package middleware

import (
	"context"
	"github.com/gogf/gf/net/ghttp"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"gxt-api-frame/library/logger"
	"io/ioutil"
	"net/http"
	"strconv"
	"time"
)

var defaultMetricPath = "/metrics"

var reqCnt = &Metric{
	ID:          "reqCnt",
	Name:        "requests_total",
	Description: "How many HTTP requests processed, partitioned by status code and HTTP method.",
	Type:        "counter_vec",
	Args:        []string{"code", "method", "host", "url"}}

var reqDur = &Metric{
	ID:          "reqDur",
	Name:        "request_duration_seconds",
	Description: "The HTTP request latencies in seconds.",
	Type:        "histogram_vec",
	Args:        []string{"code", "method", "url"},
}

var resSz = &Metric{
	ID:          "resSz",
	Name:        "response_size_bytes",
	Description: "The HTTP response sizes in bytes.",
	Type:        "summary"}

var reqSz = &Metric{
	ID:          "reqSz",
	Name:        "request_size_bytes",
	Description: "The HTTP request sizes in bytes.",
	Type:        "summary"}

var standardMetrics = []*Metric{
	reqCnt,
	reqDur,
	resSz,
	reqSz,
}

type Metric struct {
	MetricCollector prometheus.Collector
	ID              string
	Name            string
	Description     string
	Type            string
	Args            []string
}
type RequestCounterURLLabelMappingFn func(c *ghttp.Request) string

type Prometheus struct {
	reqCnt        *prometheus.CounterVec
	reqDur        *prometheus.HistogramVec
	reqSz, resSz  prometheus.Summary
	router        *ghttp.Server
	listenAddress string
	Ppg           PrometheusPushGateway

	MetricsList []*Metric
	MetricsPath string

	ReqCntURLLabelMappingFn RequestCounterURLLabelMappingFn

	// gin.Context string to use as a prometheus URL label
	URLLabelFromContext string
}
type PrometheusPushGateway struct {
	PushIntervalSeconds time.Duration
	PushGatewayURL      string
	MetricsURL          string
	Job                 string
}

// NewPrometheus generates a new set of metrics with a certain subsystem name
func NewPrometheus(subsystem string, customMetricsList ...[]*Metric) *Prometheus {

	var metricsList []*Metric

	if len(customMetricsList) > 1 {
		panic("Too many args. NewPrometheus( string, <optional []*Metric> ).")
	} else if len(customMetricsList) == 1 {
		metricsList = customMetricsList[0]
	}

	for _, metric := range standardMetrics {
		metricsList = append(metricsList, metric)
	}

	p := &Prometheus{
		MetricsList: metricsList,
		MetricsPath: defaultMetricPath,
		ReqCntURLLabelMappingFn: func(c *ghttp.Request) string {
			return c.Request.URL.Path
		},
	}

	p.registerMetrics(subsystem)

	return p
}

// Use adds the middleware to a gin engine.
func (p *Prometheus) Use(e *ghttp.Server) {
	e.Use(p.HandlerFunc())
	p.SetMetricsPath(e)
}

func (p *Prometheus) getMetrics() []byte {
	response, _ := http.Get(p.Ppg.MetricsURL)
	defer response.Body.Close()
	body, _ := ioutil.ReadAll(response.Body)
	return body
}

// NewMetric associates prometheus.Collector based on Metric.Type
func NewMetric(m *Metric, subsystem string) prometheus.Collector {
	var metric prometheus.Collector
	switch m.Type {
	case "counter_vec":
		metric = prometheus.NewCounterVec(
			prometheus.CounterOpts{
				Subsystem: subsystem,
				Name:      m.Name,
				Help:      m.Description,
			},
			m.Args,
		)
	case "counter":
		metric = prometheus.NewCounter(
			prometheus.CounterOpts{
				Subsystem: subsystem,
				Name:      m.Name,
				Help:      m.Description,
			},
		)
	case "gauge_vec":
		metric = prometheus.NewGaugeVec(
			prometheus.GaugeOpts{
				Subsystem: subsystem,
				Name:      m.Name,
				Help:      m.Description,
			},
			m.Args,
		)
	case "gauge":
		metric = prometheus.NewGauge(
			prometheus.GaugeOpts{
				Subsystem: subsystem,
				Name:      m.Name,
				Help:      m.Description,
			},
		)
	case "histogram_vec":
		metric = prometheus.NewHistogramVec(
			prometheus.HistogramOpts{
				Subsystem: subsystem,
				Name:      m.Name,
				Help:      m.Description,
			},
			m.Args,
		)
	case "histogram":
		metric = prometheus.NewHistogram(
			prometheus.HistogramOpts{
				Subsystem: subsystem,
				Name:      m.Name,
				Help:      m.Description,
			},
		)
	case "summary_vec":
		metric = prometheus.NewSummaryVec(
			prometheus.SummaryOpts{
				Subsystem: subsystem,
				Name:      m.Name,
				Help:      m.Description,
			},
			m.Args,
		)
	case "summary":
		metric = prometheus.NewSummary(
			prometheus.SummaryOpts{
				Subsystem: subsystem,
				Name:      m.Name,
				Help:      m.Description,
			},
		)
	}
	return metric
}
func (p *Prometheus) registerMetrics(subsystem string) {

	for _, metricDef := range p.MetricsList {
		metric := NewMetric(metricDef, subsystem)
		if err := prometheus.Register(metric); err != nil {
			logger.Errorf(context.Background(), "%s could not be registered in Prometheus", metricDef.Name)
		}
		switch metricDef {
		case reqCnt:
			p.reqCnt = metric.(*prometheus.CounterVec)
		case reqDur:
			p.reqDur = metric.(*prometheus.HistogramVec)
		case resSz:
			p.resSz = metric.(prometheus.Summary)
		case reqSz:
			p.reqSz = metric.(prometheus.Summary)
		}
		metricDef.MetricCollector = metric
	}
}

// SetMetricsPath set metrics paths
func (p *Prometheus) SetMetricsPath(s *ghttp.Server) {
	s.BindHandler(p.MetricsPath, prometheusHandler())
}

func prometheusHandler() ghttp.HandlerFunc {
	h := promhttp.Handler()
	return func(c *ghttp.Request) {
		h.ServeHTTP(c.Response.Writer, c.Request)
	}
}

// HandlerFunc defines handler function for middleware
func (p *Prometheus) HandlerFunc() ghttp.HandlerFunc {
	return func(c *ghttp.Request) {

		if c.Request.URL.Path == p.MetricsPath || c.Request.URL.Path == "/favicon.ico" {
			c.Middleware.Next()
			return
		}

		start := time.Now()
		reqSz := computeApproximateRequestSize(c.Request)

		c.Middleware.Next()
		status := strconv.Itoa(c.Response.Status)
		elapsed := float64(time.Since(start)) / float64(time.Second)
		resSz := float64(c.Response.BufferLength())

		url := p.ReqCntURLLabelMappingFn(c)
		if len(p.URLLabelFromContext) > 0 {
			u := c.Get(p.URLLabelFromContext)
			url = u.(string)
		}
		p.reqDur.WithLabelValues(status, c.Request.Method, url).Observe(elapsed)
		p.reqCnt.WithLabelValues(status, c.Request.Method, c.Request.Host, url).Inc()
		p.reqSz.Observe(float64(reqSz))
		p.resSz.Observe(resSz)
	}
}

func computeApproximateRequestSize(r *http.Request) int {
	s := 0
	if r.URL != nil {
		s = len(r.URL.Path)
	}

	s += len(r.Method)
	s += len(r.Proto)
	for name, values := range r.Header {
		s += len(name)
		for _, value := range values {
			s += len(value)
		}
	}
	s += len(r.Host)

	if r.ContentLength != -1 {
		s += int(r.ContentLength)
	}
	return s
}