/*
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 assumecache

import (
	"errors"
	"fmt"
	"strconv"
	"sync"

	"k8s.io/klog/v2"

	"k8s.io/apimachinery/pkg/api/meta"
	"k8s.io/client-go/tools/cache"
)

// Informer is the subset of [cache.SharedInformer] that NewAssumeCache depends upon.
type Informer interface {
	AddEventHandler(handler cache.ResourceEventHandler) (cache.ResourceEventHandlerRegistration, error)
}

// AddTestObject adds an object to the assume cache.
// Only use this for unit testing!
func AddTestObject(cache *AssumeCache, obj interface{}) {
	cache.add(obj)
}

// UpdateTestObject updates an object in the assume cache.
// Only use this for unit testing!
func UpdateTestObject(cache *AssumeCache, obj interface{}) {
	cache.update(nil, obj)
}

// DeleteTestObject deletes object in the assume cache.
// Only use this for unit testing!
func DeleteTestObject(cache *AssumeCache, obj interface{}) {
	cache.delete(obj)
}

// Sentinel errors that can be checked for with errors.Is.
var (
	ErrWrongType  = errors.New("object has wrong type")
	ErrNotFound   = errors.New("object not found")
	ErrObjectName = errors.New("cannot determine object name")
)

type WrongTypeError struct {
	TypeName string
	Object   interface{}
}

func (e WrongTypeError) Error() string {
	return fmt.Sprintf("could not convert object to type %v: %+v", e.TypeName, e.Object)
}

func (e WrongTypeError) Is(err error) bool {
	return err == ErrWrongType
}

type NotFoundError struct {
	TypeName  string
	ObjectKey string
}

func (e NotFoundError) Error() string {
	return fmt.Sprintf("could not find %v %q", e.TypeName, e.ObjectKey)
}

func (e NotFoundError) Is(err error) bool {
	return err == ErrNotFound
}

type ObjectNameError struct {
	DetailedErr error
}

func (e ObjectNameError) Error() string {
	return fmt.Sprintf("failed to get object name: %v", e.DetailedErr)
}

func (e ObjectNameError) Is(err error) bool {
	return err == ErrObjectName
}

// AssumeCache is a cache on top of the informer that allows for updating
// objects outside of informer events and also restoring the informer
// cache's version of the object. Objects are assumed to be
// Kubernetes API objects that are supported by [meta.Accessor].
//
// Objects can referenced via their key, with [cache.MetaNamespaceKeyFunc]
// as key function.
//
// AssumeCache stores two pointers to represent a single object:
//   - The pointer to the informer object.
//   - The pointer to the latest object, which could be the same as
//     the informer object, or an in-memory object.
//
// An informer update always overrides the latest object pointer.
//
// Assume() only updates the latest object pointer.
// Restore() sets the latest object pointer back to the informer object.
// Get/List() always returns the latest object pointer.
type AssumeCache struct {
	// The logger that was chosen when setting up the cache.
	// Will be used for all operations.
	logger klog.Logger

	// Synchronizes updates to store
	rwMutex sync.RWMutex

	// describes the object stored
	description string

	// Stores objInfo pointers
	store cache.Indexer

	// Index function for object
	indexFunc cache.IndexFunc
	indexName string
}

type objInfo struct {
	// name of the object
	name string

	// Latest version of object could be cached-only or from informer
	latestObj interface{}

	// Latest object from informer
	apiObj interface{}
}

func objInfoKeyFunc(obj interface{}) (string, error) {
	objInfo, ok := obj.(*objInfo)
	if !ok {
		return "", &WrongTypeError{TypeName: "objInfo", Object: obj}
	}
	return objInfo.name, nil
}

func (c *AssumeCache) objInfoIndexFunc(obj interface{}) ([]string, error) {
	objInfo, ok := obj.(*objInfo)
	if !ok {
		return []string{""}, &WrongTypeError{TypeName: "objInfo", Object: obj}
	}
	return c.indexFunc(objInfo.latestObj)
}

// NewAssumeCache creates an assume cache for general objects.
func NewAssumeCache(logger klog.Logger, informer Informer, description, indexName string, indexFunc cache.IndexFunc) *AssumeCache {
	c := &AssumeCache{
		logger:      logger,
		description: description,
		indexFunc:   indexFunc,
		indexName:   indexName,
	}
	indexers := cache.Indexers{}
	if indexName != "" && indexFunc != nil {
		indexers[indexName] = c.objInfoIndexFunc
	}
	c.store = cache.NewIndexer(objInfoKeyFunc, indexers)

	// Unit tests don't use informers
	if informer != nil {
		// Cannot fail in practice?! No-one bothers checking the error.
		_, _ = informer.AddEventHandler(
			cache.ResourceEventHandlerFuncs{
				AddFunc:    c.add,
				UpdateFunc: c.update,
				DeleteFunc: c.delete,
			},
		)
	}
	return c
}

func (c *AssumeCache) add(obj interface{}) {
	if obj == nil {
		return
	}

	name, err := cache.MetaNamespaceKeyFunc(obj)
	if err != nil {
		c.logger.Error(&ObjectNameError{err}, "Add failed")
		return
	}

	c.rwMutex.Lock()
	defer c.rwMutex.Unlock()

	if objInfo, _ := c.getObjInfo(name); objInfo != nil {
		newVersion, err := c.getObjVersion(name, obj)
		if err != nil {
			c.logger.Error(err, "Add failed: couldn't get object version")
			return
		}

		storedVersion, err := c.getObjVersion(name, objInfo.latestObj)
		if err != nil {
			c.logger.Error(err, "Add failed: couldn't get stored object version")
			return
		}

		// Only update object if version is newer.
		// This is so we don't override assumed objects due to informer resync.
		if newVersion <= storedVersion {
			c.logger.V(10).Info("Skip adding object to assume cache because version is not newer than storedVersion", "description", c.description, "cacheKey", name, "newVersion", newVersion, "storedVersion", storedVersion)
			return
		}
	}

	objInfo := &objInfo{name: name, latestObj: obj, apiObj: obj}
	if err = c.store.Update(objInfo); err != nil {
		c.logger.Info("Error occurred while updating stored object", "err", err)
	} else {
		c.logger.V(10).Info("Adding object to assume cache", "description", c.description, "cacheKey", name, "assumeCache", obj)
	}
}

func (c *AssumeCache) update(oldObj interface{}, newObj interface{}) {
	c.add(newObj)
}

func (c *AssumeCache) delete(obj interface{}) {
	if obj == nil {
		return
	}

	name, err := cache.DeletionHandlingMetaNamespaceKeyFunc(obj)
	if err != nil {
		c.logger.Error(&ObjectNameError{err}, "Failed to delete")
		return
	}

	c.rwMutex.Lock()
	defer c.rwMutex.Unlock()

	objInfo := &objInfo{name: name}
	err = c.store.Delete(objInfo)
	if err != nil {
		c.logger.Error(err, "Failed to delete", "description", c.description, "cacheKey", name)
	}
}

func (c *AssumeCache) getObjVersion(name string, obj interface{}) (int64, error) {
	objAccessor, err := meta.Accessor(obj)
	if err != nil {
		return -1, err
	}

	objResourceVersion, err := strconv.ParseInt(objAccessor.GetResourceVersion(), 10, 64)
	if err != nil {
		//nolint:errorlint // Intentionally not wrapping the error, the underlying error is an implementation detail.
		return -1, fmt.Errorf("error parsing ResourceVersion %q for %v %q: %v", objAccessor.GetResourceVersion(), c.description, name, err)
	}
	return objResourceVersion, nil
}

func (c *AssumeCache) getObjInfo(key string) (*objInfo, error) {
	obj, ok, err := c.store.GetByKey(key)
	if err != nil {
		return nil, err
	}
	if !ok {
		return nil, &NotFoundError{TypeName: c.description, ObjectKey: key}
	}

	objInfo, ok := obj.(*objInfo)
	if !ok {
		return nil, &WrongTypeError{"objInfo", obj}
	}
	return objInfo, nil
}

// Get the object by its key.
func (c *AssumeCache) Get(key string) (interface{}, error) {
	c.rwMutex.RLock()
	defer c.rwMutex.RUnlock()

	objInfo, err := c.getObjInfo(key)
	if err != nil {
		return nil, err
	}
	return objInfo.latestObj, nil
}

// GetAPIObj gets the informer cache's version by its key.
func (c *AssumeCache) GetAPIObj(key string) (interface{}, error) {
	c.rwMutex.RLock()
	defer c.rwMutex.RUnlock()

	objInfo, err := c.getObjInfo(key)
	if err != nil {
		return nil, err
	}
	return objInfo.apiObj, nil
}

// List all the objects in the cache.
func (c *AssumeCache) List(indexObj interface{}) []interface{} {
	c.rwMutex.RLock()
	defer c.rwMutex.RUnlock()

	allObjs := []interface{}{}
	var objs []interface{}
	if c.indexName != "" {
		o, err := c.store.Index(c.indexName, &objInfo{latestObj: indexObj})
		if err != nil {
			c.logger.Error(err, "List index error")
			return nil
		}
		objs = o
	} else {
		objs = c.store.List()
	}

	for _, obj := range objs {
		objInfo, ok := obj.(*objInfo)
		if !ok {
			c.logger.Error(&WrongTypeError{TypeName: "objInfo", Object: obj}, "List error")
			continue
		}
		allObjs = append(allObjs, objInfo.latestObj)
	}
	return allObjs
}

// Assume updates the object in-memory only.
//
// The version of the object must be greater or equal to
// the current object, otherwise an error is returned.
//
// Storing an object with the same version is supported
// by the assume cache, but suffers from a race: if an
// update is received via the informer while such an
// object is assumed, it gets dropped in favor of the
// newer object from the apiserver.
//
// Only assuming objects that were returned by an apiserver
// operation (Update, Patch) is safe.
func (c *AssumeCache) Assume(obj interface{}) error {
	name, err := cache.MetaNamespaceKeyFunc(obj)
	if err != nil {
		return &ObjectNameError{err}
	}

	c.rwMutex.Lock()
	defer c.rwMutex.Unlock()

	objInfo, err := c.getObjInfo(name)
	if err != nil {
		return err
	}

	newVersion, err := c.getObjVersion(name, obj)
	if err != nil {
		return err
	}

	storedVersion, err := c.getObjVersion(name, objInfo.latestObj)
	if err != nil {
		return err
	}

	if newVersion < storedVersion {
		return fmt.Errorf("%v %q is out of sync (stored: %d, assume: %d)", c.description, name, storedVersion, newVersion)
	}

	// Only update the cached object
	objInfo.latestObj = obj
	c.logger.V(4).Info("Assumed object", "description", c.description, "cacheKey", name, "version", newVersion)
	return nil
}

// Restore the informer cache's version of the object.
func (c *AssumeCache) Restore(objName string) {
	c.rwMutex.Lock()
	defer c.rwMutex.Unlock()

	objInfo, err := c.getObjInfo(objName)
	if err != nil {
		// This could be expected if object got deleted
		c.logger.V(5).Info("Restore object", "description", c.description, "cacheKey", objName, "err", err)
	} else {
		objInfo.latestObj = objInfo.apiObj
		c.logger.V(4).Info("Restored object", "description", c.description, "cacheKey", objName)
	}
}