package permissions

import (
	"container/list"
	"sync"
)

// Cache — простой LRU-кэш вычисленных прав с инвалидацией при записи
// (AGENT.md 9.1). Ключи: сервер+пользователь и комната+пользователь.
type Cache struct {
	mu       sync.Mutex
	capacity int
	items    map[guildKey]*list.Element
	channels map[channelKey]*list.Element
	order    *list.List
}

type guildKey struct {
	guildID uint64
	userID  uint64
}

type channelKey struct {
	// guildID нужен, чтобы сброс сервера (роли, тайм-аут, оверрайды) сбрасывал
	// и кэш его комнат: иначе участник с тайм-аутом продолжал писать.
	guildID   uint64
	channelID uint64
	userID    uint64
}

type cacheEntry struct {
	guild   guildKey
	channel channelKey
	value   Resolved
	isChan  bool
}

func NewCache(capacity int) *Cache {
	if capacity <= 0 {
		capacity = 1024
	}
	return &Cache{
		capacity: capacity,
		items:    make(map[guildKey]*list.Element, capacity),
		channels: make(map[channelKey]*list.Element, capacity),
		order:    list.New(),
	}
}

func (c *Cache) GetGuild(guildID, userID uint64) (Resolved, bool) {
	c.mu.Lock()
	defer c.mu.Unlock()
	element, ok := c.items[guildKey{guildID: guildID, userID: userID}]
	if !ok {
		return Resolved{}, false
	}
	c.order.MoveToFront(element)
	return element.Value.(*cacheEntry).value, true
}

func (c *Cache) PutGuild(guildID, userID uint64, value Resolved) {
	c.mu.Lock()
	defer c.mu.Unlock()
	key := guildKey{guildID: guildID, userID: userID}
	if element, ok := c.items[key]; ok {
		element.Value.(*cacheEntry).value = value
		c.order.MoveToFront(element)
		return
	}
	entry := &cacheEntry{guild: key, value: value}
	c.items[key] = c.order.PushFront(entry)
	c.evictLocked()
}

func (c *Cache) GetChannel(guildID, channelID, userID uint64) (Resolved, bool) {
	c.mu.Lock()
	defer c.mu.Unlock()
	element, ok := c.channels[channelKey{guildID: guildID, channelID: channelID, userID: userID}]
	if !ok {
		return Resolved{}, false
	}
	c.order.MoveToFront(element)
	return element.Value.(*cacheEntry).value, true
}

func (c *Cache) PutChannel(guildID, channelID, userID uint64, value Resolved) {
	c.mu.Lock()
	defer c.mu.Unlock()
	key := channelKey{guildID: guildID, channelID: channelID, userID: userID}
	if element, ok := c.channels[key]; ok {
		element.Value.(*cacheEntry).value = value
		c.order.MoveToFront(element)
		return
	}
	entry := &cacheEntry{channel: key, value: value, isChan: true}
	c.channels[key] = c.order.PushFront(entry)
	c.evictLocked()
}

// InvalidateGuild сбрасывает права всех пользователей сервера, включая кэш
// его комнат: роли, тайм-аут и оверрайды влияют и на права в комнатах.
func (c *Cache) InvalidateGuild(guildID uint64) {
	c.mu.Lock()
	defer c.mu.Unlock()
	for key, element := range c.items {
		if key.guildID == guildID {
			c.order.Remove(element)
			delete(c.items, key)
		}
	}
	for key, element := range c.channels {
		if key.guildID == guildID {
			c.order.Remove(element)
			delete(c.channels, key)
		}
	}
}

// InvalidateChannel сбрасывает кэш комнаты.
func (c *Cache) InvalidateChannel(channelID uint64) {
	c.mu.Lock()
	defer c.mu.Unlock()
	for key, element := range c.channels {
		if key.channelID == channelID {
			c.order.Remove(element)
			delete(c.channels, key)
		}
	}
}

func (c *Cache) Clear() {
	c.mu.Lock()
	defer c.mu.Unlock()
	c.items = make(map[guildKey]*list.Element, c.capacity)
	c.channels = make(map[channelKey]*list.Element, c.capacity)
	c.order.Init()
}

func (c *Cache) Len() int {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.order.Len()
}

func (c *Cache) evictLocked() {
	for c.order.Len() > c.capacity {
		oldest := c.order.Back()
		if oldest == nil {
			return
		}
		entry := oldest.Value.(*cacheEntry)
		if entry.isChan {
			delete(c.channels, entry.channel)
		} else {
			delete(c.items, entry.guild)
		}
		c.order.Remove(oldest)
	}
}