New: Mailgun connection

src/NzbDrone.Core/Notifications/Mailgun/Mailgun.cs

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+using System;
+using System.Collections.Generic;
+using FluentValidation.Results;
+using NLog;
+
+namespace NzbDrone.Core.Notifications.Mailgun
+{
+    public class MailGun : NotificationBase<MailgunSettings>
+    {
+        private readonly IMailgunProxy _proxy;
+        private readonly Logger _logger;
+        
+        public MailGun(IMailgunProxy proxy, Logger logger)
+        {
+            _proxy = proxy;
+            _logger = logger;
+        }
+
+        public override string Name => "Mailgun";
+        public override string Link => "https://mailgun.com";
+
+        public override void OnGrab(GrabMessage grabMessage)
+        {
+            _proxy.SendNotification(EPISODE_GRABBED_TITLE, grabMessage.Message, Settings);
+        }
+
+        public override void OnDownload(DownloadMessage downloadMessage)
+        {
+            _proxy.SendNotification(EPISODE_DOWNLOADED_TITLE, downloadMessage.Message, Settings);
+        }
+
+        public override void OnHealthIssue(HealthCheck.HealthCheck healthCheckMessage)
+        {
+            _proxy.SendNotification(HEALTH_ISSUE_TITLE, healthCheckMessage.Message, Settings);
+        }
+
+
+        public override ValidationResult Test()
+        {
+            var failures = new List<ValidationFailure>();
+
+            try
+            {
+                const string title = "Test Notification";
+                const string body = "This is a test message from Sonarr, though Mailgun.";
+
+                _proxy.SendNotification(title, body, Settings);
+                _logger.Info("Successsfully sent email though Mailgun.");
+            }
+            catch (Exception ex)
+            {
+                _logger.Error(ex, "Unable to send test message though Mailgun.");
+                failures.Add(new ValidationFailure("", "Unable to send test message though Mailgun."));
+            }
+            
+            return new ValidationResult(failures);
+        }
+    }
+}

src/NzbDrone.Core/Notifications/Mailgun/MailgunException.cs

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+using System;
+using NzbDrone.Common.Exceptions;
+
+namespace NzbDrone.Core.Notifications.Mailgun
+{
+    public class MailgunException : NzbDroneException
+    {
+        public MailgunException(string message) : base (message) { }
+        
+        public MailgunException(string message, Exception innerException, params object[] args)
+            : base(message, innerException, args) { }
+    }
+}

src/NzbDrone.Core/Notifications/Mailgun/MailgunProxy.cs

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+using System.Net;
+using NLog;
+using NzbDrone.Common.Http;
+using HttpMethod = NzbDrone.Common.Http.HttpMethod;
+
+namespace NzbDrone.Core.Notifications.Mailgun {
+    public interface IMailgunProxy
+    {
+        void SendNotification(string tittle, string message, MailgunSettings settings);
+    }
+    
+    public class MailgunProxy : IMailgunProxy
+    {
+        private readonly IHttpClient _httpClient;
+        private readonly Logger _logger;
+        private const string BaseUrlEu = "https://api.eu.mailgun.net/v3";
+        private const string BaseUrlUs = "https://api.mailgun.net/v3";
+
+
+        public MailgunProxy(IHttpClient httpClient, Logger logger)
+        {
+            _httpClient = httpClient;
+            _logger = logger;
+        }
+
+        public void SendNotification(string title, string message, MailgunSettings settings)
+        {
+            try
+            {
+                var request = BuildRequest(settings, $"{settings.SenderDomain}/messages", HttpMethod.POST,
+                    title, message).Build();
+                _httpClient.Execute(request);
+            }
+            catch (HttpException ex)
+            {
+                if (ex.Response.StatusCode == HttpStatusCode.Unauthorized)
+                {
+                    throw new MailgunException("Unauthorised - ApiKey is invalid");
+                }
+                
+                throw new MailgunException("Unable to connect to Mailgun. Status code: {0}", ex);
+            }
+        }
+
+
+        private HttpRequestBuilder BuildRequest(MailgunSettings settings, string resource, HttpMethod method, 
+            string messageSubject, string messageBody)
+        {
+            var loginCredentials = new NetworkCredential("api", settings.ApiKey);
+            var url = settings.UseEuEndpoint ? BaseUrlEu : BaseUrlUs;
+            var requestBuilder = new HttpRequestBuilder(url).Resource(resource);
+            
+            requestBuilder.Method = method;
+            requestBuilder.NetworkCredential = loginCredentials;
+            
+            requestBuilder.AddFormParameter("from", $"{settings.From}");
+            
+            foreach (var recipient in settings.Recipients)
+            { 
+                requestBuilder.AddFormParameter("to", $"{recipient}");
+            }
+            
+            requestBuilder.AddFormParameter("subject", $"{messageSubject}");
+            requestBuilder.AddFormParameter("text", $"{messageBody}");
+            
+            return requestBuilder;
+        }
+    }
+}

src/NzbDrone.Core/Notifications/Mailgun/MailgunSettings.cs

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+using System.Collections.Generic;
+using FluentValidation;
+using NzbDrone.Core.Annotations;
+using NzbDrone.Core.ThingiProvider;
+using NzbDrone.Core.Validation;
+
+namespace NzbDrone.Core.Notifications.Mailgun
+{
+    public class MailGunSettingsValidator : AbstractValidator<MailgunSettings>
+    {
+        public MailGunSettingsValidator()
+        {
+            RuleFor(c => c.ApiKey).NotEmpty();
+            RuleFor(c => c.From).NotEmpty();
+            RuleFor(c => c.Recipients).NotEmpty();
+        }
+    }
+    
+    public class MailgunSettings : IProviderConfig
+    {
+      private static readonly  MailGunSettingsValidator Validator = new MailGunSettingsValidator();
+
+      public MailgunSettings()
+      {
+          Recipients = new string[] { };
+      }
+      
+      
+      [FieldDefinition(0, Label = "API Key", HelpText = "The API key generated from MailGun")]
+      public string ApiKey { get; set; }
+      
+      [FieldDefinition(1, Label = "Use EU Endpoint?", HelpText = "You can choose to use the EU MailGun endpoint with this", Type = FieldType.Checkbox)]
+      public bool UseEuEndpoint { get; set; }
+      
+      [FieldDefinition(2, Label = "From Address")]
+      public string From { get; set; }
+      
+      [FieldDefinition(3, Label = "Sender Domain")]
+      public string SenderDomain { get; set; }
+      
+      [FieldDefinition(4, Label = "Recipient Address(es)", Type = FieldType.Tag)]
+      public IEnumerable<string> Recipients { get; set; }
+
+      public NzbDroneValidationResult Validate()
+      {
+          return new NzbDroneValidationResult(Validator.Validate(this));
+      }
+    }
+}