/*
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 scale

import (
	"fmt"
	"strings"
	"sync"

	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/client-go/discovery"
	scalescheme "k8s.io/client-go/scale/scheme"
	scaleappsint "k8s.io/client-go/scale/scheme/appsint"
	scaleappsv1beta1 "k8s.io/client-go/scale/scheme/appsv1beta1"
	scaleappsv1beta2 "k8s.io/client-go/scale/scheme/appsv1beta2"
	scaleautoscaling "k8s.io/client-go/scale/scheme/autoscalingv1"
	scaleextint "k8s.io/client-go/scale/scheme/extensionsint"
	scaleext "k8s.io/client-go/scale/scheme/extensionsv1beta1"
)

// ScaleKindResolver knows about the relationship between
// resources and the GroupVersionKind of their scale subresources.
type ScaleKindResolver interface {
	// ScaleForResource returns the GroupVersionKind of the
	// scale subresource for the given GroupVersionResource.
	ScaleForResource(resource schema.GroupVersionResource) (scaleVersion schema.GroupVersionKind, err error)
}

// discoveryScaleResolver is a ScaleKindResolver that uses
// a DiscoveryInterface to associate resources with their
// scale-kinds
type discoveryScaleResolver struct {
	discoveryClient discovery.ServerResourcesInterface
}

func (r *discoveryScaleResolver) ScaleForResource(inputRes schema.GroupVersionResource) (scaleVersion schema.GroupVersionKind, err error) {
	groupVerResources, err := r.discoveryClient.ServerResourcesForGroupVersion(inputRes.GroupVersion().String())
	if err != nil {
		return schema.GroupVersionKind{}, fmt.Errorf("unable to fetch discovery information for %s: %v", inputRes.String(), err)
	}

	for _, resource := range groupVerResources.APIResources {
		resourceParts := strings.SplitN(resource.Name, "/", 2)
		if len(resourceParts) != 2 || resourceParts[0] != inputRes.Resource || resourceParts[1] != "scale" {
			// skip non-scale resources, or scales for resources that we're not looking for
			continue
		}

		scaleGV := inputRes.GroupVersion()
		if resource.Group != "" && resource.Version != "" {
			scaleGV = schema.GroupVersion{
				Group:   resource.Group,
				Version: resource.Version,
			}
		}

		return scaleGV.WithKind(resource.Kind), nil
	}

	return schema.GroupVersionKind{}, fmt.Errorf("could not find scale subresource for %s in discovery information", inputRes.String())
}

// cachedScaleKindResolver is a ScaleKindResolver that caches results
// from another ScaleKindResolver, re-fetching on cache misses.
type cachedScaleKindResolver struct {
	base ScaleKindResolver

	cache map[schema.GroupVersionResource]schema.GroupVersionKind
	mu    sync.RWMutex
}

func (r *cachedScaleKindResolver) ScaleForResource(resource schema.GroupVersionResource) (schema.GroupVersionKind, error) {
	r.mu.RLock()
	gvk, isCached := r.cache[resource]
	r.mu.RUnlock()
	if isCached {
		return gvk, nil
	}

	// we could have multiple fetches of the same resources, but that's probably
	// better than limiting to only one reader at once (mu.Mutex),
	// or blocking checks for other resources while we fetch
	// (mu.Lock before fetch).
	gvk, err := r.base.ScaleForResource(resource)
	if err != nil {
		return schema.GroupVersionKind{}, err
	}

	r.mu.Lock()
	defer r.mu.Unlock()
	r.cache[resource] = gvk

	return gvk, nil
}

// NewDiscoveryScaleKindResolver creates a new ScaleKindResolver which uses information from the given
// disovery client to resolve the correct Scale GroupVersionKind for different resources.
func NewDiscoveryScaleKindResolver(client discovery.ServerResourcesInterface) ScaleKindResolver {
	base := &discoveryScaleResolver{
		discoveryClient: client,
	}

	return &cachedScaleKindResolver{
		base:  base,
		cache: make(map[schema.GroupVersionResource]schema.GroupVersionKind),
	}
}

// ScaleConverter knows how to convert between external scale versions.
type ScaleConverter struct {
	scheme            *runtime.Scheme
	internalVersioner runtime.GroupVersioner
}

// NewScaleConverter creates a new ScaleConverter for converting between
// Scales in autoscaling/v1 and extensions/v1beta1.
func NewScaleConverter() *ScaleConverter {
	scheme := runtime.NewScheme()
	scaleautoscaling.AddToScheme(scheme)
	scalescheme.AddToScheme(scheme)
	scaleext.AddToScheme(scheme)
	scaleextint.AddToScheme(scheme)
	scaleappsint.AddToScheme(scheme)
	scaleappsv1beta1.AddToScheme(scheme)
	scaleappsv1beta2.AddToScheme(scheme)

	return &ScaleConverter{
		scheme: scheme,
		internalVersioner: runtime.NewMultiGroupVersioner(
			scalescheme.SchemeGroupVersion,
			schema.GroupKind{Group: scaleext.GroupName, Kind: "Scale"},
			schema.GroupKind{Group: scaleautoscaling.GroupName, Kind: "Scale"},
			schema.GroupKind{Group: scaleappsv1beta1.GroupName, Kind: "Scale"},
			schema.GroupKind{Group: scaleappsv1beta2.GroupName, Kind: "Scale"},
		),
	}
}

// Scheme returns the scheme used by this scale converter.
func (c *ScaleConverter) Scheme() *runtime.Scheme {
	return c.scheme
}

// ConvertToVersion converts the given *external* input object to the given output *external* output group-version.
func (c *ScaleConverter) ConvertToVersion(in runtime.Object, outVersion schema.GroupVersion) (runtime.Object, error) {
	scaleInt, err := c.scheme.ConvertToVersion(in, c.internalVersioner)
	if err != nil {
		return nil, err
	}

	return c.scheme.ConvertToVersion(scaleInt, outVersion)
}
