/*
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 dns

import (
	"context"
	"fmt"
	"strings"

	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
	kubeadmconstants "k8s.io/kubernetes/cmd/kubeadm/app/constants"
	"k8s.io/kubernetes/cmd/kubeadm/app/features"
	"k8s.io/kubernetes/cmd/kubeadm/app/images"
	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
	"k8s.io/kubernetes/cmd/kubeadm/app/util/apiclient"

	apps "k8s.io/api/apps/v1"
	v1 "k8s.io/api/core/v1"
	rbac "k8s.io/api/rbac/v1"
	apierrors "k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	kuberuntime "k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/types"
	clientset "k8s.io/client-go/kubernetes"
	clientsetscheme "k8s.io/client-go/kubernetes/scheme"
	"k8s.io/klog/v2"

	"github.com/coredns/corefile-migration/migration"
	"github.com/pkg/errors"
)

const (
	unableToDecodeCoreDNS = "unable to decode CoreDNS"
	coreDNSReplicas       = 2
)

// DeployedDNSAddon returns the type of DNS addon currently deployed
func DeployedDNSAddon(client clientset.Interface) (string, error) {
	deploymentsClient := client.AppsV1().Deployments(metav1.NamespaceSystem)
	deployments, err := deploymentsClient.List(context.TODO(), metav1.ListOptions{LabelSelector: "k8s-app=kube-dns"})
	if err != nil {
		return "", errors.Wrap(err, "couldn't retrieve DNS addon deployments")
	}

	switch len(deployments.Items) {
	case 0:
		return "", nil
	case 1:
		addonImage := deployments.Items[0].Spec.Template.Spec.Containers[0].Image
		addonImageParts := strings.Split(addonImage, ":")
		addonVersion := addonImageParts[len(addonImageParts)-1]
		return addonVersion, nil
	default:
		return "", errors.Errorf("multiple DNS addon deployments found: %v", deployments.Items)
	}
}

// deployedDNSReplicas returns the replica count for the current DNS deployment
func deployedDNSReplicas(client clientset.Interface, replicas int32) (*int32, error) {
	deploymentsClient := client.AppsV1().Deployments(metav1.NamespaceSystem)
	deployments, err := deploymentsClient.List(context.TODO(), metav1.ListOptions{LabelSelector: "k8s-app=kube-dns"})
	if err != nil {
		return &replicas, errors.Wrap(err, "couldn't retrieve DNS addon deployments")
	}
	switch len(deployments.Items) {
	case 0:
		return &replicas, nil
	case 1:
		return deployments.Items[0].Spec.Replicas, nil
	default:
		return &replicas, errors.Errorf("multiple DNS addon deployments found: %v", deployments.Items)
	}
}

// EnsureDNSAddon creates the CoreDNS addon
func EnsureDNSAddon(cfg *kubeadmapi.ClusterConfiguration, client clientset.Interface) error {
	replicas, err := deployedDNSReplicas(client, coreDNSReplicas)
	if err != nil {
		return err
	}
	return coreDNSAddon(cfg, client, replicas)
}

func coreDNSAddon(cfg *kubeadmapi.ClusterConfiguration, client clientset.Interface, replicas *int32) error {
	// Get the YAML manifest
	coreDNSDeploymentBytes, err := kubeadmutil.ParseTemplate(CoreDNSDeployment, struct {
		DeploymentName, Image, OldControlPlaneTaintKey, ControlPlaneTaintKey string
		Replicas                                                             *int32
	}{
		DeploymentName: kubeadmconstants.CoreDNSDeploymentName,
		Image:          images.GetDNSImage(cfg),
		// TODO: https://github.com/kubernetes/kubeadm/issues/2200
		OldControlPlaneTaintKey: kubeadmconstants.LabelNodeRoleOldControlPlane,
		ControlPlaneTaintKey:    kubeadmconstants.LabelNodeRoleControlPlane,
		Replicas:                replicas,
	})
	if err != nil {
		return errors.Wrap(err, "error when parsing CoreDNS deployment template")
	}

	// Get the config file for CoreDNS
	coreDNSConfigMapBytes, err := kubeadmutil.ParseTemplate(CoreDNSConfigMap, struct{ DNSDomain, UpstreamNameserver, StubDomain string }{
		DNSDomain: cfg.Networking.DNSDomain,
	})
	if err != nil {
		return errors.Wrap(err, "error when parsing CoreDNS configMap template")
	}

	dnsip, err := kubeadmconstants.GetDNSIP(cfg.Networking.ServiceSubnet, features.Enabled(cfg.FeatureGates, features.IPv6DualStack))
	if err != nil {
		return err
	}

	coreDNSServiceBytes, err := kubeadmutil.ParseTemplate(CoreDNSService, struct{ DNSIP string }{
		DNSIP: dnsip.String(),
	})

	if err != nil {
		return errors.Wrap(err, "error when parsing CoreDNS service template")
	}

	if err := createCoreDNSAddon(coreDNSDeploymentBytes, coreDNSServiceBytes, coreDNSConfigMapBytes, client); err != nil {
		return err
	}
	fmt.Println("[addons] Applied essential addon: CoreDNS")
	return nil
}

func createCoreDNSAddon(deploymentBytes, serviceBytes, configBytes []byte, client clientset.Interface) error {
	coreDNSConfigMap := &v1.ConfigMap{}
	if err := kuberuntime.DecodeInto(clientsetscheme.Codecs.UniversalDecoder(), configBytes, coreDNSConfigMap); err != nil {
		return errors.Wrapf(err, "%s ConfigMap", unableToDecodeCoreDNS)
	}

	// Create the ConfigMap for CoreDNS or update/migrate it in case it already exists
	_, corefile, currentInstalledCoreDNSVersion, err := GetCoreDNSInfo(client)
	if err != nil {
		return errors.Wrap(err, "unable to fetch CoreDNS current installed version and ConfigMap.")
	}

	corefileMigrationRequired, err := isCoreDNSConfigMapMigrationRequired(corefile, currentInstalledCoreDNSVersion)
	if err != nil {
		return err
	}

	// Assume that migration is always possible, rely on migrateCoreDNSCorefile() to fail if not.
	canMigrateCorefile := true

	if corefile == "" || migration.Default("", corefile) {
		// If the Corefile is empty or default, the latest default Corefile will be applied
		if err := apiclient.CreateOrUpdateConfigMap(client, coreDNSConfigMap); err != nil {
			return err
		}
	} else if corefileMigrationRequired {
		// If migration is required, try and migrate the Corefile
		if err := migrateCoreDNSCorefile(client, coreDNSConfigMap, corefile, currentInstalledCoreDNSVersion); err != nil {
			// Errors in Corefile Migration is verified during preflight checks. This part will be executed when a user has chosen
			// to ignore preflight check errors.
			canMigrateCorefile = false
			klog.Warningf("the CoreDNS Configuration was not migrated: %v. The existing CoreDNS Corefile configuration has been retained.", err)
			if err := apiclient.CreateOrRetainConfigMap(client, coreDNSConfigMap, kubeadmconstants.CoreDNSConfigMap); err != nil {
				return err
			}
		}
	} else {
		// If the Corefile is modified and doesn't require any migration, it'll be retained for the benefit of the user
		if err := apiclient.CreateOrRetainConfigMap(client, coreDNSConfigMap, kubeadmconstants.CoreDNSConfigMap); err != nil {
			return err
		}
	}

	coreDNSClusterRoles := &rbac.ClusterRole{}
	if err := kuberuntime.DecodeInto(clientsetscheme.Codecs.UniversalDecoder(), []byte(CoreDNSClusterRole), coreDNSClusterRoles); err != nil {
		return errors.Wrapf(err, "%s ClusterRole", unableToDecodeCoreDNS)
	}

	// Create the Clusterroles for CoreDNS or update it in case it already exists
	if err := apiclient.CreateOrUpdateClusterRole(client, coreDNSClusterRoles); err != nil {
		return err
	}

	coreDNSClusterRolesBinding := &rbac.ClusterRoleBinding{}
	if err := kuberuntime.DecodeInto(clientsetscheme.Codecs.UniversalDecoder(), []byte(CoreDNSClusterRoleBinding), coreDNSClusterRolesBinding); err != nil {
		return errors.Wrapf(err, "%s ClusterRoleBinding", unableToDecodeCoreDNS)
	}

	// Create the Clusterrolebindings for CoreDNS or update it in case it already exists
	if err := apiclient.CreateOrUpdateClusterRoleBinding(client, coreDNSClusterRolesBinding); err != nil {
		return err
	}

	coreDNSServiceAccount := &v1.ServiceAccount{}
	if err := kuberuntime.DecodeInto(clientsetscheme.Codecs.UniversalDecoder(), []byte(CoreDNSServiceAccount), coreDNSServiceAccount); err != nil {
		return errors.Wrapf(err, "%s ServiceAccount", unableToDecodeCoreDNS)
	}

	// Create the ConfigMap for CoreDNS or update it in case it already exists
	if err := apiclient.CreateOrUpdateServiceAccount(client, coreDNSServiceAccount); err != nil {
		return err
	}

	coreDNSDeployment := &apps.Deployment{}
	if err := kuberuntime.DecodeInto(clientsetscheme.Codecs.UniversalDecoder(), deploymentBytes, coreDNSDeployment); err != nil {
		return errors.Wrapf(err, "%s Deployment", unableToDecodeCoreDNS)
	}

	// Create the deployment for CoreDNS or retain it in case the CoreDNS migration has failed during upgrade
	if !canMigrateCorefile {
		if err := apiclient.CreateOrRetainDeployment(client, coreDNSDeployment, kubeadmconstants.CoreDNSDeploymentName); err != nil {
			return err
		}
	} else {
		// Create the Deployment for CoreDNS or update it in case it already exists
		if err := apiclient.CreateOrUpdateDeployment(client, coreDNSDeployment); err != nil {
			return err
		}
	}

	coreDNSService := &v1.Service{}
	return createDNSService(coreDNSService, serviceBytes, client)
}

func createDNSService(dnsService *v1.Service, serviceBytes []byte, client clientset.Interface) error {
	if err := kuberuntime.DecodeInto(clientsetscheme.Codecs.UniversalDecoder(), serviceBytes, dnsService); err != nil {
		return errors.Wrap(err, "unable to decode the DNS service")
	}

	// Can't use a generic apiclient helper func here as we have to tolerate more than AlreadyExists.
	if _, err := client.CoreV1().Services(metav1.NamespaceSystem).Create(context.TODO(), dnsService, metav1.CreateOptions{}); err != nil {
		// Ignore if the Service is invalid with this error message:
		// 	Service "kube-dns" is invalid: spec.clusterIP: Invalid value: "10.96.0.10": provided IP is already allocated

		if !apierrors.IsAlreadyExists(err) && !apierrors.IsInvalid(err) {
			return errors.Wrap(err, "unable to create a new DNS service")
		}

		if _, err := client.CoreV1().Services(metav1.NamespaceSystem).Update(context.TODO(), dnsService, metav1.UpdateOptions{}); err != nil {
			return errors.Wrap(err, "unable to create/update the DNS service")
		}
	}
	return nil
}

// isCoreDNSConfigMapMigrationRequired checks if a migration of the CoreDNS ConfigMap is required.
func isCoreDNSConfigMapMigrationRequired(corefile, currentInstalledCoreDNSVersion string) (bool, error) {
	var isMigrationRequired bool

	// Current installed version is expected to be empty for init
	if currentInstalledCoreDNSVersion == "" {
		return isMigrationRequired, nil
	}
	currentInstalledCoreDNSVersion = strings.TrimLeft(currentInstalledCoreDNSVersion, "v")
	deprecated, err := migration.Deprecated(currentInstalledCoreDNSVersion, strings.TrimLeft(kubeadmconstants.CoreDNSVersion, "v"), corefile)
	if err != nil {
		return isMigrationRequired, errors.Wrap(err, "unable to get list of changes to the configuration.")
	}

	// Check if there are any plugins/options which needs to be removed or is a new default
	for _, dep := range deprecated {
		if dep.Severity == "removed" || dep.Severity == "newdefault" {
			isMigrationRequired = true
		}
	}

	return isMigrationRequired, nil
}

func migrateCoreDNSCorefile(client clientset.Interface, cm *v1.ConfigMap, corefile, currentInstalledCoreDNSVersion string) error {
	// Since the current configuration present is not the default version, try and migrate it.
	updatedCorefile, err := migration.Migrate(currentInstalledCoreDNSVersion, strings.TrimLeft(kubeadmconstants.CoreDNSVersion, "v"), corefile, false)
	if err != nil {
		return errors.Wrap(err, "unable to migrate CoreDNS ConfigMap")
	}

	// Take a copy of the existing Corefile data as `Corefile-backup` and update the ConfigMap
	if _, err := client.CoreV1().ConfigMaps(cm.ObjectMeta.Namespace).Update(context.TODO(), &v1.ConfigMap{
		ObjectMeta: metav1.ObjectMeta{
			Name:      kubeadmconstants.CoreDNSConfigMap,
			Namespace: metav1.NamespaceSystem,
		},
		Data: map[string]string{
			"Corefile":        updatedCorefile,
			"Corefile-backup": corefile,
		},
	}, metav1.UpdateOptions{}); err != nil {
		return errors.Wrap(err, "unable to update the CoreDNS ConfigMap")
	}

	// Point the CoreDNS deployment to the `Corefile-backup` data.
	if err := setCorefile(client, "Corefile-backup"); err != nil {
		return err
	}

	fmt.Println("[addons] Migrating CoreDNS Corefile")
	changes, err := migration.Deprecated(currentInstalledCoreDNSVersion, strings.TrimLeft(kubeadmconstants.CoreDNSVersion, "v"), corefile)
	if err != nil {
		return errors.Wrap(err, "unable to get list of changes to the configuration.")
	}
	// show the migration changes
	klog.V(2).Infof("the CoreDNS configuration has been migrated and applied: %v.", updatedCorefile)
	klog.V(2).Infoln("the old migration has been saved in the CoreDNS ConfigMap under the name [Corefile-backup]")
	klog.V(2).Infoln("The changes in the new CoreDNS Configuration are as follows:")
	for _, change := range changes {
		klog.V(2).Infof("%v", change.ToString())
	}
	return nil
}

// GetCoreDNSInfo gets the current CoreDNS installed and the current Corefile Configuration of CoreDNS.
func GetCoreDNSInfo(client clientset.Interface) (*v1.ConfigMap, string, string, error) {
	coreDNSConfigMap, err := client.CoreV1().ConfigMaps(metav1.NamespaceSystem).Get(context.TODO(), kubeadmconstants.CoreDNSConfigMap, metav1.GetOptions{})
	if err != nil && !apierrors.IsNotFound(err) {
		return nil, "", "", err
	}
	if apierrors.IsNotFound(err) {
		return nil, "", "", nil
	}
	corefile, ok := coreDNSConfigMap.Data["Corefile"]
	if !ok {
		return nil, "", "", errors.New("unable to find the CoreDNS Corefile data")
	}

	currentCoreDNSversion, err := DeployedDNSAddon(client)
	if err != nil {
		return nil, "", "", err
	}

	return coreDNSConfigMap, corefile, currentCoreDNSversion, nil
}

func setCorefile(client clientset.Interface, coreDNSCorefileName string) error {
	dnsDeployment, err := client.AppsV1().Deployments(metav1.NamespaceSystem).Get(context.TODO(), kubeadmconstants.CoreDNSDeploymentName, metav1.GetOptions{})
	if err != nil {
		return err
	}
	patch := fmt.Sprintf(`{"spec":{"template":{"spec":{"volumes":[{"name": "config-volume", "configMap":{"name": "coredns", "items":[{"key": "%s", "path": "Corefile"}]}}]}}}}`, coreDNSCorefileName)

	if _, err := client.AppsV1().Deployments(dnsDeployment.ObjectMeta.Namespace).Patch(context.TODO(), dnsDeployment.Name, types.StrategicMergePatchType, []byte(patch), metav1.PatchOptions{}); err != nil {
		return errors.Wrap(err, "unable to patch the CoreDNS deployment")
	}
	return nil
}
