/*
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 source

import (
	"context"
	"fmt"
	"text/template"

	log "github.com/sirupsen/logrus"
	v1 "k8s.io/api/core/v1"
	"k8s.io/apimachinery/pkg/labels"
	kubeinformers "k8s.io/client-go/informers"
	coreinformers "k8s.io/client-go/informers/core/v1"
	"k8s.io/client-go/kubernetes"

	"sigs.k8s.io/external-dns/endpoint"
	"sigs.k8s.io/external-dns/source/annotations"
	"sigs.k8s.io/external-dns/source/fqdn"
	"sigs.k8s.io/external-dns/source/informers"
)

const warningMsg = "The default behavior of exposing internal IPv6 addresses will change in the next minor version. Use --no-expose-internal-ipv6 flag to opt-in to the new behavior."

type nodeSource struct {
	client                kubernetes.Interface
	annotationFilter      string
	fqdnTemplate          *template.Template
	combineFQDNAnnotation bool

	nodeInformer         coreinformers.NodeInformer
	labelSelector        labels.Selector
	excludeUnschedulable bool
	exposeInternalIPv6   bool
}

// NewNodeSource creates a new nodeSource with the given config.
func NewNodeSource(
	ctx context.Context,
	kubeClient kubernetes.Interface,
	annotationFilter, fqdnTemplate string,
	labelSelector labels.Selector,
	exposeInternalIPv6,
	excludeUnschedulable bool,
	combineFQDNAnnotation bool) (Source, error) {
	tmpl, err := fqdn.ParseTemplate(fqdnTemplate)
	if err != nil {
		return nil, err
	}

	// Use shared informers to listen for add/update/delete of nodes.
	// Set resync period to 0, to prevent processing when nothing has changed
	informerFactory := kubeinformers.NewSharedInformerFactoryWithOptions(kubeClient, 0)
	nodeInformer := informerFactory.Core().V1().Nodes()

	// Add default resource event handler to properly initialize informer.
	_, _ = nodeInformer.Informer().AddEventHandler(informers.DefaultEventHandler())

	informerFactory.Start(ctx.Done())

	// wait for the local cache to be populated.
	if err := informers.WaitForCacheSync(context.Background(), informerFactory); err != nil {
		return nil, err
	}

	return &nodeSource{
		client:                kubeClient,
		annotationFilter:      annotationFilter,
		fqdnTemplate:          tmpl,
		combineFQDNAnnotation: combineFQDNAnnotation,
		nodeInformer:          nodeInformer,
		labelSelector:         labelSelector,
		excludeUnschedulable:  excludeUnschedulable,
		exposeInternalIPv6:    exposeInternalIPv6,
	}, nil
}

// Endpoints returns endpoint objects for each service that should be processed.
func (ns *nodeSource) Endpoints(_ context.Context) ([]*endpoint.Endpoint, error) {
	nodes, err := ns.nodeInformer.Lister().List(ns.labelSelector)
	if err != nil {
		return nil, err
	}

	nodes, err = ns.filterByAnnotations(nodes)
	if err != nil {
		return nil, err
	}

	endpoints := map[endpoint.EndpointKey]*endpoint.Endpoint{}

	// create endpoints for all nodes
	for _, node := range nodes {
		// Check the controller annotation to see if we are responsible.
		if controller, ok := node.Annotations[controllerAnnotationKey]; ok && controller != controllerAnnotationValue {
			log.Debugf("Skipping node %s because controller value does not match, found: %s, required: %s",
				node.Name, controller, controllerAnnotationValue)
			continue
		}

		if node.Spec.Unschedulable && ns.excludeUnschedulable {
			log.Debugf("Skipping node %s because it is unschedulable", node.Name)
			continue
		}

		log.Debugf("creating endpoint for node %s", node.Name)

		ttl := annotations.TTLFromAnnotations(node.Annotations, fmt.Sprintf("node/%s", node.Name))

		addrs := annotations.TargetsFromTargetAnnotation(node.Annotations)

		if len(addrs) == 0 {
			addrs, err = ns.nodeAddresses(node)
			if err != nil {
				return nil, fmt.Errorf("failed to get node address from %s: %w", node.Name, err)
			}
		}

		dnsNames, err := ns.collectDNSNames(node)
		if err != nil {
			return nil, err
		}

		for dns := range dnsNames {
			log.Debugf("adding endpoint with %d targets", len(addrs))

			for _, addr := range addrs {
				ep := endpoint.NewEndpointWithTTL(dns, suitableType(addr), ttl)
				ep.WithLabel(endpoint.ResourceLabelKey, fmt.Sprintf("node/%s", node.Name))

				log.Debugf("adding endpoint %s target %s", ep, addr)
				key := endpoint.EndpointKey{
					DNSName:    ep.DNSName,
					RecordType: ep.RecordType,
				}
				if _, ok := endpoints[key]; !ok {
					epCopy := *ep
					epCopy.RecordType = key.RecordType
					endpoints[key] = &epCopy
				}
				endpoints[key].Targets = append(endpoints[key].Targets, addr)
			}
		}
	}

	endpointsSlice := []*endpoint.Endpoint{}
	for _, ep := range endpoints {
		endpointsSlice = append(endpointsSlice, ep)
	}

	return endpointsSlice, nil
}

func (ns *nodeSource) AddEventHandler(_ context.Context, handler func()) {
	_, _ = ns.nodeInformer.Informer().AddEventHandler(eventHandlerFunc(handler))
}

// nodeAddress returns the node's externalIP and if that's not found, the node's internalIP
// basically what k8s.io/kubernetes/pkg/util/node.GetPreferredNodeAddress does
func (ns *nodeSource) nodeAddresses(node *v1.Node) ([]string, error) {
	addresses := map[v1.NodeAddressType][]string{
		v1.NodeExternalIP: {},
		v1.NodeInternalIP: {},
	}
	var internalIpv6Addresses []string

	for _, addr := range node.Status.Addresses {
		// IPv6 InternalIP addresses have special handling.
		// Refer to https://github.com/kubernetes-sigs/external-dns/pull/5192 for more details.
		if addr.Type == v1.NodeInternalIP && suitableType(addr.Address) == endpoint.RecordTypeAAAA {
			internalIpv6Addresses = append(internalIpv6Addresses, addr.Address)
		}
		addresses[addr.Type] = append(addresses[addr.Type], addr.Address)
	}

	if len(addresses[v1.NodeExternalIP]) > 0 {
		if ns.exposeInternalIPv6 {
			log.Warn(warningMsg)
			return append(addresses[v1.NodeExternalIP], internalIpv6Addresses...), nil
		}
		return addresses[v1.NodeExternalIP], nil
	}

	if len(addresses[v1.NodeInternalIP]) > 0 {
		return addresses[v1.NodeInternalIP], nil
	}

	return nil, fmt.Errorf("could not find node address for %s", node.Name)
}

// filterByAnnotations filters a list of nodes by a given annotation selector.
func (ns *nodeSource) filterByAnnotations(nodes []*v1.Node) ([]*v1.Node, error) {
	selector, err := annotations.ParseFilter(ns.annotationFilter)
	if err != nil {
		return nil, err
	}

	// empty filter returns original list
	if selector.Empty() {
		return nodes, nil
	}

	var filteredList []*v1.Node

	for _, node := range nodes {
		// include a node if its annotations match the selector
		if selector.Matches(labels.Set(node.Annotations)) {
			filteredList = append(filteredList, node)
		}
	}

	return filteredList, nil
}

// collectDNSNames returns a set of DNS names associated with the given Kubernetes Node.
// If an FQDN template is configured, it renders the template using the Node object
// to generate one or more DNS names.
// If combineFQDNAnnotation is enabled, the Node's name is also included alongside
// the templated names. If no FQDN template is provided, the result will include only
// the Node's name.
//
// Returns an error if template rendering fails.
func (ns *nodeSource) collectDNSNames(node *v1.Node) (map[string]bool, error) {
	dnsNames := make(map[string]bool)
	// If no FQDN template is configured, fallback to the node name
	if ns.fqdnTemplate == nil {
		dnsNames[node.Name] = true
		return dnsNames, nil
	}

	names, err := fqdn.ExecTemplate(ns.fqdnTemplate, node)
	if err != nil {
		return nil, err
	}

	for _, name := range names {
		dnsNames[name] = true
		log.Debugf("applied template for %s, converting to %s", node.Name, name)
	}

	if ns.combineFQDNAnnotation {
		dnsNames[node.Name] = true
	}

	return dnsNames, nil
}
