feat: implement Stripe product configuration and add token-based input validation using Microsoft.ML.Tokenizers

src/NexusReader.Infrastructure/Configuration/AiSettings.cs

@@ -6,7 +6,12 @@ public class AiSettings
 
     public string ApiKey { get; set; } = string.Empty;
     public string Model { get; set; } = "gemini-1.5-flash";
-    public int MaxInputLength { get; set; } = 15000;
+    
+    /// <summary>
+    /// Maximum number of tokens allowed for input.
+    /// </summary>
+    public int MaxInputTokens { get; set; } = 15000;
+    
     public int MaxOutputTokens { get; set; } = 1000;
     public int RetryAttempts { get; set; } = 3;
     public double Temperature { get; set; } = 0.1;

src/NexusReader.Infrastructure/Configuration/StripeSettings.cs

@@ -0,0 +1,9 @@
+namespace NexusReader.Infrastructure.Configuration;
+
+public record StripeSettings
+{
+    public const string SectionName = "Stripe";
+    public string ProProductId { get; init; } = string.Empty;
+    public string BasicProductId { get; init; } = string.Empty;
+    public string FreeProductId { get; init; } = string.Empty;
+}

src/NexusReader.Infrastructure/DependencyInjection.cs

@@ -35,6 +35,7 @@ public static class DependencyInjection
         }
 
         services.Configure<AiSettings>(configuration.GetSection(AiSettings.SectionName));
+        services.Configure<StripeSettings>(configuration.GetSection(StripeSettings.SectionName));
         var aiSettings = configuration.GetSection(AiSettings.SectionName).Get<AiSettings>() ?? new AiSettings();
 
         Console.WriteLine($"[Infrastructure] AI Configured: Model={aiSettings.Model}, KeyPresent={!string.IsNullOrWhiteSpace(aiSettings.ApiKey) && aiSettings.ApiKey != "PLACEHOLDER"}");

src/NexusReader.Infrastructure/NexusReader.Infrastructure.csproj

@@ -15,6 +15,8 @@
     <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="10.0.7" />
     <PackageReference Include="Microsoft.Extensions.AI" Version="10.5.0" />
     <PackageReference Include="Microsoft.Extensions.Resilience" Version="10.5.0" />
+    <PackageReference Include="Microsoft.ML.Tokenizers" Version="2.0.0" />
+    <PackageReference Include="Microsoft.ML.Tokenizers.Data.Cl100kBase" Version="2.0.0" />
     <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="10.0.0" />
     <PackageReference Include="Polly" Version="8.6.6" />
     <PackageReference Include="Polly.Extensions.Http" Version="3.0.0" />

src/NexusReader.Infrastructure/Services/BillingService.cs

@@ -1,7 +1,10 @@
 using Microsoft.AspNetCore.Identity;
 using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
 using NexusReader.Application.Abstractions.Services;
 using NexusReader.Domain.Entities;
+using NexusReader.Infrastructure.Configuration;
 using NexusReader.Infrastructure.Persistence;
 
 namespace NexusReader.Infrastructure.Services;
@@ -10,44 +13,83 @@ public class BillingService : IBillingService
 {
     private readonly AppDbContext _dbContext;
     private readonly UserManager<NexusUser> _userManager;
+    private readonly StripeSettings _stripeSettings;
+    private readonly ILogger<BillingService> _logger;
 
-    public BillingService(AppDbContext dbContext, UserManager<NexusUser> userManager)
+    public BillingService(
+        AppDbContext dbContext, 
+        UserManager<NexusUser> userManager,
+        IOptions<StripeSettings> stripeSettings,
+        ILogger<BillingService> logger)
     {
         _dbContext = dbContext;
         _userManager = userManager;
+        _stripeSettings = stripeSettings.Value;
+        _logger = logger;
     }
 
     public async Task<bool> HandleSubscriptionUpdatedAsync(string customerEmail, string stripeProductId)
     {
         var user = await _userManager.FindByEmailAsync(customerEmail);
-        if (user == null) return false;
+        if (user == null) 
+        {
+            _logger.LogWarning("Attempted to update subscription for non-existent user: {Email}", customerEmail);
+            return false;
+        }
 
-        // Map Stripe Product IDs to Nexus Plans
-        // These IDs would typically come from configuration
-        if (stripeProductId.Contains("pro")) 
+        if (stripeProductId == _stripeSettings.ProProductId)
         {
             user.CurrentPlan = "Pro";
             user.AITokenLimit = 50000;
         }
-        else if (stripeProductId.Contains("basic"))
+        else if (stripeProductId == _stripeSettings.BasicProductId)
         {
             user.CurrentPlan = "Basic";
             user.AITokenLimit = 10000;
         }
+        else if (stripeProductId == _stripeSettings.FreeProductId || string.IsNullOrEmpty(stripeProductId))
+        {
+            user.CurrentPlan = "Free";
+            user.AITokenLimit = 1000;
+        }
+        else
+        {
+            _logger.LogWarning("Unrecognized Stripe Product ID: {ProductId} for user {Email}. Falling back to Free tier.", stripeProductId, customerEmail);
+            user.CurrentPlan = "Free";
+            user.AITokenLimit = 1000;
+        }
+
+        var result = await _userManager.UpdateAsync(user);
+        if (!result.Succeeded)
+        {
+            _logger.LogError("Failed to update user {Email} after subscription change: {Errors}", 
+                customerEmail, string.Join(", ", result.Errors.Select(e => e.Description)));
+            return false;
+        }
 
-        await _userManager.UpdateAsync(user);
         return true;
     }
 
     public async Task<bool> HandleSubscriptionDeletedAsync(string customerEmail)
     {
         var user = await _userManager.FindByEmailAsync(customerEmail);
-        if (user == null) return false;
+        if (user == null)
+        {
+            _logger.LogWarning("Attempted to delete subscription for non-existent user: {Email}", customerEmail);
+            return false;
+        }
 
         user.CurrentPlan = "Free";
         user.AITokenLimit = 1000; // Reset to free limit
         
-        await _userManager.UpdateAsync(user);
+        var result = await _userManager.UpdateAsync(user);
+        if (!result.Succeeded)
+        {
+            _logger.LogError("Failed to reset user {Email} to Free tier after subscription deletion: {Errors}", 
+                customerEmail, string.Join(", ", result.Errors.Select(e => e.Description)));
+            return false;
+        }
+
         return true;
     }
 }

src/NexusReader.Infrastructure/Services/KnowledgeService.cs

@@ -2,6 +2,7 @@ using System.Text.Json;
 using FluentResults;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.AI;
+using Microsoft.ML.Tokenizers;
 using NexusReader.Application.Abstractions.Services;
 using NexusReader.Application.DTOs.AI;
 using NexusReader.Domain.Entities;
@@ -20,6 +21,7 @@ public class KnowledgeService : IKnowledgeService
     private readonly AppDbContext _dbContext;
     private readonly ResiliencePipeline _retryPipeline;
     private readonly AiSettings _settings;
+    private readonly Tokenizer _tokenizer;
     private const string PromptVersion = "1.0";
 
     public KnowledgeService(
@@ -32,6 +34,9 @@ public class KnowledgeService : IKnowledgeService
         _dbContext = dbContext;
         _retryPipeline = pipelineProvider.GetPipeline("ai-retry");
         _settings = settings.Value;
+        // Use Tiktoken (cl100k_base) which is a standard for modern LLMs and provides 
+        // a very reliable estimation for token usage in Gemini-based workloads.
+        _tokenizer = TiktokenTokenizer.CreateForModel("gpt-4");
     }
 
     public async Task<Result<KnowledgePacket>> GetKnowledgeAsync(string text, CancellationToken cancellationToken = default)
@@ -59,10 +64,11 @@ public class KnowledgeService : IKnowledgeService
         Console.WriteLine($"[KnowledgeService] Starting extraction ({cacheSuffix}) for text sample: {text.Substring(0, Math.Min(text.Length, 50))}...");
 
         var normalizedText = ContentHasher.Normalize(text);
-        if (normalizedText.Length > _settings.MaxInputLength)
+        
+        var tokenCount = EstimateTokenCount(normalizedText);
+        if (tokenCount > _settings.MaxInputTokens)
         {
-            normalizedText = normalizedText.Substring(0, _settings.MaxInputLength);
-            Console.WriteLine($"[KnowledgeService] WARNING: Input text truncated to {_settings.MaxInputLength} chars.");
+            return Result.Fail($"Input exceeds maximum token limit. Estimated tokens: {tokenCount}, limit: {_settings.MaxInputTokens}.");
         }
 
         var hash = ContentHasher.ComputeHash(normalizedText) + "_" + cacheSuffix;
@@ -151,4 +157,10 @@ public class KnowledgeService : IKnowledgeService
             return Result.Fail($"Failed to clear cache: {ex.Message}");
         }
     }
+
+    private int EstimateTokenCount(string text)
+    {
+        if (string.IsNullOrEmpty(text)) return 0;
+        return _tokenizer.CountTokens(text);
+    }
 }

src/NexusReader.Web.New/appsettings.json

@@ -1,7 +1,10 @@
 {
   "Stripe": {
     "ApiKey": "sk_test_placeholder",
-    "WebhookSecret": "whsec_placeholder"
+    "WebhookSecret": "whsec_placeholder",
+    "ProProductId": "prod_Pro123",
+    "BasicProductId": "prod_Basic456",
+    "FreeProductId": "prod_Free789"
   },
   "Logging": {
     "LogLevel": {
@@ -24,6 +27,7 @@
     "Google": {
       "ApiKey": "PLACEHOLDER",
       "Model": "gemini-2.5-flash-lite",
+      "MaxInputTokens": 15000,
       "MaxOutputTokens": 8192
     }
   },