// Copyright 2019 Yunion
//
// 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 (
	"fmt"
)

// Store is a generic object storage interface. Reflector knows how to watch a server
// and update a store. A generic store is provided, which allows Reflector to be used
// as a local caching system, and an LRU store, which allows Reflector to work like a
// queue of items yet to be processed.
//
// Store makes no assumptions about stored object identity; it is the responsibility
// of a Store implementation to provide a mechanism to correctly key objects and to
// define the contract for obtaining objects by some arbitrary key type.
type Store interface {
	Add(obj interface{}) error
	Update(obj interface{}) error
	Delete(obj interface{}) error
	List() []interface{}
	ListKeys() []string
	Get(obj interface{}) (item interface{}, exists bool, err error)
	GetByKey(key string) (item interface{}, exists bool, err error)

	// Replace will delete the contents of the store, using instead the
	// given list. Store takes ownership of the list, you should not reference
	// it after calling this function.
	Replace([]interface{}, string) error
	Resync() error
}

// KeyFunc knows how to make a key from an object. Implementations should be deterministic.
type KeyFunc func(obj interface{}) (string, error)

// KeyError will be returned any time a KeyFunc gives an error; it includes the object
// at fault.
type KeyError struct {
	Obj interface{}
	Err error
}

// Error gives a human-readable description of the error.
func (k KeyError) Error() string {
	return fmt.Sprintf("couldn't create key for object %+v: %v", k.Obj, k.Err)
}

// cache responsibilities are limited to:
//	1. Computing keys for objects via keyFunc
//  2. Invoking methods of a ThreadSafeStorage interface
type cache struct {
	// cacheStorage bears the burden of thread safety for the cache
	cacheStorage ThreadSafeStore
	// keyFunc is used to make the key for objects stored in and retrieved from items, and
	// should be deterministic.
	keyFunc KeyFunc
}

var _ Store = &cache{}

// Add inserts an item into the cache.
func (c *cache) Add(obj interface{}) error {
	key, err := c.keyFunc(obj)
	if err != nil {
		return KeyError{obj, err}
	}
	c.cacheStorage.Add(key, obj)
	return nil
}

// Update sets an item in the cache to its updated state.
func (c *cache) Update(obj interface{}) error {
	key, err := c.keyFunc(obj)
	if err != nil {
		return KeyError{obj, err}
	}
	c.cacheStorage.Update(key, obj)
	return nil
}

// Delete removes an item from the cache.
func (c *cache) Delete(obj interface{}) error {
	key, err := c.keyFunc(obj)
	if err != nil {
		return KeyError{obj, err}
	}
	c.cacheStorage.Delete(key)
	return nil
}

// List returns a list of all the items.
// List is completely threadsafe as long as you treat all items as immutable.
func (c *cache) List() []interface{} {
	return c.cacheStorage.List()
}

// ListKeys returns a list of all the keys of the objects currently
// in the cache.
func (c *cache) ListKeys() []string {
	return c.cacheStorage.ListKeys()
}

// GetIndexers returns the indexers of cache
func (c *cache) GetIndexers() Indexers {
	return c.cacheStorage.GetIndexers()
}

// Index returns a list of items that match on the index function
// Index is thread-safe so long as you treat all items as immutable
func (c *cache) Index(indexName string, obj interface{}) ([]interface{}, error) {
	return c.cacheStorage.Index(indexName, obj)
}

func (c *cache) IndexKeys(indexName, indexKey string) ([]string, error) {
	return c.cacheStorage.IndexKeys(indexName, indexKey)
}

// ListIndexFuncValues returns the list of generated values of an Index func
func (c *cache) ListIndexFuncValues(indexName string) []string {
	return c.cacheStorage.ListIndexFuncValues(indexName)
}

func (c *cache) ByIndex(indexName, indexKey string) ([]interface{}, error) {
	return c.cacheStorage.ByIndex(indexName, indexKey)
}

func (c *cache) AddIndexers(newIndexers Indexers) error {
	return c.cacheStorage.AddIndexers(newIndexers)
}

// Get returns the requested item, or sets exists=false.
// Get is completely threadsafe as long as you treat all items as immutable.
func (c *cache) Get(obj interface{}) (item interface{}, exists bool, err error) {
	key, err := c.keyFunc(obj)
	if err != nil {
		return nil, false, KeyError{obj, err}
	}
	return c.GetByKey(key)
}

// GetByKey returns the request item, or exists=false.
// GetByKey is completely threadsafe as long as you treat all items as immutable.
func (c *cache) GetByKey(key string) (item interface{}, exists bool, err error) {
	item, exists = c.cacheStorage.Get(key)
	return item, exists, nil
}

// Replace will delete the contents of 'c', using instead the given list.
// 'c' takes ownership of the list, you should not reference the list again
// after calling this function.
func (c *cache) Replace(list []interface{}, resourceVersion string) error {
	items := map[string]interface{}{}
	for _, item := range list {
		key, err := c.keyFunc(item)
		if err != nil {
			return KeyError{item, err}
		}
		items[key] = item
	}
	c.cacheStorage.Replace(items, resourceVersion)
	return nil
}

// Resync touches all items in the store to force processing
func (c *cache) Resync() error {
	return c.cacheStorage.Resync()
}

// NewStore returns a Store implemented simply with a map and a lock.
func NewStore(keyFunc KeyFunc) Store {
	return &cache{
		cacheStorage: NewThreadSafeStore(Indexers{}, Indices{}),
		keyFunc:      keyFunc,
	}
}

// NewIndexer returns an Indexer implemented simply with a map and a lock.
func NewIndexer(keyFunc KeyFunc, indexers Indexers) Indexer {
	return &cache{
		cacheStorage: NewThreadSafeStore(indexers, Indices{}),
		keyFunc:      keyFunc,
	}
}