Add EmailSender abstraction for sending mails using either SMTP or Ma…

…ilgun (#293)

This PR adds an `IEmailSender` abstraction along with implementations
`SmtpEmailSender` and `MailgunEmailSender`, and refactors `EmailService`
to use said abstraction. The main idea is to allow for local email
testing using an SMTP server such as
[MailHog](https://github.com/mailhog/MailHog), which has also been added
to the Docker Compose configuration.

<img width="1494" alt="image"
src="https://github.com/user-attachments/assets/99e86a78-02eb-4e82-bcb8-da70192f6667">

coffeecard/CoffeeCard.Common/Configuration/SmtpSettings.cs

@@ -0,0 +1,11 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace CoffeeCard.Common.Configuration
+{
+    public class SmtpSettings
+    {
+        [Required] public string Host { get; set; }
+        [Required] public int Port { get; set; }
+    }
+}
+

coffeecard/CoffeeCard.Library/Services/EmailService.cs

@@ -18,13 +18,13 @@ public class EmailService : IEmailService
     {
         private readonly IWebHostEnvironment _env;
         private readonly EnvironmentSettings _environmentSettings;
-        private readonly MailgunSettings _mailgunSettings;
+        private readonly IEmailSender _emailSender;
         private readonly IMapperService _mapperService;
 
-        public EmailService(MailgunSettings mailgunSettings, EnvironmentSettings environmentSettings,
+        public EmailService(IEmailSender emailSender, EnvironmentSettings environmentSettings,
             IWebHostEnvironment env, IMapperService mapperService)
         {
-            _mailgunSettings = mailgunSettings;
+            _emailSender = emailSender;
             _environmentSettings = environmentSettings;
             _env = env;
             _mapperService = mapperService;
@@ -54,7 +54,7 @@ public async Task SendInvoiceAsync(UserDto user, PurchaseDto purchase)
 
             Log.Information("Sending invoice for PurchaseId {PurchaseId} to UserId {UserId}, E-mail {Email}", purchase.Id, user.Id, user.Email);
 
-            await SendEmailAsync(message);
+            await _emailSender.SendEmailAsync(message);
         }
 
         public async Task SendRegistrationVerificationEmailAsync(User user, string token)
@@ -71,7 +71,7 @@ public async Task SendRegistrationVerificationEmailAsync(User user, string token
 
             message.Body = builder.ToMessageBody();
 
-            await SendEmailAsync(message);
+            await _emailSender.SendEmailAsync(message);
         }
 
         public async Task SendVerificationEmailForLostPwAsync(User user, string token)
@@ -87,7 +87,7 @@ public async Task SendVerificationEmailForLostPwAsync(User user, string token)
 
             message.Body = builder.ToMessageBody();
 
-            await SendEmailAsync(message);
+            await _emailSender.SendEmailAsync(message);
         }
 
         public async Task SendVerificationEmailForDeleteAccount(User user, string token)
@@ -104,7 +104,7 @@ public async Task SendVerificationEmailForDeleteAccount(User user, string token)
 
             message.Body = builder.ToMessageBody();
 
-            await SendEmailAsync(message);
+            await _emailSender.SendEmailAsync(message);
         }
 
         public async Task SendInvoiceAsyncV2(Purchase purchase, User user)
@@ -150,29 +150,5 @@ private BodyBuilder RetrieveTemplate(string templateName)
 
             return builder;
         }
-
-        private async Task SendEmailAsync(MimeMessage mail)
-        {
-            var client = new RestClient(_mailgunSettings.MailgunApiUrl)
-            {
-                Authenticator = new HttpBasicAuthenticator("api", _mailgunSettings.ApiKey)
-            };
-
-            var request = new RestRequest();
-            request.AddParameter("domain", _mailgunSettings.Domain, ParameterType.UrlSegment);
-            request.Resource = "{domain}/messages";
-            request.AddParameter("from", "Cafe Analog <[email protected]>");
-            request.AddParameter("to", mail.To[0].ToString());
-            request.AddParameter("subject", mail.Subject);
-            request.AddParameter("html", mail.HtmlBody);
-            request.Method = Method.Post;
-
-            var response = await client.ExecutePostAsync(request);
-
-            if (!response.IsSuccessful)
-            {
-                Log.Error("Error sending request to Mailgun. StatusCode: {statusCode} ErrorMessage: {errorMessage}", response.StatusCode, response.ErrorMessage);
-            }
-        }
     }
 }

coffeecard/CoffeeCard.Library/Services/IEmailSender.cs

@@ -0,0 +1,9 @@
+using System.Threading.Tasks;
+using MimeKit;
+
+namespace CoffeeCard.Library.Services;
+
+public interface IEmailSender
+{
+    public Task SendEmailAsync(MimeMessage email);
+}

coffeecard/CoffeeCard.Library/Services/MailgunEmailSender.cs

@@ -0,0 +1,34 @@
+using System.Threading.Tasks;
+using CoffeeCard.Common.Configuration;
+using MimeKit;
+using RestSharp;
+using RestSharp.Authenticators;
+using Serilog;
+
+namespace CoffeeCard.Library.Services;
+
+public class MailgunEmailSender(MailgunSettings mailgunSettings) : IEmailSender
+{
+    public async Task SendEmailAsync(MimeMessage mail)
+    {
+        using var client = new RestClient(mailgunSettings.MailgunApiUrl);
+        client.Authenticator = new HttpBasicAuthenticator("api", mailgunSettings.ApiKey);
+
+        var request = new RestRequest();
+        request.AddParameter("domain", mailgunSettings.Domain, ParameterType.UrlSegment);
+        request.Resource = "{domain}/messages";
+        request.AddParameter("from", "Cafe Analog <[email protected]>");
+        request.AddParameter("to", mail.To[0].ToString());
+        request.AddParameter("subject", mail.Subject);
+        request.AddParameter("html", mail.HtmlBody);
+        request.Method = Method.Post;
+
+        var response = await client.ExecutePostAsync(request);
+
+        if (!response.IsSuccessful)
+        {
+            Log.Error("Error sending request to Mailgun. StatusCode: {statusCode} ErrorMessage: {errorMessage}",
+                response.StatusCode, response.ErrorMessage);
+        }
+    }
+}

coffeecard/CoffeeCard.Library/Services/SmtpEmailSender.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Threading.Tasks;
+using CoffeeCard.Common.Configuration;
+using MailKit.Net.Smtp;
+using MimeKit;
+using Serilog;
+
+namespace CoffeeCard.Library.Services;
+
+public class SmtpEmailSender(SmtpSettings smtpSettings) : IEmailSender
+{
+    public async Task SendEmailAsync(MimeMessage mail)
+    {
+        mail.From.Add(new MailboxAddress("Cafe Analog", "[email protected]"));
+
+        try
+        {
+            using var smtpClient = new SmtpClient();
+            await smtpClient.ConnectAsync(smtpSettings.Host, smtpSettings.Port);
+            await smtpClient.SendAsync(mail);
+            await smtpClient.DisconnectAsync(true);
+        }
+        catch (Exception ex)
+        {
+            Log.Error("Error sending request to SMTP server. Error: {errorMessage}", ex.Message);
+        }
+    }
+}

coffeecard/CoffeeCard.WebApi/Startup.cs

@@ -76,6 +76,15 @@ public void ConfigureServices(IServiceCollection services)
             services.AddScoped<Library.Services.v2.IAccountService, Library.Services.v2.AccountService>();
             services.AddScoped<IPurchaseService, PurchaseService>();
             services.AddScoped<IMapperService, MapperService>();
+            if (_environment.IsDevelopment())
+            {
+                services.AddTransient<IEmailSender, SmtpEmailSender>();
+                services.AddSingleton(_configuration.GetSection("SmtpSettings").Get<SmtpSettings>());
+            }
+            else
+            {
+                services.AddTransient<IEmailSender, MailgunEmailSender>();
+            }
             services.AddScoped<IEmailService, EmailService>();
             services.AddScoped<IVoucherService, VoucherService>();
             services.AddScoped<IProgrammeService, ProgrammeService>();

coffeecard/CoffeeCard.WebApi/appsettings.json

@@ -23,6 +23,10 @@
     "EmailBaseUrl": "https://localhost",
     "MailgunApiUrl": "https://api.mailgun.net/v3"
   },
+  "SmtpSettings": {
+    "Host": "mailhog",
+    "Port": 1025
+  },
   "MobilePaySettingsV2": {
     "ApiUrl": "https://invalidurl.test/",
     "ApiKey": "DummyKey",

coffeecard/docker-compose.yml

@@ -35,3 +35,9 @@ services:
     volumes:
       - ./CoffeeCard.WebApi/appsettings.json:/app/appsettings.json:z
       - ~/.aspnet/https:/https:ro
+
+  mailhog:
+    image: mailhog/mailhog
+    ports:
+      - "1025:1025"
+      - "8025:8025"