Program.cs

using CityInfo.API;
using CityInfo.API.Services;
using Microsoft.AspNetCore.StaticFiles;
using Serilog;

// Configure Serilog logger...

Log.Logger = new LoggerConfiguration()
    .MinimumLevel.Debug()
    .WriteTo.Console()
    .WriteTo.File("logs/cityinfo.txt", rollingInterval: RollingInterval.Day)
    .CreateLogger();

var builder = WebApplication.CreateBuilder(args);
builder.Host.UseSerilog(); // use serilog instead of defualt

// Add services to the container.

builder.Services.AddControllers(options =>
{
    options.ReturnHttpNotAcceptable = true;
})
.AddNewtonsoftJson()
.AddXmlDataContractSerializerFormatters();

builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddSingleton<FileExtensionContentTypeProvider>();
builder.Services.AddSingleton<CitiesDataStore>();

#if DEBUG
builder.Services.AddTransient<IMailService, LocalMailService>(); // transient service because it is lightweight and stateless, for now.
#else
builder.Services.AddTransient<IMailService, CloudMailService>();
#endif // compiler directives to differentiate which service we want stemming from same interface.

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

app.UseHttpsRedirection();

app.UseRouting();

app.UseAuthorization();

app.UseEndpoints(endpoints =>
{
    endpoints.MapControllers();
});

app.MapControllers();

app.Run();