/*
Copyright 2014 Google Inc. All rights reserved.

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 exists

import (
	"fmt"
	"io"

	"github.com/GoogleCloudPlatform/kubernetes/pkg/admission"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
	apierrors "github.com/GoogleCloudPlatform/kubernetes/pkg/api/errors"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/api/latest"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/api/meta"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/client"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/client/cache"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/fields"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/labels"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/runtime"
	"github.com/GoogleCloudPlatform/kubernetes/pkg/watch"
)

func init() {
	admission.RegisterPlugin("NamespaceExists", func(client client.Interface, config io.Reader) (admission.Interface, error) {
		return NewExists(client), nil
	})
}

// exists is an implementation of admission.Interface.
// It rejects all incoming requests in a namespace context if the namespace does not exist.
// It is useful in deployments that want to enforce pre-declaration of a Namespace resource.
type exists struct {
	client client.Interface
	store  cache.Store
}

func (e *exists) Admit(a admission.Attributes) (err error) {
	defaultVersion, kind, err := latest.RESTMapper.VersionAndKindForResource(a.GetResource())
	if err != nil {
		return err
	}
	mapping, err := latest.RESTMapper.RESTMapping(kind, defaultVersion)
	if err != nil {
		return err
	}
	if mapping.Scope.Name() != meta.RESTScopeNameNamespace {
		return nil
	}
	namespace := &api.Namespace{
		ObjectMeta: api.ObjectMeta{
			Name:      a.GetNamespace(),
			Namespace: "",
		},
		Status: api.NamespaceStatus{},
	}
	_, exists, err := e.store.Get(namespace)
	if err != nil {
		return err
	}
	if exists {
		return nil
	}
	obj := a.GetObject()
	name := "Unknown"
	if obj != nil {
		name, _ = meta.NewAccessor().Name(obj)
	}
	return apierrors.NewForbidden(kind, name, fmt.Errorf("Namespace %s does not exist", a.GetNamespace()))
}

func NewExists(c client.Interface) admission.Interface {
	store := cache.NewStore(cache.MetaNamespaceKeyFunc)
	reflector := cache.NewReflector(
		&cache.ListWatch{
			ListFunc: func() (runtime.Object, error) {
				return c.Namespaces().List(labels.Everything(), fields.Everything())
			},
			WatchFunc: func(resourceVersion string) (watch.Interface, error) {
				return c.Namespaces().Watch(labels.Everything(), fields.Everything(), resourceVersion)
			},
		},
		&api.Namespace{},
		store,
		0,
	)
	reflector.Run()
	return &exists{
		client: c,
		store:  store,
	}
}