package main

import (
	"flag"
	"fmt"
	"log"
	"math/rand"
	"net/http"
	"strings"
	"time"

	"github.com/gorilla/mux"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

var (
	addr = flag.String("listen-address", ":8080", "The address to listen on for HTTP requests.")
)

var (
	requestTimes = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "request_times",
		Help: "请求次数",
	}, []string{"method", "url", "host"})
	// 多个label，需要与requestTimes.WithLabelValues(strings.ToLower(r.Method), r.URL.String())一一对应，
	// 效果为可用promql  request_times{method="get",url="/metrics",host="172.20.16.185:8080"}查询

	requestTime = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Name: "request_time",
		Help: "每次请求花费的时间",
	}, []string{"method", "url", "host"})

	// 需要计算，开销大
	requestSummary = prometheus.NewSummaryVec(prometheus.SummaryOpts{
		Name:       "request_time_summary",
		Help:       "summary test",
		Objectives: map[float64]float64{0.5: 0.05, 0.9: 0.01, 0.99: 0.001},
		// 0.5，0.9，0.99表示分位数，0.05，0.01，0.001表示可接收的误差，比如0.5分位的值为10，其实这个10可能是(0.45,0.55)这个区间内的某个值，太过精确会导致cpu压力过大
	}, []string{"request_time"})

	// Histogram只计数，不计算，开销小
	// 线性桶
	requestHistogram = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "request_time_histogram",
		Help:    "histogram LinearBuckets test",
		Buckets: prometheus.LinearBuckets(1, 2, 20), // 初始为1，间隔为2，一共20个取值，Buckets会隐式添加 `+Inf` 值作为取值区间的最大值
		// request_time_histogram_bucket{instance="172.20.16.185:8080", job="my_metrics", le="1.0", request_time="request_time"}
		// request_time_histogram_bucket{instance="172.20.16.185:8080", job="my_metrics", le="3.0", request_time="request_time"}
		// ...
		// 会生成如上所示的指标，le: 小于等于
		// 即，比如第一个数据的值，表示为小于等于1.0的个数，此处即为响应时间小于等于1.0的请求的个数
	}, []string{"request_time"})

	// 默认桶
	requestHistogramDef = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "request_time_histogram_def_buckets",
		Help:    "histogram DefBuckets test",
		Buckets: prometheus.DefBuckets,
	}, []string{"request_time"})

	// 指数桶
	requestHistogramExponentialBuckets = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "request_time_histogram_exponential_buckets",
		Help:    "histogram ExponentialBuckets test",
		Buckets: prometheus.ExponentialBuckets(1, 2, 20), // 初始值为1，指数为2增长，20个取值
	}, []string{"request_time"})
	// 不同的桶根据具体情况而定
)

func init() {
	// Add Go module build info.
	// 也可prometheus.MustRegister(xx, yy)
	prometheus.MustRegister(requestTime)
	prometheus.MustRegister(requestTimes)
	prometheus.MustRegister(requestSummary)
	prometheus.MustRegister(requestHistogram, requestHistogramDef, requestHistogramExponentialBuckets)
}

func main() {
	flag.Parse()
	r := mux.NewRouter()
	r.HandleFunc("/", handler)
	r.Use(metricsMiddleware)

	r.Handle("/metrics", promhttp.HandlerFor(
		prometheus.DefaultGatherer,
		promhttp.HandlerOpts{
			// Opt into OpenMetrics to support exemplars.
			EnableOpenMetrics: true,
		},
	))
	log.Fatal(http.ListenAndServe(*addr, r))
}

func metricsMiddleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now().Unix()
		next.ServeHTTP(w, r)
		end := time.Now().Unix()
		requestTime.WithLabelValues(strings.ToLower(r.Method), r.URL.String(), r.Host).Set(float64(end - start))
		requestTimes.WithLabelValues(strings.ToLower(r.Method), r.URL.String(), r.Host).Add(1)
		requestSummary.WithLabelValues("request_time").Observe(float64(end - start))
		requestHistogram.WithLabelValues("request_time").Observe(float64(end - start))
		requestHistogramDef.WithLabelValues("request_time").Observe(float64(end - start))
		requestHistogramExponentialBuckets.WithLabelValues("request_time").Observe(float64(end - start))
	})
}

func handler(w http.ResponseWriter, r *http.Request) {
	x := rand.Intn(3)
	time.Sleep(time.Duration(x) * time.Second)
	_, _ = w.Write([]byte("handler response"))
	fmt.Println("print handler")
}

// 清除数据，各项数据都会清零
func dataClear() {
	requestTime.Reset()
	requestTimes.Reset()
	requestHistogram.Reset()
	requestHistogramExponentialBuckets.Reset()
	requestHistogramDef.Reset()
	requestSummary.Reset()
}