Stripe.Checkout;
+using System.Security.Claims;
+
+namespace QuestionsApi.Controllers;
+
+[ApiController]
+[Route("api/access")]
+public sealed class AccessPurchasesController(
+    AccessPurchaseStore purchases,
+    AccessStore access,
+    IStripeAccessGateway stripe,
+    IConfiguration configuration,
+    ILogger<AccessPurchasesController> logger) : ControllerBase
+{
+    [HttpPost("web-checkouts")]
+    [Authorize(Roles = "USER,SUPER")]
+    public async Task<IActionResult> CreateCheckout(CreateAccessCheckoutRequest request, CancellationToken cancellationToken)
+    {
+        if (!AccessCatalog.Products.TryGetValue(request.Sku.Trim(), out var product))
+            return BadRequest("Unknown access product.");
+        var purchase = await purchases.CreateAsync(UserId(), product);
+        try
+        {
+            var checkout = await stripe.CreateCheckoutAsync(purchase, product, cancellationToken);
+            await purchases.AttachSessionAsync(purchase.Id!, checkout.SessionId);
+            return StatusCode(StatusCodes.Status201Created, new AccessCheckoutResponse
+            {
+                PurchaseId = purchase.Id!,
+                CheckoutUrl = checkout.CheckoutUrl,
+                Sku = product.Sku,
+                AmountCents = product.AmountCents
+            });
+        }
+        catch (Exception exception)
+        {
+            await purchases.MarkCheckoutFailedAsync(purchase.Id!);
+            logger.LogError(exception, "Unable to create access checkout {PurchaseId}", purchase.Id);
+            return Problem(statusCode: StatusCodes.Status502BadGateway,
+                title: "Access checkout unavailable",
+                detail: "The secure checkout could not be started. Please try again.");
+        }
+    }
+
+    [HttpGet("purchases/{id}")]
+    [Authorize(Roles = "USER,SUPER")]
+    public async Task<IActionResult> GetPurchase(string id) =>
+        await purchases.GetOwnedAsync(id.Trim(), UserId()) is { } purchase
+            ? Ok(AccessPurchaseStore.ToStatus(purchase))
+            : NotFound();
+
+    [HttpPost("stripe-webhook")]
+    [AllowAnonymous]
+    public async Task<IActionResult> StripeWebhook(CancellationToken cancellationToken)
+    {
+        var webhookSecret = configuration["Stripe:AccessWebhookSecret"];
+        if (string.IsNullOrWhiteSpace(webhookSecret))
+            return Problem(statusCode: 503, title: "Stripe webhook is not configured");
+        using var reader = new StreamReader(Request.Body);
+        var json = await reader.ReadToEndAsync(cancellationToken);
+        Event stripeEvent;
+        try
+        {
+            stripeEvent = EventUtility.ConstructEvent(json, Request.Headers["Stripe-Signature"], webhookSecret);
+        }
+        catch (StripeException exception)
+        {
+            logger.LogWarning(exception, "Rejected access webhook with an invalid signature");
+            return BadRequest("Invalid Stripe signature");
+        }
+        if (stripeEvent.Data.Object is not Session session) return Ok();
+        var status = stripeEvent.Type switch
+        {
+            "checkout.session.completed" when session.PaymentStatus == "paid" => AccessPurchaseStatus.Paid,
+            "checkout.session.async_payment_succeeded" => AccessPurchaseStatus.Paid,
+            "checkout.session.async_payment_failed" => AccessPurchaseStatus.Failed,
+            "checkout.session.expired" => AccessPurchaseStatus.Expired,
+            _ => ""
+        };
+        if (status.Length == 0) return Ok();
+        var purchaseId = session.ClientReferenceId;
+        if (string.IsNullOrWhiteSpace(purchaseId) &&
+            session.Metadata.TryGetValue("access_purchase_id", out var metadataId))
+            purchaseId = metadataId;
+        var purchase = await purchases.ApplyProviderStatusAsync(
+            purchaseId ?? "", session.Id, session.AmountTotal ?? 0, session.Currency ?? "",
+            status, session.PaymentIntentId ?? "", stripeEvent.Id);
+        if (purchase is null) return Ok();
+        if (status == AccessPurchaseStatus.Paid &&
+            AccessCatalog.Products.TryGetValue(purchase.Sku, out var product))
+        {
+            await access.ApplyProductGrantAsync(purchase.UserId, product, $"purchase:{purchase.Id}");
+            await purchases.MarkGrantAppliedAsync(purchase.Id!);
+        }
+        return Ok();
+    }
+
+    private string UserId() => User.FindFirstValue(ClaimTypes.NameIdentifier)
+        ?? User.FindFirstValue(ClaimTypes.Name)
+        ?? User.Identity?.Name
+        ?? throw new UnauthorizedAccessException();
+}

api/QuestionsApi/Controllers/ExamSimulationsController.cs

@@ -9,7 +9,7 @@ namespace QuestionsApi.Controllers;
 [ApiController]
 [Route("api/exam-simulations")]
 [Authorize(Roles = "USER,SUPER")]
-public class ExamSimulationsController(ExamSimulationStore simulations) : ControllerBase
+public class ExamSimulationsController(ExamSimulationStore simulations, AccessStore access) : ControllerBase
 {
     [HttpGet("readiness")]
     public async Task<IActionResult> Readiness() => Ok(await simulations.GetReadinessAsync(UserId()));
@@ -17,12 +17,28 @@ public class ExamSimulationsController(ExamSimulationStore simulations) : Contro
     [HttpPost]
     public async Task<IActionResult> Create()
     {
+        var operationId = $"exam-create:{Guid.NewGuid():N}";
+        if (!User.IsInRole("SUPER") && !await access.TryConsumeExamTokenAsync(UserId(), operationId))
+            return StatusCode(StatusCodes.Status402PaymentRequired, new
+            {
+                code = "exam_token_required",
+                message = "An exam simulation token is required."
+            });
         try
         {
             var simulation = await simulations.CreateAsync(UserId());
             return Ok(await simulations.ToResponseAsync(simulation));
         }
-        catch (InvalidOperationException exception) { return Conflict(exception.Message); }
+        catch (InvalidOperationException exception)
+        {
+            if (!User.IsInRole("SUPER")) await access.RefundExamTokenAsync(UserId(), operationId);
+            return Conflict(exception.Message);
+        }
+        catch
+        {
+            if (!User.IsInRole("SUPER")) await access.RefundExamTokenAsync(UserId(), operationId);
+            throw;
+        }
     }
 
     [HttpGet("preview-results")]

api/QuestionsApi/Controllers/QuestionsController.cs

@@ -19,6 +19,7 @@ public class QuestionsController : ControllerBase
     private readonly ServiceMetrics _metrics;
     private readonly QuestionBookmarkStore _bookmarks;
     private readonly ReviewQueueStore _reviewQueue;
+    private readonly AccessStore _access;
 
     public QuestionsController(
         QuestionStore questions,
@@ -28,7 +29,8 @@ public class QuestionsController : ControllerBase
         AnswerStatisticsStore statistics,
         ServiceMetrics metrics,
         QuestionBookmarkStore bookmarks,
-        ReviewQueueStore reviewQueue)
+        ReviewQueueStore reviewQueue,
+        AccessStore access)
     {
         _questions = questions;
         _attempts = attempts;
@@ -38,6 +40,7 @@ public class QuestionsController : ControllerBase
         _metrics = metrics;
         _bookmarks = bookmarks;
         _reviewQueue = reviewQueue;
+        _access = access;
     }
 
     [HttpGet("systems")]
@@ -52,6 +55,13 @@ public class QuestionsController : ControllerBase
     [Authorize(Roles = "USER,SUPER")]
     public async Task<IActionResult> Search([FromBody] QuestionSearchRequest req)
     {
+        if (!await _access.CanLoadQuestionAsync(UserId(), User.IsInRole("SUPER")))
+            return StatusCode(StatusCodes.Status403Forbidden, new
+            {
+                code = "qbank_limit_reached",
+                message = "Your free QBank allowance is exhausted. Redeem or activate an access pass to continue.",
+                access = await _access.GetStatusAsync(UserId())
+            });
         var questions = await _questions.SearchAsync(req, User.IsInRole("SUPER"));
         var percentages = await _statistics.GetPercentagesByQuestionAsync(questions.Select(q => q.ExternalId));
         var questionElos = await _ratings.GetQuestionElosAsync(questions.Select(q => q.ExternalId));
@@ -117,6 +127,8 @@ public class QuestionsController : ControllerBase
             return BadRequest("questionExternalId required");
         if (string.IsNullOrWhiteSpace(req.ChoiceId))
             return BadRequest("choiceId required");
+        if (string.IsNullOrWhiteSpace(req.CompletionId) || req.CompletionId.Trim().Length > 100)
+            return BadRequest("completionId required and must be 100 characters or fewer");
 
         var question = await _questions.GetByExternalIdAsync(req.QuestionExternalId.Trim());
         if (question is null || (!QuestionVisibility.IsVisibleToStudent(question.IsPublished, question.FlaggedForReviewUtc != null) && !User.IsInRole("SUPER")))
@@ -146,6 +158,15 @@ public class QuestionsController : ControllerBase
             ?? "";
         if (string.IsNullOrWhiteSpace(userId))
             return Unauthorized();
+        var completionId = req.CompletionId.Trim();
+        if (!await _access.ClaimQuestionAsync(userId, completionId, question.ExternalId, User.IsInRole("SUPER")))
+            return StatusCode(StatusCodes.Status403Forbidden, new
+            {
+                code = "qbank_limit_reached",
+                message = "Your free QBank allowance is exhausted.",
+                access = await _access.GetStatusAsync(userId)
+            });
+        var bankCycle = await _access.GetBankCycleAsync(userId);
 
         var record = await _attempts.RecordFirstAttemptAsync(
             question.ExternalId,
@@ -154,7 +175,9 @@ public class QuestionsController : ControllerBase
             req.ChoiceId.Trim() == question.CorrectChoiceId,
             false,
             presentedChoiceIds,
-            req.DurationSeconds);
+            req.DurationSeconds,
+            bankCycle,
+            completionId);
         if (record.Inserted)
         {
             _metrics.AttemptCreated();
@@ -172,6 +195,8 @@ public class QuestionsController : ControllerBase
             _metrics.AttemptDuplicate();
         }
         await _reviewQueue.AddFromFirstAttemptAsync(record.Attempt);
+        if (record.Inserted && !User.IsInRole("SUPER"))
+            await _access.TryAwardCreditAsync(userId, $"qbank-credit:{record.Attempt.Id}");
 
         var ratingOwner = Guid.NewGuid().ToString("N");
         var shouldRate = await _attempts.TryAcquireRatingLeaseAsync(
@@ -204,7 +229,8 @@ public class QuestionsController : ControllerBase
                 question,
                 await _statistics.GetPercentagesForQuestionAsync(question.ExternalId)),
             QuestionElo = rating.QuestionElo,
-            Rating = rating
+            Rating = rating,
+            Access = await _access.GetStatusAsync(userId, User.IsInRole("SUPER"))
         });
     }
 
@@ -252,7 +278,7 @@ public class QuestionsController : ControllerBase
 
     [HttpPost("{externalId}/skip")]
     [Authorize(Roles = "USER,SUPER")]
-    public async Task<IActionResult> Skip(string externalId)
+    public async Task<IActionResult> Skip(string externalId, [FromQuery] string completionId)
     {
         if (string.IsNullOrWhiteSpace(externalId))
             return BadRequest("externalId required");
@@ -264,13 +290,28 @@ public class QuestionsController : ControllerBase
         var userId = CurrentUserId();
         if (string.IsNullOrWhiteSpace(userId))
             return Unauthorized();
+        if (string.IsNullOrWhiteSpace(completionId) || completionId.Trim().Length > 100)
+            return BadRequest("completionId required and must be 100 characters or fewer");
+        completionId = completionId.Trim();
+        if (!await _access.ClaimQuestionAsync(userId, completionId, question.ExternalId, User.IsInRole("SUPER")))
+            return StatusCode(StatusCodes.Status403Forbidden, new
+            {
+                code = "qbank_limit_reached",
+                message = "Your free QBank allowance is exhausted.",
+                access = await _access.GetStatusAsync(userId)
+            });
+        var bankCycle = await _access.GetBankCycleAsync(userId);
 
         var record = await _attempts.RecordFirstAttemptAsync(
             question.ExternalId,
             userId,
             "",
             false,
-            true);
+            true,
+            null,
+            0,
+            bankCycle,
+            completionId);
         if (record.Inserted)
             _metrics.AttemptCreated();
         else
@@ -304,7 +345,8 @@ public class QuestionsController : ControllerBase
                 question,
                 await _statistics.GetPercentagesForQuestionAsync(question.ExternalId)),
             QuestionElo = rating.QuestionElo,
-            Rating = rating
+            Rating = rating,
+            Access = await _access.GetStatusAsync(userId, User.IsInRole("SUPER"))
         });
     }
 

api/QuestionsApi/Models/AccessModels.cs

@@ -0,0 +1,146 @@
+using MongoDB.Bson;
+using MongoDB.Bson.Serialization.Attributes;
+
+namespace QuestionsApi.Models;
+
+public static class AccessCatalog
+{
+    public const int FreeQuestionLimit = 20;
+    public const int CreditEarningLimit = 20;
+    public const int DayPassCreditCost = 100;
+
+    public static readonly IReadOnlyDictionary<string, AccessProduct> Products =
+        new Dictionary<string, AccessProduct>(StringComparer.Ordinal)
+        {
+            ["access_day_1"] = new("access_day_1", "One-day QBank token", 100, "usd", AccessGrant.DayToken),
+            ["access_week_1"] = new("access_week_1", "Seven-day QBank token", 500, "usd", AccessGrant.WeekToken),
+            ["access_month_1"] = new("access_month_1", "Thirty-day QBank token", 2000, "usd", AccessGrant.MonthToken),
+            ["exam_token_1"] = new("exam_token_1", "Exam simulation token", 199, "usd", AccessGrant.ExamToken),
+            ["qbank_reset_1"] = new("qbank_reset_1", "QBank reset token", 499, "usd", AccessGrant.ResetToken)
+        };
+}
+
+public static class AccessGrant
+{
+    public const string DayToken = "day_token";
+    public const string WeekToken = "week_token";
+    public const string MonthToken = "month_token";
+    public const string ExamToken = "exam_token";
+    public const string ResetToken = "reset_token";
+}
+
+public sealed record AccessProduct(string Sku, string Name, long AmountCents, string Currency, string Grant);
+
+public sealed class AccessEvent
+{
+    public string Id { get; set; } = "";
+    public string SubjectId { get; set; } = "";
+    public DateTime CreatedUtc { get; set; }
+}
+
+public sealed class UserAccessAccount
+{
+    [BsonId]
+    [BsonRepresentation(BsonType.ObjectId)]
+    public string? Id { get; set; }
+    public string UserId { get; set; } = "";
+    public int Credits { get; set; }
+    public int DayTokens { get; set; }
+    public int WeekTokens { get; set; }
+    public int MonthTokens { get; set; }
+    public int ExamTokens { get; set; }
+    public int ResetTokens { get; set; }
+    public int BankCycle { get; set; }
+    public DateTime? UnlimitedUntilUtc { get; set; }
+    public List<AccessEvent> RecentUsage { get; set; } = [];
+    public List<AccessEvent> RecentCredits { get; set; } = [];
+    public List<string> AppliedOperationIds { get; set; } = [];
+    public int Revision { get; set; }
+    public DateTime UpdatedUtc { get; set; } = DateTime.UtcNow;
+}
+
+public sealed class AccessStatusResponse
+{
+    public int FreeQuestionLimit { get; set; } = AccessCatalog.FreeQuestionLimit;
+    public int QuestionsUsed { get; set; }
+    public int QuestionsRemaining { get; set; }
+    public DateTime? NextQuestionAvailableUtc { get; set; }
+    public int Credits { get; set; }
+    public int DayPassCreditCost { get; set; } = AccessCatalog.DayPassCreditCost;
+    public int DayTokens { get; set; }
+    public int WeekTokens { get; set; }
+    public int MonthTokens { get; set; }
+    public int ExamTokens { get; set; }
+    public int ResetTokens { get; set; }
+    public int BankCycle { get; set; }
+    public bool Unlimited { get; set; }
+    public DateTime? UnlimitedUntilUtc { get; set; }
+    public List<AccessProduct> Products { get; set; } = [];
+}
+
+public sealed class ActivateAccessTokenRequest
+{
+    public string Token { get; set; } = "";
+    public string OperationId { get; set; } = "";
+}
+
+public sealed class RedeemCreditsRequest
+{
+    public string OperationId { get; set; } = "";
+}
+
+public sealed class ResetQBankRequest
+{
+    public string Confirmation { get; set; } = "";
+    public string OperationId { get; set; } = "";
+}
+
+public sealed class CreateAccessCheckoutRequest
+{
+    public string Sku { get; set; } = "";
+}
+
+public sealed class AccessCheckoutResponse
+{
+    public string PurchaseId { get; set; } = "";
+    public string CheckoutUrl { get; set; } = "";
+    public string Sku { get; set; } = "";
+    public long AmountCents { get; set; }
+}
+
+public static class AccessPurchaseStatus
+{
+    public const string Pending = "pending";
+    public const string Paid = "paid";
+    public const string Failed = "failed";
+    public const string Expired = "expired";
+    public const string Refunded = "refunded";
+}
+
+public sealed class AccessPurchase
+{
+    [BsonId]
+    [BsonRepresentation(BsonType.ObjectId)]
+    public string? Id { get; set; }
+    public string UserId { get; set; } = "";
+    public string Sku { get; set; } = "";
+    public long AmountCents { get; set; }
+    public string Currency { get; set; } = "usd";
+    public string Status { get; set; } = AccessPurchaseStatus.Pending;
+    public string Provider { get; set; } = "stripe";
+    public string ProviderSessionId { get; set; } = "";
+    public string ProviderPaymentId { get; set; } = "";
+    public List<string> ProviderEventIds { get; set; } = [];
+    public bool GrantApplied { get; set; }
+    public DateTime CreatedUtc { get; set; } = DateTime.UtcNow;
+    public DateTime UpdatedUtc { get; set; } = DateTime.UtcNow;
+}
+
+public sealed class AccessPurchaseStatusResponse
+{
+    public string PurchaseId { get; set; } = "";
+    public string Sku { get; set; } = "";
+    public long AmountCents { get; set; }
+    public string Currency { get; set; } = "";
+    public string Status { get; set; } = "";
+}

api/QuestionsApi/Models/QuestionAttempt.cs

@@ -11,6 +11,8 @@ public class QuestionAttempt
 
     public string QuestionExternalId { get; set; } = "";
     public string UserId { get; set; } = "";
+    public int BankCycle { get; set; }
+    public string CompletionId { get; set; } = "";
     public string ChoiceId { get; set; } = "";
     public List<string> PresentedChoiceIds { get; set; } = [];
     public bool TracksPresentation { get; set; }

api/QuestionsApi/Models/QuestionRequests.cs

@@ -45,6 +45,7 @@ public class FlagQuestionRequest
 
 public class FirstQuestionAttemptRequest
 {
+    public string CompletionId { get; set; } = "";
     public string QuestionExternalId { get; set; } = "";
     public string ChoiceId { get; set; } = "";
     public List<string> PresentedChoiceIds { get; set; } = [];

api/QuestionsApi/Models/QuestionResponse.cs

@@ -141,6 +141,7 @@ public class FirstQuestionAttemptResponse
     public Dictionary<string, int> ChoiceSelectionPercentages { get; set; } = [];
     public int QuestionElo { get; set; } = 1000;
     public RatingChangeResponse? Rating { get; set; }
+    public AccessStatusResponse? Access { get; set; }
 }
 
 public class SkipQuestionResponse
@@ -150,6 +151,7 @@ public class SkipQuestionResponse
     public Dictionary<string, int> ChoiceSelectionPercentages { get; set; } = [];
     public int QuestionElo { get; set; } = 1000;
     public RatingChangeResponse? Rating { get; set; }
+    public AccessStatusResponse? Access { get; set; }
 }
 
 public static class RatingCategory

api/QuestionsApi/Program.cs

@@ -66,6 +66,10 @@ builder.Services.Configure<ForwardedHeadersOptions>(options =>
 });
 
 builder.Services.AddSingleton<MongoDatabaseProvider>();
+builder.Services.AddSingleton(TimeProvider.System);
+builder.Services.AddSingleton<AccessStore>();
+builder.Services.AddSingleton<AccessPurchaseStore>();
+builder.Services.AddSingleton<IStripeAccessGateway, StripeAccessGateway>();
 builder.Services.AddSingleton<QuestionStore>();
 builder.Services.AddSingleton<QuestionAttemptStore>();
 builder.Services.AddSingleton<AnswerStatisticsStore>();

api/QuestionsApi/Services/AccessPurchaseStore.cs

@@ -0,0 +1,96 @@
+using MongoDB.Driver;
+using QuestionsApi.Models;
+
+namespace QuestionsApi.Services;
+
+public sealed class AccessPurchaseStore
+{
+    private readonly IMongoCollection<AccessPurchase> _purchases;
+
+    public AccessPurchaseStore(MongoDatabaseProvider mongo)
+    {
+        _purchases = mongo.Database.GetCollection<AccessPurchase>("AccessPurchases");
+        _purchases.Indexes.CreateMany([
+            new CreateIndexModel<AccessPurchase>(
+                Builders<AccessPurchase>.IndexKeys.Ascending(value => value.UserId).Descending(value => value.CreatedUtc)),
+            new CreateIndexModel<AccessPurchase>(
+                Builders<AccessPurchase>.IndexKeys.Ascending(value => value.ProviderSessionId),
+                new CreateIndexOptions<AccessPurchase>
+                {
+                    Unique = true,
+                    PartialFilterExpression = Builders<AccessPurchase>.Filter.Ne(value => value.ProviderSessionId, "")
+                })
+        ]);
+    }
+
+    public async Task<AccessPurchase> CreateAsync(string userId, AccessProduct product)
+    {
+        var purchase = new AccessPurchase
+        {
+            UserId = userId,
+            Sku = product.Sku,
+            AmountCents = product.AmountCents,
+            Currency = product.Currency
+        };
+        await _purchases.InsertOneAsync(purchase);
+        return purchase;
+    }
+
+    public async Task<AccessPurchase?> GetOwnedAsync(string id, string userId) =>
+        await _purchases.Find(value => value.Id == id && value.UserId == userId).FirstOrDefaultAsync();
+
+    public async Task<AccessPurchase?> GetAsync(string id) =>
+        await _purchases.Find(value => value.Id == id).FirstOrDefaultAsync();
+
+    public Task AttachSessionAsync(string id, string sessionId) =>
+        _purchases.UpdateOneAsync(
+            value => value.Id == id && value.Status == AccessPurchaseStatus.Pending,
+            Builders<AccessPurchase>.Update
+                .Set(value => value.ProviderSessionId, sessionId)
+                .Set(value => value.UpdatedUtc, DateTime.UtcNow));
+
+    public Task MarkCheckoutFailedAsync(string id) =>
+        _purchases.UpdateOneAsync(
+            value => value.Id == id && value.Status == AccessPurchaseStatus.Pending,
+            Builders<AccessPurchase>.Update
+                .Set(value => value.Status, AccessPurchaseStatus.Failed)
+                .Set(value => value.UpdatedUtc, DateTime.UtcNow));
+
+    public async Task<AccessPurchase?> ApplyProviderStatusAsync(
+        string id, string sessionId, long amountCents, string currency,
+        string status, string paymentId, string eventId)
+    {
+        if (string.IsNullOrWhiteSpace(id) || string.IsNullOrWhiteSpace(sessionId)) return null;
+        var filters = Builders<AccessPurchase>.Filter;
+        var filter = filters.Eq(value => value.Id, id) &
+            filters.Eq(value => value.AmountCents, amountCents) &
+            filters.Eq(value => value.Currency, currency.ToLowerInvariant()) &
+            (filters.Eq(value => value.ProviderSessionId, sessionId) |
+             filters.Eq(value => value.ProviderSessionId, "")) &
+            filters.Not(filters.AnyEq(value => value.ProviderEventIds, eventId));
+        var update = Builders<AccessPurchase>.Update
+            .Set(value => value.Status, status)
+            .Set(value => value.ProviderSessionId, sessionId)
+            .Set(value => value.ProviderPaymentId, paymentId)
+            .AddToSet(value => value.ProviderEventIds, eventId)
+            .Set(value => value.UpdatedUtc, DateTime.UtcNow);
+        return await _purchases.FindOneAndUpdateAsync(filter, update,
+            new FindOneAndUpdateOptions<AccessPurchase> { ReturnDocument = ReturnDocument.After });
+    }
+
+    public Task MarkGrantAppliedAsync(string id) =>
+        _purchases.UpdateOneAsync(
+            value => value.Id == id && value.Status == AccessPurchaseStatus.Paid,
+            Builders<AccessPurchase>.Update
+                .Set(value => value.GrantApplied, true)
+                .Set(value => value.UpdatedUtc, DateTime.UtcNow));
+
+    public static AccessPurchaseStatusResponse ToStatus(AccessPurchase purchase) => new()
+    {
+        PurchaseId = purchase.Id ?? "",
+        Sku = purchase.Sku,
+        AmountCents = purchase.AmountCents,
+        Currency = purchase.Currency,
+        Status = purchase.Status
+    };
+}

api/QuestionsApi/Services/AccessStore.cs

@@ -0,0 +1,258 @@
+using MongoDB.Driver;
+using QuestionsApi.Models;
+
+namespace QuestionsApi.Services;
+
+public sealed class AccessStore
+{
+    private readonly IMongoCollection<UserAccessAccount> _accounts;
+    private readonly TimeProvider _time;
+
+    public AccessStore(MongoDatabaseProvider mongo, TimeProvider time)
+    {
+        _accounts = mongo.Database.GetCollection<UserAccessAccount>("UserAccessAccounts");
+        _time = time;
+        _accounts.Indexes.CreateOne(new CreateIndexModel<UserAccessAccount>(
+            Builders<UserAccessAccount>.IndexKeys.Ascending(value => value.UserId),
+            new CreateIndexOptions { Unique = true, Name = "uq_access_user" }));
+    }
+
+    public async Task<AccessStatusResponse> GetStatusAsync(string userId, bool bypass = false)
+    {
+        var now = _time.GetUtcNow().UtcDateTime;
+        await EnsureAndCleanAsync(userId, now);
+        var account = await _accounts.Find(value => value.UserId == userId).FirstAsync();
+        return ToStatus(account, now, bypass);
+    }
+
+    public async Task<int> GetBankCycleAsync(string userId)
+    {
+        var now = _time.GetUtcNow().UtcDateTime;
+        await EnsureAndCleanAsync(userId, now);
+        return (await _accounts.Find(value => value.UserId == userId).FirstAsync()).BankCycle;
+    }
+
+    public async Task<bool> CanLoadQuestionAsync(string userId, bool bypass)
+    {
+        if (bypass) return true;
+        var status = await GetStatusAsync(userId);
+        return status.Unlimited || status.QuestionsRemaining > 0;
+    }
+
+    public async Task<bool> ClaimQuestionAsync(string userId, string completionId, string questionExternalId, bool bypass)
+    {
+        if (bypass) return true;
+        var now = _time.GetUtcNow().UtcDateTime;
+        await EnsureAndCleanAsync(userId, now);
+        var filters = Builders<UserAccessAccount>.Filter;
+        var exactClaim = filters.ElemMatch(value => value.RecentUsage,
+            item => item.Id == completionId && item.SubjectId == questionExternalId);
+        if (await _accounts.Find(filters.Eq(value => value.UserId, userId) & exactClaim).AnyAsync())
+            return true;
+        var capacity = new BsonDocumentFilterDefinition<UserAccessAccount>(new MongoDB.Bson.BsonDocument(
+            "$expr", new MongoDB.Bson.BsonDocument("$lt", new MongoDB.Bson.BsonArray
+            {
+                new MongoDB.Bson.BsonDocument("$size", "$RecentUsage"),
+                AccessCatalog.FreeQuestionLimit
+            })));
+        var filter = filters.Eq(value => value.UserId, userId) &
+            filters.Not(filters.ElemMatch(value => value.RecentUsage, item => item.Id == completionId)) &
+            (filters.Gt(value => value.UnlimitedUntilUtc, now) |
+             capacity);
+        var update = Builders<UserAccessAccount>.Update
+            .AddToSet(value => value.RecentUsage, new AccessEvent
+            {
+                Id = completionId,
+                SubjectId = questionExternalId,
+                CreatedUtc = now
+            })
+            .Set(value => value.UpdatedUtc, now)
+            .Inc(value => value.Revision, 1);
+        if ((await _accounts.UpdateOneAsync(filter, update)).MatchedCount == 1)
+            return true;
+        return await _accounts.Find(filters.Eq(value => value.UserId, userId) & exactClaim).AnyAsync();
+    }
+
+    public async Task<bool> TryAwardCreditAsync(string userId, string operationId)
+    {
+        var now = _time.GetUtcNow().UtcDateTime;
+        await EnsureAndCleanAsync(userId, now);
+        var filters = Builders<UserAccessAccount>.Filter;
+        var capacity = new BsonDocumentFilterDefinition<UserAccessAccount>(new MongoDB.Bson.BsonDocument(
+            "$expr", new MongoDB.Bson.BsonDocument("$lt", new MongoDB.Bson.BsonArray
+            {
+                new MongoDB.Bson.BsonDocument("$size", "$RecentCredits"),
+                AccessCatalog.CreditEarningLimit
+            })));
+        var filter = filters.Eq(value => value.UserId, userId) &
+            filters.Not(filters.AnyEq(value => value.AppliedOperationIds, operationId)) &
+            capacity;
+        var update = Builders<UserAccessAccount>.Update
+            .Inc(value => value.Credits, 1)
+            .AddToSet(value => value.AppliedOperationIds, operationId)
+            .Push(value => value.RecentCredits, new AccessEvent { Id = operationId, CreatedUtc = now })
+            .Set(value => value.UpdatedUtc, now)
+            .Inc(value => value.Revision, 1);
+        return (await _accounts.UpdateOneAsync(filter, update)).ModifiedCount == 1;
+    }
+
+    public Task<AccessStatusResponse?> RedeemCreditsAsync(string userId, string operationId) =>
+        SpendAndExtendAsync(userId, operationId, AccessCatalog.DayPassCreditCost, null, TimeSpan.FromHours(24));
+
+    public Task<AccessStatusResponse?> ActivateTokenAsync(string userId, string operationId, string token) =>
+        token.Trim().ToLowerInvariant() switch
+        {
+            "day" => SpendAndExtendAsync(userId, operationId, 0, nameof(UserAccessAccount.DayTokens), TimeSpan.FromHours(24)),
+            "week" => SpendAndExtendAsync(userId, operationId, 0, nameof(UserAccessAccount.WeekTokens), TimeSpan.FromHours(168)),
+            "month" => SpendAndExtendAsync(userId, operationId, 0, nameof(UserAccessAccount.MonthTokens), TimeSpan.FromHours(720)),
+            _ => Task.FromResult<AccessStatusResponse?>(null)
+        };
+
+    public async Task<bool> TryConsumeExamTokenAsync(string userId, string operationId)
+    {
+        var now = _time.GetUtcNow().UtcDateTime;
+        await EnsureAndCleanAsync(userId, now);
+        var filters = Builders<UserAccessAccount>.Filter;
+        var filter = filters.Eq(value => value.UserId, userId) &
+            filters.Gt(value => value.ExamTokens, 0) &
+            filters.Not(filters.AnyEq(value => value.AppliedOperationIds, operationId));
+        var update = Builders<UserAccessAccount>.Update
+            .Inc(value => value.ExamTokens, -1)
+            .AddToSet(value => value.AppliedOperationIds, operationId)
+            .Set(value => value.UpdatedUtc, now)
+            .Inc(value => value.Revision, 1);
+        return (await _accounts.UpdateOneAsync(filter, update)).ModifiedCount == 1;
+    }
+
+    public async Task RefundExamTokenAsync(string userId, string operationId)
+    {
+        var now = _time.GetUtcNow().UtcDateTime;
+        var filter = Builders<UserAccessAccount>.Filter.Eq(value => value.UserId, userId) &
+            Builders<UserAccessAccount>.Filter.AnyEq(value => value.AppliedOperationIds, operationId);
+        await _accounts.UpdateOneAsync(filter, Builders<UserAccessAccount>.Update
+            .Inc(value => value.ExamTokens, 1)
+            .Pull(value => value.AppliedOperationIds, operationId)
+            .Set(value => value.UpdatedUtc, now));
+    }
+
+    public async Task<int?> ApplyResetAsync(string userId, string operationId)
+    {
+        var now = _time.GetUtcNow().UtcDateTime;
+        await EnsureAndCleanAsync(userId, now);
+        var filters = Builders<UserAccessAccount>.Filter;
+        var filter = filters.Eq(value => value.UserId, userId) &
+            filters.Gt(value => value.ResetTokens, 0) &
+            filters.Not(filters.AnyEq(value => value.AppliedOperationIds, operationId));
+        var updated = await _accounts.FindOneAndUpdateAsync(
+            filter,
+            Builders<UserAccessAccount>.Update
+                .Inc(value => value.ResetTokens, -1)
+                .Inc(value => value.BankCycle, 1)
+                .AddToSet(value => value.AppliedOperationIds, operationId)
+                .Set(value => value.UpdatedUtc, now)
+                .Inc(value => value.Revision, 1),
+            new FindOneAndUpdateOptions<UserAccessAccount> { ReturnDocument = ReturnDocument.After });
+        return updated?.BankCycle;
+    }
+
+    public async Task<bool> ApplyProductGrantAsync(string userId, AccessProduct product, string operationId)
+    {
+        var now = _time.GetUtcNow().UtcDateTime;
+        await EnsureAndCleanAsync(userId, now);
+        var filters = Builders<UserAccessAccount>.Filter;
+        var filter = filters.Eq(value => value.UserId, userId) &
+            filters.Not(filters.AnyEq(value => value.AppliedOperationIds, operationId));
+        var update = Builders<UserAccessAccount>.Update
+            .AddToSet(value => value.AppliedOperationIds, operationId)
+            .Set(value => value.UpdatedUtc, now)
+            .Inc(value => value.Revision, 1);
+        update = product.Grant switch
+        {
+            AccessGrant.DayToken => update.Inc(value => value.DayTokens, 1),
+            AccessGrant.WeekToken => update.Inc(value => value.WeekTokens, 1),
+            AccessGrant.MonthToken => update.Inc(value => value.MonthTokens, 1),
+            AccessGrant.ExamToken => update.Inc(value => value.ExamTokens, 1),
+            AccessGrant.ResetToken => update.Inc(value => value.ResetTokens, 1),
+            _ => update
+        };
+        return (await _accounts.UpdateOneAsync(filter, update)).ModifiedCount == 1;
+    }
+
+    private async Task<AccessStatusResponse?> SpendAndExtendAsync(
+        string userId, string operationId, int credits, string? tokenProperty, TimeSpan duration)
+    {
+        if (string.IsNullOrWhiteSpace(operationId)) return null;
+        var now = _time.GetUtcNow().UtcDateTime;
+        await EnsureAndCleanAsync(userId, now);
+        var filters = Builders<UserAccessAccount>.Filter;
+        var filter = filters.Eq(value => value.UserId, userId) &
+            filters.Not(filters.AnyEq(value => value.AppliedOperationIds, operationId));
+        if (credits > 0) filter &= filters.Gte(value => value.Credits, credits);
+        filter &= tokenProperty switch
+        {
+            nameof(UserAccessAccount.DayTokens) => filters.Gt(value => value.DayTokens, 0),
+            nameof(UserAccessAccount.WeekTokens) => filters.Gt(value => value.WeekTokens, 0),
+            nameof(UserAccessAccount.MonthTokens) => filters.Gt(value => value.MonthTokens, 0),
+            _ => FilterDefinition<UserAccessAccount>.Empty
+        };
+        var account = await _accounts.Find(filter).FirstOrDefaultAsync();
+        if (account is null) return null;
+        var start = account.UnlimitedUntilUtc is { } expiry && expiry > now ? expiry : now;
+        var update = Builders<UserAccessAccount>.Update
+            .Set(value => value.UnlimitedUntilUtc, start.Add(duration))
+            .AddToSet(value => value.AppliedOperationIds, operationId)
+            .Set(value => value.UpdatedUtc, now)
+            .Inc(value => value.Revision, 1);
+        if (credits > 0) update = update.Inc(value => value.Credits, -credits);
+        update = tokenProperty switch
+        {
+            nameof(UserAccessAccount.DayTokens) => update.Inc(value => value.DayTokens, -1),
+            nameof(UserAccessAccount.WeekTokens) => update.Inc(value => value.WeekTokens, -1),
+            nameof(UserAccessAccount.MonthTokens) => update.Inc(value => value.MonthTokens, -1),
+            _ => update
+        };
+        var applied = await _accounts.UpdateOneAsync(
+            filter & filters.Eq(value => value.Revision, account.Revision), update);
+        return applied.ModifiedCount == 1 ? await GetStatusAsync(userId) : null;
+    }
+
+    private async Task EnsureAndCleanAsync(string userId, DateTime now)
+    {
+        await _accounts.UpdateOneAsync(
+            value => value.UserId == userId,
+            Builders<UserAccessAccount>.Update
+                .SetOnInsert(value => value.UserId, userId)
+                .SetOnInsert(value => value.UpdatedUtc, now),
+            new UpdateOptions { IsUpsert = true });
+        var cutoff = now.AddHours(-24);
+        await _accounts.UpdateOneAsync(
+            value => value.UserId == userId,
+            Builders<UserAccessAccount>.Update
+                .PullFilter(value => value.RecentUsage, item => item.CreatedUtc <= cutoff)
+                .PullFilter(value => value.RecentCredits, item => item.CreatedUtc <= cutoff));
+    }
+
+    private static AccessStatusResponse ToStatus(UserAccessAccount account, DateTime now, bool bypass)
+    {
+        var unlimited = bypass || account.UnlimitedUntilUtc > now;
+        var used = account.RecentUsage.Count;
+        return new AccessStatusResponse
+        {
+            QuestionsUsed = used,
+            QuestionsRemaining = unlimited ? AccessCatalog.FreeQuestionLimit : Math.Max(0, AccessCatalog.FreeQuestionLimit - used),
+            NextQuestionAvailableUtc = !unlimited && used >= AccessCatalog.FreeQuestionLimit
+                ? account.RecentUsage.MinBy(value => value.CreatedUtc)?.CreatedUtc.AddHours(24)
+                : null,
+            Credits = account.Credits,
+            DayTokens = account.DayTokens,
+            WeekTokens = account.WeekTokens,
+            MonthTokens = account.MonthTokens,
+            ExamTokens = account.ExamTokens,
+            ResetTokens = account.ResetTokens,
+            BankCycle = account.BankCycle,
+            Unlimited = unlimited,
+            UnlimitedUntilUtc = account.UnlimitedUntilUtc,
+            Products = AccessCatalog.Products.Values.ToList()
+        };
+    }
+}

api/QuestionsApi/Services/DashboardStore.cs

@@ -20,6 +20,7 @@ public sealed class DashboardStore
     private readonly FlashcardScheduleStore _flashcardSchedules;
     private readonly RatingStore _ratingStore;
     private readonly CcsRatingStore _ccsRatingStore;
+    private readonly AccessStore _accessStore;
     private readonly IMongoCollection<UserRating> _ratings;
 
     public static readonly string[] Step3Systems =
@@ -48,7 +49,8 @@ public sealed class DashboardStore
         FlashcardStudyService flashcards,
         FlashcardScheduleStore flashcardSchedules,
         RatingStore ratingStore,
-        CcsRatingStore ccsRatingStore)
+        CcsRatingStore ccsRatingStore,
+        AccessStore accessStore)
     {
         _attempts = mongo.Database.GetCollection<QuestionAttempt>("QuestionAttempts");
         _ccsRatings = mongo.Database.GetCollection<CcsUserRating>("CcsUserRatings");
@@ -65,6 +67,7 @@ public sealed class DashboardStore
         _flashcardSchedules = flashcardSchedules;
         _ratingStore = ratingStore;
         _ccsRatingStore = ccsRatingStore;
+        _accessStore = accessStore;
     }
 
     public async Task<DashboardResponse> GetAsync(string userId, DateTime nowUtc)
@@ -72,7 +75,9 @@ public sealed class DashboardStore
         var today = nowUtc.Date;
         var trendStart = today.AddDays(-29);
         var weekStart = today.AddDays(-6);
-        var attemptsTask = _attempts.Find(value => value.UserId == userId).ToListAsync();
+        var bankCycleTask = _accessStore.GetBankCycleAsync(userId);
+        var bankCycle = await bankCycleTask;
+        var attemptsTask = _attempts.Find(value => value.UserId == userId && value.BankCycle == bankCycle).ToListAsync();
         var ratingTask = _ratingStore.GetOrInitializeHistoryAsync(userId, nowUtc);
         var ccsRatingTask = _ccsRatingStore.GetOrInitializeHistoryAsync(userId, nowUtc);
         var ccsAttemptsTask = _ccsAttempts.Find(value => value.UserId == userId && value.CreatedUtc >= trendStart).ToListAsync();

api/QuestionsApi/Services/QuestionAttemptStore.cs

@@ -15,12 +15,20 @@ public class QuestionAttemptStore
     {
         _col = mongo.Database.GetCollection<QuestionAttempt>("QuestionAttempts");
 
+        try
+        {
+            _col.Indexes.DropOne("QuestionExternalId_1_UserId_1");
+        }
+        catch (MongoCommandException exception) when (exception.Code is 26 or 27)
+        {
+        }
         var firstAttemptIndex = Builders<QuestionAttempt>.IndexKeys
             .Ascending(a => a.QuestionExternalId)
-            .Ascending(a => a.UserId);
+            .Ascending(a => a.UserId)
+            .Ascending(a => a.BankCycle);
         _col.Indexes.CreateOne(new CreateIndexModel<QuestionAttempt>(
             firstAttemptIndex,
-            new CreateIndexOptions { Unique = true }));
+            new CreateIndexOptions { Unique = true, Name = "uq_question_user_cycle" }));
 
         var questionIndex = Builders<QuestionAttempt>.IndexKeys.Ascending(a => a.QuestionExternalId);
         _col.Indexes.CreateOne(new CreateIndexModel<QuestionAttempt>(questionIndex));
@@ -38,12 +46,16 @@ public class QuestionAttemptStore
         bool isCorrect,
         bool isSkip = false,
         IReadOnlyCollection<string>? presentedChoiceIds = null,
-        int durationSeconds = 0)
+        int durationSeconds = 0,
+        int bankCycle = 0,
+        string completionId = "")
     {
         var attempt = new QuestionAttempt
         {
             QuestionExternalId = questionExternalId,
             UserId = userId,
+            BankCycle = bankCycle,
+            CompletionId = completionId,
             ChoiceId = choiceId,
             PresentedChoiceIds = presentedChoiceIds?.ToList() ?? [],
             TracksPresentation = presentedChoiceIds is { Count: > 0 },
@@ -63,7 +75,7 @@ public class QuestionAttemptStore
         catch (MongoWriteException ex) when (ex.WriteError.Category == ServerErrorCategory.DuplicateKey)
         {
             var existing = await _col
-                .Find(a => a.QuestionExternalId == questionExternalId && a.UserId == userId)
+                .Find(a => a.QuestionExternalId == questionExternalId && a.UserId == userId && a.BankCycle == bankCycle)
                 .FirstAsync();
             return new QuestionAttemptRecordResult { Inserted = false, Attempt = existing };
         }
@@ -75,10 +87,13 @@ public class QuestionAttemptStore
             Builders<QuestionAttempt>.Filter.Gte(attempt => attempt.CreatedUtc, sinceUtc))
             .ToListAsync();
 
-    public Task<List<string>> GetUserQuestionIdsAsync(string userId) =>
+    public Task<List<string>> GetUserQuestionIdsAsync(string userId, int? bankCycle = null) =>
         _col.Distinct(
             attempt => attempt.QuestionExternalId,
-            Builders<QuestionAttempt>.Filter.Eq(attempt => attempt.UserId, userId))
+            Builders<QuestionAttempt>.Filter.Eq(attempt => attempt.UserId, userId) &
+            (bankCycle is null
+                ? FilterDefinition<QuestionAttempt>.Empty
+                : Builders<QuestionAttempt>.Filter.Eq(attempt => attempt.BankCycle, bankCycle.Value)))
             .ToListAsync();
 
     public IMongoCollection<QuestionAttempt> Collection => _col;

api/QuestionsApi/Services/RatingStore.cs

@@ -41,6 +41,18 @@ public class RatingStore
         return await EnsureHistoryBaselineAsync(rating, nowUtc);
     }
 
+    public Task ResetUserAsync(string userId, DateTime nowUtc) =>
+        _users.UpdateOneAsync(
+            rating => rating.UserId == userId,
+            Builders<UserRating>.Update
+                .Set(rating => rating.OverallElo, BaseElo)
+                .Set(rating => rating.RatedQuestionCount, 0)
+                .Set(rating => rating.CategoryElos, DefaultCategoryElos())
+                .Set(rating => rating.HistoryBaselineElo, null)
+                .Set(rating => rating.HistoryStartedUtc, null)
+                .Set(rating => rating.UpdatedUtc, nowUtc),
+            new UpdateOptions { IsUpsert = false });
+
     public async Task<Dictionary<string, int>> GetQuestionElosAsync(IEnumerable<string> externalIds)
     {
         var ids = externalIds.Where(id => !string.IsNullOrWhiteSpace(id)).Distinct().ToList();

api/QuestionsApi/Services/StripeAccessGateway.cs

@@ -0,0 +1,63 @@
+using QuestionsApi.Models;
+using Stripe;
+using Stripe.Checkout;
+
+namespace QuestionsApi.Services;
+
+public interface IStripeAccessGateway
+{
+    Task<StripeCheckoutResult> CreateCheckoutAsync(AccessPurchase purchase, AccessProduct product, CancellationToken cancellationToken);
+}
+
+public sealed class StripeAccessGateway(IConfiguration configuration) : IStripeAccessGateway
+{
+    public async Task<StripeCheckoutResult> CreateCheckoutAsync(
+        AccessPurchase purchase, AccessProduct product, CancellationToken cancellationToken)
+    {
+        var secretKey = configuration["Stripe:SecretKey"];
+        if (string.IsNullOrWhiteSpace(secretKey)) throw new InvalidOperationException("Stripe secret key is not configured.");
+        var successUrl = configuration["Stripe:AccessSuccessUrl"]
+            ?? "https://doctor.ranaze.com/donation-complete.html?session_id={CHECKOUT_SESSION_ID}";
+        var cancelUrl = configuration["Stripe:AccessCancelUrl"]
+            ?? "https://doctor.ranaze.com/donation-canceled.html";
+        var metadata = new Dictionary<string, string>
+        {
+            ["access_purchase_id"] = purchase.Id ?? "",
+            ["access_sku"] = product.Sku,
+            ["user_id"] = purchase.UserId
+        };
+        var service = new SessionService(new StripeClient(secretKey));
+        var session = await service.CreateAsync(new SessionCreateOptions
+        {
+            Mode = "payment",
+            SuccessUrl = successUrl,
+            CancelUrl = cancelUrl,
+            ClientReferenceId = purchase.Id,
+            CustomerCreation = "always",
+            BillingAddressCollection = "auto",
+            AutomaticTax = new SessionAutomaticTaxOptions { Enabled = true },
+            Metadata = metadata,
+            PaymentIntentData = new SessionPaymentIntentDataOptions { Metadata = metadata },
+            LineItems =
+            [
+                new SessionLineItemOptions
+                {
+                    Quantity = 1,
+                    PriceData = new SessionLineItemPriceDataOptions
+                    {
+                        Currency = product.Currency,
+                        UnitAmount = product.AmountCents,
+                        ProductData = new SessionLineItemPriceDataProductDataOptions
+                        {
+                            Name = product.Name,
+                            Description = "A manually activated RanaZe access entitlement."
+                        }
+                    }
+                }
+            ]
+        }, null, cancellationToken);
+        if (string.IsNullOrWhiteSpace(session.Id) || string.IsNullOrWhiteSpace(session.Url))
+            throw new InvalidOperationException("Stripe did not return a checkout URL.");
+        return new StripeCheckoutResult(session.Id, session.Url);
+    }
+}

api/QuestionsApi/Services/UserProfileStore.cs

@@ -19,7 +19,8 @@ public sealed class UserProfileStore
         "Step3Outcomes", "QuestionReports", "CcsCaseReports", "AppFeedback", "UserStudyProfiles",
         "ExternalIdentities", "ExternalAuthTransactions",
         "FlashcardDecks", "FlashcardNotes", "FlashcardSchedules", "FlashcardReviewLogs",
-        "FlashcardMediaAssets", "FlashcardSettings", "FlashcardImportPreviews"
+        "FlashcardMediaAssets", "FlashcardSettings", "FlashcardImportPreviews",
+        "UserAccessAccounts", "AccessPurchases"
     ];
 
     public UserProfileStore(MongoDatabaseProvider mongo)

api/QuestionsApi/appsettings.Development.json

@@ -4,7 +4,9 @@
   "AnswerStatistics": { "ReconcileSeconds": 300 },
   "Stripe": {
     "SuccessUrl": "https://doctor.ranaze.com/donation-complete.html?session_id={CHECKOUT_SESSION_ID}",
-    "CancelUrl": "https://doctor.ranaze.com/donation-canceled.html"
+    "CancelUrl": "https://doctor.ranaze.com/donation-canceled.html",
+    "AccessSuccessUrl": "https://doctor.ranaze.com/donation-complete.html?session_id={CHECKOUT_SESSION_ID}",
+    "AccessCancelUrl": "https://doctor.ranaze.com/donation-canceled.html"
   },
   "Jwt": { "Key": "SuperUltraSecureJwtKeyWithAtLeast32Chars!!", "Issuer": "promiscuity", "Audience": "promiscuity-auth-api" },
   "PasswordReset": {

api/QuestionsApi/appsettings.json

@@ -4,7 +4,9 @@
   "AnswerStatistics": { "ReconcileSeconds": 300 },
   "Stripe": {
     "SuccessUrl": "https://doctor.ranaze.com/donation-complete.html?session_id={CHECKOUT_SESSION_ID}",
-    "CancelUrl": "https://doctor.ranaze.com/donation-canceled.html"
+    "CancelUrl": "https://doctor.ranaze.com/donation-canceled.html",
+    "AccessSuccessUrl": "https://doctor.ranaze.com/donation-complete.html?session_id={CHECKOUT_SESSION_ID}",
+    "AccessCancelUrl": "https://doctor.ranaze.com/donation-canceled.html"
   },
   "Steam": {
     "Realm": "https://s3q.ranaze.com",