4 files changed, 95 insertions, 2 deletions

diff --git a/TwoStepsAuthenticator.TestApp/MainWindow.xaml.cs b/TwoStepsAuthenticator.TestApp/MainWindow.xaml.cs
index 3a1ae68..43469af 100644
--- a/TwoStepsAuthenticator.TestApp/MainWindow.xaml.cs
+++ b/TwoStepsAuthenticator.TestApp/MainWindow.xaml.cs
@@ -31,7 +31,7 @@ namespace TwoStepsAuthenticatorTestApp
 
         private void Button_Click(object sender, RoutedEventArgs e)
         {
-            model.GetCode();
+            model.GetCode();            
         }
     }
 }
diff --git a/TwoStepsAuthenticator/Authenticator.cs b/TwoStepsAuthenticator/Authenticator.cs
index de383d9..d196525 100644
--- a/TwoStepsAuthenticator/Authenticator.cs
+++ b/TwoStepsAuthenticator/Authenticator.cs
@@ -9,6 +9,12 @@ namespace TwoStepsAuthenticator
 {
     public class Authenticator
     {
+        private static UsedCodesManager usedCodes = new UsedCodesManager();
+
+        public string GenerateKey()
+        {
+            throw new NotImplementedException();
+        }
 
         public string GetCode(string secret)
         {
@@ -55,17 +61,24 @@ namespace TwoStepsAuthenticator
 
         public bool CheckCode(string secret, string code)
         {
+            if (usedCodes.IsCodeUsed(secret, code))
+                return false;
+
             var baseTime = DateTime.Now;
-            for (int i = -2; i <= 2; i++)
+            for (int i = -2; i <= 1; i++)
             {
                 var checkTime = baseTime.AddSeconds(30 * i);
                 if (GetCode(secret, checkTime) == code)
+                {
+                    usedCodes.AddCode(secret, code);
                     return true;
+                }
             }
 
             return false;
         }
 
 
+
     }
 }
diff --git a/TwoStepsAuthenticator/TwoStepsAuthenticator.csproj b/TwoStepsAuthenticator/TwoStepsAuthenticator.csproj
index 7e9e1e0..b628bfd 100644
--- a/TwoStepsAuthenticator/TwoStepsAuthenticator.csproj
+++ b/TwoStepsAuthenticator/TwoStepsAuthenticator.csproj
@@ -42,6 +42,7 @@
     <Compile Include="Base32Encoding.cs" />
     <Compile Include="Authenticator.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
+    <Compile Include="UsedCodesManager.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
diff --git a/TwoStepsAuthenticator/UsedCodesManager.cs b/TwoStepsAuthenticator/UsedCodesManager.cs
new file mode 100644
index 0000000..d60e1cb
--- /dev/null
+++ b/TwoStepsAuthenticator/UsedCodesManager.cs
@@ -0,0 +1,79 @@
+using System;
+using System.Collections.Generic;
+//using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Timers;
+
+namespace TwoStepsAuthenticator
+{
+    internal class UsedCodesManager
+    {
+        private class UsedCode
+        {
+            public UsedCode(String secret, String code)
+            {
+                this.UseDate = DateTime.Now;
+                this.Code = secret + code;
+            }
+
+            public DateTime UseDate { get; set; }
+            public String Code { get; set; }
+
+            public override bool Equals(object obj)
+            {
+                return obj.ToString().Equals(Code);
+            }
+            public override string ToString()
+            {
+                return Code;
+            }
+            public override int GetHashCode()
+            {
+                return Code.GetHashCode();
+            }
+        }
+
+        private Queue<UsedCode> codes;
+        private object codeLock = new object();
+        private Timer cleaner;
+
+        public UsedCodesManager()
+        {
+            codes = new Queue<UsedCode>();
+            cleaner = new Timer(TimeSpan.FromSeconds(5).TotalMilliseconds);
+            cleaner.Elapsed += cleaner_Elapsed;
+            cleaner.Start();
+        }
+
+        void cleaner_Elapsed(object sender, ElapsedEventArgs e)
+        {
+            var timeToClean = DateTime.Now.AddSeconds(-5);
+            lock (codeLock)
+            {
+                while (codes.Count > 0 && codes.Peek().UseDate < timeToClean)
+                {
+                    codes.Dequeue();
+                }
+            }
+        }
+
+        public void AddCode(String secret, String code)
+        {
+            lock (codeLock)
+            {
+                codes.Enqueue(new UsedCode(secret, code));
+            }
+        }
+
+        public bool IsCodeUsed(String secret, String code)
+        {
+            lock (codeLock)
+            {
+                return codes.Contains(new UsedCode(secret, code));
+            }
+        }
+    }
+
+
+}