From 849bdc9d337a749b2ff667bc2854edd499597007 Mon Sep 17 00:00:00 2001
From: Julius Volz <julius.volz@gmail.com>
Date: Mon, 26 Aug 2019 19:45:14 +0200
Subject: [PATCH] Add holiday-based metrics

Signed-off-by: Julius Volz <julius.volz@gmail.com>
---
 holiday.go | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 main.go    |  1 +
 2 files changed, 62 insertions(+)
 create mode 100644 holiday.go

diff --git a/holiday.go b/holiday.go
new file mode 100644
index 0000000..bd2efbc
--- /dev/null
+++ b/holiday.go
@@ -0,0 +1,61 @@
+package main
+
+import (
+	"math"
+	"math/rand"
+	"sync/atomic"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+var (
+	isHoliday = prometheus.NewGauge(
+		prometheus.GaugeOpts{
+			Namespace: namespace,
+			Name:      "is_holiday",
+			Help:      "Set to 1 if it is currently a holiday, 0 otherwise.",
+		})
+
+	shippedItems = prometheus.NewCounter(
+		prometheus.CounterOpts{
+			Namespace: namespace,
+			Name:      "items_shipped_total",
+			Help:      "The total number of shipped items. Affected heavily by whether it's currently a holiday.",
+		})
+
+	isHolidayVar = uint64(0)
+)
+
+func init() {
+	prometheus.MustRegister(isHoliday)
+	prometheus.MustRegister(shippedItems)
+}
+
+func runHolidaySim(dayLength time.Duration, holidayRatio float64) {
+	start := time.Now()
+	go func() {
+		for {
+			shippedItems.Inc()
+			factor := 2 + math.Sin(1+2*math.Pi*float64(time.Since(start))/float64(dayLength))
+			d := 100 * factor
+			if isHolidayVar == 1 {
+				d *= 1.8
+			}
+			time.Sleep(time.Duration(d) * time.Millisecond)
+		}
+	}()
+
+	ticker := time.NewTicker(dayLength)
+	for {
+		if rand.Float64() > holidayRatio {
+			isHoliday.Set(0)
+			atomic.StoreUint64(&isHolidayVar, 0)
+		} else {
+			isHoliday.Set(1)
+			atomic.StoreUint64(&isHolidayVar, 1)
+		}
+
+		<-ticker.C
+	}
+}
diff --git a/main.go b/main.go
index 09c702c..e7f14bf 100644
--- a/main.go
+++ b/main.go
@@ -27,6 +27,7 @@ func main() {
 	go runBatchJobs(time.Minute, 10*time.Second, 0.25)
 	go runCPUSim(4, 0.3, 0.2)
 	go runDiskSim(160*1e9, 0.5*1e6)
+	go runHolidaySim(5*time.Minute, 0.2)
 
 	select {}
 }