/*
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 configuration

import (
	"fmt"
	"sort"
	"sync/atomic"

	"k8s.io/api/admissionregistration/v1beta1"
	"k8s.io/apimachinery/pkg/labels"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apiserver/pkg/admission/plugin/webhook/generic"
	"k8s.io/client-go/informers"
	admissionregistrationlisters "k8s.io/client-go/listers/admissionregistration/v1beta1"
	"k8s.io/client-go/tools/cache"
)

// mutatingWebhookConfigurationManager collects the mutating webhook objects so that they can be called.
type mutatingWebhookConfigurationManager struct {
	configuration *atomic.Value
	lister        admissionregistrationlisters.MutatingWebhookConfigurationLister
	hasSynced     func() bool
}

var _ generic.Source = &mutatingWebhookConfigurationManager{}

func NewMutatingWebhookConfigurationManager(f informers.SharedInformerFactory) generic.Source {
	informer := f.Admissionregistration().V1beta1().MutatingWebhookConfigurations()
	manager := &mutatingWebhookConfigurationManager{
		configuration: &atomic.Value{},
		lister:        informer.Lister(),
		hasSynced:     informer.Informer().HasSynced,
	}

	// Start with an empty list
	manager.configuration.Store(&v1beta1.MutatingWebhookConfiguration{})

	// On any change, rebuild the config
	informer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc:    func(_ interface{}) { manager.updateConfiguration() },
		UpdateFunc: func(_, _ interface{}) { manager.updateConfiguration() },
		DeleteFunc: func(_ interface{}) { manager.updateConfiguration() },
	})

	return manager
}

// Webhooks returns the merged MutatingWebhookConfiguration.
func (m *mutatingWebhookConfigurationManager) Webhooks() []v1beta1.Webhook {
	return m.configuration.Load().(*v1beta1.MutatingWebhookConfiguration).Webhooks
}

func (m *mutatingWebhookConfigurationManager) HasSynced() bool {
	return m.hasSynced()
}

func (m *mutatingWebhookConfigurationManager) updateConfiguration() {
	configurations, err := m.lister.List(labels.Everything())
	if err != nil {
		utilruntime.HandleError(fmt.Errorf("error updating configuration: %v", err))
		return
	}
	m.configuration.Store(mergeMutatingWebhookConfigurations(configurations))
}

func mergeMutatingWebhookConfigurations(configurations []*v1beta1.MutatingWebhookConfiguration) *v1beta1.MutatingWebhookConfiguration {
	var ret v1beta1.MutatingWebhookConfiguration
	// The internal order of webhooks for each configuration is provided by the user
	// but configurations themselves can be in any order. As we are going to run these
	// webhooks in serial, they are sorted here to have a deterministic order.
	sort.SliceStable(configurations, MutatingWebhookConfigurationSorter(configurations).ByName)
	for _, c := range configurations {
		ret.Webhooks = append(ret.Webhooks, c.Webhooks...)
	}
	return &ret
}

type MutatingWebhookConfigurationSorter []*v1beta1.MutatingWebhookConfiguration

func (a MutatingWebhookConfigurationSorter) ByName(i, j int) bool {
	return a[i].Name < a[j].Name
}