feat: Adds a new service to control email sending concurrency

src/SnackFlow.Api/appsettings.json

@@ -3,7 +3,10 @@
     "DefaultConnection": "Host=localhost;Database=snackflow_db;Username=postgres;Password=root;Port=5432"
   },
   "AWS": {
-    "Region": "us-east-1"
+    "Region": "us-east-1",
+    "SES": {
+      "MaxConcurrentEmails": 3
+    }
   },
   "AccessTokenSettings": {
     "Key": "Common/Certificates/access-token-jwt-key.pfx",

src/SnackFlow.Application/Abstractions/Services/Concurrency/IEmailConcurrencyService.cs

@@ -0,0 +1,19 @@
+namespace SnackFlow.Application.Abstractions.Services.Concurrency;
+
+/// <summary>
+/// Fornece funcionalidade para gerenciar concorrência durante operações relacionadas a emails.
+/// </summary>
+public interface IEmailConcurrencyService
+{
+    /// <summary>
+    /// Obtém um bloqueio de concorrência para gerenciar o acesso durante operações relacionadas a e-mails.
+    /// </summary>
+    /// <param name="cancellationToken">
+    /// Um token para monitorar solicitações de cancelamento.
+    /// </param>
+    /// <returns>
+    /// Uma tarefa que representa uma operação assíncrona. O resultado contém um objeto descartável
+    /// que deve ser descartado para liberar o bloqueio.
+    /// </returns>
+    Task<IDisposable> AcquireAsync(CancellationToken cancellationToken = default);
+}

src/SnackFlow.Infrastructure/DependencyInjection.cs

@@ -13,10 +13,12 @@
 using Serilog.Events;
 using SnackFlow.Application.Abstractions.Schedulers;
 using SnackFlow.Application.Abstractions.Services;
+using SnackFlow.Application.Abstractions.Services.Concurrency;
 using SnackFlow.Domain.Repositories;
 using SnackFlow.Infrastructure.Jobs;
 using SnackFlow.Infrastructure.Schedulers;
 using SnackFlow.Infrastructure.Services;
+using SnackFlow.Infrastructure.Services.Concurrency;
 using SnackFlow.Infrastructure.Services.EmailTemplateService;
 
 namespace SnackFlow.Infrastructure;
@@ -92,6 +94,7 @@ private static void AddRepositories(this IServiceCollection services)
 
     private static void AddServices(this IServiceCollection services)
     {
+        // Transient
         services.AddTransient<ICertificateService, CertificateService>();
         services.AddTransient<IEmailTemplateService, EmailTemplateService>();
         services.AddTransient<IEmailService, EmailService>();
@@ -100,6 +103,9 @@ private static void AddServices(this IServiceCollection services)
         services.AddTransient<ITokenService, JwtTokenService>();
         services.AddTransient<IUserCreationService,  UserCreationService>();
         services.AddTransient<ICurrentUserService, CurrentUserService>();
+
+        // Singleton
+        services.AddSingleton<IEmailConcurrencyService, EmailConcurrencyService>();
     }
 
     private static void AddAwsServices(this IServiceCollection services, IConfiguration configuration)

src/SnackFlow.Infrastructure/Jobs/SendingEmailJob.cs

@@ -3,18 +3,21 @@
 using Newtonsoft.Json.Linq;
 using Quartz;
 using SnackFlow.Application.Abstractions.Services;
+using SnackFlow.Application.Abstractions.Services.Concurrency;
 using SnackFlow.Domain.Constants;
 
 namespace SnackFlow.Infrastructure.Jobs;
 
 public sealed class SendingEmailJob(
     IEmailService emailService,
     IEmailTemplateService templateEmailService,
+    IEmailConcurrencyService emailConcurrencyService,
     ILogger<SendingEmailJob> logger) 
     : IJob
 {
     public async Task Execute(IJobExecutionContext context)
     {
+        using var semaphoreRelease = await emailConcurrencyService.AcquireAsync();
         var jobDataMap = context.Trigger.JobDataMap;
         try
         {

src/SnackFlow.Infrastructure/Services/Concurrency/EmailConcurrencyService.cs

@@ -0,0 +1,27 @@
+using Microsoft.Extensions.Configuration;
+using SnackFlow.Application.Abstractions.Services.Concurrency;
+
+namespace SnackFlow.Infrastructure.Services.Concurrency;
+
+public sealed class EmailConcurrencyService
+    : IEmailConcurrencyService
+{
+    private readonly SemaphoreSlim _semaphoreSlim;
+
+    public EmailConcurrencyService(IConfiguration configuration)
+    {
+        var maxConcurrent = configuration.GetValue("AWS:SES:MaxConcurrentEmails", 3);
+        _semaphoreSlim = new SemaphoreSlim(maxConcurrent, maxConcurrent);
+    }
+
+    public async Task<IDisposable> AcquireAsync(CancellationToken cancellationToken = default)
+    {
+        await _semaphoreSlim.WaitAsync(cancellationToken);
+        return new SemaphoreReleaser(_semaphoreSlim);
+    }
+
+    private sealed class SemaphoreReleaser(SemaphoreSlim semaphoreSlim) : IDisposable
+    {
+        public void Dispose() => semaphoreSlim.Dispose();
+    }
+}