/*
Copyright 2016 The Kubernetes Authors.
Copyright 2020 Authors of Arktos - file modified.

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 winuserspace

import (
	"errors"
	"fmt"
	"net"
	"reflect"
	"strconv"
	"sync"
	"time"

	"k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/types"
	"k8s.io/klog"
	"k8s.io/kubernetes/pkg/proxy"
	"k8s.io/kubernetes/pkg/util/slice"
)

var (
	ErrMissingServiceEntry = errors.New("missing service entry")
	ErrMissingEndpoints    = errors.New("missing endpoints")
)

type affinityState struct {
	clientIP string
	//clientProtocol  api.Protocol //not yet used
	//sessionCookie   string       //not yet used
	endpoint string
	lastUsed time.Time
}

type affinityPolicy struct {
	affinityType v1.ServiceAffinity
	affinityMap  map[string]*affinityState // map client IP -> affinity info
	ttlSeconds   int
}

// LoadBalancerRR is a round-robin load balancer.
type LoadBalancerRR struct {
	lock     sync.RWMutex
	services map[proxy.ServicePortName]*balancerState
}

// Ensure this implements LoadBalancer.
var _ LoadBalancer = &LoadBalancerRR{}

type balancerState struct {
	endpoints []string // a list of "ip:port" style strings
	index     int      // current index into endpoints
	affinity  affinityPolicy
}

func newAffinityPolicy(affinityType v1.ServiceAffinity, ttlSeconds int) *affinityPolicy {
	return &affinityPolicy{
		affinityType: affinityType,
		affinityMap:  make(map[string]*affinityState),
		ttlSeconds:   ttlSeconds,
	}
}

// NewLoadBalancerRR returns a new LoadBalancerRR.
func NewLoadBalancerRR() *LoadBalancerRR {
	return &LoadBalancerRR{
		services: map[proxy.ServicePortName]*balancerState{},
	}
}

func (lb *LoadBalancerRR) NewService(svcPort proxy.ServicePortName, affinityType v1.ServiceAffinity, ttlSeconds int) error {
	klog.V(4).Infof("LoadBalancerRR NewService %q", svcPort)
	lb.lock.Lock()
	defer lb.lock.Unlock()
	lb.newServiceInternal(svcPort, affinityType, ttlSeconds)
	return nil
}

// This assumes that lb.lock is already held.
func (lb *LoadBalancerRR) newServiceInternal(svcPort proxy.ServicePortName, affinityType v1.ServiceAffinity, ttlSeconds int) *balancerState {
	if ttlSeconds == 0 {
		ttlSeconds = int(v1.DefaultClientIPServiceAffinitySeconds) //default to 3 hours if not specified.  Should 0 be unlimited instead????
	}

	if _, exists := lb.services[svcPort]; !exists {
		lb.services[svcPort] = &balancerState{affinity: *newAffinityPolicy(affinityType, ttlSeconds)}
		klog.V(4).Infof("LoadBalancerRR service %q did not exist, created", svcPort)
	} else if affinityType != "" {
		lb.services[svcPort].affinity.affinityType = affinityType
	}
	return lb.services[svcPort]
}

func (lb *LoadBalancerRR) DeleteService(svcPort proxy.ServicePortName) {
	klog.V(4).Infof("LoadBalancerRR DeleteService %q", svcPort)
	lb.lock.Lock()
	defer lb.lock.Unlock()
	delete(lb.services, svcPort)
}

// return true if this service is using some form of session affinity.
func isSessionAffinity(affinity *affinityPolicy) bool {
	// Should never be empty string, but checking for it to be safe.
	if affinity.affinityType == "" || affinity.affinityType == v1.ServiceAffinityNone {
		return false
	}
	return true
}

// NextEndpoint returns a service endpoint.
// The service endpoint is chosen using the round-robin algorithm.
func (lb *LoadBalancerRR) NextEndpoint(svcPort proxy.ServicePortName, srcAddr net.Addr, sessionAffinityReset bool) (string, error) {
	// Coarse locking is simple.  We can get more fine-grained if/when we
	// can prove it matters.
	lb.lock.Lock()
	defer lb.lock.Unlock()

	state, exists := lb.services[svcPort]
	if !exists || state == nil {
		return "", ErrMissingServiceEntry
	}
	if len(state.endpoints) == 0 {
		return "", ErrMissingEndpoints
	}
	klog.V(4).Infof("NextEndpoint for service %q, srcAddr=%v: endpoints: %+v", svcPort, srcAddr, state.endpoints)

	sessionAffinityEnabled := isSessionAffinity(&state.affinity)

	var ipaddr string
	if sessionAffinityEnabled {
		// Caution: don't shadow ipaddr
		var err error
		ipaddr, _, err = net.SplitHostPort(srcAddr.String())
		if err != nil {
			return "", fmt.Errorf("malformed source address %q: %v", srcAddr.String(), err)
		}
		if !sessionAffinityReset {
			sessionAffinity, exists := state.affinity.affinityMap[ipaddr]
			if exists && int(time.Since(sessionAffinity.lastUsed).Seconds()) < state.affinity.ttlSeconds {
				// Affinity wins.
				endpoint := sessionAffinity.endpoint
				sessionAffinity.lastUsed = time.Now()
				klog.V(4).Infof("NextEndpoint for service %q from IP %s with sessionAffinity %#v: %s", svcPort, ipaddr, sessionAffinity, endpoint)
				return endpoint, nil
			}
		}
	}
	// Take the next endpoint.
	endpoint := state.endpoints[state.index]
	state.index = (state.index + 1) % len(state.endpoints)

	if sessionAffinityEnabled {
		var affinity *affinityState
		affinity = state.affinity.affinityMap[ipaddr]
		if affinity == nil {
			affinity = new(affinityState) //&affinityState{ipaddr, "TCP", "", endpoint, time.Now()}
			state.affinity.affinityMap[ipaddr] = affinity
		}
		affinity.lastUsed = time.Now()
		affinity.endpoint = endpoint
		affinity.clientIP = ipaddr
		klog.V(4).Infof("Updated affinity key %s: %#v", ipaddr, state.affinity.affinityMap[ipaddr])
	}

	return endpoint, nil
}

type hostPortPair struct {
	host string
	port int
}

func isValidEndpoint(hpp *hostPortPair) bool {
	return hpp.host != "" && hpp.port > 0
}

func flattenValidEndpoints(endpoints []hostPortPair) []string {
	// Convert Endpoint objects into strings for easier use later.  Ignore
	// the protocol field - we'll get that from the Service objects.
	var result []string
	for i := range endpoints {
		hpp := &endpoints[i]
		if isValidEndpoint(hpp) {
			result = append(result, net.JoinHostPort(hpp.host, strconv.Itoa(hpp.port)))
		}
	}
	return result
}

// Remove any session affinity records associated to a particular endpoint (for example when a pod goes down).
func removeSessionAffinityByEndpoint(state *balancerState, svcPort proxy.ServicePortName, endpoint string) {
	for _, affinity := range state.affinity.affinityMap {
		if affinity.endpoint == endpoint {
			klog.V(4).Infof("Removing client: %s from affinityMap for service %q", affinity.endpoint, svcPort)
			delete(state.affinity.affinityMap, affinity.clientIP)
		}
	}
}

// Loop through the valid endpoints and then the endpoints associated with the Load Balancer.
// Then remove any session affinity records that are not in both lists.
// This assumes the lb.lock is held.
func (lb *LoadBalancerRR) updateAffinityMap(svcPort proxy.ServicePortName, newEndpoints []string) {
	allEndpoints := map[string]int{}
	for _, newEndpoint := range newEndpoints {
		allEndpoints[newEndpoint] = 1
	}
	state, exists := lb.services[svcPort]
	if !exists {
		return
	}
	for _, existingEndpoint := range state.endpoints {
		allEndpoints[existingEndpoint] = allEndpoints[existingEndpoint] + 1
	}
	for mKey, mVal := range allEndpoints {
		if mVal == 1 {
			klog.V(2).Infof("Delete endpoint %s for service %q", mKey, svcPort)
			removeSessionAffinityByEndpoint(state, svcPort, mKey)
		}
	}
}

// buildPortsToEndpointsMap builds a map of portname -> all ip:ports for that
// portname. Explode Endpoints.Subsets[*] into this structure.
func buildPortsToEndpointsMap(endpoints *v1.Endpoints) map[string][]hostPortPair {
	portsToEndpoints := map[string][]hostPortPair{}
	for i := range endpoints.Subsets {
		ss := &endpoints.Subsets[i]
		for i := range ss.Ports {
			port := &ss.Ports[i]
			for i := range ss.Addresses {
				addr := &ss.Addresses[i]
				portsToEndpoints[port.Name] = append(portsToEndpoints[port.Name], hostPortPair{addr.IP, int(port.Port)})
				// Ignore the protocol field - we'll get that from the Service objects.
			}
		}
	}
	return portsToEndpoints
}

func (lb *LoadBalancerRR) OnEndpointsAdd(endpoints *v1.Endpoints, tenantPartitionId int) {
	portsToEndpoints := buildPortsToEndpointsMap(endpoints)

	lb.lock.Lock()
	defer lb.lock.Unlock()

	for portname := range portsToEndpoints {
		svcPort := proxy.ServicePortName{NamespacednameWithTenantSource: types.NamespacednameWithTenantSource{
			TenantPartitionId: tenantPartitionId, Tenant: endpoints.Tenant, Namespace: endpoints.Namespace, Name: endpoints.Name},
			Port: portname}
		newEndpoints := flattenValidEndpoints(portsToEndpoints[portname])
		state, exists := lb.services[svcPort]

		if !exists || state == nil || len(newEndpoints) > 0 {
			klog.V(1).Infof("LoadBalancerRR: Setting endpoints for %s to %+v", svcPort, newEndpoints)
			lb.updateAffinityMap(svcPort, newEndpoints)
			// OnEndpointsAdd can be called without NewService being called externally.
			// To be safe we will call it here.  A new service will only be created
			// if one does not already exist.  The affinity will be updated
			// later, once NewService is called.
			state = lb.newServiceInternal(svcPort, v1.ServiceAffinity(""), 0)
			state.endpoints = slice.ShuffleStrings(newEndpoints)

			// Reset the round-robin index.
			state.index = 0
		}
	}
}

func (lb *LoadBalancerRR) OnEndpointsUpdate(oldEndpoints, endpoints *v1.Endpoints, tenantPartitionId int) {
	portsToEndpoints := buildPortsToEndpointsMap(endpoints)
	oldPortsToEndpoints := buildPortsToEndpointsMap(oldEndpoints)
	registeredEndpoints := make(map[proxy.ServicePortName]bool)

	lb.lock.Lock()
	defer lb.lock.Unlock()

	for portname := range portsToEndpoints {
		svcPort := proxy.ServicePortName{
			NamespacednameWithTenantSource: types.NamespacednameWithTenantSource{
				TenantPartitionId: tenantPartitionId, Tenant: endpoints.Tenant, Namespace: endpoints.Namespace, Name: endpoints.Name},
			Port: portname}
		newEndpoints := flattenValidEndpoints(portsToEndpoints[portname])
		state, exists := lb.services[svcPort]

		curEndpoints := []string{}
		if state != nil {
			curEndpoints = state.endpoints
		}

		if !exists || state == nil || len(curEndpoints) != len(newEndpoints) || !slicesEquiv(slice.CopyStrings(curEndpoints), newEndpoints) {
			klog.V(1).Infof("LoadBalancerRR: Setting endpoints for %s to %+v", svcPort, newEndpoints)
			lb.updateAffinityMap(svcPort, newEndpoints)
			// OnEndpointsUpdate can be called without NewService being called externally.
			// To be safe we will call it here.  A new service will only be created
			// if one does not already exist.  The affinity will be updated
			// later, once NewService is called.
			state = lb.newServiceInternal(svcPort, v1.ServiceAffinity(""), 0)
			state.endpoints = slice.ShuffleStrings(newEndpoints)

			// Reset the round-robin index.
			state.index = 0
		}
		registeredEndpoints[svcPort] = true
	}

	for portname := range oldPortsToEndpoints {
		svcPort := proxy.ServicePortName{NamespacednameWithTenantSource: types.NamespacednameWithTenantSource{
			TenantPartitionId: tenantPartitionId, Tenant: endpoints.Tenant, Namespace: endpoints.Namespace, Name: endpoints.Name},
			Port: portname}
		if _, exists := registeredEndpoints[svcPort]; !exists {
			klog.V(2).Infof("LoadBalancerRR: Removing endpoints for %s", svcPort)
			// Reset but don't delete.
			state := lb.services[svcPort]
			state.endpoints = []string{}
			state.index = 0
			state.affinity.affinityMap = map[string]*affinityState{}
		}
	}
}

func (lb *LoadBalancerRR) OnEndpointsDelete(endpoints *v1.Endpoints, tenantPartitionId int) {
	portsToEndpoints := buildPortsToEndpointsMap(endpoints)

	lb.lock.Lock()
	defer lb.lock.Unlock()

	for portname := range portsToEndpoints {
		svcPort := proxy.ServicePortName{
			NamespacednameWithTenantSource: types.NamespacednameWithTenantSource{
				TenantPartitionId: tenantPartitionId,
				Tenant:            endpoints.Tenant,
				Namespace:         endpoints.Namespace,
				Name:              endpoints.Name},
			Port: portname}
		klog.V(2).Infof("LoadBalancerRR: Removing endpoints for %s", svcPort)
		// If the service is still around, reset but don't delete.
		if state, ok := lb.services[svcPort]; ok {
			state.endpoints = []string{}
			state.index = 0
			state.affinity.affinityMap = map[string]*affinityState{}
		}
	}
}

func (lb *LoadBalancerRR) OnEndpointsSynced(tenantPartitionId int) {
}

// Tests whether two slices are equivalent.  This sorts both slices in-place.
func slicesEquiv(lhs, rhs []string) bool {
	if len(lhs) != len(rhs) {
		return false
	}
	if reflect.DeepEqual(slice.SortStrings(lhs), slice.SortStrings(rhs)) {
		return true
	}
	return false
}

func (lb *LoadBalancerRR) CleanupStaleStickySessions(svcPort proxy.ServicePortName) {
	lb.lock.Lock()
	defer lb.lock.Unlock()

	state, exists := lb.services[svcPort]
	if !exists {
		return
	}
	for ip, affinity := range state.affinity.affinityMap {
		if int(time.Since(affinity.lastUsed).Seconds()) >= state.affinity.ttlSeconds {
			klog.V(4).Infof("Removing client %s from affinityMap for service %q", affinity.clientIP, svcPort)
			delete(state.affinity.affinityMap, ip)
		}
	}
}
