/*
Copyright 2020 The Knative 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 validation

import (
	"context"
	"fmt"
	"sort"
	"strings"

	"github.com/gobuffalo/flect"
	"go.uber.org/zap"
	admissionregistrationv1 "k8s.io/api/admissionregistration/v1"
	corev1 "k8s.io/api/core/v1"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apimachinery/pkg/types"
	"k8s.io/client-go/kubernetes"
	admissionlisters "k8s.io/client-go/listers/admissionregistration/v1"
	corelisters "k8s.io/client-go/listers/core/v1"

	"knative.dev/pkg/controller"
	"knative.dev/pkg/kmp"
	"knative.dev/pkg/logging"
	"knative.dev/pkg/ptr"
	pkgreconciler "knative.dev/pkg/reconciler"
	"knative.dev/pkg/system"
	"knative.dev/pkg/webhook"
	certresources "knative.dev/pkg/webhook/certificates/resources"
	"knative.dev/pkg/webhook/resourcesemantics"
)

// reconciler implements the AdmissionController for resources
type reconciler struct {
	webhook.StatelessAdmissionImpl
	pkgreconciler.LeaderAwareFuncs

	key       types.NamespacedName
	path      string
	handlers  map[schema.GroupVersionKind]resourcesemantics.GenericCRD
	callbacks map[schema.GroupVersionKind]Callback

	withContext func(context.Context) context.Context

	client       kubernetes.Interface
	vwhlister    admissionlisters.ValidatingWebhookConfigurationLister
	secretlister corelisters.SecretLister

	disallowUnknownFields bool
	secretName            string
}

var (
	_ controller.Reconciler                = (*reconciler)(nil)
	_ pkgreconciler.LeaderAware            = (*reconciler)(nil)
	_ webhook.AdmissionController          = (*reconciler)(nil)
	_ webhook.StatelessAdmissionController = (*reconciler)(nil)
)

// Path implements AdmissionController
func (ac *reconciler) Path() string {
	return ac.path
}

// Reconcile implements controller.Reconciler
func (ac *reconciler) Reconcile(ctx context.Context, key string) error {
	logger := logging.FromContext(ctx)

	if !ac.IsLeaderFor(ac.key) {
		return controller.NewSkipKey(key)
	}

	// Look up the webhook secret, and fetch the CA cert bundle.
	secret, err := ac.secretlister.Secrets(system.Namespace()).Get(ac.secretName)
	if err != nil {
		logger.Errorw("Error fetching secret", zap.Error(err))
		return err
	}
	caCert, ok := secret.Data[certresources.CACert]
	if !ok {
		return fmt.Errorf("secret %q is missing %q key", ac.secretName, certresources.CACert)
	}

	// Reconcile the webhook configuration.
	return ac.reconcileValidatingWebhook(ctx, caCert)
}

func (ac *reconciler) reconcileValidatingWebhook(ctx context.Context, caCert []byte) error {
	logger := logging.FromContext(ctx)

	rules := make([]admissionregistrationv1.RuleWithOperations, 0, len(ac.handlers)+len(ac.callbacks))
	for gvk, config := range ac.handlers {
		plural := strings.ToLower(flect.Pluralize(gvk.Kind))

		// If SupportedVerbs has not been given, provide the legacy defaults
		// of Create, Update, and Delete
		supportedVerbs := []admissionregistrationv1.OperationType{
			admissionregistrationv1.Create,
			admissionregistrationv1.Update,
			admissionregistrationv1.Delete,
		}

		if vl, ok := config.(resourcesemantics.VerbLimited); ok {
			logging.FromContext(ctx).Debugf("Using custom Verbs")
			supportedVerbs = vl.SupportedVerbs()
		}
		logging.FromContext(ctx).Debugf("Registering verbs: %s", supportedVerbs)

		resources := []string{}
		// If SupportedSubResources has not been given, provide the legacy
		// defaults of main resource, and status
		if srl, ok := config.(resourcesemantics.SubResourceLimited); ok {
			logging.FromContext(ctx).Debugf("Using custom SubResources")
			for _, subResource := range srl.SupportedSubResources() {
				if subResource == "" {
					// Special case the actual plural if given
					resources = append(resources, plural)
				} else {
					resources = append(resources, plural+subResource)
				}
			}
		} else {
			resources = append(resources, plural, plural+"/status")
		}
		logging.FromContext(ctx).Debugf("Registering SubResources: %s", resources)
		rules = append(rules, admissionregistrationv1.RuleWithOperations{
			Operations: supportedVerbs,
			Rule: admissionregistrationv1.Rule{
				APIGroups:   []string{gvk.Group},
				APIVersions: []string{gvk.Version},
				Resources:   resources,
			},
		})
	}
	for gvk, callback := range ac.callbacks {
		if _, ok := ac.handlers[gvk]; ok {
			continue
		}
		plural := strings.ToLower(flect.Pluralize(gvk.Kind))
		resources := []string{plural, plural + "/status"}

		verbs := make([]admissionregistrationv1.OperationType, 0, len(callback.supportedVerbs))
		for verb := range callback.supportedVerbs {
			verbs = append(verbs, admissionregistrationv1.OperationType(verb))
		}
		// supportedVerbs is a map which doesn't provide a stable order in for loops.
		sort.Slice(verbs, func(i, j int) bool { return string(verbs[i]) < string(verbs[j]) })

		rules = append(rules, admissionregistrationv1.RuleWithOperations{
			Operations: verbs,
			Rule: admissionregistrationv1.Rule{
				APIGroups:   []string{gvk.Group},
				APIVersions: []string{gvk.Version},
				Resources:   resources,
			},
		})
	}

	for _, r := range rules {
		logging.FromContext(ctx).Debugf("Rule: %+v", r)
	}

	// Sort the rules by Group, Version, Kind so that things are deterministically ordered.
	sort.Slice(rules, func(i, j int) bool {
		lhs, rhs := rules[i], rules[j]
		if lhs.APIGroups[0] != rhs.APIGroups[0] {
			return lhs.APIGroups[0] < rhs.APIGroups[0]
		}
		if lhs.APIVersions[0] != rhs.APIVersions[0] {
			return lhs.APIVersions[0] < rhs.APIVersions[0]
		}
		return lhs.Resources[0] < rhs.Resources[0]
	})

	configuredWebhook, err := ac.vwhlister.Get(ac.key.Name)
	if err != nil {
		return fmt.Errorf("error retrieving webhook: %w", err)
	}

	current := configuredWebhook.DeepCopy()

	// Set the owner to namespace.
	ns, err := ac.client.CoreV1().Namespaces().Get(ctx, system.Namespace(), metav1.GetOptions{})
	if err != nil {
		return fmt.Errorf("failed to fetch namespace: %w", err)
	}
	nsRef := *metav1.NewControllerRef(ns, corev1.SchemeGroupVersion.WithKind("Namespace"))
	current.OwnerReferences = []metav1.OwnerReference{nsRef}

	for i, wh := range current.Webhooks {
		if wh.Name != current.Name {
			continue
		}
		cur := &current.Webhooks[i]
		cur.Rules = rules

		cur.NamespaceSelector = webhook.EnsureLabelSelectorExpressions(
			cur.NamespaceSelector,
			&metav1.LabelSelector{
				MatchExpressions: []metav1.LabelSelectorRequirement{{
					Key:      "webhooks.knative.dev/exclude",
					Operator: metav1.LabelSelectorOpDoesNotExist,
				}},
			})

		cur.ClientConfig.CABundle = caCert
		if cur.ClientConfig.Service == nil {
			return fmt.Errorf("missing service reference for webhook: %s", wh.Name)
		}
		cur.ClientConfig.Service.Path = ptr.String(ac.Path())
	}

	if ok, err := kmp.SafeEqual(configuredWebhook, current); err != nil {
		return fmt.Errorf("error diffing webhooks: %w", err)
	} else if !ok {
		logger.Info("Updating webhook")
		vwhclient := ac.client.AdmissionregistrationV1().ValidatingWebhookConfigurations()
		if _, err := vwhclient.Update(ctx, current, metav1.UpdateOptions{}); err != nil {
			return fmt.Errorf("failed to update webhook: %w", err)
		}
	} else {
		logger.Info("Webhook is valid")
	}
	return nil
}
