// Copyright 2021 ByteDance Inc.
//
// 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 asynccache

import (
	"fmt"
	"log"
	"sync"
	"sync/atomic"
	"time"

	sf "golang.org/x/sync/singleflight"
)

// Options controls the behavior of AsyncCache.
type Options struct {
	RefreshDuration time.Duration
	Fetcher         func(key string) (interface{}, error)

	// If EnableExpire is true, ExpireDuration MUST be set.
	EnableExpire   bool
	ExpireDuration time.Duration

	ErrorHandler  func(key string, err error)
	ChangeHandler func(key string, oldData, newData interface{})
	DeleteHandler func(key string, oldData interface{})

	IsSame     func(key string, oldData, newData interface{}) bool
	ErrLogFunc func(str string)
}

// AsyncCache .
type AsyncCache interface {
	// SetDefault sets the default value of given key if it is new to the cache.
	// It is useful for cache warming up.
	// Param val should not be nil.
	SetDefault(key string, val interface{}) (exist bool)

	// Get tries to fetch a value corresponding to the given key from the cache.
	// If error occurs during the first time fetching, it will be cached until the
	// sequential fetching triggered by the refresh goroutine succeed.
	Get(key string) (val interface{}, err error)

	// GetOrSet tries to fetch a value corresponding to the given key from the cache.
	// If the key is not yet cached or error occurs, the default value will be set.
	GetOrSet(key string, defaultVal interface{}) (val interface{})

	// Dump dumps all cache entries.
	// This will not cause expire to refresh.
	Dump() map[string]interface{}

	// DeleteIf deletes cached entries that match the `shouldDelete` predicate.
	DeleteIf(shouldDelete func(key string) bool)

	// Close closes the async cache.
	// This should be called when the cache is no longer needed, or may lead to resource leak.
	Close()
}

// asyncCache .
type asyncCache struct {
	sfg  sf.Group
	opt  Options
	data sync.Map
}

type tickerType int

const (
	refreshTicker tickerType = iota
	expireTicker
)

type sharedTicker struct {
	sync.Mutex
	started  bool
	stopChan chan bool
	ticker   *time.Ticker
	caches   map[*asyncCache]struct{}
}

var (
	// 共用 ticker
	refreshTickerMap, expireTickerMap sync.Map
)

type entry struct {
	val    atomic.Value
	expire int32 // 0 means useful, 1 will expire
	err    Error
}

func (e *entry) Store(x interface{}, err error) {
	if x != nil {
		e.val.Store(x)
	} else {
		e.val = atomic.Value{}
	}
	e.err.Store(err)
}

func (e *entry) Touch() {
	atomic.StoreInt32(&e.expire, 0)
}

// NewAsyncCache creates an AsyncCache.
func NewAsyncCache(opt Options) AsyncCache {
	c := &asyncCache{
		sfg: sf.Group{},
		opt: opt,
	}
	if c.opt.ErrLogFunc == nil {
		c.opt.ErrLogFunc = func(str string) {
			log.Println(str)
		}
	}
	if c.opt.EnableExpire {
		if c.opt.ExpireDuration == 0 {
			panic("asynccache: invalid ExpireDuration")
		}
		ti, _ := expireTickerMap.LoadOrStore(c.opt.ExpireDuration,
			&sharedTicker{caches: make(map[*asyncCache]struct{}), stopChan: make(chan bool, 1)})
		et := ti.(*sharedTicker)
		et.Lock()
		et.caches[c] = struct{}{}
		if !et.started {
			et.started = true
			et.ticker = time.NewTicker(c.opt.ExpireDuration)
			go et.tick(et.ticker, expireTicker)
		}
		et.Unlock()
	}

	ti, _ := refreshTickerMap.LoadOrStore(c.opt.RefreshDuration,
		&sharedTicker{caches: make(map[*asyncCache]struct{}), stopChan: make(chan bool, 1)})
	rt := ti.(*sharedTicker)
	rt.Lock()
	rt.caches[c] = struct{}{}
	if !rt.started {
		rt.started = true
		rt.ticker = time.NewTicker(c.opt.RefreshDuration)
		go rt.tick(rt.ticker, refreshTicker)
	}
	rt.Unlock()
	return c
}

// SetDefault sets the default value of given key if it is new to the cache.
func (c *asyncCache) SetDefault(key string, val interface{}) bool {
	ety := &entry{}
	ety.Store(val, nil)
	actual, exist := c.data.LoadOrStore(key, ety)
	if exist {
		actual.(*entry).Touch()
	}
	return exist
}

// Get tries to fetch a value corresponding to the given key from the cache.
// If error occurs during in the first time fetching, it will be cached until the
// sequential fetchings triggered by the refresh goroutine succeed.
func (c *asyncCache) Get(key string) (val interface{}, err error) {
	var ok bool
	val, ok = c.data.Load(key)
	if ok {
		e := val.(*entry)
		e.Touch()
		return e.val.Load(), e.err.Load()
	}

	val, err, _ = c.sfg.Do(key, func() (v interface{}, e error) {
		v, e = c.opt.Fetcher(key)
		ety := &entry{}
		ety.Store(v, e)
		c.data.Store(key, ety)
		return
	})
	return
}

// GetOrSet tries to fetch a value corresponding to the given key from the cache.
// If the key is not yet cached or fetching failed, the default value will be set.
func (c *asyncCache) GetOrSet(key string, def interface{}) (val interface{}) {
	if v, ok := c.data.Load(key); ok {
		e := v.(*entry)
		if e.err.Load() != nil {
			ety := &entry{}
			ety.Store(def, nil)
			c.data.Store(key, ety)
			return def
		}
		e.Touch()
		return e.val.Load()
	}

	val, _, _ = c.sfg.Do(key, func() (interface{}, error) {
		v, e := c.opt.Fetcher(key)
		if e != nil {
			v = def
		}
		ety := &entry{}
		ety.Store(v, nil)
		c.data.Store(key, ety)
		return v, nil
	})
	return
}

// Dump dumps all cached entries.
func (c *asyncCache) Dump() map[string]interface{} {
	data := make(map[string]interface{})
	c.data.Range(func(key, val interface{}) bool {
		k, ok := key.(string)
		if !ok {
			c.opt.ErrLogFunc(fmt.Sprintf("invalid key: %v, type: %T is not string", k, k))
			c.data.Delete(key)
			return true
		}
		data[k] = val.(*entry).val.Load()
		return true
	})
	return data
}

// DeleteIf deletes cached entries that match the `shouldDelete` predicate.
func (c *asyncCache) DeleteIf(shouldDelete func(key string) bool) {
	c.data.Range(func(key, value interface{}) bool {
		s := key.(string)
		if shouldDelete(s) {
			if c.opt.DeleteHandler != nil {
				go c.opt.DeleteHandler(s, value)
			}
			c.data.Delete(key)
		}
		return true
	})
}

// Close stops the background goroutine.
func (c *asyncCache) Close() {
	// close refresh ticker
	ti, _ := refreshTickerMap.Load(c.opt.RefreshDuration)
	rt := ti.(*sharedTicker)
	rt.Lock()
	delete(rt.caches, c)
	if len(rt.caches) == 0 {
		rt.stopChan <- true
		rt.started = false
	}
	rt.Unlock()

	if c.opt.EnableExpire {
		// close expire ticker
		ti, _ := expireTickerMap.Load(c.opt.ExpireDuration)
		et := ti.(*sharedTicker)
		et.Lock()
		delete(et.caches, c)
		if len(et.caches) == 0 {
			et.stopChan <- true
			et.started = false
		}
		et.Unlock()
	}
}

// tick .
// pass ticker but not use t.ticker directly is to ignore race.
func (t *sharedTicker) tick(ticker *time.Ticker, tt tickerType) {
	var wg sync.WaitGroup
	defer ticker.Stop()
	for {
		select {
		case <-ticker.C:
			t.Lock()
			for c := range t.caches {
				wg.Add(1)
				go func(c *asyncCache) {
					defer wg.Done()
					if tt == expireTicker {
						c.expire()
					} else {
						c.refresh()
					}
				}(c)
			}
			wg.Wait()
			t.Unlock()
		case stop := <-t.stopChan:
			if stop {
				return
			}
		}
	}
}

func (c *asyncCache) expire() {
	c.data.Range(func(key, value interface{}) bool {
		k, ok := key.(string)
		if !ok {
			c.opt.ErrLogFunc(fmt.Sprintf("invalid key: %v, type: %T is not string", k, k))
			c.data.Delete(key)
			return true
		}
		e, ok := value.(*entry)
		if !ok {
			c.opt.ErrLogFunc(fmt.Sprintf("invalid key: %v, type: %T is not entry", k, value))
			c.data.Delete(key)
			return true
		}
		if !atomic.CompareAndSwapInt32(&e.expire, 0, 1) {
			if c.opt.DeleteHandler != nil {
				go c.opt.DeleteHandler(k, value)
			}
			c.data.Delete(key)
		}

		return true
	})
}

func (c *asyncCache) refresh() {
	c.data.Range(func(key, value interface{}) bool {
		k, ok := key.(string)
		if !ok {
			c.opt.ErrLogFunc(fmt.Sprintf("invalid key: %v, type: %T is not string", k, k))
			c.data.Delete(key)
			return true
		}
		e, ok := value.(*entry)
		if !ok {
			c.opt.ErrLogFunc(fmt.Sprintf("invalid key: %v, type: %T is not entry", k, value))
			c.data.Delete(key)
			return true
		}

		newVal, err := c.opt.Fetcher(k)
		if err != nil {
			if c.opt.ErrorHandler != nil {
				go c.opt.ErrorHandler(k, err)
			}
			if e.err.Load() != nil {
				e.err.Store(err)
			}
			return true
		}

		if c.opt.IsSame != nil && !c.opt.IsSame(k, e.val.Load(), newVal) {
			if c.opt.ChangeHandler != nil {
				go c.opt.ChangeHandler(k, e.val.Load(), newVal)
			}
		}

		e.Store(newVal, err)
		return true
	})
}