/*
Copyright 2019 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 watchers

import (
	"context"
	"fmt"
	"time"

	v1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/watch"
	"k8s.io/client-go/kubernetes"
	"k8s.io/klog/v2"
	"k8s.io/kops/dns-controller/pkg/dns"
	"k8s.io/kops/dns-controller/pkg/util"
	kopsutil "k8s.io/kops/pkg/apis/kops/util"
	"k8s.io/kops/upup/pkg/fi/utils"
)

// NodeController watches for nodes
//
// Unlike other watchers, NodeController only creates alias records referenced by records from other controllers
type NodeController struct {
	util.Stoppable
	client   kubernetes.Interface
	scope    dns.Scope
	haveType map[dns.RecordType]bool
}

// NewNodeController creates a NodeController
func NewNodeController(client kubernetes.Interface, dnsContext dns.Context, internalRecordTypes []dns.RecordType) (*NodeController, error) {
	scope, err := dnsContext.CreateScope("node")
	if err != nil {
		return nil, fmt.Errorf("error building dns scope: %v", err)
	}

	c := &NodeController{
		client:   client,
		scope:    scope,
		haveType: map[dns.RecordType]bool{},
	}

	for _, recordType := range internalRecordTypes {
		c.haveType[recordType] = true
	}

	return c, nil
}

// Run starts the NodeController.
func (c *NodeController) Run() {
	klog.Infof("starting node controller")

	stopCh := c.StopChannel()
	go c.runWatcher(stopCh)

	<-stopCh
	klog.Infof("shutting down node controller")
}

func (c *NodeController) runWatcher(stopCh <-chan struct{}) {
	runOnce := func() (bool, error) {
		ctx := context.TODO()

		var listOpts metav1.ListOptions
		klog.V(4).Infof("querying without field filter")

		// Note we need to watch all the nodes, to set up alias targets
		allKeys := c.scope.AllKeys()
		nodeList, err := c.client.CoreV1().Nodes().List(ctx, listOpts)
		if err != nil {
			return false, fmt.Errorf("error listing nodes: %v", err)
		}
		foundKeys := make(map[string]bool)
		for i := range nodeList.Items {
			node := &nodeList.Items[i]
			klog.V(4).Infof("found node: %v", node.Name)
			key := c.updateNodeRecords(node)
			foundKeys[key] = true
		}
		for _, key := range allKeys {
			if !foundKeys[key] {
				// The node previously existed, but no longer exists; delete it from the scope
				klog.V(2).Infof("removing node not found in list: %s", key)
				c.scope.Replace(key, nil)
			}
		}
		c.scope.MarkReady()

		listOpts.Watch = true
		listOpts.ResourceVersion = nodeList.ResourceVersion
		watcher, err := c.client.CoreV1().Nodes().Watch(ctx, listOpts)
		if err != nil {
			return false, fmt.Errorf("error watching nodes: %v", err)
		}
		ch := watcher.ResultChan()
		for {
			select {
			case <-stopCh:
				klog.Infof("Got stop signal")
				return true, nil
			case event, ok := <-ch:
				if !ok {
					klog.Infof("node watch channel closed")
					return false, nil
				}

				node := event.Object.(*v1.Node)
				klog.V(4).Infof("node changed: %s %v", event.Type, node.Name)

				switch event.Type {
				case watch.Added, watch.Modified:
					c.updateNodeRecords(node)

				case watch.Deleted:
					c.scope.Replace( /* no namespace for nodes */ node.Name, nil)
				}
			}
		}
	}

	for {
		stop, err := runOnce()
		if stop {
			return
		}

		if err != nil {
			klog.Warningf("Unexpected error in event watch, will retry: %v", err)
			time.Sleep(10 * time.Second)
		}
	}
}

// updateNodeRecords will apply the records for the specified node.  It returns the key that was set.
func (c *NodeController) updateNodeRecords(node *v1.Node) string {
	var records []dns.Record

	// Alias targets

	// node/<name>/internal -> InternalIP
	for _, a := range node.Status.Addresses {
		if a.Type != v1.NodeInternalIP {
			continue
		}
		var recordType dns.RecordType = dns.RecordTypeA
		if utils.IsIPv6IP(a.Address) {
			recordType = dns.RecordTypeAAAA
		}
		if !c.haveType[recordType] {
			continue
		}
		records = append(records, dns.Record{
			RecordType:  recordType,
			FQDN:        "node/" + node.Name + "/internal",
			Value:       a.Address,
			AliasTarget: true,
		})
	}

	// node/<name>/external -> ExternalIP
	for _, a := range node.Status.Addresses {
		if a.Type != v1.NodeExternalIP && (a.Type != v1.NodeInternalIP || !utils.IsIPv6IP(a.Address)) {
			continue
		}
		var recordType dns.RecordType = dns.RecordTypeA
		if utils.IsIPv6IP(a.Address) {
			recordType = dns.RecordTypeAAAA
		}
		records = append(records, dns.Record{
			RecordType:  recordType,
			FQDN:        "node/" + node.Name + "/external",
			Value:       a.Address,
			AliasTarget: true,
		})
	}

	// node/role=<role>/external -> ExternalIP
	// node/role=<role>/internal -> InternalIP
	{
		role := kopsutil.GetNodeRole(node)
		// Default to node
		if role == "" {
			role = "node"
		}

		for _, a := range node.Status.Addresses {
			var roleType string
			switch a.Type {
			case v1.NodeInternalIP:
				roleType = dns.RoleTypeInternal
			case v1.NodeExternalIP:
				roleType = dns.RoleTypeExternal
			}
			var recordType dns.RecordType = dns.RecordTypeA
			if utils.IsIPv6IP(a.Address) {
				recordType = dns.RecordTypeAAAA
			}
			records = append(records, dns.Record{
				RecordType:  recordType,
				FQDN:        dns.AliasForNodesInRole(role, roleType),
				Value:       a.Address,
				AliasTarget: true,
			})
		}
	}

	key := /* no namespace for nodes */ node.Name
	c.scope.Replace(key, records)
	return key
}
