using Microsoft.Extensions.Hosting;

namespace Microsoft.Extensions.DependencyInjection
{
	/// <summary>
	/// Extensions for the <see cref="IServiceCollection"/>.
	/// </summary>
	public static class ServiceCollectionExtensions
	{
		/// <summary>
		/// Adds a hosted service that is instanciated only once.
		/// </summary>
		/// <typeparam name="TService">The type of the service to add.</typeparam>
		/// <param name="services">The <see cref="IServiceCollection"/> to add the service to.</param>
		/// <returns>A reference to this instance after the operation has completed.</returns>
		public static IServiceCollection AddSingletonHostedService<TService>(this IServiceCollection services)
			where TService : class, IHostedService
		{
			services.AddSingleton<TService>();
			services.AddSingleton<IHostedService, BackgroundServiceStarter<TService>>();
			return services;
		}
	}
}