package fs

import (
	"ZhenTuLocalPassiveAdapter/config"
	"ZhenTuLocalPassiveAdapter/dto"
	"container/list"
	"fmt"
	"sync"
	"time"

	"github.com/patrickmn/go-cache"
	"golang.org/x/sync/singleflight"
)

const (
	defaultFileListCacheTTLSeconds = 30
	defaultFileListCacheMaxEntries = 256
	fileListCacheCleanupInterval   = 1 * time.Minute
)

func getFileListCacheTTL() time.Duration {
	ttlSeconds := config.Config.Record.Cache.FileListTTLSeconds
	if ttlSeconds <= 0 {
		ttlSeconds = defaultFileListCacheTTLSeconds
	}
	return time.Duration(ttlSeconds) * time.Second
}

func getFileListCacheMaxEntries() int {
	maxEntries := config.Config.Record.Cache.FileListMaxEntries
	if maxEntries <= 0 {
		maxEntries = defaultFileListCacheMaxEntries
	}
	return maxEntries
}

type fileListCache struct {
	cache      *cache.Cache
	maxEntries int

	mu       sync.Mutex
	lru      *list.List
	elements map[string]*list.Element

	group singleflight.Group
}

func newFileListCache(ttl time.Duration, maxEntries int) *fileListCache {
	if ttl <= 0 {
		ttl = defaultFileListCacheTTLSeconds * time.Second
	}
	if maxEntries <= 0 {
		maxEntries = defaultFileListCacheMaxEntries
	}

	c := cache.New(ttl, fileListCacheCleanupInterval)
	result := &fileListCache{
		cache:      c,
		maxEntries: maxEntries,
		lru:        list.New(),
		elements:   make(map[string]*list.Element, maxEntries),
	}
	c.OnEvicted(func(key string, value any) {
		result.removeFromLru(key)
	})
	return result
}

func (c *fileListCache) GetOrLoad(key string, loader func() ([]dto.File, error)) ([]dto.File, bool, bool, error) {
	if files, ok := c.Get(key); ok {
		return files, true, false, nil
	}

	value, err, shared := c.group.Do(key, func() (any, error) {
		if files, ok := c.Get(key); ok {
			return files, nil
		}
		files, err := loader()
		if err != nil {
			return nil, err
		}
		c.Set(key, files)
		return files, nil
	})
	if err != nil {
		return nil, false, shared, err
	}
	files, ok := value.([]dto.File)
	if !ok {
		return nil, false, shared, fmt.Errorf("缓存返回类型错误: key=%s", key)
	}
	return files, false, shared, nil
}

func (c *fileListCache) Get(key string) ([]dto.File, bool) {
	value, ok := c.cache.Get(key)
	if !ok {
		c.removeFromLru(key)
		return nil, false
	}
	files, ok := value.([]dto.File)
	if !ok {
		c.cache.Delete(key)
		c.removeFromLru(key)
		return nil, false
	}
	c.touch(key)
	return files, true
}

func (c *fileListCache) Set(key string, files []dto.File) {
	c.cache.Set(key, files, cache.DefaultExpiration)
	c.touch(key)
	c.evictIfNeeded()
}

func (c *fileListCache) touch(key string) {
	c.mu.Lock()
	defer c.mu.Unlock()

	if el, ok := c.elements[key]; ok {
		c.lru.MoveToFront(el)
		return
	}
	c.elements[key] = c.lru.PushFront(key)
}

func (c *fileListCache) removeFromLru(key string) {
	c.mu.Lock()
	defer c.mu.Unlock()

	el, ok := c.elements[key]
	if !ok {
		return
	}
	c.lru.Remove(el)
	delete(c.elements, key)
}

func (c *fileListCache) evictIfNeeded() {
	for {
		c.mu.Lock()
		if len(c.elements) <= c.maxEntries {
			c.mu.Unlock()
			return
		}
		el := c.lru.Back()
		if el == nil {
			c.mu.Unlock()
			return
		}
		key := el.Value.(string)
		c.lru.Remove(el)
		delete(c.elements, key)
		c.mu.Unlock()

		// 注意：不要在持有 c.mu 时调用 c.cache.Delete，否则会和 OnEvicted 回调产生锁顺序死锁风险
		c.cache.Delete(key)
	}
}