package cache

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"math/rand"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"github.com/redis/go-redis/v9"

	redisPkg "carrot_bbs/internal/pkg/redis"
)

// Cache 缓存接口
type Cache interface {
	// Set 设置缓存值，支持TTL
	Set(key string, value interface{}, ttl time.Duration)
	// Get 获取缓存值
	Get(key string) (interface{}, bool)
	// Delete 删除缓存
	Delete(key string)
	// DeleteByPrefix 根据前缀删除缓存
	DeleteByPrefix(prefix string)
	// Clear 清空所有缓存
	Clear()
	// Exists 检查键是否存在
	Exists(key string) bool
	// Increment 增加计数器的值
	Increment(key string) int64
	// IncrementBy 增加指定值
	IncrementBy(key string, value int64) int64
}

// cacheItem 缓存项（用于内存缓存降级）
type cacheItem struct {
	value      interface{}
	expiration int64 // 过期时间戳（纳秒）
}

const nullMarkerValue = "__carrot_cache_null__"

type cacheMetrics struct {
	hit         atomic.Int64
	miss        atomic.Int64
	decodeError atomic.Int64
	setError    atomic.Int64
	invalidate  atomic.Int64
}

var metrics cacheMetrics
var loadLocks sync.Map

type MetricsSnapshot struct {
	Hit         int64
	Miss        int64
	DecodeError int64
	SetError    int64
	Invalidate  int64
}

type Settings struct {
	Enabled            bool
	KeyPrefix          string
	DefaultTTL         time.Duration
	NullTTL            time.Duration
	JitterRatio        float64
	PostListTTL        time.Duration
	ConversationTTL    time.Duration
	UnreadCountTTL     time.Duration
	GroupMembersTTL    time.Duration
	DisableFlushDB     bool
}

var settings = Settings{
	Enabled:         true,
	DefaultTTL:      30 * time.Second,
	NullTTL:         5 * time.Second,
	JitterRatio:     0.1,
	PostListTTL:     30 * time.Second,
	ConversationTTL: 60 * time.Second,
	UnreadCountTTL:  30 * time.Second,
	GroupMembersTTL: 120 * time.Second,
	DisableFlushDB:  true,
}

func Configure(s Settings) {
	settings.Enabled = s.Enabled
	if s.KeyPrefix != "" {
		settings.KeyPrefix = s.KeyPrefix
	}
	if s.DefaultTTL > 0 {
		settings.DefaultTTL = s.DefaultTTL
	}
	if s.NullTTL > 0 {
		settings.NullTTL = s.NullTTL
	}
	if s.JitterRatio > 0 {
		settings.JitterRatio = s.JitterRatio
	}
	if s.PostListTTL > 0 {
		settings.PostListTTL = s.PostListTTL
	}
	if s.ConversationTTL > 0 {
		settings.ConversationTTL = s.ConversationTTL
	}
	if s.UnreadCountTTL > 0 {
		settings.UnreadCountTTL = s.UnreadCountTTL
	}
	if s.GroupMembersTTL > 0 {
		settings.GroupMembersTTL = s.GroupMembersTTL
	}
	settings.DisableFlushDB = s.DisableFlushDB
}

func GetSettings() Settings {
	return settings
}

func normalizeKey(key string) string {
	if settings.KeyPrefix == "" {
		return key
	}
	return settings.KeyPrefix + ":" + key
}

func normalizePrefix(prefix string) string {
	if settings.KeyPrefix == "" {
		return prefix
	}
	return settings.KeyPrefix + ":" + prefix
}

func GetMetricsSnapshot() MetricsSnapshot {
	return MetricsSnapshot{
		Hit:         metrics.hit.Load(),
		Miss:        metrics.miss.Load(),
		DecodeError: metrics.decodeError.Load(),
		SetError:    metrics.setError.Load(),
		Invalidate:  metrics.invalidate.Load(),
	}
}

// isExpired 检查是否过期
func (item *cacheItem) isExpired() bool {
	if item.expiration == 0 {
		return false
	}
	return time.Now().UnixNano() > item.expiration
}

// MemoryCache 内存缓存实现（降级使用）
type MemoryCache struct {
	items sync.Map
	// cleanupInterval 清理过期缓存的间隔
	cleanupInterval time.Duration
	// stopCleanup 停止清理协程的通道
	stopCleanup chan struct{}
}

// NewMemoryCache 创建内存缓存
func NewMemoryCache() *MemoryCache {
	c := &MemoryCache{
		cleanupInterval: 1 * time.Minute,
		stopCleanup:     make(chan struct{}),
	}
	// 启动后台清理协程
	go c.cleanup()
	return c
}

// Set 设置缓存值
func (c *MemoryCache) Set(key string, value interface{}, ttl time.Duration) {
	key = normalizeKey(key)
	var expiration int64
	if ttl > 0 {
		expiration = time.Now().Add(ttl).UnixNano()
	}
	c.items.Store(key, &cacheItem{
		value:      value,
		expiration: expiration,
	})
}

// Get 获取缓存值
func (c *MemoryCache) Get(key string) (interface{}, bool) {
	key = normalizeKey(key)
	val, ok := c.items.Load(key)
	if !ok {
		return nil, false
	}

	item := val.(*cacheItem)
	if item.isExpired() {
		c.items.Delete(key)
		return nil, false
	}

	return item.value, true
}

// Delete 删除缓存
func (c *MemoryCache) Delete(key string) {
	key = normalizeKey(key)
	metrics.invalidate.Add(1)
	c.items.Delete(key)
}

// DeleteByPrefix 根据前缀删除缓存
func (c *MemoryCache) DeleteByPrefix(prefix string) {
	prefix = normalizePrefix(prefix)
	c.items.Range(func(key, value interface{}) bool {
		if keyStr, ok := key.(string); ok {
			if strings.HasPrefix(keyStr, prefix) {
				metrics.invalidate.Add(1)
				c.items.Delete(key)
			}
		}
		return true
	})
}

// Clear 清空所有缓存
func (c *MemoryCache) Clear() {
	c.items.Range(func(key, value interface{}) bool {
		metrics.invalidate.Add(1)
		c.items.Delete(key)
		return true
	})
}

// Exists 检查键是否存在
func (c *MemoryCache) Exists(key string) bool {
	_, ok := c.Get(key)
	return ok
}

// Increment 增加计数器的值
func (c *MemoryCache) Increment(key string) int64 {
	return c.IncrementBy(key, 1)
}

// IncrementBy 增加指定值
func (c *MemoryCache) IncrementBy(key string, value int64) int64 {
	key = normalizeKey(key)
	for {
		val, ok := c.items.Load(key)
		if !ok {
			// 键不存在，创建新值
			c.items.Store(key, &cacheItem{
				value:      value,
				expiration: 0,
			})
			return value
		}

		item := val.(*cacheItem)
		if item.isExpired() {
			// 已过期，创建新值
			c.items.Store(key, &cacheItem{
				value:      value,
				expiration: 0,
			})
			return value
		}

		// 尝试更新
		currentValue, ok := item.value.(int64)
		if !ok {
			// 类型不匹配，覆盖为新值
			c.items.Store(key, &cacheItem{
				value:      value,
				expiration: item.expiration,
			})
			return value
		}

		newValue := currentValue + value
		// 使用 CAS 操作确保并发安全
		if c.items.CompareAndSwap(key, val, &cacheItem{
			value:      newValue,
			expiration: item.expiration,
		}) {
			return newValue
		}
		// CAS 失败，重试
	}
}

// cleanup 定期清理过期缓存
func (c *MemoryCache) cleanup() {
	ticker := time.NewTicker(c.cleanupInterval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			c.cleanExpired()
		case <-c.stopCleanup:
			return
		}
	}
}

// cleanExpired 清理过期缓存
func (c *MemoryCache) cleanExpired() {
	count := 0
	c.items.Range(func(key, value interface{}) bool {
		item := value.(*cacheItem)
		if item.isExpired() {
			c.items.Delete(key)
			count++
		}
		return true
	})
	if count > 0 {
		log.Printf("[Cache] Cleaned %d expired items", count)
	}
}

// Stop 停止缓存清理协程
func (c *MemoryCache) Stop() {
	close(c.stopCleanup)
}

// RedisCache Redis缓存实现
type RedisCache struct {
	client *redisPkg.Client
	ctx    context.Context
}

// NewRedisCache 创建Redis缓存
func NewRedisCache(client *redisPkg.Client) *RedisCache {
	return &RedisCache{
		client: client,
		ctx:    context.Background(),
	}
}

// Set 设置缓存值
func (c *RedisCache) Set(key string, value interface{}, ttl time.Duration) {
	key = normalizeKey(key)
	// 将值序列化为JSON
	data, err := json.Marshal(value)
	if err != nil {
		metrics.setError.Add(1)
		log.Printf("[RedisCache] Failed to marshal value for key %s: %v", key, err)
		return
	}

	if err := c.client.Set(c.ctx, key, data, ttl); err != nil {
		metrics.setError.Add(1)
		log.Printf("[RedisCache] Failed to set key %s: %v", key, err)
	}
}

// Get 获取缓存值
func (c *RedisCache) Get(key string) (interface{}, bool) {
	key = normalizeKey(key)
	data, err := c.client.Get(c.ctx, key)
	if err != nil {
		if err == redis.Nil {
			return nil, false
		}
		log.Printf("[RedisCache] Failed to get key %s: %v", key, err)
		return nil, false
	}

	// 返回原始字符串，由调用侧决定如何解码为目标类型
	return data, true
}

// Delete 删除缓存
func (c *RedisCache) Delete(key string) {
	key = normalizeKey(key)
	metrics.invalidate.Add(1)
	if err := c.client.Del(c.ctx, key); err != nil {
		log.Printf("[RedisCache] Failed to delete key %s: %v", key, err)
	}
}

// DeleteByPrefix 根据前缀删除缓存
func (c *RedisCache) DeleteByPrefix(prefix string) {
	prefix = normalizePrefix(prefix)
	// 使用原生客户端执行SCAN命令
	rdb := c.client.GetClient()
	var cursor uint64
	for {
		keys, nextCursor, err := rdb.Scan(c.ctx, cursor, prefix+"*", 100).Result()
		if err != nil {
			log.Printf("[RedisCache] Failed to scan keys with prefix %s: %v", prefix, err)
			return
		}

		if len(keys) > 0 {
			metrics.invalidate.Add(int64(len(keys)))
			if err := c.client.Del(c.ctx, keys...); err != nil {
				log.Printf("[RedisCache] Failed to delete keys with prefix %s: %v", prefix, err)
			}
		}

		cursor = nextCursor
		if cursor == 0 {
			break
		}
	}
}

// Clear 清空所有缓存
func (c *RedisCache) Clear() {
	if settings.DisableFlushDB {
		log.Printf("[RedisCache] Skip FlushDB because cache.disable_flushdb=true")
		return
	}
	metrics.invalidate.Add(1)
	rdb := c.client.GetClient()
	if err := rdb.FlushDB(c.ctx).Err(); err != nil {
		log.Printf("[RedisCache] Failed to clear cache: %v", err)
	}
}

// Exists 检查键是否存在
func (c *RedisCache) Exists(key string) bool {
	key = normalizeKey(key)
	n, err := c.client.Exists(c.ctx, key)
	if err != nil {
		log.Printf("[RedisCache] Failed to check existence of key %s: %v", key, err)
		return false
	}
	return n > 0
}

// Increment 增加计数器的值
func (c *RedisCache) Increment(key string) int64 {
	return c.IncrementBy(key, 1)
}

// IncrementBy 增加指定值
func (c *RedisCache) IncrementBy(key string, value int64) int64 {
	key = normalizeKey(key)
	rdb := c.client.GetClient()
	result, err := rdb.IncrBy(c.ctx, key, value).Result()
	if err != nil {
		log.Printf("[RedisCache] Failed to increment key %s: %v", key, err)
		return 0
	}
	return result
}

// 全局缓存实例
var globalCache Cache
var once sync.Once

// InitCache 初始化全局缓存实例（使用Redis）
func InitCache(redisClient *redisPkg.Client) {
	once.Do(func() {
		if redisClient != nil {
			globalCache = NewRedisCache(redisClient)
			log.Println("[Cache] Initialized Redis cache")
		} else {
			globalCache = NewMemoryCache()
			log.Println("[Cache] Initialized Memory cache (Redis not available)")
		}
	})
}

// GetCache 获取全局缓存实例
func GetCache() Cache {
	if globalCache == nil {
		// 如果未初始化，返回内存缓存作为降级
		log.Println("[Cache] Warning: Cache not initialized, using Memory cache")
		return NewMemoryCache()
	}
	return globalCache
}

// GetRedisClient 从缓存中获取Redis客户端（仅在Redis模式下有效）
func GetRedisClient() (*redisPkg.Client, error) {
	if redisCache, ok := globalCache.(*RedisCache); ok {
		return redisCache.client, nil
	}
	return nil, fmt.Errorf("cache is not using Redis backend")
}

func SetWithJitter(c Cache, key string, value interface{}, ttl time.Duration, jitterRatio float64) {
	if !settings.Enabled {
		return
	}
	c.Set(key, value, ApplyTTLJitter(ttl, jitterRatio))
}

func SetNull(c Cache, key string, ttl time.Duration) {
	if !settings.Enabled {
		return
	}
	c.Set(key, nullMarkerValue, ttl)
}

func ApplyTTLJitter(ttl time.Duration, jitterRatio float64) time.Duration {
	if ttl <= 0 || jitterRatio <= 0 {
		return ttl
	}
	if jitterRatio > 1 {
		jitterRatio = 1
	}
	maxJitter := int64(float64(ttl) * jitterRatio)
	if maxJitter <= 0 {
		return ttl
	}
	delta := rand.Int63n(maxJitter + 1)
	return ttl + time.Duration(delta)
}

func GetTyped[T any](c Cache, key string) (T, bool) {
	var zero T
	if !settings.Enabled {
		return zero, false
	}
	raw, ok := c.Get(key)
	if !ok {
		metrics.miss.Add(1)
		return zero, false
	}
	if str, ok := raw.(string); ok && str == nullMarkerValue {
		metrics.hit.Add(1)
		return zero, false
	}

	if typed, ok := raw.(T); ok {
		metrics.hit.Add(1)
		return typed, true
	}

	var out T
	switch v := raw.(type) {
	case string:
		if err := json.Unmarshal([]byte(v), &out); err != nil {
			metrics.decodeError.Add(1)
			return zero, false
		}
		metrics.hit.Add(1)
		return out, true
	case []byte:
		if err := json.Unmarshal(v, &out); err != nil {
			metrics.decodeError.Add(1)
			return zero, false
		}
		metrics.hit.Add(1)
		return out, true
	default:
		data, err := json.Marshal(v)
		if err != nil {
			metrics.decodeError.Add(1)
			return zero, false
		}
		if err := json.Unmarshal(data, &out); err != nil {
			metrics.decodeError.Add(1)
			return zero, false
		}
		metrics.hit.Add(1)
		return out, true
	}
}

func GetOrLoadTyped[T any](
	c Cache,
	key string,
	ttl time.Duration,
	jitterRatio float64,
	nullTTL time.Duration,
	loader func() (T, error),
) (T, error) {
	if cached, ok := GetTyped[T](c, key); ok {
		return cached, nil
	}

	lockValue, _ := loadLocks.LoadOrStore(key, &sync.Mutex{})
	lock := lockValue.(*sync.Mutex)
	lock.Lock()
	defer lock.Unlock()

	if cached, ok := GetTyped[T](c, key); ok {
		return cached, nil
	}

	loaded, err := loader()
	if err != nil {
		var zero T
		return zero, err
	}

	encoded, marshalErr := json.Marshal(loaded)
	if marshalErr == nil && string(encoded) == "null" && nullTTL > 0 {
		SetNull(c, key, nullTTL)
		return loaded, nil
	}

	SetWithJitter(c, key, loaded, ttl, jitterRatio)
	return loaded, nil
}