feat: add actual metrics using prometheus-net

Foxnouns.Backend/Services/MetricsCollectionService.cs

@@ -0,0 +1,66 @@
+using System.Diagnostics;
+using Foxnouns.Backend.Database;
+using Microsoft.EntityFrameworkCore;
+using NodaTime;
+using Prometheus;
+
+namespace Foxnouns.Backend.Services;
+
+public class MetricsCollectionService(
+    ILogger logger,
+    IServiceProvider services,
+    IClock clock)
+{
+    private readonly ILogger _logger = logger.ForContext<MetricsCollectionService>();
+
+    private static readonly Duration Month = Duration.FromDays(30);
+    private static readonly Duration Week = Duration.FromDays(7);
+    private static readonly Duration Day = Duration.FromDays(1);
+
+    public async Task CollectMetricsAsync(CancellationToken ct = default)
+    {
+        var timer = FoxnounsMetrics.MetricsCollectionTime.NewTimer();
+        var now = clock.GetCurrentInstant();
+
+        await using var scope = services.CreateAsyncScope();
+        await using var db = scope.ServiceProvider.GetRequiredService<DatabaseContext>();
+
+        var users = await db.Users.Where(u => !u.Deleted).Select(u => u.LastActive).ToListAsync(ct);
+        FoxnounsMetrics.UsersCount.Set(users.Count);
+        FoxnounsMetrics.UsersActiveMonthCount.Set(users.Count(i => i > now - Month));
+        FoxnounsMetrics.UsersActiveWeekCount.Set(users.Count(i => i > now - Week));
+        FoxnounsMetrics.UsersActiveDayCount.Set(users.Count(i => i > now - Day));
+
+        var memberCount = await db.Members.Include(m => m.User)
+            .Where(m => !m.Unlisted && !m.User.ListHidden && !m.User.Deleted).CountAsync(ct);
+        FoxnounsMetrics.MemberCount.Set(memberCount);
+
+        var process = Process.GetCurrentProcess();
+        FoxnounsMetrics.ProcessPhysicalMemory.Set(process.WorkingSet64);
+        FoxnounsMetrics.ProcessVirtualMemory.Set(process.VirtualMemorySize64);
+        FoxnounsMetrics.ProcessPrivateMemory.Set(process.PrivateMemorySize64);
+        FoxnounsMetrics.ProcessThreads.Set(process.Threads.Count);
+        FoxnounsMetrics.ProcessHandles.Set(process.HandleCount);
+
+        _logger.Information("Collected metrics in {DurationMilliseconds} ms",
+            timer.ObserveDuration().TotalMilliseconds);
+    }
+}
+
+public class BackgroundMetricsCollectionService(ILogger logger, MetricsCollectionService innerService)
+    : BackgroundService
+{
+    private readonly ILogger _logger = logger.ForContext<BackgroundMetricsCollectionService>();
+
+    protected override async Task ExecuteAsync(CancellationToken ct)
+    {
+        _logger.Information("Metrics are disabled, periodically collecting metrics manually");
+
+        using var timer = new PeriodicTimer(TimeSpan.FromMinutes(1));
+        while (await timer.WaitForNextTickAsync(ct))
+        {
+            _logger.Debug("Collecting metrics");
+            await innerService.CollectMetricsAsync(ct);
+        }
+    }
+}