Fix for issue #32

Author: dr-o-ne

Web/Managers/ScheduledEmailManager.cs

@@ -1,18 +1,14 @@
-using System;
-using System.Diagnostics;
 using System.IO;
 using System.Linq;
-using System.Text;
-using System.Security.Cryptography;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Hosting;
 using QueryTree.Models;
-using Microsoft.Extensions.PlatformAbstractions;
 using Newtonsoft.Json;
 using MimeKit;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Caching.Memory;
+using QueryTree.Services;
 
 namespace QueryTree.Managers
 {
@@ -24,22 +20,25 @@ public interface IScheduledEmailManager
 
     public class ScheduledEmailManager : IScheduledEmailManager
     {
-        private IEmailSender _emailSender;
-        private IConfiguration _config;
-        private ApplicationDbContext _db;
-        private DbManager _dbMgr;
-        private IHostingEnvironment _env;
-        private ConvertManager _convertManager;
-
-
-        public ScheduledEmailManager(
-            IEmailSender emailSender,
-            IConfiguration config, 
+		private readonly IEmailSenderService _emailSenderService;
+		private readonly IEmailSender _emailSender;
+		private readonly IConfiguration _config;
+		private readonly ApplicationDbContext _db;
+		private readonly DbManager _dbMgr;
+		private readonly IHostingEnvironment _env;
+		private readonly ConvertManager _convertManager;
+
+
+		public ScheduledEmailManager(
+			IEmailSenderService emailSenderService,
+			IEmailSender emailSender,
+			IConfiguration config, 
             ApplicationDbContext db,
             IHostingEnvironment env,
             IMemoryCache cache,
             IPasswordManager passwordManager)
         {
+			_emailSenderService = emailSenderService;
             _emailSender = emailSender;
             _config = config;
             _db = db;
@@ -54,8 +53,13 @@ public void BuildScheduledEmail(string queryName, string editUrl, string recipie
 			{
 				return;
 			}
-            
-            var query = _db.Queries
+
+			if(!_emailSenderService.TrySetDelivered(queryId)) 
+			{
+				return;
+			}
+
+			var query = _db.Queries
                 .Include(q => q.DatabaseConnection)
                 .FirstOrDefault(q => q.QueryID == queryId);
 

Web/Services/EmailSenderService.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+
+namespace QueryTree.Services 
+{
+	public sealed class EmailSenderService : IEmailSenderService 
+	{
+		private const int TimeoutInSeconds = 60;
+		private readonly object _locker = new object();
+		private readonly Dictionary<int, DateTime> _messageDeliveryTime = new Dictionary<int, DateTime>();
+
+		public bool TrySetDelivered(int messageId) 
+		{
+
+			DateTime deliveredTime;
+			if (!_messageDeliveryTime.TryGetValue(messageId, out deliveredTime) || deliveredTime.AddSeconds(TimeoutInSeconds) <= DateTime.UtcNow) 			
+			{
+				lock(_locker) 
+				{
+					if (!_messageDeliveryTime.TryGetValue(messageId, out deliveredTime) || deliveredTime.AddSeconds(TimeoutInSeconds) <= DateTime.UtcNow) 
+					{
+						_messageDeliveryTime[messageId] = DateTime.UtcNow;
+						return true;
+					}
+				}
+			}
+
+			return false;
+		}
+
+	}
+}

Web/Services/IEmailSenderService.cs

@@ -0,0 +1,7 @@
+namespace QueryTree.Services 
+{
+	public interface IEmailSenderService 
+	{
+		bool TrySetDelivered(int messageId);
+	}
+}

Web/Startup.cs

@@ -15,6 +15,7 @@
 using Microsoft.Extensions.Logging;
 using QueryTree.Models;
 using QueryTree.Managers;
+using QueryTree.Services;
 
 namespace QueryTree
 {
@@ -65,8 +66,9 @@ public void ConfigureServices(IServiceCollection services)
                 options.User.RequireUniqueEmail = true;
             });
 
-            // Add application services.
-            services.AddTransient<IEmailSender, EmailSender>();
+			// Add application services.
+			services.AddSingleton<IEmailSenderService, EmailSenderService>();
+			services.AddTransient<IEmailSender, EmailSender>();
             services.AddTransient<IPasswordManager, PasswordManager>(); // Allows controllers to set/get/delete database credentials
             services.AddTransient<IScheduledEmailManager, ScheduledEmailManager>();
 			services.AddMemoryCache();