/*
Copyright 2017 The Kubernetes Authors.

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 (
	"fmt"
	"strconv"
	"time"

	"github.com/prometheus/client_golang/prometheus"

	"k8s.io/apiserver/pkg/admission"
)

const (
	namespace = "apiserver"
	subsystem = "admission"
)

var (
	// Use buckets ranging from 25 ms to ~2.5 seconds.
	latencyBuckets       = prometheus.ExponentialBuckets(25000, 2.5, 5)
	latencySummaryMaxAge = 5 * time.Hour

	// Metrics provides access to all admission metrics.
	Metrics = newAdmissionMetrics()
)

// ObserverFunc is a func that emits metrics.
type ObserverFunc func(elapsed time.Duration, rejected bool, attr admission.Attributes, stepType string, extraLabels ...string)

const (
	stepValidate = "validate"
	stepAdmit    = "admit"
)

// WithControllerMetrics is a decorator for named admission handlers.
func WithControllerMetrics(i admission.Interface, name string) admission.Interface {
	return WithMetrics(i, Metrics.ObserveAdmissionController, name)
}

// WithStepMetrics is a decorator for a whole admission phase, i.e. admit or validation.admission step.
func WithStepMetrics(i admission.Interface) admission.Interface {
	return WithMetrics(i, Metrics.ObserveAdmissionStep)
}

// WithMetrics is a decorator for admission handlers with a generic observer func.
func WithMetrics(i admission.Interface, observer ObserverFunc, extraLabels ...string) admission.Interface {
	return &pluginHandlerWithMetrics{
		Interface:   i,
		observer:    observer,
		extraLabels: extraLabels,
	}
}

// pluginHandlerWithMetrics decorates a admission handler with metrics.
type pluginHandlerWithMetrics struct {
	admission.Interface
	observer    ObserverFunc
	extraLabels []string
}

// Admit performs a mutating admission control check and emit metrics.
func (p pluginHandlerWithMetrics) Admit(a admission.Attributes) error {
	mutatingHandler, ok := p.Interface.(admission.MutationInterface)
	if !ok {
		return nil
	}

	start := time.Now()
	err := mutatingHandler.Admit(a)
	p.observer(time.Since(start), err != nil, a, stepAdmit, p.extraLabels...)
	return err
}

// Validate performs a non-mutating admission control check and emits metrics.
func (p pluginHandlerWithMetrics) Validate(a admission.Attributes) error {
	validatingHandler, ok := p.Interface.(admission.ValidationInterface)
	if !ok {
		return nil
	}

	start := time.Now()
	err := validatingHandler.Validate(a)
	p.observer(time.Since(start), err != nil, a, stepValidate, p.extraLabels...)
	return err
}

// AdmissionMetrics instruments admission with prometheus metrics.
type AdmissionMetrics struct {
	step       *metricSet
	controller *metricSet
	webhook    *metricSet
}

// newAdmissionMetrics create a new AdmissionMetrics, configured with default metric names.
func newAdmissionMetrics() *AdmissionMetrics {
	// Admission metrics for a step of the admission flow. The entire admission flow is broken down into a series of steps
	// Each step is identified by a distinct type label value.
	step := newMetricSet("step",
		[]string{"type", "operation", "rejected"},
		"Admission sub-step %s, broken out for each operation and API resource and step type (validate or admit).", true)

	// Built-in admission controller metrics. Each admission controller is identified by name.
	controller := newMetricSet("controller",
		[]string{"name", "type", "operation", "rejected"},
		"Admission controller %s, identified by name and broken out for each operation and API resource and type (validate or admit).", false)

	// Admission webhook metrics. Each webhook is identified by name.
	webhook := newMetricSet("webhook",
		[]string{"name", "type", "operation", "rejected"},
		"Admission webhook %s, identified by name and broken out for each operation and API resource and type (validate or admit).", false)

	step.mustRegister()
	controller.mustRegister()
	webhook.mustRegister()
	return &AdmissionMetrics{step: step, controller: controller, webhook: webhook}
}

func (m *AdmissionMetrics) reset() {
	m.step.reset()
	m.controller.reset()
	m.webhook.reset()
}

// ObserveAdmissionStep records admission related metrics for a admission step, identified by step type.
func (m *AdmissionMetrics) ObserveAdmissionStep(elapsed time.Duration, rejected bool, attr admission.Attributes, stepType string, extraLabels ...string) {
	m.step.observe(elapsed, append(extraLabels, stepType, string(attr.GetOperation()), strconv.FormatBool(rejected))...)
}

// ObserveAdmissionController records admission related metrics for a built-in admission controller, identified by it's plugin handler name.
func (m *AdmissionMetrics) ObserveAdmissionController(elapsed time.Duration, rejected bool, attr admission.Attributes, stepType string, extraLabels ...string) {
	m.controller.observe(elapsed, append(extraLabels, stepType, string(attr.GetOperation()), strconv.FormatBool(rejected))...)
}

// ObserveWebhook records admission related metrics for a admission webhook.
func (m *AdmissionMetrics) ObserveWebhook(elapsed time.Duration, rejected bool, attr admission.Attributes, stepType string, extraLabels ...string) {
	m.webhook.observe(elapsed, append(extraLabels, stepType, string(attr.GetOperation()), strconv.FormatBool(rejected))...)
}

type metricSet struct {
	latencies        *prometheus.HistogramVec
	latenciesSummary *prometheus.SummaryVec
}

func newMetricSet(name string, labels []string, helpTemplate string, hasSummary bool) *metricSet {
	var summary *prometheus.SummaryVec
	if hasSummary {
		summary = prometheus.NewSummaryVec(
			prometheus.SummaryOpts{
				Namespace: namespace,
				Subsystem: subsystem,
				Name:      fmt.Sprintf("%s_admission_latencies_seconds_summary", name),
				Help:      fmt.Sprintf(helpTemplate, "latency summary"),
				MaxAge:    latencySummaryMaxAge,
			},
			labels,
		)
	}

	return &metricSet{
		latencies: prometheus.NewHistogramVec(
			prometheus.HistogramOpts{
				Namespace: namespace,
				Subsystem: subsystem,
				Name:      fmt.Sprintf("%s_admission_latencies_seconds", name),
				Help:      fmt.Sprintf(helpTemplate, "latency histogram"),
				Buckets:   latencyBuckets,
			},
			labels,
		),

		latenciesSummary: summary,
	}
}

// MustRegister registers all the prometheus metrics in the metricSet.
func (m *metricSet) mustRegister() {
	prometheus.MustRegister(m.latencies)
	if m.latenciesSummary != nil {
		prometheus.MustRegister(m.latenciesSummary)
	}
}

// Reset resets all the prometheus metrics in the metricSet.
func (m *metricSet) reset() {
	m.latencies.Reset()
	if m.latenciesSummary != nil {
		m.latenciesSummary.Reset()
	}
}

// Observe records an observed admission event to all metrics in the metricSet.
func (m *metricSet) observe(elapsed time.Duration, labels ...string) {
	elapsedMicroseconds := float64(elapsed / time.Microsecond)
	m.latencies.WithLabelValues(labels...).Observe(elapsedMicroseconds)
	if m.latenciesSummary != nil {
		m.latenciesSummary.WithLabelValues(labels...).Observe(elapsedMicroseconds)
	}
}
