/*
Copyright 2018 The Jetstack cert-manager contributors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package main

import (
	"context"
	"net/http"
	"time"

	"github.com/golang/glog"
	"github.com/gorilla/mux"
	"github.com/prometheus/client_golang/prometheus"
)

const (
	prometheusMetricsServerAddress         = "0.0.0.0:9402"
	prometheusMetricsServerShutdownTimeout = 10 * time.Second
	prometheusMetricsServerReadTimeout     = 8 * time.Second
	prometheusMetricsServerWriteTimeout    = 8 * time.Second
	prometheusMetricsServerMaxHeaderBytes  = 1 << 20
)

type prometheusMetricsServer struct {
	http.Server
}

func prometheusHandler() http.Handler {
	return prometheus.Handler()
}

func newPrometheusMetricsServer() *prometheusMetricsServer {

	r := mux.NewRouter()
	r.Handle("/metrics", prometheusHandler())

	// Create server and register prometheus metrics handler
	s := &prometheusMetricsServer{
		Server: http.Server{
			Addr:           prometheusMetricsServerAddress,
			ReadTimeout:    prometheusMetricsServerReadTimeout,
			WriteTimeout:   prometheusMetricsServerWriteTimeout,
			MaxHeaderBytes: prometheusMetricsServerMaxHeaderBytes,
			Handler:        r,
		},
	}

	return s
}

func (s *prometheusMetricsServer) WaitShutdown(stopCh <-chan struct{}) {
	<-stopCh
	glog.Info("Stopping Prometheus metrics server...")

	ctx, cancel := context.WithTimeout(context.Background(), prometheusMetricsServerShutdownTimeout)
	defer cancel()

	if err := s.Shutdown(ctx); err != nil {
		glog.Errorf("Prometheus metrics server shutdown error: %v", err)
		return
	}

	glog.Info("Prometheus metrics server gracefully stopped")
}

func StartPrometheusMetricsServer(stopCh <-chan struct{}) {
	s := newPrometheusMetricsServer()

	go func() {

		glog.Infof("Listening on http://%s", s.Addr)
		if err := s.ListenAndServe(); err != nil {
			glog.Errorf("Error running prometheus metrics server: %s", err.Error())
			return
		}

		glog.Infof("Prometheus metrics server exited")

	}()

	s.WaitShutdown(stopCh)
}