/*
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 memory

import (
	"context"
	"errors"
	"fmt"
	"sync"
	"syscall"

	openapi_v2 "github.com/google/gnostic-models/openapiv2"

	errorsutil "k8s.io/apimachinery/pkg/api/errors"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime/schema"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/version"
	"k8s.io/client-go/discovery"
	"k8s.io/client-go/openapi"
	cachedopenapi "k8s.io/client-go/openapi/cached"
	restclient "k8s.io/client-go/rest"
	"k8s.io/klog/v2"
)

type cacheEntry struct {
	resourceList *metav1.APIResourceList
	err          error
}

// memCacheClient can Invalidate() to stay up-to-date with discovery
// information.
//
// TODO: Switch to a watch interface. Right now it will poll after each
// Invalidate() call.
type memCacheClient struct {
	delegate discovery.DiscoveryInterfaceWithContext

	lock                        sync.RWMutex
	groupToServerResources      map[string]*cacheEntry
	groupList                   *metav1.APIGroupList
	cacheValid                  bool
	openapiClient               *cachedopenapi.Client
	receivedAggregatedDiscovery bool
}

// Error Constants
var (
	ErrCacheNotFound = errors.New("not found")
)

// Server returning empty ResourceList for Group/Version.
type emptyResponseError struct {
	gv string
}

func (e *emptyResponseError) Error() string {
	return fmt.Sprintf("received empty response for: %s", e.gv)
}

var _ discovery.CachedDiscoveryInterface = &memCacheClient{}
var _ discovery.CachedDiscoveryInterfaceWithContext = &memCacheClient{}

// isTransientConnectionError checks whether given error is "Connection refused" or
// "Connection reset" error which usually means that apiserver is temporarily
// unavailable.
func isTransientConnectionError(err error) bool {
	var errno syscall.Errno
	if errors.As(err, &errno) {
		return errno == syscall.ECONNREFUSED || errno == syscall.ECONNRESET
	}
	return false
}

func isTransientError(err error) bool {
	// Context cancelation is transient, retrying with a different context can work.
	if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
		return true
	}

	if isTransientConnectionError(err) {
		return true
	}

	if t, ok := err.(errorsutil.APIStatus); ok && t.Status().Code >= 500 {
		return true
	}

	return errorsutil.IsTooManyRequests(err)
}

// ServerResourcesForGroupVersion returns the supported resources for a group and version.
func (d *memCacheClient) ServerResourcesForGroupVersion(groupVersion string) (*metav1.APIResourceList, error) {
	return d.ServerResourcesForGroupVersionWithContext(context.Background(), groupVersion)
}

// ServerResourcesForGroupVersion returns the supported resources for a group and version.
func (d *memCacheClient) ServerResourcesForGroupVersionWithContext(ctx context.Context, groupVersion string) (*metav1.APIResourceList, error) {
	d.lock.Lock()
	defer d.lock.Unlock()
	if !d.cacheValid {
		if err := d.refreshLocked(ctx); err != nil {
			return nil, err
		}
	}
	cachedVal, ok := d.groupToServerResources[groupVersion]
	if !ok {
		return nil, ErrCacheNotFound
	}

	if cachedVal.err != nil && isTransientError(cachedVal.err) {
		r, err := d.serverResourcesForGroupVersion(ctx, groupVersion)
		if err != nil {
			// Don't log "empty response" as an error; it is a common response for metrics.
			if _, emptyErr := err.(*emptyResponseError); emptyErr {
				// Log at same verbosity as disk cache.
				klog.FromContext(ctx).V(3).Info(err.Error())
			} else {
				utilruntime.HandleErrorWithContext(ctx, err, "Couldn't get resource list", "gv", groupVersion)
			}
		}
		cachedVal = &cacheEntry{r, err}
		d.groupToServerResources[groupVersion] = cachedVal
	}

	return cachedVal.resourceList, cachedVal.err
}

// ServerGroupsAndResources returns the groups and supported resources for all groups and versions.
//
// ServerGroupsAndResourcesWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use ServerGroupsAndResourcesWithContext instead.
func (d *memCacheClient) ServerGroupsAndResources() ([]*metav1.APIGroup, []*metav1.APIResourceList, error) {
	return d.ServerGroupsAndResourcesWithContext(context.Background())
}

// ServerGroupsAndResources returns the groups and supported resources for all groups and versions.
func (d *memCacheClient) ServerGroupsAndResourcesWithContext(ctx context.Context) ([]*metav1.APIGroup, []*metav1.APIResourceList, error) {
	return discovery.ServerGroupsAndResourcesWithContext(ctx, d)
}

// GroupsAndMaybeResources returns the list of APIGroups, and possibly the map of group/version
// to resources. The returned groups will never be nil, but the resources map can be nil
// if there are no cached resources.
//
// GroupsAndMaybeResourcesWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use GroupsAndMaybeResourcesWithContext instead.
func (d *memCacheClient) GroupsAndMaybeResources() (*metav1.APIGroupList, map[schema.GroupVersion]*metav1.APIResourceList, map[schema.GroupVersion]error, error) {
	return d.GroupsAndMaybeResourcesWithContext(context.Background())
}

// GroupsAndMaybeResourcesWithContext returns the list of APIGroups, and possibly the map of group/version
// to resources. The returned groups will never be nil, but the resources map can be nil
// if there are no cached resources.
func (d *memCacheClient) GroupsAndMaybeResourcesWithContext(ctx context.Context) (*metav1.APIGroupList, map[schema.GroupVersion]*metav1.APIResourceList, map[schema.GroupVersion]error, error) {
	if err := ctx.Err(); err != nil {
		return nil, nil, nil, err
	}

	d.lock.Lock()
	defer d.lock.Unlock()

	if !d.cacheValid {
		if err := d.refreshLocked(ctx); err != nil {
			return nil, nil, nil, err
		}
	}
	// Build the resourceList from the cache?
	var resourcesMap map[schema.GroupVersion]*metav1.APIResourceList
	var failedGVs map[schema.GroupVersion]error
	if d.receivedAggregatedDiscovery && len(d.groupToServerResources) > 0 {
		resourcesMap = map[schema.GroupVersion]*metav1.APIResourceList{}
		failedGVs = map[schema.GroupVersion]error{}
		for gv, cacheEntry := range d.groupToServerResources {
			groupVersion, err := schema.ParseGroupVersion(gv)
			if err != nil {
				return nil, nil, nil, fmt.Errorf("failed to parse group version (%v): %v", gv, err)
			}
			if cacheEntry.err != nil {
				failedGVs[groupVersion] = cacheEntry.err
			} else {
				resourcesMap[groupVersion] = cacheEntry.resourceList
			}
		}
	}
	return d.groupList, resourcesMap, failedGVs, nil
}

// ServerGroupsWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use ServerGroupsWithContext instead.
func (d *memCacheClient) ServerGroups() (*metav1.APIGroupList, error) {
	return d.ServerGroupsWithContext(context.Background())
}

func (d *memCacheClient) ServerGroupsWithContext(ctx context.Context) (*metav1.APIGroupList, error) {
	groups, _, _, err := d.GroupsAndMaybeResourcesWithContext(ctx)
	if err != nil {
		return nil, err
	}
	return groups, nil
}

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

// ServerPreferredResourcesWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use ServerPreferredResourcesWithContext instead.
func (d *memCacheClient) ServerPreferredResources() ([]*metav1.APIResourceList, error) {
	return d.ServerPreferredResourcesWithContext(context.Background())
}

func (d *memCacheClient) ServerPreferredResourcesWithContext(ctx context.Context) ([]*metav1.APIResourceList, error) {
	return discovery.ServerPreferredResourcesWithContext(ctx, d)
}

// ServerPreferredNamespacedResourcesWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use ServerPreferredNamespacedResourcesWithContext instead.
func (d *memCacheClient) ServerPreferredNamespacedResources() ([]*metav1.APIResourceList, error) {
	return d.ServerPreferredNamespacedResourcesWithContext(context.Background())
}

func (d *memCacheClient) ServerPreferredNamespacedResourcesWithContext(ctx context.Context) ([]*metav1.APIResourceList, error) {
	return discovery.ServerPreferredNamespacedResourcesWithContext(ctx, d)
}

// ServerVersionWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use ServerVersionWithContext instead.
func (d *memCacheClient) ServerVersion() (*version.Info, error) {
	return d.ServerVersionWithContext(context.Background())
}

func (d *memCacheClient) ServerVersionWithContext(ctx context.Context) (*version.Info, error) {
	return d.delegate.ServerVersionWithContext(ctx)
}

// OpenAPISchemaWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use OpenAPISchemaWithContext instead.
func (d *memCacheClient) OpenAPISchema() (*openapi_v2.Document, error) {
	return d.OpenAPISchemaWithContext(context.Background())
}

func (d *memCacheClient) OpenAPISchemaWithContext(ctx context.Context) (*openapi_v2.Document, error) {
	return d.delegate.OpenAPISchemaWithContext(ctx)
}

// OpenAPIV3WithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use OpenAPIV3WithContext instead.
func (d *memCacheClient) OpenAPIV3() openapi.Client {
	return d.openAPIV3(context.Background())
}

func (d *memCacheClient) OpenAPIV3WithContext(ctx context.Context) openapi.ClientWithContext {
	return d.openAPIV3(ctx)
}

func (d *memCacheClient) openAPIV3(ctx context.Context) *cachedopenapi.Client {
	// Must take lock since Invalidate call may modify openapiClient
	d.lock.Lock()
	defer d.lock.Unlock()

	if d.openapiClient == nil {
		d.openapiClient = cachedopenapi.NewClientWithContext(d.delegate.OpenAPIV3WithContext(ctx))
	}

	return d.openapiClient
}

// FreshWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use FreshWithContext instead.
func (d *memCacheClient) Fresh() bool {
	return d.FreshWithContext(context.Background())
}

func (d *memCacheClient) FreshWithContext(ctx context.Context) bool {
	d.lock.RLock()
	defer d.lock.RUnlock()
	// Return whether the cache is populated at all. It is still possible that
	// a single entry is missing due to transient errors and the attempt to read
	// that entry will trigger retry.
	return d.cacheValid
}

// Invalidate enforces that no cached data that is older than the current time
// is used.
//
// InvalidateWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use InvalidateWithContext instead.
func (d *memCacheClient) Invalidate() {
	d.InvalidateWithContext(context.Background())
}

// InvalidateWithContext enforces that no cached data that is older than the current time
// is used.
func (d *memCacheClient) InvalidateWithContext(ctx context.Context) {
	d.lock.Lock()
	defer d.lock.Unlock()
	d.cacheValid = false
	d.groupToServerResources = nil
	d.groupList = nil
	d.openapiClient = nil
	d.receivedAggregatedDiscovery = false
	ad, ok := d.delegate.(discovery.CachedDiscoveryInterfaceWithContext)
	if !ok {
		//nolint:staticcheck // Intentionally using the old interface here.
		ad2, ok2 := d.delegate.(discovery.CachedDiscoveryInterface)
		if ok2 {
			ad = discovery.ToCachedDiscoveryInterfaceWithContext(ad2)
			ok = true
		}
	}
	if ok {
		ad.InvalidateWithContext(ctx)
	}
}

// refreshLocked refreshes the state of cache. The caller must hold d.lock for
// writing.
func (d *memCacheClient) refreshLocked(ctx context.Context) error {
	// TODO: Could this multiplicative set of calls be replaced by a single call
	// to ServerResources? If it's possible for more than one resulting
	// APIResourceList to have the same GroupVersion, the lists would need merged.
	var gl *metav1.APIGroupList
	var err error

	ad, ok := d.delegate.(discovery.AggregatedDiscoveryInterfaceWithContext)
	if !ok {
		//nolint:staticcheck // Intentionally using the old interface here.
		if ad2, ok2 := d.delegate.(discovery.AggregatedDiscoveryInterface); ok2 {
			ad = discovery.ToAggregatedDiscoveryInterfaceWithContext(ad2)
			ok = true
		}
	}
	if ok {
		var resources map[schema.GroupVersion]*metav1.APIResourceList
		var failedGVs map[schema.GroupVersion]error
		gl, resources, failedGVs, err = ad.GroupsAndMaybeResourcesWithContext(ctx)
		if resources != nil && err == nil {
			// Cache the resources.
			d.groupToServerResources = map[string]*cacheEntry{}
			d.groupList = gl
			for gv, resources := range resources {
				d.groupToServerResources[gv.String()] = &cacheEntry{resources, nil}
			}
			// Cache GroupVersion discovery errors
			for gv, err := range failedGVs {
				d.groupToServerResources[gv.String()] = &cacheEntry{nil, err}
			}
			d.receivedAggregatedDiscovery = true
			d.cacheValid = true
			return nil
		}
	} else {
		gl, err = d.delegate.ServerGroupsWithContext(ctx)
	}
	if err != nil || len(gl.Groups) == 0 {
		utilruntime.HandleErrorWithContext(ctx, err, "Couldn't get current server API group list")
		return err
	}

	wg := &sync.WaitGroup{}
	resultLock := &sync.Mutex{}
	rl := map[string]*cacheEntry{}
	for _, g := range gl.Groups {
		for _, v := range g.Versions {
			gv := v.GroupVersion
			wg.Add(1)
			go func() {
				defer wg.Done()
				defer utilruntime.HandleCrashWithContext(ctx)

				r, err := d.serverResourcesForGroupVersion(ctx, gv)
				if err != nil {
					// Don't log "empty response" as an error; it is a common response for metrics.
					if _, emptyErr := err.(*emptyResponseError); emptyErr {
						// Log at same verbosity as disk cache.
						klog.FromContext(ctx).V(3).Info(err.Error())
					} else {
						utilruntime.HandleErrorWithContext(ctx, err, "Couldn't get resource list", "groupVersion", gv)
					}
				}

				resultLock.Lock()
				defer resultLock.Unlock()
				rl[gv] = &cacheEntry{r, err}
			}()
		}
	}
	wg.Wait()

	d.groupToServerResources, d.groupList = rl, gl
	d.cacheValid = true
	return nil
}

func (d *memCacheClient) serverResourcesForGroupVersion(ctx context.Context, groupVersion string) (*metav1.APIResourceList, error) {
	r, err := d.delegate.ServerResourcesForGroupVersionWithContext(ctx, groupVersion)
	if err != nil {
		return r, err
	}
	if len(r.APIResources) == 0 {
		return r, &emptyResponseError{gv: groupVersion}
	}
	return r, nil
}

// WithLegacy returns current memory-cached discovery client;
// current client does not support legacy-only discovery.
//
// WithLegacyWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use WithLegacyWithContext instead.
func (d *memCacheClient) WithLegacy() discovery.DiscoveryInterface {
	return d
}

// WithLegacyWithContext returns current memory-cached discovery client;
// current client does not support legacy-only discovery.
func (d *memCacheClient) WithLegacyWithContext(ctx context.Context) discovery.DiscoveryInterfaceWithContext {
	return d
}

// NewMemCacheClient creates a new CachedDiscoveryInterface which caches
// discovery information in memory and will stay up-to-date if Invalidate is
// called with regularity.
//
// NOTE: The client will NOT resort to live lookups on cache misses.
//
// NewMemCacheClientWithContext is a better alternative because it supports contextual logging and cancellation.
//
// Contextual logging: Use NewMemCacheClientWithContext instead.
func NewMemCacheClient(delegate discovery.DiscoveryInterface) discovery.CachedDiscoveryInterface {
	return newMemCacheClient(discovery.ToDiscoveryInterfaceWithContext(delegate))
}

// NewMemCacheClientWithContext creates a new CachedDiscoveryInterfaceWithContext which caches
// discovery information in memory and will stay up-to-date if Invalidate is
// called with regularity.
//
// NOTE: The client will NOT resort to live lookups on cache misses.
func NewMemCacheClientWithContext(delegate discovery.DiscoveryInterfaceWithContext) discovery.CachedDiscoveryInterfaceWithContext {
	return newMemCacheClient(delegate)
}

func newMemCacheClient(delegate discovery.DiscoveryInterfaceWithContext) *memCacheClient {
	return &memCacheClient{
		delegate:                    delegate,
		groupToServerResources:      map[string]*cacheEntry{},
		receivedAggregatedDiscovery: false,
	}
}