From e451849768234b43f9f4d6f2880617905c2c6638 Mon Sep 17 00:00:00 2001
From: Daniele Teti <d.teti@bittime.it>
Date: Wed, 12 Apr 2023 17:49:30 +0200
Subject: [PATCH] Improved Prometheus Middleware

---
 .../Controllers.Articles.pas                  |  6 +--
 .../MVCFramework.Middleware.Prometheus.pas    | 53 ++++++++++++++++---
 2 files changed, 50 insertions(+), 9 deletions(-)

diff --git a/samples/prometheus/articles_crud_server_prometheus/Controllers.Articles.pas b/samples/prometheus/articles_crud_server_prometheus/Controllers.Articles.pas
index 12441afa..ff42dd2e 100644
--- a/samples/prometheus/articles_crud_server_prometheus/Controllers.Articles.pas
+++ b/samples/prometheus/articles_crud_server_prometheus/Controllers.Articles.pas
@@ -70,7 +70,7 @@ procedure TArticlesController.CreateArticle(const Article: TArticle);
 begin
   GetArticlesService.Add(Article);
   Render201Created('/articles/' + Article.id.ToString, 'Article Created');
-  Metrics.Inc('new_article');
+  Metrics.IncCounterValue('new_article');
 end;
 
 procedure TArticlesController.CreateArticles(const ArticleList: TObjectList<TArticle>);
@@ -84,7 +84,7 @@ begin
       GetArticlesService.Add(lArticle);
     end;
     GetArticlesService.Commit;
-    Metrics.Inc('new_article', ArticleList.Count);
+    Metrics.IncCounterValue('new_article', ArticleList.Count);
   except
     GetArticlesService.Rollback;
     raise;
@@ -130,7 +130,7 @@ begin
       lDict := ObjectDict().Add('data', GetArticlesService.GetArticles(Search));
     end;
     Render(lDict);
-    Metrics.Inc('searches');
+    Metrics.IncCounterValue('searches');
   except
     on E: EServiceException do
     begin
diff --git a/samples/prometheus/articles_crud_server_prometheus/MVCFramework.Middleware.Prometheus.pas b/samples/prometheus/articles_crud_server_prometheus/MVCFramework.Middleware.Prometheus.pas
index 34f64893..5412b99e 100644
--- a/samples/prometheus/articles_crud_server_prometheus/MVCFramework.Middleware.Prometheus.pas
+++ b/samples/prometheus/articles_crud_server_prometheus/MVCFramework.Middleware.Prometheus.pas
@@ -24,12 +24,19 @@ type
     constructor Create(const PrometheusRoute: String = '/metrics'; const OnBeforeMetricsGet: TProc = nil);
   end;
 
+  {Simplified access to the most common Prometheus metrics}
   Metrics = class sealed
   public
-    class procedure Inc(const MetricName: string; const Amount: Double = 1); overload;
-    class procedure Inc(const MetricName: string; const Amount: Double; const Labels: TArray<String>); overload;
+    // "Counter" metric
+    class procedure IncCounterValue(const MetricName: string; const Amount: Double = 1); overload;
+    class procedure IncCounterValue(const MetricName: string; const Amount: Double; const Labels: TArray<String>); overload;
+    // "Gauge" metric
     class procedure SetGaugeValue(const MetricName: string; const Amount: Double = 1); overload;
     class procedure SetGaugeValue(const MetricName: string; const Amount: Double; const Labels: TArray<String>); overload;
+    class procedure IncGaugeValue(const MetricName: string; const Amount: Double = 1); overload;
+    class procedure IncGaugeValue(const MetricName: string; const Amount: Double; const Labels: TArray<String>); overload;
+    class procedure DecGaugeValue(const MetricName: string; const Amount: Double = -1); overload;
+    class procedure DecGaugeValue(const MetricName: string; const Amount: Double; const Labels: TArray<String>); overload;
   end;
 
 
@@ -61,7 +68,7 @@ end;
 procedure TMVCPrometheusMiddleware.OnAfterRouting(AContext: TWebContext;
   const AHandled: Boolean);
 begin
-  Metrics.Inc('http_requests_handled', 1,
+  Metrics.IncCounterValue('http_requests_handled', 1,
     [AContext.Request.PathInfo, IntToStr(AContext.Response.StatusCode)]);
 end;
 
@@ -78,7 +85,7 @@ begin
   if not SameText(AContext.Request.PathInfo, fPrometheusRoute) then
   begin
     // Get the metric counter and increment it.
-    Metrics.Inc('http_requests_count');
+    Metrics.IncCounterValue('http_requests_count');
   end
   else
   begin
@@ -101,7 +108,7 @@ end;
 
 { Metrics }
 
-class procedure Metrics.Inc(const MetricName: string; const Amount: Double);
+class procedure Metrics.IncCounterValue(const MetricName: string; const Amount: Double);
 begin
   TCollectorRegistry
     .DefaultRegistry
@@ -109,7 +116,24 @@ begin
     .Inc(Amount);
 end;
 
-class procedure Metrics.Inc(const MetricName: string; const Amount: Double;
+class procedure Metrics.DecGaugeValue(const MetricName: string;
+  const Amount: Double; const Labels: TArray<String>);
+begin
+  TCollectorRegistry.DefaultRegistry
+    .GetCollector<TGauge>(MetricName)
+    .Labels(Labels)
+    .Dec(Amount);
+end;
+
+class procedure Metrics.DecGaugeValue(const MetricName: string;
+  const Amount: Double);
+begin
+  TCollectorRegistry.DefaultRegistry
+    .GetCollector<TGauge>(MetricName)
+    .Dec(Amount);
+end;
+
+class procedure Metrics.IncCounterValue(const MetricName: string; const Amount: Double;
   const Labels: TArray<String>);
 begin
   TCollectorRegistry
@@ -119,6 +143,23 @@ begin
     .Inc(Amount);
 end;
 
+class procedure Metrics.IncGaugeValue(const MetricName: string;
+  const Amount: Double);
+begin
+  TCollectorRegistry.DefaultRegistry
+    .GetCollector<TGauge>(MetricName)
+    .Inc(Amount);
+end;
+
+class procedure Metrics.IncGaugeValue(const MetricName: string;
+  const Amount: Double; const Labels: TArray<String>);
+begin
+  TCollectorRegistry.DefaultRegistry
+    .GetCollector<TGauge>(MetricName)
+    .Labels(Labels)
+    .Inc(Amount);
+end;
+
 class procedure Metrics.SetGaugeValue(const MetricName: string;
   const Amount: Double; const Labels: TArray<String>);
 begin