package localcache

import (
	"context"
	"hash/fnv"
	"unsafe"

	"github.com/openimsdk/open-im-server/v3/pkg/localcache/link"
	"github.com/openimsdk/open-im-server/v3/pkg/localcache/lru"
)

type Cache[V any] interface {
	Get(ctx context.Context, key string, fetch func(ctx context.Context) (V, error)) (V, error)
	GetLink(ctx context.Context, key string, fetch func(ctx context.Context) (V, error), link ...string) (V, error)
	Del(ctx context.Context, key ...string)
	DelLocal(ctx context.Context, key ...string)
	Stop()
}

func LRUStringHash(key string) uint64 {
	h := fnv.New64a()
	h.Write(*(*[]byte)(unsafe.Pointer(&key)))
	return h.Sum64()
}

func New[V any](opts ...Option) Cache[V] {
	opt := defaultOption()
	for _, o := range opts {
		o(opt)
	}

	c := cache[V]{opt: opt}
	if opt.localSlotNum > 0 && opt.localSlotSize > 0 {
		createSimpleLRU := func() lru.LRU[string, V] {
			if opt.expirationEvict {
				return lru.NewExpirationLRU[string, V](opt.localSlotSize, opt.localSuccessTTL, opt.localFailedTTL, opt.target, c.onEvict)
			} else {
				return lru.NewLazyLRU[string, V](opt.localSlotSize, opt.localSuccessTTL, opt.localFailedTTL, opt.target, c.onEvict)
			}
		}
		if opt.localSlotNum == 1 {
			c.local = createSimpleLRU()
		} else {
			c.local = lru.NewSlotLRU[string, V](opt.localSlotNum, LRUStringHash, createSimpleLRU)
		}
		if opt.linkSlotNum > 0 {
			c.link = link.New(opt.linkSlotNum)
		}
	}
	return &c
}

type cache[V any] struct {
	opt   *option
	link  link.Link
	local lru.LRU[string, V]
}

func (c *cache[V]) onEvict(key string, value V) {
	if c.link != nil {
		// Do not delete other keys while the underlying LRU still holds its lock;
		// defer linked deletions to avoid re-entering the same slot and deadlocking.
		if lks := c.link.Del(key); len(lks) > 0 {
			go c.delLinked(key, lks)
		}
	}
}

func (c *cache[V]) delLinked(src string, keys map[string]struct{}) {
	for k := range keys {
		if src != k {
			c.local.Del(k)
		}
	}
}

func (c *cache[V]) del(key ...string) {
	if c.local == nil {
		return
	}
	for _, k := range key {
		c.local.Del(k)
		if c.link != nil {
			lks := c.link.Del(k)
			for k := range lks {
				c.local.Del(k)
			}
		}
	}
}

func (c *cache[V]) Get(ctx context.Context, key string, fetch func(ctx context.Context) (V, error)) (V, error) {
	return c.GetLink(ctx, key, fetch)
}

func (c *cache[V]) GetLink(ctx context.Context, key string, fetch func(ctx context.Context) (V, error), link ...string) (V, error) {
	if c.local != nil {
		return c.local.Get(key, func() (V, error) {
			if len(link) > 0 && c.link != nil {
				c.link.Link(key, link...)
			}
			return fetch(ctx)
		})
	} else {
		return fetch(ctx)
	}
}

func (c *cache[V]) Del(ctx context.Context, key ...string) {
	for _, fn := range c.opt.delFn {
		fn(ctx, key...)
	}
	c.del(key...)
}

func (c *cache[V]) DelLocal(ctx context.Context, key ...string) {
	c.del(key...)
}

func (c *cache[V]) Stop() {
	c.local.Stop()
}