package metrics

import (
	"net/http"

	"github.com/containous/mux"
	"github.com/containous/traefik/types"
	"github.com/go-kit/kit/metrics/prometheus"
	stdprometheus "github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

const (
	metricNamePrefix = "traefik_"

	reqsTotalName    = metricNamePrefix + "requests_total"
	reqDurationName  = metricNamePrefix + "request_duration_seconds"
	retriesTotalName = metricNamePrefix + "backend_retries_total"
)

// PrometheusHandler expose Prometheus routes
type PrometheusHandler struct{}

// AddRoutes add Prometheus routes on a router
func (h PrometheusHandler) AddRoutes(router *mux.Router) {
	router.Methods(http.MethodGet).Path("/metrics").Handler(promhttp.Handler())
}

// RegisterPrometheus registers all Prometheus metrics.
// It must be called only once and failing to register the metrics will lead to a panic.
func RegisterPrometheus(config *types.Prometheus) Registry {
	buckets := []float64{0.1, 0.3, 1.2, 5.0}
	if config.Buckets != nil {
		buckets = config.Buckets
	}

	reqCounter := prometheus.NewCounterFrom(stdprometheus.CounterOpts{
		Name: reqsTotalName,
		Help: "How many HTTP requests processed, partitioned by status code and method.",
	}, []string{"service", "code", "method"})
	reqDurationHistogram := prometheus.NewHistogramFrom(stdprometheus.HistogramOpts{
		Name:    reqDurationName,
		Help:    "How long it took to process the request.",
		Buckets: buckets,
	}, []string{"service", "code"})
	retryCounter := prometheus.NewCounterFrom(stdprometheus.CounterOpts{
		Name: retriesTotalName,
		Help: "How many request retries happened in total.",
	}, []string{"service"})

	return &standardRegistry{
		enabled:              true,
		reqsCounter:          reqCounter,
		reqDurationHistogram: reqDurationHistogram,
		retriesCounter:       retryCounter,
	}
}