ServiceLocator.cs

namespace OrderProcessing;

/// <summary>
/// The service locator plays the middleman and allow consumers
/// to find and connect with various services.
/// Possible improvements:
/// 1) The service locator itself might be a singleton. Usually, there is no need to have two instances of a service locator.
/// 2) Lazy initialization of services might be considered.
///    In the example above, the constructor creates new instances for all possible services.
///    Initialization might be deferred until some client actually requests a particular service.
/// 3) The mapping between interfaces and implementation might be more flexible using metadata
///    (e.g.through application configuration files).
/// </summary>
public class ServiceLocator : IServiceLocator
{
    private readonly Dictionary<string, object> _services;

    public ServiceLocator()
    {
        // Services can be pre-populated, but users could add them dynamically too.
        _services = new Dictionary<string, object>()
        {
            { nameof(PaymentProcessor), new PaymentProcessor() },
            { nameof(NotificationManager), new NotificationManager() },
        };
    }

    public void AddService<T>(T service) where T : notnull =>
        _services.Add(typeof(T).Name, service);

    public void AddService<T>(string serviceName, T service) where T : notnull =>
        _services.Add(serviceName, service);

    public T GetService<T>() where T : notnull =>
        (T)_services[typeof(T).Name];

    public object GetService<T>(string serviceName) where T : notnull =>
        (T)_services[serviceName];

    /*public void AddService(string serviceName)
    {
        // What if we have app.config with similar content?
        // <configuration>
        //      <appSettings>
        //          <add key="logger" value="OrderProcessing.NotificationManager"/>
        //      </appSettings>
        // </configuration>

        var configurationEntry = ConfigurationManager.AppSettings[serviceName];

        // Initialize notification manager through reflection
        var notificationManager = Assembly.GetExecutingAssembly().CreateInstance(configurationEntry);

        AddService(serviceName, notificationManager);
    }*/
}