/*
Copyright 2015 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 (
	"sync"
	"time"

	"k8s.io/apimachinery/pkg/runtime"
	"k8s.io/apimachinery/pkg/util/clock"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apimachinery/pkg/util/wait"
)

// This file implements a low-level controller that is used in
// sharedIndexInformer, which is an implementation of
// SharedIndexInformer.  Such informers, in turn, are key components
// in the high level controllers that form the backbone of the
// Kubernetes control plane.  Look at those for examples, or the
// example in
// https://github.com/kubernetes/client-go/tree/master/examples/workqueue
// .

// Config contains all the settings for one of these low-level controllers.
type Config struct {
	// The queue for your objects - has to be a DeltaFIFO due to
	// assumptions in the implementation. Your Process() function
	// should accept the output of this Queue's Pop() method.
	Queue

	// Something that can list and watch your objects.
	ListerWatcher

	// Something that can process a popped Deltas.
	Process ProcessFunc

	// ObjectType is an example object of the type this controller is
	// expected to handle.  Only the type needs to be right, except
	// that when that is `unstructured.Unstructured` the object's
	// `"apiVersion"` and `"kind"` must also be right.
	ObjectType runtime.Object

	// FullResyncPeriod is the period at which ShouldResync is considered.
	FullResyncPeriod time.Duration

	// ShouldResync is periodically used by the reflector to determine
	// whether to Resync the Queue. If ShouldResync is `nil` or
	// returns true, it means the reflector should proceed with the
	// resync.
	ShouldResync ShouldResyncFunc

	// If true, when Process() returns an error, re-enqueue the object.
	// TODO: add interface to let you inject a delay/backoff or drop
	//       the object completely if desired. Pass the object in
	//       question to this interface as a parameter.  This is probably moot
	//       now that this functionality appears at a higher level.
	RetryOnError bool
}

// ShouldResyncFunc is a type of function that indicates if a reflector should perform a
// resync or not. It can be used by a shared informer to support multiple event handlers with custom
// resync periods.
type ShouldResyncFunc func() bool

// ProcessFunc processes a single object.
type ProcessFunc func(obj interface{}) error

// `*controller` implements Controller
type controller struct {
	config         Config
	reflector      *Reflector
	reflectorMutex sync.RWMutex
	clock          clock.Clock
}

// Controller is a low-level controller that is parameterized by a
// Config and used in sharedIndexInformer.
type Controller interface {
	// Run does two things.  One is to construct and run a Reflector
	// to pump objects/notifications from the Config's ListerWatcher
	// to the Config's Queue and possibly invoke the occasional Resync
	// on that Queue.  The other is to repeatedly Pop from the Queue
	// and process with the Config's ProcessFunc.  Both of these
	// continue until `stopCh` is closed.
	Run(stopCh <-chan struct{})

	// HasSynced delegates to the Config's Queue
	HasSynced() bool

	// LastSyncResourceVersion delegates to the Reflector when there
	// is one, otherwise returns the empty string
	LastSyncResourceVersion() string
}

// New makes a new Controller from the given Config.
func New(c *Config) Controller {
	ctlr := &controller{
		config: *c,
		clock:  &clock.RealClock{},
	}
	return ctlr
}

// Run begins processing items, and will continue until a value is sent down stopCh or it is closed.
// It's an error to call Run more than once.
// Run blocks; call via go.
func (c *controller) Run(stopCh <-chan struct{}) {
	defer utilruntime.HandleCrash()
	go func() {
		<-stopCh
		c.config.Queue.Close()
	}()
	r := NewReflector(
		c.config.ListerWatcher,
		c.config.ObjectType,
		c.config.Queue,
		c.config.FullResyncPeriod,
	)
	r.ShouldResync = c.config.ShouldResync
	r.clock = c.clock

	c.reflectorMutex.Lock()
	c.reflector = r
	c.reflectorMutex.Unlock()

	var wg wait.Group
	defer wg.Wait()

	wg.StartWithChannel(stopCh, r.Run)

	wait.Until(c.processLoop, time.Second, stopCh)
}

// Returns true once this controller has completed an initial resource listing
func (c *controller) HasSynced() bool {
	return c.config.Queue.HasSynced()
}

func (c *controller) LastSyncResourceVersion() string {
	c.reflectorMutex.RLock()
	defer c.reflectorMutex.RUnlock()
	if c.reflector == nil {
		return ""
	}
	return c.reflector.LastSyncResourceVersion()
}

// processLoop drains the work queue.
// TODO: Consider doing the processing in parallel. This will require a little thought
// to make sure that we don't end up processing the same object multiple times
// concurrently.
//
// TODO: Plumb through the stopCh here (and down to the queue) so that this can
// actually exit when the controller is stopped. Or just give up on this stuff
// ever being stoppable. Converting this whole package to use Context would
// also be helpful.
func (c *controller) processLoop() {
	for {
		obj, err := c.config.Queue.Pop(PopProcessFunc(c.config.Process))
		if err != nil {
			if err == ErrFIFOClosed {
				return
			}
			if c.config.RetryOnError {
				// This is the safe way to re-enqueue.
				c.config.Queue.AddIfNotPresent(obj)
			}
		}
	}
}

// ResourceEventHandler can handle notifications for events that happen to a
// resource. The events are informational only, so you can't return an
// error.
//  * OnAdd is called when an object is added.
//  * OnUpdate is called when an object is modified. Note that oldObj is the
//      last known state of the object-- it is possible that several changes
//      were combined together, so you can't use this to see every single
//      change. OnUpdate is also called when a re-list happens, and it will
//      get called even if nothing changed. This is useful for periodically
//      evaluating or syncing something.
//  * OnDelete will get the final state of the item if it is known, otherwise
//      it will get an object of type DeletedFinalStateUnknown. This can
//      happen if the watch is closed and misses the delete event and we don't
//      notice the deletion until the subsequent re-list.
type ResourceEventHandler interface {
	OnAdd(obj interface{})
	OnUpdate(oldObj, newObj interface{})
	OnDelete(obj interface{})
}

// ResourceEventHandlerFuncs is an adaptor to let you easily specify as many or
// as few of the notification functions as you want while still implementing
// ResourceEventHandler.
type ResourceEventHandlerFuncs struct {
	AddFunc    func(obj interface{})
	UpdateFunc func(oldObj, newObj interface{})
	DeleteFunc func(obj interface{})
}

// OnAdd calls AddFunc if it's not nil.
func (r ResourceEventHandlerFuncs) OnAdd(obj interface{}) {
	if r.AddFunc != nil {
		r.AddFunc(obj)
	}
}

// OnUpdate calls UpdateFunc if it's not nil.
func (r ResourceEventHandlerFuncs) OnUpdate(oldObj, newObj interface{}) {
	if r.UpdateFunc != nil {
		r.UpdateFunc(oldObj, newObj)
	}
}

// OnDelete calls DeleteFunc if it's not nil.
func (r ResourceEventHandlerFuncs) OnDelete(obj interface{}) {
	if r.DeleteFunc != nil {
		r.DeleteFunc(obj)
	}
}

// FilteringResourceEventHandler applies the provided filter to all events coming
// in, ensuring the appropriate nested handler method is invoked. An object
// that starts passing the filter after an update is considered an add, and an
// object that stops passing the filter after an update is considered a delete.
type FilteringResourceEventHandler struct {
	FilterFunc func(obj interface{}) bool
	Handler    ResourceEventHandler
}

// OnAdd calls the nested handler only if the filter succeeds
func (r FilteringResourceEventHandler) OnAdd(obj interface{}) {
	if !r.FilterFunc(obj) {
		return
	}
	r.Handler.OnAdd(obj)
}

// OnUpdate ensures the proper handler is called depending on whether the filter matches
func (r FilteringResourceEventHandler) OnUpdate(oldObj, newObj interface{}) {
	newer := r.FilterFunc(newObj)
	older := r.FilterFunc(oldObj)
	switch {
	case newer && older:
		r.Handler.OnUpdate(oldObj, newObj)
	case newer && !older:
		r.Handler.OnAdd(newObj)
	case !newer && older:
		r.Handler.OnDelete(oldObj)
	default:
		// do nothing
	}
}

// OnDelete calls the nested handler only if the filter succeeds
func (r FilteringResourceEventHandler) OnDelete(obj interface{}) {
	if !r.FilterFunc(obj) {
		return
	}
	r.Handler.OnDelete(obj)
}

// DeletionHandlingMetaNamespaceKeyFunc checks for
// DeletedFinalStateUnknown objects before calling
// MetaNamespaceKeyFunc.
func DeletionHandlingMetaNamespaceKeyFunc(obj interface{}) (string, error) {
	if d, ok := obj.(DeletedFinalStateUnknown); ok {
		return d.Key, nil
	}
	return MetaNamespaceKeyFunc(obj)
}

// NewInformer returns a Store and a controller for populating the store
// while also providing event notifications. You should only used the returned
// Store for Get/List operations; Add/Modify/Deletes will cause the event
// notifications to be faulty.
//
// Parameters:
//  * lw is list and watch functions for the source of the resource you want to
//    be informed of.
//  * objType is an object of the type that you expect to receive.
//  * resyncPeriod: if non-zero, will re-list this often (you will get OnUpdate
//    calls, even if nothing changed). Otherwise, re-list will be delayed as
//    long as possible (until the upstream source closes the watch or times out,
//    or you stop the controller).
//  * h is the object you want notifications sent to.
//
func NewInformer(
	lw ListerWatcher,
	objType runtime.Object,
	resyncPeriod time.Duration,
	h ResourceEventHandler,
) (Store, Controller) {
	// This will hold the client state, as we know it.
	clientState := NewStore(DeletionHandlingMetaNamespaceKeyFunc)

	return clientState, newInformer(lw, objType, resyncPeriod, h, clientState)
}

// NewIndexerInformer returns a Indexer and a controller for populating the index
// while also providing event notifications. You should only used the returned
// Index for Get/List operations; Add/Modify/Deletes will cause the event
// notifications to be faulty.
//
// Parameters:
//  * lw is list and watch functions for the source of the resource you want to
//    be informed of.
//  * objType is an object of the type that you expect to receive.
//  * resyncPeriod: if non-zero, will re-list this often (you will get OnUpdate
//    calls, even if nothing changed). Otherwise, re-list will be delayed as
//    long as possible (until the upstream source closes the watch or times out,
//    or you stop the controller).
//  * h is the object you want notifications sent to.
//  * indexers is the indexer for the received object type.
//
func NewIndexerInformer(
	lw ListerWatcher,
	objType runtime.Object,
	resyncPeriod time.Duration,
	h ResourceEventHandler,
	indexers Indexers,
) (Indexer, Controller) {
	// This will hold the client state, as we know it.
	clientState := NewIndexer(DeletionHandlingMetaNamespaceKeyFunc, indexers)

	return clientState, newInformer(lw, objType, resyncPeriod, h, clientState)
}

// newInformer returns a controller for populating the store while also
// providing event notifications.
//
// Parameters
//  * lw is list and watch functions for the source of the resource you want to
//    be informed of.
//  * objType is an object of the type that you expect to receive.
//  * resyncPeriod: if non-zero, will re-list this often (you will get OnUpdate
//    calls, even if nothing changed). Otherwise, re-list will be delayed as
//    long as possible (until the upstream source closes the watch or times out,
//    or you stop the controller).
//  * h is the object you want notifications sent to.
//  * clientState is the store you want to populate
//
func newInformer(
	lw ListerWatcher,
	objType runtime.Object,
	resyncPeriod time.Duration,
	h ResourceEventHandler,
	clientState Store,
) Controller {
	// This will hold incoming changes. Note how we pass clientState in as a
	// KeyLister, that way resync operations will result in the correct set
	// of update/delete deltas.
	fifo := NewDeltaFIFOWithOptions(DeltaFIFOOptions{
		KnownObjects:          clientState,
		EmitDeltaTypeReplaced: true,
	})

	cfg := &Config{
		Queue:            fifo,
		ListerWatcher:    lw,
		ObjectType:       objType,
		FullResyncPeriod: resyncPeriod,
		RetryOnError:     false,

		Process: func(obj interface{}) error {
			// from oldest to newest
			for _, d := range obj.(Deltas) {
				switch d.Type {
				case Sync, Replaced, Added, Updated:
					if old, exists, err := clientState.Get(d.Object); err == nil && exists {
						if err := clientState.Update(d.Object); err != nil {
							return err
						}
						h.OnUpdate(old, d.Object)
					} else {
						if err := clientState.Add(d.Object); err != nil {
							return err
						}
						h.OnAdd(d.Object)
					}
				case Deleted:
					if err := clientState.Delete(d.Object); err != nil {
						return err
					}
					h.OnDelete(d.Object)
				}
			}
			return nil
		},
	}
	return New(cfg)
}
