Record system license metrics

Author: tiksn

src/API.Core/DefaultCoreModule.cs

@@ -2,6 +2,7 @@
 using Fossa.API.Core.Entities;
 using Fossa.API.Core.Relationship;
 using Fossa.API.Core.Services;
+using Fossa.API.Core.Telemetry;
 using Fossa.API.Core.TimeZone;
 using TIKSN.Data.BareEntityResolvers;
 using TIKSN.Identity;
@@ -51,6 +52,11 @@ protected override void Load(ContainerBuilder builder)
       .AsImplementedInterfaces()
       .InstancePerLifetimeScope();
 
+    builder
+      .RegisterType<SystemLicenseMetricsRecorder>()
+      .AsImplementedInterfaces()
+      .SingleInstance();
+
     builder
       .RegisterType<CompanyLicenseCreator>()
       .AsImplementedInterfaces()

src/API.Core/Services/SystemLicenseRetriever.cs

@@ -1,4 +1,5 @@
 using Fossa.API.Core.Repositories;
+using Fossa.API.Core.Telemetry;
 using Fossa.Licensing;
 using Microsoft.Extensions.Hosting;
 using TIKSN.Deployment;
@@ -12,17 +13,20 @@ public class SystemLicenseRetriever : ISystemLicenseRetriever
   private readonly IHostEnvironment _hostEnvironment;
   private readonly ILicenseFactory<SystemEntitlements, SystemLicenseEntitlements> _licenseFactory;
   private readonly ILicenseFileRepository _licenseFileRepository;
+  private readonly ISystemLicenseMetricsRecorder _systemLicenseMetricsRecorder;
   private readonly ISystemPropertiesQueryRepository _systemPropertiesQueryRepository;
 
   public SystemLicenseRetriever(
     ILicenseFileRepository licenseFileRepository,
     ILicenseFactory<SystemEntitlements, SystemLicenseEntitlements> licenseFactory,
+    ISystemLicenseMetricsRecorder systemLicenseMetricsRecorder,
     ICertificateProvider certificateProvider,
     IHostEnvironment hostEnvironment,
     ISystemPropertiesQueryRepository systemPropertiesQueryRepository)
   {
     _licenseFileRepository = licenseFileRepository ?? throw new ArgumentNullException(nameof(licenseFileRepository));
     _licenseFactory = licenseFactory ?? throw new ArgumentNullException(nameof(licenseFactory));
+    _systemLicenseMetricsRecorder = systemLicenseMetricsRecorder ?? throw new ArgumentNullException(nameof(systemLicenseMetricsRecorder));
     _certificateProvider = certificateProvider ?? throw new ArgumentNullException(nameof(certificateProvider));
     _hostEnvironment = hostEnvironment ?? throw new ArgumentNullException(nameof(hostEnvironment));
     _systemPropertiesQueryRepository = systemPropertiesQueryRepository ?? throw new ArgumentNullException(nameof(systemPropertiesQueryRepository));
@@ -41,12 +45,16 @@ public async Task<Validation<Error, License<SystemEntitlements>>> GetAsync(Cance
 
     var licenseValidation = _licenseFactory.Create(licenseData, certificate);
 
-    return licenseValidation
+    licenseValidation = licenseValidation
       .Validate(
         license => license.Entitlements.SystemId == systemPropertiesEntity.SystemID,
         11751858, "Current System License is issued to another system.")
       .Validate(
         license => _hostEnvironment.MatchesEnvironment(license.Entitlements.EnvironmentName),
         19509088, "Current System License is issued for another deployment environment.");
+
+    _systemLicenseMetricsRecorder.Record(licenseValidation);
+
+    return licenseValidation;
   }
 }

src/API.Core/Telemetry/ISystemLicenseMetricsRecorder.cs

@@ -0,0 +1,13 @@
+using Fossa.Licensing;
+using TIKSN.Licensing;
+
+namespace Fossa.API.Core.Telemetry;
+
+public interface ISystemLicenseMetricsRecorder
+{
+  /// <summary>
+  /// Records the system license metrics.
+  /// </summary>
+  /// <param name="license">The license to record.</param>
+  void Record(Validation<Error, License<SystemEntitlements>> license);
+}

src/API.Core/Telemetry/SystemLicenseMetricsRecorder.cs

@@ -0,0 +1,43 @@
+using System.Diagnostics.Metrics;
+using Fossa.Licensing;
+using TIKSN.Licensing;
+
+namespace Fossa.API.Core.Telemetry;
+
+public class SystemLicenseMetricsRecorder : ISystemLicenseMetricsRecorder
+{
+  private readonly Gauge<double> _daysLeft;
+  private readonly TimeProvider _timeProvider;
+
+  public SystemLicenseMetricsRecorder(
+    TimeProvider timeProvider,
+    IMeterFactory meterFactory)
+  {
+    var meter = meterFactory.Create("Fossa.API.Core.Telemetry");
+    _daysLeft = meter.CreateGauge<double>("fossa.api.core.telemetry.system_license_days_left");
+    _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
+  }
+
+  public void Record(Validation<Error, License<SystemEntitlements>> license)
+  {
+    _daysLeft.Record(
+      license.Match(
+        validLicense => CalculateTimeLeft(validLicense).TotalDays,
+        _ => 0.0),
+      new KeyValuePair<string, object?>("license_status",
+        license.Match(
+          validLicense => "valid",
+          _ => "invalid")));
+  }
+
+  private TimeSpan CalculateTimeLeft(License<SystemEntitlements> validLicense)
+  {
+    var now = _timeProvider.GetUtcNow();
+    if (validLicense.Terms.NotAfter <= now)
+    {
+      return TimeSpan.Zero;
+    }
+
+    return validLicense.Terms.NotAfter.Subtract(now);
+  }
+}