package metrics

import (
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"net/http"
	"sync"
)

const (
	namespace                      = "middleman"
	registeredRegexPrefix          = "registered_regex_"
	registeredRegexTotalName       = registeredRegexPrefix + "total"
	incomingHTTPRequestPrefix      = "incoming_http_requests_"
	incomingHTTPRequestTotalName   = incomingHTTPRequestPrefix + "total"
	processingDurationPrefix       = "processing_duration_"
	processingDurationName         = processingDurationPrefix + "seconds"
	processedHTTPRequestsPrefix    = "processed_http_requests_"
	processedHTTPRequestsTotalName = processedHTTPRequestsPrefix + "total"
	healthcheckResponseTimePrefix  = "healthcheck_response_time_"
	healthcheckResponseTimeName    = healthcheckResponseTimePrefix + "seconds"
	nameResolutionDurationPrefix   = "name_resolution_duration_"
	nameResolutionDurationName     = nameResolutionDurationPrefix + "seconds"
)

var (
	once                      sync.Once
	promRegistry              = prometheus.NewRegistry()
	RegisteredRegexCounterVec = prometheus.NewCounterVec(prometheus.CounterOpts{
		Namespace: namespace,
		Name:      registeredRegexTotalName,
		Help:      "Total number of registered regex",
	}, []string{"client", "http_method", "regex"})
	IncomingHTTPRequestCounterVec = prometheus.NewCounterVec(prometheus.CounterOpts{
		Namespace: namespace,
		Name:      incomingHTTPRequestTotalName,
		Help:      "Total number of incoming HTTP requests",
	}, []string{"client", "http_method", "path"})
	ProcessingDurationHistogramVec = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Namespace: namespace,
		Name:      processingDurationName,
		Help:      "Number of seconds to process an incoming request",
	}, []string{"client", "http_method", "path"})
	ProcessedHTTPRequestCounterVec = prometheus.NewCounterVec(prometheus.CounterOpts{
		Namespace: namespace,
		Name:      processedHTTPRequestsTotalName,
		Help:      "Total number of processed HTTP requests",
	}, []string{"client", "http_methods", "path", "status_code"})
	HealthcheckResponseTimeGauge = prometheus.NewGauge(prometheus.GaugeOpts{
		Namespace: namespace,
		Name:      healthcheckResponseTimeName,
		Help:      "Number of seconds to perform healthcheck request",
	})
	NameResolutionDurationGauge = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Namespace: namespace,
		Name:      nameResolutionDurationName,
		Help:      "Number of seconds to perform name resolution using the local resolver",
	}, []string{"client"})
)

func PrometheusHandler() http.Handler {
	return promhttp.HandlerFor(promRegistry, promhttp.HandlerOpts{})
}

func RegisterPrometheus() {
	once.Do(func() {
		promRegistry.MustRegister(RegisteredRegexCounterVec)
		promRegistry.MustRegister(IncomingHTTPRequestCounterVec)
		promRegistry.MustRegister(ProcessingDurationHistogramVec)
		promRegistry.MustRegister(ProcessedHTTPRequestCounterVec)
		promRegistry.MustRegister(HealthcheckResponseTimeGauge)
		promRegistry.MustRegister(NameResolutionDurationGauge)
	})
}