feat(backend/infra): add health checks, CORS, Serilog logging, and exception middleware

- Add Microsoft.Extensions.Diagnostics.HealthChecks.EntityFrameworkCore package
- Add Serilog.AspNetCore and Serilog.Sinks.Console packages
- Configure Serilog with bootstrap logger and configuration
- Add Health Checks endpoint at /health with DbContext check
- Configure CORS with AllowAll policy for development
- Create ApiResponse, ApiErrorResponse, and PaginatedResponse models
- Create ExceptionMiddleware for global error handling
- Restructure Program.cs with try-catch-finally for proper logging

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

GermanApp/GermanApp.csproj

@@ -19,6 +19,10 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
+    <PackageReference Include="Microsoft.Extensions.Diagnostics.HealthChecks" Version="9.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Diagnostics.HealthChecks.EntityFrameworkCore" Version="9.0.0" />
+    <PackageReference Include="Serilog.AspNetCore" Version="8.0.0" />
+    <PackageReference Include="Serilog.Sinks.Console" Version="5.0.0" />
   </ItemGroup>
 
 </Project>

GermanApp/Program.cs

@@ -5,21 +5,59 @@ using GermanApp.Infrastructure.Data.DbContext;
 using GermanApp.Infrastructure.Data.Repositories;
 using GermanApp.Infrastructure.Data.SeedData;
 using GermanApp.Presentation.Endpoints;
+using GermanApp.Shared.Middleware;
 using Microsoft.EntityFrameworkCore;
+using Serilog;
 
-var builder = WebApplication.CreateBuilder(args);
+// Configure Serilog
+Log.Logger = new LoggerConfiguration()
+    .MinimumLevel.Debug()
+    .WriteTo.Console()
+    .CreateBootstrapLogger();
 
-// Add services to the container.
-// Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
-builder.Services.AddOpenApi();
-
-// ============================================
-// INFRASTRUCTURE LAYER - Database & External Services
-// ============================================
-
-// Add DbContext with PostgreSQL
-builder.Services.AddDbContext<AppDbContext>(options =>
+try
 {
+    var builder = WebApplication.CreateBuilder(args);
+
+    // Add Serilog to the builder
+    builder.Host.UseSerilog((ctx, lc) => lc
+        .MinimumLevel.Debug()
+        .WriteTo.Console()
+        .ReadFrom.Configuration(ctx.Configuration));
+
+    // ============================================
+    // PRESENTATION LAYER - API Configuration
+    // ============================================
+
+    // Add services to the container.
+    builder.Services.AddOpenApi();
+
+    // Add Health Checks
+    builder.Services.AddHealthChecks()
+        .AddDbContextCheck<AppDbContext>();
+
+    // Configure CORS
+    builder.Services.AddCors(options =>
+    {
+        options.AddPolicy("AllowAll", builder =>
+        {
+            builder.AllowAnyOrigin()
+                   .AllowAnyMethod()
+                   .AllowAnyHeader();
+        });
+    });
+
+    // Add services for Minimal APIs
+    builder.Services.AddEndpointsApiExplorer();
+    builder.Services.AddSwaggerGen();
+
+    // ============================================
+    // INFRASTRUCTURE LAYER - Database & External Services
+    // ============================================
+
+    // Add DbContext with PostgreSQL
+    builder.Services.AddDbContext<AppDbContext>(options =>
+    {
         // Using PostgreSQL for production and development
         options.UseNpgsql(builder.Configuration.GetConnectionString("DefaultConnection") 
             ?? "Host=localhost;Port=5432;Database=DeutschLernen;Username=postgres;Password=postgres");
@@ -30,45 +68,47 @@ builder.Services.AddDbContext<AppDbContext>(options =>
             options.EnableSensitiveDataLogging();
             options.EnableDetailedErrors();
         }
-});
+    });
 
-// Register repositories (Infrastructure implementations of Domain interfaces)
-builder.Services.AddScoped<ILessonRepository, LessonRepository>();
+    // Register repositories (Infrastructure implementations of Domain interfaces)
+    builder.Services.AddScoped<ILessonRepository, LessonRepository>();
 
-// ============================================
-// APPLICATION LAYER - Use Cases & Services
-// ============================================
+    // ============================================
+    // APPLICATION LAYER - Use Cases & Services
+    // ============================================
 
-// Register command handlers
-builder.Services.AddScoped<ICommandHandler<CreateLessonCommand, LessonDto>, CreateLessonCommandHandler>();
+    // Register command handlers
+    builder.Services.AddScoped<ICommandHandler<CreateLessonCommand, LessonDto>, CreateLessonCommandHandler>();
 
-// ============================================
-// PRESENTATION LAYER - API
-// ============================================
+    var app = builder.Build();
 
-// Add services for Minimal APIs
-builder.Services.AddEndpointsApiExplorer();
-builder.Services.AddSwaggerGen();
+    // Configure the HTTP request pipeline.
     
-var app = builder.Build();
+    // Use exception middleware first (to catch all exceptions)
+    app.UseExceptionMiddleware();
 
-// Configure the HTTP request pipeline.
-if (app.Environment.IsDevelopment())
-{
+    if (app.Environment.IsDevelopment())
+    {
         app.MapOpenApi();
         app.UseSwagger();
         app.UseSwaggerUI();
-}
+    }
 
-// Seed database with initial data
-app.SeedDatabase();
+    // Use CORS
+    app.UseCors("AllowAll");
 
-// Map Clean Architecture endpoints
-app.MapLessonsEndpoints();
+    // Use Health Checks
+    app.MapHealthChecks("/health");
 
-// Keep original WeatherForecast endpoint for reference
-app.MapGet("/weatherforecast", () =>
-{
+    // Seed database with initial data
+    app.SeedDatabase();
+
+    // Map Clean Architecture endpoints
+    app.MapLessonsEndpoints();
+
+    // Keep original WeatherForecast endpoint for reference
+    app.MapGet("/weatherforecast", () =>
+    {
         var summaries = new[]
         {
             "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
@@ -83,10 +123,19 @@ app.MapGet("/weatherforecast", () =>
             ))
             .ToArray();
         return forecast;
-})
-.WithName("GetWeatherForecast");
+    })
+    .WithName("GetWeatherForecast");
 
-app.Run();
+    app.Run();
+}
+catch (Exception ex)
+{
+    Log.Fatal(ex, "Application terminated unexpectedly");
+}
+finally
+{
+    Log.CloseAndFlush();
+}
 
 // Existing record for reference
 record WeatherForecast(DateOnly Date, int TemperatureC, string? Summary)

GermanApp/Shared/Middleware/ExceptionMiddleware.cs

@@ -0,0 +1,62 @@
+using System.Net;
+using System.Text.Json;
+using GermanApp.Shared.Models;
+
+namespace GermanApp.Shared.Middleware;
+
+/// <summary>
+/// Global exception handling middleware.
+/// Catches exceptions and returns consistent error responses.
+/// </summary>
+public class ExceptionMiddleware
+{
+    private readonly RequestDelegate _next;
+    private readonly ILogger<ExceptionMiddleware> _logger;
+
+    public ExceptionMiddleware(RequestDelegate next, ILogger<ExceptionMiddleware> logger)
+    {
+        _next = next;
+        _logger = logger;
+    }
+
+    public async Task InvokeAsync(HttpContext httpContext)
+    {
+        try
+        {
+            await _next(httpContext);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Unhandled exception occurred: {Message}", ex.Message);
+            await HandleExceptionAsync(httpContext, ex);
+        }
+    }
+
+    private static Task HandleExceptionAsync(HttpContext context, Exception exception)
+    {
+        context.Response.ContentType = "application/json";
+        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
+
+        var response = new ApiErrorResponse(
+            "An unexpected error occurred. Please try again later.",
+            context.Response.StatusCode,
+            exception.Message
+        );
+
+        var options = new JsonSerializerOptions
+        {
+            PropertyNamingPolicy = JsonNamingPolicy.CamelCase
+        };
+
+        return context.Response.WriteAsync(JsonSerializer.Serialize(response, options));
+    }
+}
+
+/// <summary>
+/// Extension method to add exception middleware.
+/// </summary>
+public static class ExceptionMiddlewareExtensions
+{
+    public static IApplicationBuilder UseExceptionMiddleware(this IApplicationBuilder builder) =>
+        builder.UseMiddleware<ExceptionMiddleware>();
+}

GermanApp/Shared/Models/ApiResponse.cs

@@ -0,0 +1,47 @@
+namespace GermanApp.Shared.Models;
+
+/// <summary>
+/// Base API response wrapper for consistent API responses.
+/// </summary>
+/// <typeparam name="T">The data type of the response</typeparam>
+public record ApiResponse<T>(T Data, string Message = "Success", bool Success = true)
+{
+    /// <summary>
+    /// Creates a successful response.
+    /// </summary>
+    public static ApiResponse<T> Ok(T data, string message = "Success") =>
+        new ApiResponse<T>(data, message, true);
+}
+
+/// <summary>
+/// API error response for consistent error handling.
+/// </summary>
+public record ApiErrorResponse(string Message, int StatusCode, string? Details = null)
+{
+    public bool Success => false;
+
+    /// <summary>
+    /// Creates an error response.
+    /// </summary>
+    public static ApiErrorResponse Error(string message, int statusCode, string? details = null) =>
+        new ApiErrorResponse(message, statusCode, details);
+}
+
+/// <summary>
+/// Paginated API response.
+/// </summary>
+/// <typeparam name="T">The data type of the items</typeparam>
+public record PaginatedResponse<T>(IEnumerable<T> Items, int PageNumber, int PageSize, int TotalCount, int TotalPages)
+{
+    /// <summary>
+    /// Creates a paginated response.
+    /// </summary>
+    public static PaginatedResponse<T> Create(IEnumerable<T> items, int pageNumber, int pageSize, int totalCount) =>
+        new PaginatedResponse<T>(
+            items,
+            pageNumber,
+            pageSize,
+            totalCount,
+            (int)Math.Ceiling(totalCount / (double)pageSize)
+        );
+}