backend/internal/cache/cache.go

package cache

import (
	"cmp"
	"context"
	"encoding/json"
	"math/rand"
	"sync"
	"time"
)

// 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

	// ==================== Hash 操作 ====================
	// HSet 设置 Hash 字段
	HSet(ctx context.Context, key string, field string, value interface{}) error
	// HMSet 批量设置 Hash 字段
	HMSet(ctx context.Context, key string, values map[string]interface{}) error
	// HGet 获取 Hash 字段值
	HGet(ctx context.Context, key string, field string) (string, error)
	// HMGet 批量获取 Hash 字段值
	HMGet(ctx context.Context, key string, fields ...string) ([]interface{}, error)
	// HGetAll 获取 Hash 所有字段
	HGetAll(ctx context.Context, key string) (map[string]string, error)
	// HDel 删除 Hash 字段
	HDel(ctx context.Context, key string, fields ...string) error

	// ==================== Sorted Set 操作 ====================
	// ZAdd 添加 Sorted Set 成员
	ZAdd(ctx context.Context, key string, score float64, member string) error
	// ZRangeByScore 按分数范围获取成员（升序）
	ZRangeByScore(ctx context.Context, key string, min, max string, offset, count int64) ([]string, error)
	// ZRevRangeByScore 按分数范围获取成员（降序）
	ZRevRangeByScore(ctx context.Context, key string, max, min string, offset, count int64) ([]string, error)
	// ZRem 删除 Sorted Set 成员
	ZRem(ctx context.Context, key string, members ...interface{}) error
	// ZCard 获取 Sorted Set 成员数量
	ZCard(ctx context.Context, key string) (int64, error)

	// ==================== 计数器操作 ====================
	// Incr 原子递增（返回新值）
	Incr(ctx context.Context, key string) (int64, error)
	// Expire 设置过期时间
	Expire(ctx context.Context, key string, ttl time.Duration) error
}

const nullMarkerValue = "__carrot_cache_null__"

var loadLocks sync.Map

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 {
	return cmp.Or(settings.KeyPrefix, "") + ":" + key
}

func normalizePrefix(prefix string) string {
	return cmp.Or(settings.KeyPrefix, "") + ":" + prefix
}

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 {
		recordMiss()
		return zero, false
	}
	if str, ok := raw.(string); ok && str == nullMarkerValue {
		recordHit()
		return zero, false
	}

	if typed, ok := raw.(T); ok {
		recordHit()
		return typed, true
	}

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