AccessQueueService/Data/IAccessQueueRepo.cs

@@ -1,10 +1,12 @@
-using AccessQueueService.Models;
+using System.Runtime.Serialization;
+using AccessQueueService.Models;
 using Microsoft.Extensions.Configuration;
 
 namespace AccessQueueService.Data
 {
     public interface IAccessQueueRepo
     {
+        public string ToState();
         public int GetUnexpiredTicketsCount();
         public int GetActiveTicketsCount(DateTime activeCutoff);
         public int GetQueueCount();

AccessQueueService/Data/TakeANumberAccessQueueRepo.cs

@@ -1,16 +1,18 @@
-using AccessQueueService.Models;
+using System.Runtime.Serialization;
+using System.Text.Json;
+using AccessQueueService.Models;
 using Microsoft.Extensions.Configuration;
 
 namespace AccessQueueService.Data
 {
     public class TakeANumberAccessQueueRepo : IAccessQueueRepo
     {
-        private readonly Dictionary<string, AccessTicket> _accessTickets = [];
+        private Dictionary<string, AccessTicket> _accessTickets = [];
         private Dictionary<string, ulong> _queueNumbers = [];
         private Dictionary<ulong, AccessTicket> _accessQueue = [];
 
         internal ulong _nowServing = 0;
-        internal ulong _nextUnusedTicket = 0; 
+        internal ulong _nextUnusedTicket = 0;
 
         public int GetUnexpiredTicketsCount() => _accessTickets.Count(t => t.Value.ExpiresOn > DateTime.UtcNow);
         public int GetActiveTicketsCount(DateTime activeCutoff) => _accessTickets
@@ -18,21 +20,21 @@ namespace AccessQueueService.Data
         public int GetQueueCount() => (int)(_nextUnusedTicket - _nowServing);
         public int GetRequestsAhead(string userId)
         {
-            if(_queueNumbers.TryGetValue(userId, out var queueNumber))
+            if (_queueNumbers.TryGetValue(userId, out var queueNumber))
             {
-                if(_accessQueue.TryGetValue(queueNumber, out var ticket))
+                if (_accessQueue.TryGetValue(queueNumber, out var ticket))
                 {
                     ticket.LastActive = DateTime.UtcNow;
                     return queueNumber >= _nowServing ? (int)(queueNumber - _nowServing) : -1;
                 }
             }
             return -1;
-            
+
         }
 
         public void Enqueue(AccessTicket ticket)
         {
-            if(_nextUnusedTicket >= long.MaxValue)
+            if (_nextUnusedTicket >= long.MaxValue)
             {
                 // Prevent overflow
                 Optimize();
@@ -61,7 +63,7 @@ namespace AccessQueueService.Data
             var activeCutoff = now.AddSeconds(-activeSeconds);
             var numberOfActiveUsers = _accessTickets.Count(t => t.Value.ExpiresOn > now && t.Value.LastActive > activeCutoff);
             var openSpots = capacityLimit - numberOfActiveUsers;
-            if(openSpots <= 0)
+            if (openSpots <= 0)
             {
                 return true;
             }
@@ -102,7 +104,7 @@ namespace AccessQueueService.Data
 
         public bool RemoveUser(string userId)
         {
-            if(_queueNumbers.TryGetValue(userId, out var queueNumber))
+            if (_queueNumbers.TryGetValue(userId, out var queueNumber))
             {
                 _accessQueue.Remove(queueNumber);
                 _queueNumbers.Remove(userId);
@@ -126,5 +128,51 @@ namespace AccessQueueService.Data
             _nowServing = 0;
             _nextUnusedTicket = newIndex;
         }
+
+        public string ToState()
+        {
+            var state = new TakeANumberAccessQueueRepoState
+            {
+                AccessTickets = _accessTickets,
+                AccessQueue = _accessQueue,
+            };
+
+            return JsonSerializer.Serialize(state);
+        }
+
+        public static TakeANumberAccessQueueRepo FromState(string stateJson)
+        {
+            var state = JsonSerializer.Deserialize<TakeANumberAccessQueueRepoState?>(stateJson);
+            if (state?.AccessTickets == null || state?.AccessQueue == null)
+            {
+                return new();
+            }
+
+            var _accessTickets = state.AccessTickets;
+            var _accessQueue = state.AccessQueue;
+            var _nextUnusedTicket = 0ul;
+            var _nowServing = ulong.MaxValue;
+            Dictionary<string, ulong> _queueNumbers = [];
+            foreach (var queueItem in state.AccessQueue)
+            {
+                _queueNumbers.Add(queueItem.Value.UserId, queueItem.Key);
+                _nextUnusedTicket = Math.Max(_nextUnusedTicket, queueItem.Key);
+                _nowServing = Math.Min(_nowServing, queueItem.Key);
+            }
+
+            if (_nowServing == ulong.MaxValue)
+            {
+                _nowServing = 0;
+            }
+
+            return new()
+            {
+                _accessQueue = _accessQueue,
+                _accessTickets = _accessTickets,
+                _nextUnusedTicket = _nextUnusedTicket,
+                _nowServing = _nowServing,
+                _queueNumbers = _queueNumbers
+            };
+        }
     }
 }

AccessQueueService/Models/TakeANumberAccessQueueRepoState.cs

@@ -0,0 +1,8 @@
+namespace AccessQueueService.Models
+{
+    public class TakeANumberAccessQueueRepoState
+    {
+        public Dictionary<string, AccessTicket> AccessTickets { get; set; } = [];
+        public Dictionary<ulong, AccessTicket> AccessQueue { get; set; } = [];
+    }
+}

AccessQueueService/Program.cs

@@ -17,8 +17,25 @@ builder.Services.AddControllers();
 builder.Services.AddEndpointsApiExplorer();
 builder.Services.AddSwaggerGen();
 builder.Services.AddSingleton<IAccessService, AccessService>();
-builder.Services.AddSingleton<IAccessQueueRepo, TakeANumberAccessQueueRepo>();
+builder.Services.AddSingleton<IAccessQueueRepo>(sp =>
+{
+    string? filePath = builder.Configuration.GetValue<string>("AccessQueue:BackupFilePath");
+    if (!string.IsNullOrWhiteSpace(filePath) && File.Exists(filePath))
+    {
+        try
+        {
+            var json = File.ReadAllText(filePath);
+            return TakeANumberAccessQueueRepo.FromState(json);
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"Failed to load state from {filePath}. Error message: {ex.Message}");
+        }
+    }
+    return new TakeANumberAccessQueueRepo();
+});
 builder.Services.AddHostedService<AccessCleanupBackgroundService>();
+builder.Services.AddHostedService<AccessQueueSerializerService>();
 
 var app = builder.Build();
 

AccessQueueService/Services/AccessQueueSerializerService.cs

@@ -0,0 +1,43 @@
+using System.Text.Json;
+using AccessQueueService.Data;
+
+namespace AccessQueueService.Services
+{
+    public class AccessQueueSerializerService : BackgroundService
+    {
+        private readonly IAccessQueueRepo _accessRepo;
+        private readonly IConfiguration _config;
+        private readonly ILogger<AccessQueueSerializerService> _logger;
+
+        public AccessQueueSerializerService(IAccessQueueRepo accessRepo, IConfiguration config, ILogger<AccessQueueSerializerService> logger)
+        {
+            _accessRepo = accessRepo;
+            _config = config;
+            _logger = logger;
+        }
+
+        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+        {
+            var backupIntervalSeconds = _config.GetValue<int>("AccessQueue:BackupIntervalSeconds") * 1000;
+            var backupPath = _config.GetValue<string>("AccessQueue:BackupFilePath");
+            if (backupIntervalSeconds == 0 || string.IsNullOrEmpty(backupPath))
+            {
+                return;
+            }
+            while (!stoppingToken.IsCancellationRequested)
+            {
+                try
+                {
+                    _logger.LogInformation($"Writing backup to {backupPath}");
+                    var stateJson = _accessRepo.ToState();
+                    File.WriteAllText(backupPath, stateJson);
+                }
+                catch (Exception ex)
+                {
+                    _logger.LogError(ex, "Exception occurred during background cleanup.");
+                }
+                await Task.Delay(backupIntervalSeconds, stoppingToken);
+            }
+        }
+    }
+}

AccessQueueService/appsettings.json

@@ -23,12 +23,14 @@
       "Application": "AccessQueueService"
     }
   },
-  "AccessQueue": {
-    "CapacityLimit": 100,
-    "ActivitySeconds": 900,
-    "ExpirationSeconds": 43200,
-    "RollingExpiration": true,
-    "CleanupIntervalSeconds": 60
-  },
+    "AccessQueue": {
+        "CapacityLimit": 100,
+        "ActivitySeconds": 900,
+        "ExpirationSeconds": 43200,
+        "RollingExpiration": true,
+        "CleanupIntervalSeconds": 60,
+        "BackupFilePath": "Logs\\backup.json",
+        "BackupIntervalSeconds": 5
+    },
   "AllowedHosts": "*"
 }