package main

import (
	"github.com/prometheus/client_golang/prometheus"
	"net/http"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"time"
	"math/rand"
	"fmt"
)

// Counter类型的Metric
var httpRequestCount = prometheus.NewCounterVec(
	prometheus.CounterOpts{
		Name: "http_request_count", // Metric的name
		Help: "http request count"}, // Metric的说明信息
	[]string{"endpoint"}) // Metric有一个Label，名称是endpoint，Metric形如 http_request_count(endpoint="")

// Gauge类型的Metric
var orderNum = prometheus.NewGauge(
	prometheus.GaugeOpts{
		Name: "order_num",
		Help: "order num"})

// Summary类型的Metric
var httpRequestDuration = prometheus.NewSummaryVec(
	prometheus.SummaryOpts{
		Name: "http_request_duration",
		Help: "http request duration",
	},
	[]string{"endpoint"},
)

// 将Metric注册到本地的Prometheus
func init() {
	prometheus.MustRegister(httpRequestCount)
	prometheus.MustRegister(orderNum)
	prometheus.MustRegister(httpRequestDuration)
}


func main() {
    // Exporter
	http.Handle("/metrics", promhttp.Handler()) // 对外暴露metrics接口，等待Prometheus来拉取
	http.HandleFunc("/hello/", hello) // 处理业务请求，并变更Metric信息
	ipport := "127.0.0.1:8888"
	fmt.Println("服务器启动%s", ipport)
	err := http.ListenAndServe(ipport, nil)
	if err != nil {
		fmt.Println(err)
	}
}

func hello(w http.ResponseWriter, r *http.Request) {
	fmt.Printf("process one request = %s\\n", r.URL.Path)
    // Counter类型的Metric只能增
	httpRequestCount.WithLabelValues(r.URL.Path).Inc()
	start := time.Now()
	n := rand.Intn(100)
    // Gauge类型的Metric可增可减
	if n >= 90 {
		orderNum.Dec()
		time.Sleep(100 * time.Millisecond)
	} else {
		orderNum.Inc()
		time.Sleep(50 * time.Millisecond)
	}
    // Summary类型Metric
	elapsed := (float64)(time.Since(start) / time.Millisecond)
	httpRequestDuration.WithLabelValues(r.URL.Path).Observe(elapsed)
	w.Write([]byte("ok"))
}

// Counter类型的Metric
var httpRequestCount = prometheus.NewCounterVec(
	prometheus.CounterOpts{
		Name: "http_request_count", // Metric的name
		Help: "http request count"}, // Metric的说明信息
	[]string{"endpoint"}) // Metric有一个Label，名称是endpoint，Metric形如 http_request_count(endpoint="")

// Counter定义
type CounterVec struct {
	*MetricVec
}

// MetricVec定义
type MetricVec struct {
	*metricMap // Metric最终是存在这里

	curry []curriedLabelValue

	// hashAdd and hashAddByte can be replaced for testing collision handling.
	hashAdd     func(h uint64, s string) uint64
	hashAddByte func(h uint64, b byte) uint64
}

// @Param lvs 表示label values
func (v *CounterVec) WithLabelValues(lvs ...string) Counter {
	c, err := v.GetMetricWithLabelValues(lvs...) // 根据label的值来找对应的Metric
	if err != nil {
		panic(err)
	}
	return c
}

// 根据label的值来找对应的Metric
// @Param lvs表示label value
func (v *CounterVec) GetMetricWithLabelValues(lvs ...string) (Counter, error) {
	metric, err := v.MetricVec.GetMetricWithLabelValues(lvs...)
	if metric != nil {
		return metric.(Counter), err
	}
	return nil, err
}

// 根据label值找对应的metric
func (m *MetricVec) GetMetricWithLabelValues(lvs ...string) (Metric, error) {
	h, err := m.hashLabelValues(lvs) // 获取label对应的hash值，非重点不展开讲，这块的核心是，若hash值一样，则对应的Metric是同一个
	if err != nil {
		return nil, err
	}
    // 根据hash值从metricMap里get对应的metric
    // 若不存在则新创建一个metric并放入到metricMap里
	return m.metricMap.getOrCreateMetricWithLabelValues(h, lvs, m.curry), nil
}

// metricMap定义，Exporter的Metric都存在这个结构中
type metricMap struct {
	mtx       sync.RWMutex // Protects metrics.
	metrics   map[uint64][]metricWithLabelValues // Metric最终存到一个map里，key=根据label值计算出的hash值，value=Metric元信息
	desc      *Desc
	newMetric func(labelValues ...string) Metric
}

type metricWithLabelValues struct {
	values []string // label的值
	metric Metric // Metric的meta信息
}

// Prometheus拉取的入口
http.Handle("/metrics", promhttp.Handler())

// http.go promhttp.Handler()
func Handler() http.Handler {
	return InstrumentMetricHandler(
		prometheus.DefaultRegisterer, HandlerFor(prometheus.DefaultGatherer, HandlerOpts{}),
	)
}


// http.go HandlerFor
func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler {
	// 省略部分代码
	mfs, err := reg.Gather() // 收集Metric信息
	// 省略部分代码
}

// prometheus.DefaultGatherer
// registry.go 
var (
	defaultRegistry              = NewRegistry() // DefaultGatherer就是defaultRegistry
	DefaultRegisterer Registerer = defaultRegistry
	DefaultGatherer   Gatherer   = defaultRegistry
)

// registry.go 
// Gather implements Gatherer. 负责收集metrics信息
func (r *Registry) Gather() ([]*dto.MetricFamily, error) {
	// 省略部分代码
    // 声明Counter类型的Metric后，需要MustRegist注册到Registry，最终就是保存在collectorsByID里
    // Counter类型本身就是一个collector
	for _, collector := range r.collectorsByID {
		checkedCollectors <- collector
	}
	// 省略部分代码
	collectWorker := func() {
		for {
			select {
			case collector := <-checkedCollectors:
				collector.Collect(checkedMetricChan) // 执行Counter的Collect，见下文
			case collector := <-uncheckedCollectors:
				collector.Collect(uncheckedMetricChan)
			default:
				return
			}
			wg.Done()
		}
	}

	// 省略部分代码
}


// vec.go
// Collect implements Collector.
// Counter类型的Collect方法
func (m *MetricVec) Collect(ch chan<- Metric) { m.metricMap.Collect(ch) }

// vec.go
// Collect implements Collector.
// 返回metricMap里所有的Metric
func (m *metricMap) Collect(ch chan<- Metric) {
	m.mtx.RLock()
	defer m.mtx.RUnlock()

	for _, metrics := range m.metrics {
		for _, metric := range metrics {
			ch <- metric.metric
		}
	}
}