Backend Architecture

var builder = WebApplication.CreateBuilder(args);

// ─── 1. Environment Detection ───────────────────────────
var moduleName = Environment.GetEnvironmentVariable("MODULE_NAME") ?? "";
var isMonolith = string.IsNullOrEmpty(moduleName);
var isGateway = moduleName.Equals("Gateway", StringComparison.OrdinalIgnoreCase);

// ─── 2. Core Infrastructure (must come first) ───────────
builder.Services.AddInfrastructureServices(builder.Configuration);
builder.Services.AddCorsConfiguration(builder.Configuration);
builder.Services.AddRateLimitingConfiguration();
builder.Services.AddCoreInfrastructure(builder.Configuration);

// ─── 3. Module Registration (guarded by mode) ───────────
var handlerAssemblies = new List<Assembly>();
if (isMonolith || moduleName == "Identity")
{
    handlerAssemblies.Add(typeof(Identity.Application.DependencyInjection));
    builder.Services.AddIdentityModule(builder.Configuration);
}

// ─── 4. Application Layer (needs module assemblies) ─────
builder.Services.AddCoreApplication(handlerAssemblies);

// ─── 5. Build & Configure Pipeline ─────────────────────
var app = builder.Build();
app.UseMiddleware<RequestLoggingMiddleware>();
app.UseMiddleware<AuditableMiddleware>();
app.UseRateLimiter();
app.UseAuthentication();
app.UseAuthorization();
app.MapControllers();
app.Run();

public static class DependencyInjection
{
    public static IServiceCollection AddIdentityModule(
        this IServiceCollection services,
        IConfiguration configuration)
    {
        // 1. DbContext registration (multi-provider)
        services.AddDbContext<IdentityDbContext>(options =>
        {
            var provider = configuration["DatabaseProvider"];
            switch (provider)
            {
                case "SqlServer":
                    options.UseSqlServer(connectionString);
                    break;
                case "PostgreSQL":
                    options.UseNpgsql(connectionString);
                    break;
                case "Oracle":
                    options.UseOracle(connectionString);
                    break;
            }
        });

        // 2. Repository registrations
        services.AddScoped<IAdminRepository, AdminRepository>();
        services.AddScoped<IUserRepository, UserRepository>();
        services.AddScoped<IRoleRepository, RoleRepository>();

        // 3. Module-specific services
        services.AddScoped<IPermissionService, PermissionService>();
        services.AddScoped<IJwtService, JwtService>();

        // 4. Module registration (for runtime introspection)
        services.AddSingleton<IModuleRegistration, IdentityModuleRegistration>();

        return services;
    }
}