/*
Copyright 2016 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 setdefault

import (
	"context"
	"fmt"
	"io"

	"k8s.io/klog/v2"

	storagev1 "k8s.io/api/storage/v1"
	"k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apimachinery/pkg/labels"
	"k8s.io/apiserver/pkg/admission"
	genericadmissioninitializer "k8s.io/apiserver/pkg/admission/initializer"
	"k8s.io/client-go/informers"
	storagev1listers "k8s.io/client-go/listers/storage/v1"
	api "k8s.io/kubernetes/pkg/apis/core"
	"k8s.io/kubernetes/pkg/apis/core/helper"
	storageutil "k8s.io/kubernetes/pkg/apis/storage/util"
)

const (
	// PluginName is the name of this admission controller plugin
	PluginName = "DefaultStorageClass"
)

// Register registers a plugin
func Register(plugins *admission.Plugins) {
	plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
		plugin := newPlugin()
		return plugin, nil
	})
}

// claimDefaulterPlugin holds state for and implements the admission plugin.
type claimDefaulterPlugin struct {
	*admission.Handler

	lister storagev1listers.StorageClassLister
}

var _ admission.Interface = &claimDefaulterPlugin{}
var _ admission.MutationInterface = &claimDefaulterPlugin{}
var _ = genericadmissioninitializer.WantsExternalKubeInformerFactory(&claimDefaulterPlugin{})

// newPlugin creates a new admission plugin.
func newPlugin() *claimDefaulterPlugin {
	return &claimDefaulterPlugin{
		Handler: admission.NewHandler(admission.Create),
	}
}

func (a *claimDefaulterPlugin) SetExternalKubeInformerFactory(f informers.SharedInformerFactory) {
	informer := f.Storage().V1().StorageClasses()
	a.lister = informer.Lister()
	a.SetReadyFunc(informer.Informer().HasSynced)
}

// ValidateInitialization ensures lister is set.
func (a *claimDefaulterPlugin) ValidateInitialization() error {
	if a.lister == nil {
		return fmt.Errorf("missing lister")
	}
	return nil
}

// Admit sets the default value of a PersistentVolumeClaim's storage class, in case the user did
// not provide a value.
//
// 1.  Find available StorageClasses.
// 2.  Figure which is the default
// 3.  Write to the PVClaim
func (a *claimDefaulterPlugin) Admit(ctx context.Context, attr admission.Attributes, o admission.ObjectInterfaces) error {
	if attr.GetResource().GroupResource() != api.Resource("persistentvolumeclaims") {
		return nil
	}

	if len(attr.GetSubresource()) != 0 {
		return nil
	}

	pvc, ok := attr.GetObject().(*api.PersistentVolumeClaim)
	// if we can't convert then we don't handle this object so just return
	if !ok {
		return nil
	}

	if helper.PersistentVolumeClaimHasClass(pvc) {
		// The user asked for a class.
		return nil
	}

	klog.V(4).Infof("no storage class for claim %s (generate: %s)", pvc.Name, pvc.GenerateName)

	def, err := getDefaultClass(a.lister)
	if err != nil {
		return admission.NewForbidden(attr, err)
	}
	if def == nil {
		// No default class selected, do nothing about the PVC.
		return nil
	}

	klog.V(4).Infof("defaulting storage class for claim %s (generate: %s) to %s", pvc.Name, pvc.GenerateName, def.Name)
	pvc.Spec.StorageClassName = &def.Name
	return nil
}

// getDefaultClass returns the default StorageClass from the store, or nil.
func getDefaultClass(lister storagev1listers.StorageClassLister) (*storagev1.StorageClass, error) {
	list, err := lister.List(labels.Everything())
	if err != nil {
		return nil, err
	}

	defaultClasses := []*storagev1.StorageClass{}
	for _, class := range list {
		if storageutil.IsDefaultAnnotation(class.ObjectMeta) {
			defaultClasses = append(defaultClasses, class)
			klog.V(4).Infof("getDefaultClass added: %s", class.Name)
		}
	}

	if len(defaultClasses) == 0 {
		return nil, nil
	}
	if len(defaultClasses) > 1 {
		klog.V(4).Infof("getDefaultClass %d defaults found", len(defaultClasses))
		return nil, errors.NewInternalError(fmt.Errorf("%d default StorageClasses were found", len(defaultClasses)))
	}
	return defaultClasses[0], nil
}
