// Copyright (c) 2017-2021 Tigera, Inc. All rights reserved.
//
// 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.

// This boilerplate code is based on proxiers in k8s.io/kubernetes/pkg/proxy to
// allow reuse of the rest of the proxy package without change

package proxy

import (
	"context"
	"fmt"
	"net"
	"strings"
	"sync"
	"time"

	"github.com/pkg/errors"
	log "github.com/sirupsen/logrus"
	v1 "k8s.io/api/core/v1"
	discovery "k8s.io/api/discovery/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/labels"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/selection"
	"k8s.io/apimachinery/pkg/types"
	"k8s.io/client-go/informers"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/tools/events"
	k8sp "k8s.io/kubernetes/pkg/proxy"
	"k8s.io/kubernetes/pkg/proxy/apis"
	"k8s.io/kubernetes/pkg/proxy/config"
	"k8s.io/kubernetes/pkg/proxy/healthcheck"
	"k8s.io/kubernetes/pkg/proxy/util"
	"k8s.io/kubernetes/pkg/util/async"
)

// Proxy watches for updates of Services and Endpoints, maintains their mapping
// and programs it into the dataplane
type Proxy interface {
	// Stop stops the proxy and waits for its exit
	Stop()

	setIpFamily(int)
}

type ProxyFrontend interface {
	Proxy
	SetSyncer(DPSyncer)
}

// DPSyncerState groups the information passed to the DPSyncer's Apply
type DPSyncerState struct {
	SvcMap   k8sp.ServicePortMap
	EpsMap   k8sp.EndpointsMap
	NodeZone string
}

// DPSyncer is an interface representing the dataplane syncer that applies the
// observed changes to the dataplane
type DPSyncer interface {
	Apply(state DPSyncerState) error
	ConntrackScanStart()
	ConntrackScanEnd()
	ConntrackFrontendHasBackend(ip net.IP, port uint16, backendIP net.IP, backendPort uint16, proto uint8) bool
	ConntrackDestIsService(ip net.IP, port uint16, proto uint8) bool
	Stop()
	SetTriggerFn(func())
	HasSynced() bool
}

type proxy struct {
	initState

	hostname string
	nodeZone string
	k8s      kubernetes.Interface
	ipFamily int

	epsChanges *k8sp.EndpointsChangeTracker
	svcChanges *k8sp.ServiceChangeTracker

	svcMap k8sp.ServicePortMap
	epsMap k8sp.EndpointsMap

	dpSyncer  DPSyncer
	syncerLck sync.Mutex
	// executes periodic the dataplane updates
	runner *async.BoundedFrequencyRunner
	// ensures that only one invocation runs at any time
	runnerLck sync.Mutex
	// sets the minimal distance between to sync to avoid overloading the
	// dataplane in case of frequent changes
	minDPSyncPeriod time.Duration

	// how often to fully sync with k8s - 0 is never
	syncPeriod time.Duration

	// event recorder to update node events
	recorder        events.EventRecorder
	svcHealthServer healthcheck.ServiceHealthServer
	healthzServer   *healthcheck.ProxierHealthServer

	stopCh   chan struct{}
	stopWg   sync.WaitGroup
	stopOnce sync.Once
}

type stoppableRunner interface {
	Run(stopCh <-chan struct{})
}

// New returns a new Proxy for the given k8s interface
func New(k8s kubernetes.Interface, dp DPSyncer, hostname string, opts ...Option) (ProxyFrontend, error) {

	if k8s == nil {
		return nil, errors.New("no k8s client")
	}

	if dp == nil {
		return nil, errors.New("no dataplane syncer")
	}

	p := &proxy{
		k8s:      k8s,
		dpSyncer: dp,
		hostname: hostname,
		ipFamily: 4,
		svcMap:   make(k8sp.ServicePortMap),
		epsMap:   make(k8sp.EndpointsMap),

		recorder: new(loggerRecorder),

		minDPSyncPeriod: 30 * time.Second, // XXX revisit the default

		stopCh: make(chan struct{}),
	}

	for _, o := range opts {
		if err := o(p); err != nil {
			return nil, errors.WithMessage(err, "applying option")
		}
	}

	// We need to create the runner first as once we start getting updates, they
	// will kick it
	p.runner = async.NewBoundedFrequencyRunner("dp-sync-runner",
		p.invokeDPSyncer, p.minDPSyncPeriod, time.Hour /* XXX might be infinite? */, 1)
	dp.SetTriggerFn(p.runner.Run)

	ipVersion := p.v1IPFamily()
	p.healthzServer = healthcheck.NewProxierHealthServer("0.0.0.0:10256", p.minDPSyncPeriod)
	p.svcHealthServer = healthcheck.NewServiceHealthServer(p.hostname, p.recorder, util.NewNodePortAddresses(ipVersion, []string{"0.0.0.0/0"}), p.healthzServer)

	p.epsChanges = k8sp.NewEndpointsChangeTracker(p.hostname,
		nil, // change if you want to provide more ctx
		ipVersion,
		p.recorder,
		nil,
	)
	p.svcChanges = k8sp.NewServiceChangeTracker(makeServiceInfo, ipVersion, p.recorder, nil)

	noProxyName, err := labels.NewRequirement(apis.LabelServiceProxyName, selection.DoesNotExist, nil)
	if err != nil {
		return nil, fmt.Errorf("noProxyName selector: %s", err)
	}

	noHeadlessEndpoints, err := labels.NewRequirement(v1.IsHeadlessService, selection.DoesNotExist, nil)
	if err != nil {
		return nil, fmt.Errorf("noHeadlessEndpoints selector: %s", err)
	}

	labelSelector := labels.NewSelector()
	labelSelector = labelSelector.Add(*noProxyName, *noHeadlessEndpoints)

	informerFactory := informers.NewSharedInformerFactoryWithOptions(k8s, p.syncPeriod,
		informers.WithTweakListOptions(func(options *metav1.ListOptions) {
			options.LabelSelector = labelSelector.String()
		}))

	svcConfig := config.NewServiceConfig(
		context.TODO(),
		informerFactory.Core().V1().Services(),
		p.syncPeriod,
	)
	svcConfig.RegisterEventHandler(p)

	var epsRunner stoppableRunner

	epsConfig := config.NewEndpointSliceConfig(context.TODO(), informerFactory.Discovery().V1().EndpointSlices(), p.syncPeriod)
	epsConfig.RegisterEventHandler(p)
	epsRunner = epsConfig

	p.startRoutine(func() { p.runner.Loop(p.stopCh) })
	p.startRoutine(func() { epsRunner.Run(p.stopCh) })
	p.startRoutine(func() { informerFactory.Start(p.stopCh) })
	p.startRoutine(func() { svcConfig.Run(p.stopCh) })

	return p, nil
}

func (p *proxy) v1IPFamily() v1.IPFamily {
	pr := v1.IPv4Protocol
	if p.ipFamily != 4 {
		pr = v1.IPv6Protocol
	}

	return pr
}

func (p *proxy) setIpFamily(ipFamily int) {
	p.ipFamily = ipFamily
}

func (p *proxy) Stop() {
	p.stopOnce.Do(func() {
		log.Info("Proxy stopping")
		// Pass empty update to close all the health checks.
		_ = p.svcHealthServer.SyncServices(map[types.NamespacedName]uint16{})
		_ = p.svcHealthServer.SyncEndpoints(map[types.NamespacedName]int{})
		p.dpSyncer.Stop()
		close(p.stopCh)
		p.stopWg.Wait()
		log.Info("Proxy stopped")
	})
}

func (p *proxy) startRoutine(f func()) {
	p.stopWg.Add(1)
	go func() {
		defer p.stopWg.Done()
		f()
	}()
}

func (p *proxy) syncDP() {
	p.runner.Run()
}

func (p *proxy) forceSyncDP() {
	p.invokeDPSyncer()
}

func (p *proxy) invokeDPSyncer() {
	if !p.isInitialized() {
		return
	}

	p.runnerLck.Lock()
	defer p.runnerLck.Unlock()

	_ = p.svcMap.Update(p.svcChanges)
	_ = p.epsMap.Update(p.epsChanges)

	if err := p.svcHealthServer.SyncServices(p.svcMap.HealthCheckNodePorts()); err != nil {
		log.WithError(err).Error("Error syncing healthcheck services")
	}
	if err := p.svcHealthServer.SyncEndpoints(p.epsMap.LocalReadyEndpoints()); err != nil {
		log.WithError(err).Error("Error syncing healthcheck endpoints")
	}

	p.syncerLck.Lock()
	err := p.dpSyncer.Apply(DPSyncerState{
		SvcMap:   p.svcMap,
		EpsMap:   p.epsMap,
		NodeZone: p.nodeZone,
	})
	p.syncerLck.Unlock()

	if err != nil {
		log.WithError(err).Errorf("applying changes failed")
		// TODO log the error or panic as the best might be to restart
		// completely to wipe out the loaded bpf maps
	}

	if p.healthzServer != nil {
		p.healthzServer.Updated(p.v1IPFamily())
	}
}

func (p *proxy) OnServiceAdd(svc *v1.Service) {
	p.OnServiceUpdate(nil, svc)
}

func (p *proxy) OnServiceUpdate(old, curr *v1.Service) {
	if p.svcChanges.Update(old, curr) && p.isInitialized() {
		p.syncDP()
	}
}

func (p *proxy) OnServiceDelete(svc *v1.Service) {
	p.OnServiceUpdate(svc, nil)
}

func (p *proxy) OnServiceSynced() {
	p.setSvcsSynced()
	p.forceSyncDP()
}

func (p *proxy) OnEndpointSliceAdd(eps *discovery.EndpointSlice) {
	if p.IPFamily() != eps.AddressType {
		return
	}
	if p.epsChanges.EndpointSliceUpdate(eps, false) && p.isInitialized() {
		p.syncDP()
	}
}

func (p *proxy) OnEndpointSliceUpdate(_, eps *discovery.EndpointSlice) {
	if p.IPFamily() != eps.AddressType {
		return
	}
	if p.epsChanges.EndpointSliceUpdate(eps, false) && p.isInitialized() {
		p.syncDP()
	}
}

func (p *proxy) OnEndpointSliceDelete(eps *discovery.EndpointSlice) {
	if p.IPFamily() != eps.AddressType {
		return
	}
	if p.epsChanges.EndpointSliceUpdate(eps, true) && p.isInitialized() {
		p.syncDP()
	}
}

func (p *proxy) OnEndpointSlicesSynced() {
	p.setEpsSynced()
	p.forceSyncDP()
}

func (p *proxy) SetSyncer(s DPSyncer) {
	p.syncerLck.Lock()
	p.dpSyncer.Stop()
	p.dpSyncer = s
	p.syncerLck.Unlock()

	p.forceSyncDP()
}

func (p *proxy) IPFamily() discovery.AddressType {
	if p.ipFamily == 4 {
		return discovery.AddressTypeIPv4
	}
	return discovery.AddressTypeIPv6
}

type initState struct {
	lck        sync.RWMutex
	svcsSynced bool
	epsSynced  bool
}

func (is *initState) isInitialized() bool {
	is.lck.RLock()
	defer is.lck.RUnlock()
	return is.svcsSynced && is.epsSynced
}

func (is *initState) setSvcsSynced() {
	is.lck.Lock()
	defer is.lck.Unlock()
	is.svcsSynced = true
}

func (is *initState) setEpsSynced() {
	is.lck.Lock()
	defer is.lck.Unlock()
	is.epsSynced = true
}

type loggerRecorder struct{}

func (r *loggerRecorder) Eventf(regarding runtime.Object, related runtime.Object, eventtype, reason, action, note string, args ...interface{}) {
}

const (
	ReapTerminatingUDPAnnotation   = "projectcalico.org/udpConntrackCleanup"
	ReapTerminatingUDPImmediatelly = "TerminatingImmediately"

	ExcludeServiceAnnotation = "projectcalico.org/natExcludeService"
)

type ServiceAnnotations interface {
	ReapTerminatingUDP() bool
	ExcludeService() bool
}

type servicePortAnnotations struct {
	reapTerminatingUDP bool
	excludeService     bool
}

func (s *servicePortAnnotations) ReapTerminatingUDP() bool {
	return s.reapTerminatingUDP
}

func (s *servicePortAnnotations) ExcludeService() bool {
	return s.excludeService
}

type servicePort struct {
	k8sp.ServicePort
	servicePortAnnotations
}

func makeServiceInfo(_ *v1.ServicePort, s *v1.Service, baseSvc *k8sp.BaseServicePortInfo) k8sp.ServicePort {
	svc := &servicePort{
		ServicePort: baseSvc,
	}

	if v, ok := s.ObjectMeta.Annotations[ExcludeServiceAnnotation]; ok && v == "true" {
		svc.excludeService = true
		goto out
	}

	if baseSvc.Protocol() == v1.ProtocolUDP {
		if v, ok := s.ObjectMeta.Annotations[ReapTerminatingUDPAnnotation]; ok && strings.EqualFold(v, ReapTerminatingUDPImmediatelly) {
			svc.reapTerminatingUDP = true
		}
	}

out:
	return svc
}
