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package main

import (
	"fmt"
	"math/rand"
	"net/http"
	"os"
	"time"

	"github.com/gorilla/handlers"
	"github.com/gorilla/mux"
	"github.com/prometheus/client_golang/prometheus"
	promhttp "github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/sirupsen/logrus"
)

var (
	// Counter vector to which we can attach labels. That creates many key-value
	// label combinations. So in our case we count requests by status code separetly.
	counter = prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "hello_requests_total",
			Help: "Total number of /hello requests.",
		},
		[]string{"status"},
	)
)

func init() {
	prometheus.MustRegister(counter)
}

func main() {
	var log = logrus.New()
	// set the log output
	log.Out = os.Stdout
	// set the log level
	log.Level = logrus.DebugLevel
	// Routes consist of a path and a handler function.
	r := mux.NewRouter()
	// sample log.Info
	log.Info("http server is ready")
	// sample log.Debug
	log.Debug("i am only visible in debug mode\n")
	// exposes /hello endpoint with the helloHandler handler
	r.HandleFunc("/hello", helloHandler)
	// exposes /metrics endpoint with standard golang metrics used by prometheus
	r.Handle("/metrics", promhttp.Handler())
	// wrap a logger arount the mux router
	loggedRouter := handlers.LoggingHandler(os.Stdout, r)
	// wrap a prometheus instrument handler around the logger
	prometheusRouter := prometheus.InstrumentHandlerWithOpts(prometheus.SummaryOpts{}, loggedRouter)
	// Bind to a port and pass our loggedRouter in
	log.Fatal(http.ListenAndServe(":8080", prometheusRouter))

}

func doSomeWork() int {
	time.Sleep(time.Duration(rand.Intn(1000)) * time.Millisecond)

	statusCodes := [...]int{
		http.StatusOK,
		http.StatusBadRequest,
		http.StatusUnauthorized,
		http.StatusInternalServerError,
	}
	return statusCodes[rand.Intn(len(statusCodes))]
}

func helloHandler(w http.ResponseWriter, r *http.Request) {
	var status int

	defer func(begun time.Time) {
		// hello_requests_total{status="200"} 2385
		counter.With(prometheus.Labels{
			"status": fmt.Sprint(status),
		}).Inc()
	}(time.Now())

	status = doSomeWork()
	w.WriteHeader(status)
	w.Write([]byte("Hello, World!\n"))
}