/*
Copyright 2014 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 cache

import (
	"context"
	"errors"
	"fmt"
	"io"
	"math/rand"
	"reflect"
	"sync"
	"time"

	apierrs "k8s.io/apimachinery/pkg/api/errors"
	"k8s.io/apimachinery/pkg/api/meta"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/util/clock"
	"k8s.io/apimachinery/pkg/util/naming"
	utilnet "k8s.io/apimachinery/pkg/util/net"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/util/wait"
	"k8s.io/apimachinery/pkg/watch"
	"k8s.io/client-go/tools/pager"
	"k8s.io/klog"
	"k8s.io/utils/trace"
)

// Reflector watches a specified resource and causes all changes to be reflected in the given store.
type Reflector struct {
	// name identifies this reflector. By default it will be a file:line if possible.
	name string
	// metrics tracks basic metric information about the reflector
	metrics *reflectorMetrics

	// The type of object we expect to place in the store.
	expectedType reflect.Type
	// The destination to sync up with the watch source
	store Store
	// listerWatcher is used to perform lists and watches.
	listerWatcher ListerWatcher
	// period controls timing between one watch ending and
	// the beginning of the next one.
	period       time.Duration
	resyncPeriod time.Duration
	ShouldResync func() bool
	// clock allows tests to manipulate time
	clock clock.Clock
	// lastSyncResourceVersion is the resource version token last
	// observed when doing a sync with the underlying store
	// it is thread safe, but not synchronized with the underlying store
	lastSyncResourceVersion string
	// lastSyncResourceVersionMutex guards read/write access to lastSyncResourceVersion
	lastSyncResourceVersionMutex sync.RWMutex
	// WatchListPageSize is the requested chunk size of initial and resync watch lists.
	// Defaults to pager.PageSize.
	WatchListPageSize int64
}

var (
	// We try to spread the load on apiserver by setting timeouts for
	// watch requests - it is random in [minWatchTimeout, 2*minWatchTimeout].
	minWatchTimeout = 5 * time.Minute
)

// NewNamespaceKeyedIndexerAndReflector creates an Indexer and a Reflector
// The indexer is configured to key on namespace
func NewNamespaceKeyedIndexerAndReflector(lw ListerWatcher, expectedType interface{}, resyncPeriod time.Duration) (indexer Indexer, reflector *Reflector) {
	indexer = NewIndexer(MetaNamespaceKeyFunc, Indexers{NamespaceIndex: MetaNamespaceIndexFunc})
	reflector = NewReflector(lw, expectedType, indexer, resyncPeriod)
	return indexer, reflector
}

// NewReflector creates a new Reflector object which will keep the given store up to
// date with the server's contents for the given resource. Reflector promises to
// only put things in the store that have the type of expectedType, unless expectedType
// is nil. If resyncPeriod is non-zero, then lists will be executed after every
// resyncPeriod, so that you can use reflectors to periodically process everything as
// well as incrementally processing the things that change.
func NewReflector(lw ListerWatcher, expectedType interface{}, store Store, resyncPeriod time.Duration) *Reflector {
	return NewNamedReflector(naming.GetNameFromCallsite(internalPackages...), lw, expectedType, store, resyncPeriod)
}

// NewNamedReflector same as NewReflector, but with a specified name for logging
func NewNamedReflector(name string, lw ListerWatcher, expectedType interface{}, store Store, resyncPeriod time.Duration) *Reflector {
	r := &Reflector{
		name:          name,
		listerWatcher: lw,
		store:         store,
		expectedType:  reflect.TypeOf(expectedType),
		period:        time.Second,
		resyncPeriod:  resyncPeriod,
		clock:         &clock.RealClock{},
	}
	return r
}

// internalPackages are packages that ignored when creating a default reflector name. These packages are in the common
// call chains to NewReflector, so they'd be low entropy names for reflectors
var internalPackages = []string{"client-go/tools/cache/"}

// Run starts a watch and handles watch events. Will restart the watch if it is closed.
// Run will exit when stopCh is closed.
func (r *Reflector) Run(stopCh <-chan struct{}) {
	klog.V(3).Infof("Starting reflector %v (%s) from %s", r.expectedType, r.resyncPeriod, r.name)
	wait.Until(func() {
		if err := r.ListAndWatch(stopCh); err != nil {
			utilruntime.HandleError(err)
		}
	}, r.period, stopCh)
}

var (
	// nothing will ever be sent down this channel
	neverExitWatch <-chan time.Time = make(chan time.Time)

	// Used to indicate that watching stopped so that a resync could happen.
	errorResyncRequested = errors.New("resync channel fired")

	// Used to indicate that watching stopped because of a signal from the stop
	// channel passed in from a client of the reflector.
	errorStopRequested = errors.New("Stop requested")
)

// resyncChan returns a channel which will receive something when a resync is
// required, and a cleanup function.
func (r *Reflector) resyncChan() (<-chan time.Time, func() bool) {
	if r.resyncPeriod == 0 {
		return neverExitWatch, func() bool { return false }
	}
	// The cleanup function is required: imagine the scenario where watches
	// always fail so we end up listing frequently. Then, if we don't
	// manually stop the timer, we could end up with many timers active
	// concurrently.
	t := r.clock.NewTimer(r.resyncPeriod)
	return t.C(), t.Stop
}

// ListAndWatch first lists all items and get the resource version at the moment of call,
// and then use the resource version to watch.
// It returns error if ListAndWatch didn't even try to initialize watch.
func (r *Reflector) ListAndWatch(stopCh <-chan struct{}) error {
	klog.V(3).Infof("Listing and watching %v from %s", r.expectedType, r.name)
	var resourceVersion string

	// Explicitly set "0" as resource version - it's fine for the List()
	// to be served from cache and potentially be delayed relative to
	// etcd contents. Reflector framework will catch up via Watch() eventually.
	options := metav1.ListOptions{ResourceVersion: "0"}

	if err := func() error {
		initTrace := trace.New("Reflector ListAndWatch", trace.Field{"name", r.name})
		defer initTrace.LogIfLong(10 * time.Second)
		var list runtime.Object
		var err error
		listCh := make(chan struct{}, 1)
		panicCh := make(chan interface{}, 1)
		go func() {
			defer func() {
				if r := recover(); r != nil {
					panicCh <- r
				}
			}()
			// Attempt to gather list in chunks, if supported by listerWatcher, if not, the first
			// list request will return the full response.
			pager := pager.New(pager.SimplePageFunc(func(opts metav1.ListOptions) (runtime.Object, error) {
				return r.listerWatcher.List(opts)
			}))
			if r.WatchListPageSize != 0 {
				pager.PageSize = r.WatchListPageSize
			}
			// Pager falls back to full list if paginated list calls fail due to an "Expired" error.
			list, err = pager.List(context.Background(), options)
			close(listCh)
		}()
		select {
		case <-stopCh:
			return nil
		case r := <-panicCh:
			panic(r)
		case <-listCh:
		}
		if err != nil {
			return fmt.Errorf("%s: Failed to list %v: %v", r.name, r.expectedType, err)
		}
		initTrace.Step("Objects listed")
		listMetaInterface, err := meta.ListAccessor(list)
		if err != nil {
			return fmt.Errorf("%s: Unable to understand list result %#v: %v", r.name, list, err)
		}
		resourceVersion = listMetaInterface.GetResourceVersion()
		initTrace.Step("Resource version extracted")
		items, err := meta.ExtractList(list)
		if err != nil {
			return fmt.Errorf("%s: Unable to understand list result %#v (%v)", r.name, list, err)
		}
		initTrace.Step("Objects extracted")
		if err := r.syncWith(items, resourceVersion); err != nil {
			return fmt.Errorf("%s: Unable to sync list result: %v", r.name, err)
		}
		initTrace.Step("SyncWith done")
		r.setLastSyncResourceVersion(resourceVersion)
		initTrace.Step("Resource version updated")
		return nil
	}(); err != nil {
		return err
	}

	resyncerrc := make(chan error, 1)
	cancelCh := make(chan struct{})
	defer close(cancelCh)
	go func() {
		resyncCh, cleanup := r.resyncChan()
		defer func() {
			cleanup() // Call the last one written into cleanup
		}()
		for {
			select {
			case <-resyncCh:
			case <-stopCh:
				return
			case <-cancelCh:
				return
			}
			if r.ShouldResync == nil || r.ShouldResync() {
				klog.V(4).Infof("%s: forcing resync", r.name)
				if err := r.store.Resync(); err != nil {
					resyncerrc <- err
					return
				}
			}
			cleanup()
			resyncCh, cleanup = r.resyncChan()
		}
	}()

	for {
		// give the stopCh a chance to stop the loop, even in case of continue statements further down on errors
		select {
		case <-stopCh:
			return nil
		default:
		}

		timeoutSeconds := int64(minWatchTimeout.Seconds() * (rand.Float64() + 1.0))
		options = metav1.ListOptions{
			ResourceVersion: resourceVersion,
			// We want to avoid situations of hanging watchers. Stop any wachers that do not
			// receive any events within the timeout window.
			TimeoutSeconds: &timeoutSeconds,
			// To reduce load on kube-apiserver on watch restarts, you may enable watch bookmarks.
			// Reflector doesn't assume bookmarks are returned at all (if the server do not support
			// watch bookmarks, it will ignore this field).
			AllowWatchBookmarks: true,
		}

		// start the clock before sending the request, since some proxies won't flush headers until after the first watch event is sent
		start := r.clock.Now()
		w, err := r.listerWatcher.Watch(options)
		if err != nil {
			switch err {
			case io.EOF:
				// watch closed normally
			case io.ErrUnexpectedEOF:
				klog.V(1).Infof("%s: Watch for %v closed with unexpected EOF: %v", r.name, r.expectedType, err)
			default:
				utilruntime.HandleError(fmt.Errorf("%s: Failed to watch %v: %v", r.name, r.expectedType, err))
			}
			// If this is "connection refused" error, it means that most likely apiserver is not responsive.
			// It doesn't make sense to re-list all objects because most likely we will be able to restart
			// watch where we ended.
			// If that's the case wait and resend watch request.
			if utilnet.IsConnectionRefused(err) {
				time.Sleep(time.Second)
				continue
			}
			return nil
		}

		if err := r.watchHandler(start, w, &resourceVersion, resyncerrc, stopCh); err != nil {
			if err != errorStopRequested {
				switch {
				case apierrs.IsResourceExpired(err):
					klog.V(4).Infof("%s: watch of %v ended with: %v", r.name, r.expectedType, err)
				default:
					klog.Warningf("%s: watch of %v ended with: %v", r.name, r.expectedType, err)
				}
			}
			return nil
		}
	}
}

// syncWith replaces the store's items with the given list.
func (r *Reflector) syncWith(items []runtime.Object, resourceVersion string) error {
	found := make([]interface{}, 0, len(items))
	for _, item := range items {
		found = append(found, item)
	}
	return r.store.Replace(found, resourceVersion)
}

// watchHandler watches w and keeps *resourceVersion up to date.
func (r *Reflector) watchHandler(start time.Time, w watch.Interface, resourceVersion *string, errc chan error, stopCh <-chan struct{}) error {
	eventCount := 0

	// Stopping the watcher should be idempotent and if we return from this function there's no way
	// we're coming back in with the same watch interface.
	defer w.Stop()

loop:
	for {
		select {
		case <-stopCh:
			return errorStopRequested
		case err := <-errc:
			return err
		case event, ok := <-w.ResultChan():
			if !ok {
				break loop
			}
			if event.Type == watch.Error {
				return apierrs.FromObject(event.Object)
			}
			if e, a := r.expectedType, reflect.TypeOf(event.Object); e != nil && e != a {
				utilruntime.HandleError(fmt.Errorf("%s: expected type %v, but watch event object had type %v", r.name, e, a))
				continue
			}
			meta, err := meta.Accessor(event.Object)
			if err != nil {
				utilruntime.HandleError(fmt.Errorf("%s: unable to understand watch event %#v", r.name, event))
				continue
			}
			newResourceVersion := meta.GetResourceVersion()
			switch event.Type {
			case watch.Added:
				err := r.store.Add(event.Object)
				if err != nil {
					utilruntime.HandleError(fmt.Errorf("%s: unable to add watch event object (%#v) to store: %v", r.name, event.Object, err))
				}
			case watch.Modified:
				err := r.store.Update(event.Object)
				if err != nil {
					utilruntime.HandleError(fmt.Errorf("%s: unable to update watch event object (%#v) to store: %v", r.name, event.Object, err))
				}
			case watch.Deleted:
				// TODO: Will any consumers need access to the "last known
				// state", which is passed in event.Object? If so, may need
				// to change this.
				err := r.store.Delete(event.Object)
				if err != nil {
					utilruntime.HandleError(fmt.Errorf("%s: unable to delete watch event object (%#v) from store: %v", r.name, event.Object, err))
				}
			case watch.Bookmark:
				// A `Bookmark` means watch has synced here, just update the resourceVersion
			default:
				utilruntime.HandleError(fmt.Errorf("%s: unable to understand watch event %#v", r.name, event))
			}
			*resourceVersion = newResourceVersion
			r.setLastSyncResourceVersion(newResourceVersion)
			eventCount++
		}
	}

	watchDuration := r.clock.Since(start)
	if watchDuration < 1*time.Second && eventCount == 0 {
		return fmt.Errorf("very short watch: %s: Unexpected watch close - watch lasted less than a second and no items received", r.name)
	}
	klog.V(4).Infof("%s: Watch close - %v total %v items received", r.name, r.expectedType, eventCount)
	return nil
}

// LastSyncResourceVersion is the resource version observed when last sync with the underlying store
// The value returned is not synchronized with access to the underlying store and is not thread-safe
func (r *Reflector) LastSyncResourceVersion() string {
	r.lastSyncResourceVersionMutex.RLock()
	defer r.lastSyncResourceVersionMutex.RUnlock()
	return r.lastSyncResourceVersion
}

func (r *Reflector) setLastSyncResourceVersion(v string) {
	r.lastSyncResourceVersionMutex.Lock()
	defer r.lastSyncResourceVersionMutex.Unlock()
	r.lastSyncResourceVersion = v
}
