Migrate existing code

Services/Dhcp/DhcpWatcher.cs

@@ -0,0 +1,50 @@
+using System.Collections.Immutable;
+
+using DotNetDDI.Options;
+
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Options;
+
+namespace DotNetDDI.Services.Dhcp;
+
+public class DhcpWatcher : IHostedService
+{
+	private readonly ImmutableArray<IHostedService> _services;
+
+	public DhcpWatcher(IOptions<DhcpOptions> options, IDhcpWatcherFactory factory)
+	{
+		var dhcpOptions = options.Value;
+		var services = ImmutableArray.CreateBuilder<IHostedService>();
+		if (dhcpOptions.Kea is { } keaOptions)
+		{
+			services.Add(factory.KeaService(keaOptions));
+		}
+
+		_services = services.DrainToImmutable();
+	}
+
+	public Task StartAsync(CancellationToken cancellationToken = default)
+	{
+		Task[] tasks = new Task[_services.Length];
+		for (int i = 0; i < tasks.Length; i++)
+		{
+			tasks[i] = _services[i].StartAsync(cancellationToken);
+		}
+
+		return Task.WhenAll(tasks);
+	}
+
+	public async Task StopAsync(CancellationToken cancellationToken = default)
+	{
+		Task[] tasks = new Task[_services.Length];
+		for (int i = 0; i < tasks.Length; i++)
+		{
+			tasks[i] = _services[i].StopAsync(cancellationToken);
+		}
+
+		var waitTask = Task.WhenAll(tasks);
+		TaskCompletionSource taskCompletionSource = new();
+		using var registration = cancellationToken.Register(s => ((TaskCompletionSource)s!).SetCanceled(), taskCompletionSource);
+		await Task.WhenAny(waitTask, taskCompletionSource.Task).ConfigureAwait(false);
+	}
+}