From 3483b0ffaea3e1a2b4ee6e4959f7a2190136fef5 Mon Sep 17 00:00:00 2001
From: Ken Hibino <ken.hibino7@gmail.com>
Date: Tue, 30 Nov 2021 07:06:26 -0800
Subject: [PATCH] WIP: (api): Update metrics handler to take options

---
 handler.go         |  2 +-
 metrics_handler.go | 60 ++++++++++++++++++++++++++++++----------------
 2 files changed, 41 insertions(+), 21 deletions(-)

diff --git a/handler.go b/handler.go
index 350f12a..542bb28 100644
--- a/handler.go
+++ b/handler.go
@@ -188,7 +188,7 @@ func muxRouter(opts Options, rc redis.UniversalClient, inspector *asynq.Inspecto
 	}
 
 	// Time series metrics endpoints.
-	api.HandleFunc("/metrics", newGetMetricsHandlerFunc(http.DefaultClient)).Methods("GET")
+	api.HandleFunc("/metrics", newGetMetricsHandlerFunc(http.DefaultClient, opts.PrometheusAddress)).Methods("GET")
 
 	// Everything else, route to uiAssetsHandler.
 	router.NotFoundHandler = &uiAssetsHandler{
diff --git a/metrics_handler.go b/metrics_handler.go
index 337f49c..41baed3 100644
--- a/metrics_handler.go
+++ b/metrics_handler.go
@@ -14,29 +14,21 @@ type getMetricsResponse struct {
 	// TODO
 }
 
-func unixTimeString(t time.Time) string {
-	return strconv.Itoa(int(t.Unix()))
+type metricsFetchOptions struct {
+	// Specifies the number of seconds to scan for metrics.
+	duration time.Duration
+
+	// Specifies the end time when fetching metrics.
+	endTime time.Time
 }
 
-func newGetMetricsHandlerFunc(client *http.Client) http.HandlerFunc {
+func newGetMetricsHandlerFunc(client *http.Client, prometheusAddr string) http.HandlerFunc {
+	// Optional query params:
+	// `duration_sec`: specifies the number of seconds to scan
+	// `end_time`:     specifies the end_time in Unix time seconds
 	return func(w http.ResponseWriter, r *http.Request) {
-		const (
-			baseAddr = "http://localhost:9090"
-			apiPath  = "/api/v1/query_range"
-			promQL   = "asynq_queue_size"
-		)
-		var b strings.Builder
-		v := url.Values{}
-		b.WriteString(baseAddr)
-		b.WriteString(apiPath)
-		v.Add("query", promQL)
-		now := time.Now()
-		v.Add("start", unixTimeString(now.Add(-30*time.Minute)))
-		v.Add("end", unixTimeString(now))
-		v.Add("step", (1 * time.Minute).String())
-		b.WriteString("?")
-		b.WriteString(v.Encode())
-		url := b.String()
+		opts := extractMetricsFetchOptions(r)
+		url := buildPrometheusURL(prometheusAddr, "asynq_queue_size", opts)
 		fmt.Printf("DEBUG: url: %s\n", url)
 		resp, err := client.Get(url)
 		if err != nil {
@@ -50,3 +42,31 @@ func newGetMetricsHandlerFunc(client *http.Client) http.HandlerFunc {
 		}
 	}
 }
+
+const prometheusAPIPath = "/api/v1/query_range"
+
+func extractMetricsFetchOptions(r *http.Request) *metricsFetchOptions {
+	// TODO: Extract these options from the request if any, and default to these values if none are specified
+	return &metricsFetchOptions{
+		duration: 60 * time.Minute,
+		endTime:  time.Now(),
+	}
+}
+
+func buildPrometheusURL(baseAddr, promQL string, opts *metricsFetchOptions) string {
+	var b strings.Builder
+	b.WriteString(strings.TrimSuffix(baseAddr, "/"))
+	b.WriteString(prometheusAPIPath)
+	v := url.Values{}
+	v.Add("query", promQL)
+	v.Add("start", unixTimeString(opts.endTime.Add(-opts.duration)))
+	v.Add("end", unixTimeString(opts.endTime))
+	v.Add("step", (1 * time.Minute).String())
+	b.WriteString("?")
+	b.WriteString(v.Encode())
+	return b.String()
+}
+
+func unixTimeString(t time.Time) string {
+	return strconv.Itoa(int(t.Unix()))
+}