// Copyright 2019-2020 Authors of Cilium
//
// 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 metrics

import (
	"context"
	"net/http"

	operatorOption "github.com/cilium/cilium/operator/option"
	"github.com/cilium/cilium/pkg/logging"
	"github.com/cilium/cilium/pkg/logging/logfields"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

var (
	log = logging.DefaultLogger.WithField(logfields.LogSubsys, "metrics")
)

const Namespace = "cilium_operator"

var (
	Registry   *prometheus.Registry
	shutdownCh chan struct{}
)

func Register() {
	log.Info("Registering Operator metrics")

	Registry = prometheus.NewPedanticRegistry()
	registerMetrics()

	m := http.NewServeMux()
	m.Handle("/metrics", promhttp.HandlerFor(Registry, promhttp.HandlerOpts{}))
	srv := &http.Server{
		Addr:    operatorOption.Config.OperatorPrometheusServeAddr,
		Handler: m,
	}

	shutdownCh = make(chan struct{})
	go func() {
		go func() {
			err := srv.ListenAndServe()
			switch err {
			case http.ErrServerClosed:
				log.Info("Metrics server shutdown successfully")
				return
			default:
				log.WithError(err).Fatal("Metrics server ListenAndServe failed")
			}
		}()

		<-shutdownCh
		log.Info("Received shutdown signal")
		if err := srv.Shutdown(context.TODO()); err != nil {
			log.WithError(err).Error("Shutdown operator metrics server failed")
		}
	}()
}

func Unregister() {
	log.Info("Shutting down metrics server")

	if shutdownCh == nil {
		return
	}

	shutdownCh <- struct{}{}
}

var (
	// IdentityGCSize records the identity GC results
	IdentityGCSize *prometheus.GaugeVec

	// IdentityGCRuns records how many times identity GC has run
	IdentityGCRuns *prometheus.GaugeVec
)

const (
	// LabelStatus marks the status of a resource or completed task
	LabelStatus = "status"

	// LabelOutcome indicates whether the outcome of the operation was successful or not
	LabelOutcome = "outcome"

	// Label values

	// LabelValueOutcomeSuccess is used as a successful outcome of an operation
	LabelValueOutcomeSuccess = "success"

	// LabelValueOutcomeFail is used as an unsuccessful outcome of an operation
	LabelValueOutcomeFail = "fail"
)

func registerMetrics() []prometheus.Collector {
	// Builtin process metrics
	Registry.MustRegister(prometheus.NewProcessCollector(prometheus.ProcessCollectorOpts{Namespace: Namespace}))

	// Custom metrics
	var collectors []prometheus.Collector

	IdentityGCSize = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Namespace: Namespace,
		Name:      "identity_gc_entries_total",
		Help:      "The number of alive and deleted identities at the end of a garbage collector run",
	}, []string{LabelStatus})
	collectors = append(collectors, IdentityGCSize)

	IdentityGCRuns = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Namespace: Namespace,
		Name:      "identity_gc_runs_total",
		Help:      "The number of times identity garbage collector has run",
	}, []string{LabelOutcome})
	collectors = append(collectors, IdentityGCRuns)

	Registry.MustRegister(collectors...)

	return collectors
}