Started implementing metrics system

Moonlight.ApiServer/Services/MetricsBackgroundService.cs

@@ -0,0 +1,78 @@
+using System.Diagnostics.Metrics;
+using Moonlight.ApiServer.Configuration;
+using Moonlight.ApiServer.Interfaces;
+
+namespace Moonlight.ApiServer.Services;
+
+public class MetricsBackgroundService : BackgroundService
+{
+    private readonly ILogger<MetricsBackgroundService> Logger;
+    private readonly IServiceProvider ServiceProvider;
+    private readonly AppConfiguration Configuration;
+
+    private readonly IMetric[] Metrics;
+    private readonly Meter Meter;
+
+    public MetricsBackgroundService(
+        IServiceProvider serviceProvider,
+        IMeterFactory meterFactory,
+        IEnumerable<IMetric> metrics,
+        ILogger<MetricsBackgroundService> logger,
+        AppConfiguration configuration
+    )
+    {
+        ServiceProvider = serviceProvider;
+        Logger = logger;
+        Configuration = configuration;
+
+        Meter = meterFactory.Create("moonlight");
+
+        Metrics = metrics.ToArray();
+    }
+
+    private async Task Initialize()
+    {
+        Logger.LogDebug(
+            "Initializing metrics: {names}",
+            string.Join(", ", Metrics.Select(x => x.GetType().FullName))
+        );
+
+        foreach (var metric in Metrics)
+            await metric.Initialize(Meter);
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        await Initialize();
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            using var scope = ServiceProvider.CreateScope();
+
+            foreach (var metric in Metrics)
+            {
+                try
+                {
+                    await metric.Run(scope.ServiceProvider, stoppingToken);
+                }
+                catch (TaskCanceledException)
+                {
+                    // Ignored
+                }
+                catch (Exception e)
+                {
+                    Logger.LogError(
+                        "An unhandled error occured while collecting metric {name}: {e}",
+                        metric.GetType().FullName,
+                        e
+                    );
+                }
+            }
+
+            await Task.Delay(
+                TimeSpan.FromSeconds(Configuration.Metrics.Interval),
+                stoppingToken
+            );
+        }
+    }
+}