package cache

import (
	"encoding/json"
	"fmt"
	"git.nobla.cn/golang/kos/pkg/cache"
	xxhash "github.com/cespare/xxhash/v2"
	"gorm.io/gorm"
	"gorm.io/gorm/callbacks"
	"os"
	"strconv"
	"time"
)

const (
	DisableCache = "DISABLE_CACHE"
	DurationKey  = "gorm:cache_duration"
)

type Cacher struct {
	rawQuery func(db *gorm.DB)
}

func (c *Cacher) Name() string {
	return "gorm:cache"
}

func (c *Cacher) Initialize(db *gorm.DB) (err error) {
	c.rawQuery = db.Callback().Query().Get("gorm:query")
	err = db.Callback().Query().Replace("gorm:query", c.Query)
	return
}

// buildCacheKey 构建一个缓存的KEY
func (c *Cacher) buildCacheKey(db *gorm.DB) string {
	s := strconv.FormatUint(xxhash.Sum64String(db.Statement.SQL.String()+fmt.Sprintf("%v", db.Statement.Vars)), 10)
	return s
}

// getDuration 获取缓存时长
func (c *Cacher) getDuration(db *gorm.DB) time.Duration {
	var (
		ok       bool
		v        any
		duration time.Duration
	)
	if v, ok = db.InstanceGet(DurationKey); !ok {
		return 0
	}
	if duration, ok = v.(time.Duration); !ok {
		return 0
	}
	return duration
}

// tryLoad 尝试从缓存读取数据
func (c *Cacher) tryLoad(key string, db *gorm.DB) (err error) {
	var (
		ok  bool
		buf []byte
	)
	if buf, ok = cache.Get(db.Statement.Context, key); ok {
		err = json.Unmarshal(buf, db.Statement.Dest)
	} else {
		err = os.ErrNotExist
	}
	return
}

// storeCache 存储缓存数据
func (c *Cacher) storeCache(key string, db *gorm.DB, duration time.Duration) (err error) {
	var (
		buf []byte
	)
	if buf, err = json.Marshal(db.Statement.Dest); err == nil {
		cache.SetEx(db.Statement.Context, key, buf, duration)
	}
	return
}

func (c *Cacher) Query(db *gorm.DB) {
	var (
		err      error
		cacheKey string
		duration time.Duration
	)
	duration = c.getDuration(db)
	if duration <= 0 {
		c.rawQuery(db)
		return
	}
	callbacks.BuildQuerySQL(db)
	cacheKey = c.buildCacheKey(db)
	if err = c.tryLoad(cacheKey, db); err == nil {
		return
	}
	c.rawQuery(db)
	if db.Error == nil {
		//store cache
		if err = c.storeCache(cacheKey, db, duration); err != nil {
			_ = db.AddError(err)
		}
	}
}

func New() *Cacher {
	return &Cacher{}
}