/*
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 util

import (
	"errors"
	"io/ioutil"
	"os"
	"path/filepath"
	"sync"
	"time"

	"github.com/golang/glog"
	"github.com/googleapis/gnostic/OpenAPIv2"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/version"
	"k8s.io/client-go/discovery"
	restclient "k8s.io/client-go/rest"
	"k8s.io/kubernetes/pkg/kubectl/scheme"
)

// CachedDiscoveryClient implements the functions that discovery server-supported API groups,
// versions and resources.
type CachedDiscoveryClient struct {
	delegate discovery.DiscoveryInterface

	// cacheDirectory is the directory where discovery docs are held.  It must be unique per host:port combination to work well.
	cacheDirectory string

	// ttl is how long the cache should be considered valid
	ttl time.Duration

	// mutex protects the variables below
	mutex sync.Mutex

	// ourFiles are all filenames of cache files created by this process
	ourFiles map[string]struct{}
	// invalidated is true if all cache files should be ignored that are not ours (e.g. after Invalidate() was called)
	invalidated bool
	// fresh is true if all used cache files were ours
	fresh bool
}

var _ discovery.CachedDiscoveryInterface = &CachedDiscoveryClient{}

// ServerResourcesForGroupVersion returns the supported resources for a group and version.
func (d *CachedDiscoveryClient) ServerResourcesForGroupVersion(groupVersion string) (*metav1.APIResourceList, error) {
	filename := filepath.Join(d.cacheDirectory, groupVersion, "serverresources.json")
	cachedBytes, err := d.getCachedFile(filename)
	// don't fail on errors, we either don't have a file or won't be able to run the cached check. Either way we can fallback.
	if err == nil {
		cachedResources := &metav1.APIResourceList{}
		if err := runtime.DecodeInto(scheme.Codecs.UniversalDecoder(), cachedBytes, cachedResources); err == nil {
			glog.V(10).Infof("returning cached discovery info from %v", filename)
			return cachedResources, nil
		}
	}

	liveResources, err := d.delegate.ServerResourcesForGroupVersion(groupVersion)
	if err != nil {
		glog.V(3).Infof("skipped caching discovery info due to %v", err)
		return liveResources, err
	}
	if liveResources == nil || len(liveResources.APIResources) == 0 {
		glog.V(3).Infof("skipped caching discovery info, no resources found")
		return liveResources, err
	}

	if err := d.writeCachedFile(filename, liveResources); err != nil {
		glog.V(3).Infof("failed to write cache to %v due to %v", filename, err)
	}

	return liveResources, nil
}

// ServerResources returns the supported resources for all groups and versions.
func (d *CachedDiscoveryClient) ServerResources() ([]*metav1.APIResourceList, error) {
	apiGroups, err := d.ServerGroups()
	if err != nil {
		return nil, err
	}
	groupVersions := metav1.ExtractGroupVersions(apiGroups)
	result := []*metav1.APIResourceList{}
	for _, groupVersion := range groupVersions {
		resources, err := d.ServerResourcesForGroupVersion(groupVersion)
		if err != nil {
			return nil, err
		}
		result = append(result, resources)
	}
	return result, nil
}

func (d *CachedDiscoveryClient) ServerGroups() (*metav1.APIGroupList, error) {
	filename := filepath.Join(d.cacheDirectory, "servergroups.json")
	cachedBytes, err := d.getCachedFile(filename)
	// don't fail on errors, we either don't have a file or won't be able to run the cached check. Either way we can fallback.
	if err == nil {
		cachedGroups := &metav1.APIGroupList{}
		if err := runtime.DecodeInto(scheme.Codecs.UniversalDecoder(), cachedBytes, cachedGroups); err == nil {
			glog.V(10).Infof("returning cached discovery info from %v", filename)
			return cachedGroups, nil
		}
	}

	liveGroups, err := d.delegate.ServerGroups()
	if err != nil {
		glog.V(3).Infof("skipped caching discovery info due to %v", err)
		return liveGroups, err
	}
	if liveGroups == nil || len(liveGroups.Groups) == 0 {
		glog.V(3).Infof("skipped caching discovery info, no groups found")
		return liveGroups, err
	}

	if err := d.writeCachedFile(filename, liveGroups); err != nil {
		glog.V(3).Infof("failed to write cache to %v due to %v", filename, err)
	}

	return liveGroups, nil
}

func (d *CachedDiscoveryClient) getCachedFile(filename string) ([]byte, error) {
	// after invalidation ignore cache files not created by this process
	d.mutex.Lock()
	_, ourFile := d.ourFiles[filename]
	if d.invalidated && !ourFile {
		d.mutex.Unlock()
		return nil, errors.New("cache invalidated")
	}
	d.mutex.Unlock()

	file, err := os.Open(filename)
	if err != nil {
		return nil, err
	}
	defer file.Close()

	fileInfo, err := file.Stat()
	if err != nil {
		return nil, err
	}

	if time.Now().After(fileInfo.ModTime().Add(d.ttl)) {
		return nil, errors.New("cache expired")
	}

	// the cache is present and its valid.  Try to read and use it.
	cachedBytes, err := ioutil.ReadAll(file)
	if err != nil {
		return nil, err
	}

	d.mutex.Lock()
	defer d.mutex.Unlock()
	d.fresh = d.fresh && ourFile

	return cachedBytes, nil
}

func (d *CachedDiscoveryClient) writeCachedFile(filename string, obj runtime.Object) error {
	if err := os.MkdirAll(filepath.Dir(filename), 0755); err != nil {
		return err
	}

	bytes, err := runtime.Encode(scheme.Codecs.LegacyCodec(), obj)
	if err != nil {
		return err
	}

	f, err := ioutil.TempFile(filepath.Dir(filename), filepath.Base(filename)+".")
	if err != nil {
		return err
	}
	defer os.Remove(f.Name())
	_, err = f.Write(bytes)
	if err != nil {
		return err
	}

	err = os.Chmod(f.Name(), 0755)
	if err != nil {
		return err
	}

	name := f.Name()
	err = f.Close()
	if err != nil {
		return err
	}

	// atomic rename
	d.mutex.Lock()
	defer d.mutex.Unlock()
	err = os.Rename(name, filename)
	if err == nil {
		d.ourFiles[filename] = struct{}{}
	}
	return err
}

func (d *CachedDiscoveryClient) RESTClient() restclient.Interface {
	return d.delegate.RESTClient()
}

func (d *CachedDiscoveryClient) ServerPreferredResources() ([]*metav1.APIResourceList, error) {
	return d.delegate.ServerPreferredResources()
}

func (d *CachedDiscoveryClient) ServerPreferredNamespacedResources() ([]*metav1.APIResourceList, error) {
	return d.delegate.ServerPreferredNamespacedResources()
}

func (d *CachedDiscoveryClient) ServerVersion() (*version.Info, error) {
	return d.delegate.ServerVersion()
}

func (d *CachedDiscoveryClient) OpenAPISchema() (*openapi_v2.Document, error) {
	return d.delegate.OpenAPISchema()
}

func (d *CachedDiscoveryClient) Fresh() bool {
	d.mutex.Lock()
	defer d.mutex.Unlock()

	return d.fresh
}

func (d *CachedDiscoveryClient) Invalidate() {
	d.mutex.Lock()
	defer d.mutex.Unlock()

	d.ourFiles = map[string]struct{}{}
	d.fresh = true
	d.invalidated = true
}

// NewCachedDiscoveryClient creates a new DiscoveryClient.  cacheDirectory is the directory where discovery docs are held.  It must be unique per host:port combination to work well.
func NewCachedDiscoveryClient(delegate discovery.DiscoveryInterface, cacheDirectory string, ttl time.Duration) *CachedDiscoveryClient {
	return &CachedDiscoveryClient{
		delegate:       delegate,
		cacheDirectory: cacheDirectory,
		ttl:            ttl,
		ourFiles:       map[string]struct{}{},
		fresh:          true,
	}
}