feat(discord): add health check hosted service

Issue #32

src/GmRelay.DiscordBot/Infrastructure/Health/DiscordHealthCheckHostedService.cs

@@ -0,0 +1,101 @@
+using System.Net;
+
+namespace GmRelay.DiscordBot.Infrastructure.Health;
+
+public sealed class DiscordHealthCheckHostedService : IHostedService
+{
+    private readonly ILogger<DiscordHealthCheckHostedService> _logger;
+    private readonly string _prefix;
+    private HttpListener? _listener;
+    private CancellationTokenSource? _cts;
+    private Task? _listenerTask;
+
+    public DiscordHealthCheckHostedService(
+        ILogger<DiscordHealthCheckHostedService> logger,
+        IConfiguration configuration)
+    {
+        _logger = logger;
+        _prefix = configuration.GetValue("HealthCheck:Prefix", "http://+:8082/")!;
+    }
+
+    public Task StartAsync(CancellationToken cancellationToken)
+    {
+        _cts = new CancellationTokenSource();
+        _listener = new HttpListener();
+        _listener.Prefixes.Add(_prefix);
+        _listener.Start();
+
+        _logger.LogInformation("Discord health check server started on {Prefix}", _prefix);
+
+        _listenerTask = Task.Run(async () => await ListenAsync(_cts.Token), cancellationToken);
+
+        return Task.CompletedTask;
+    }
+
+    public async Task StopAsync(CancellationToken cancellationToken)
+    {
+        _cts?.Cancel();
+        _listener?.Stop();
+
+        if (_listenerTask != null)
+        {
+            await Task.WhenAny(_listenerTask, Task.Delay(TimeSpan.FromSeconds(5), cancellationToken));
+        }
+
+        _listener?.Close();
+        _logger.LogInformation("Discord health check server stopped");
+    }
+
+    private async Task ListenAsync(CancellationToken cancellationToken)
+    {
+        while (_listener?.IsListening == true && !cancellationToken.IsCancellationRequested)
+        {
+            try
+            {
+                var context = await _listener.GetContextAsync();
+                _ = Task.Run(() => HandleRequestAsync(context), cancellationToken);
+            }
+            catch (HttpListenerException) when (cancellationToken.IsCancellationRequested)
+            {
+                break;
+            }
+            catch (ObjectDisposedException)
+            {
+                break;
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "Error in Discord health check listener");
+            }
+        }
+    }
+
+    private async Task HandleRequestAsync(HttpListenerContext context)
+    {
+        var response = context.Response;
+        try
+        {
+            var request = context.Request;
+
+            if (request.Url?.AbsolutePath == "/health")
+            {
+                response.StatusCode = (int)HttpStatusCode.OK;
+                response.ContentType = "application/json";
+                var body = "{\"status\":\"healthy\"}"u8.ToArray();
+                await response.OutputStream.WriteAsync(body);
+            }
+            else
+            {
+                response.StatusCode = (int)HttpStatusCode.NotFound;
+            }
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Error handling Discord health check request");
+        }
+        finally
+        {
+            response.Close();
+        }
+    }
+}

tests/GmRelay.Bot.Tests/Infrastructure/Health/DiscordHealthCheckHostedServiceTests.cs

@@ -0,0 +1,53 @@
+using System.Net;
+using System.Net.Sockets;
+using GmRelay.DiscordBot.Infrastructure.Health;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging.Abstractions;
+
+namespace GmRelay.Bot.Tests.Infrastructure.Health;
+
+public sealed class DiscordHealthCheckHostedServiceTests : IDisposable
+{
+    private readonly DiscordHealthCheckHostedService _service;
+    private readonly int _port;
+
+    public DiscordHealthCheckHostedServiceTests()
+    {
+        _port = GetAvailablePort();
+        var config = new ConfigurationBuilder()
+            .AddInMemoryCollection(new Dictionary<string, string?>
+            {
+                ["HealthCheck:Prefix"] = $"http://localhost:{_port}/"
+            })
+            .Build();
+
+        _service = new DiscordHealthCheckHostedService(
+            NullLogger<DiscordHealthCheckHostedService>.Instance,
+            config);
+    }
+
+    public void Dispose()
+    {
+        _service.StopAsync(CancellationToken.None).Wait(TimeSpan.FromSeconds(5));
+    }
+
+    [Fact]
+    public async Task HealthEndpoint_ShouldReturn200_WhenServiceIsRunning()
+    {
+        await _service.StartAsync(CancellationToken.None);
+
+        using var client = new HttpClient { Timeout = TimeSpan.FromSeconds(5) };
+        var response = await client.GetAsync($"http://localhost:{_port}/health");
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+    }
+
+    private static int GetAvailablePort()
+    {
+        var listener = new TcpListener(IPAddress.Loopback, 0);
+        listener.Start();
+        var port = ((IPEndPoint)listener.LocalEndpoint).Port;
+        listener.Stop();
+        return port;
+    }
+}