package lid

import (
	"context"
	"stat/common/mongos"
	"time"

	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
)

const notFindMsg = "mongo: no documents in result"

type IdModel struct {
	BusinessId  string    `bson:"business_id"` //业务id
	Step        int64     `bson:"step"`        //步长
	MaxId       int64     `bson:"max_id"`      //最大id
	Description string    `bson:"description"` //描述
	CreatedAt   time.Time `bson:"createdAt"`   //创建时间
	UpdatedAt   time.Time `bson:"updatedAt"`   //更改时间
}

type Lid struct {
	db         *mongo.Collection // 数据库连接
	businessId string            // 业务id
	ch         chan int64        // id缓冲池
	min, max   int64             // id段最小值，最大值
}

// NewLid 创建一个lid,db:数据库连接；businessId：业务id;len：缓冲池大小
func NewLid(db *mongo.Collection, businessId string, len int) (*Lid, error) {
	lid := Lid{
		db:         db,
		businessId: businessId,
		ch:         make(chan int64, len),
	}
	go lid.productId()
	return &lid, nil
}

// Get 获取自增id
func (l *Lid) Get() int64 {
	return <-l.ch
}

// productId 生产id
func (l *Lid) productId() {
	l.reset()
	for {
		if l.min >= l.max {
			l.reset()

		}

		l.min++
		l.ch <- l.min
	}
}

// reset 不断尝试从数据库获取，直到成功
func (l *Lid) reset() {
	for {
		err := l.getFromDB()
		if err == nil {
			return
		}
		time.Sleep(time.Second)
		continue
	}
}

// getFromDB 从数据库获取id段
func (l *Lid) getFromDB() error {
	var (
		maxId   int64
		step    int64
		idModel IdModel
	)
	txErr := mongos.Transaction(context.Background(), func(sctx mongo.SessionContext) (err error) {
		err = l.db.FindOne(sctx, bson.M{"business_id": l.businessId}).Decode(&idModel)
		if err != nil {
			if err.Error() == notFindMsg {
				_, err = l.db.InsertOne(sctx, bson.M{"business_id": l.businessId, "max_id": 0, "step": 10, "description": "id自增器", "createdAt": time.Now(), "updatedAt": time.Now()})
				if err != nil {
					return
				}
			} else {
				return
			}
		}
		maxId = idModel.MaxId
		step = idModel.Step
		_, err = l.db.UpdateOne(sctx, bson.M{"business_id": l.businessId}, bson.M{"$set": bson.M{"max_id": maxId + step}})
		if err != nil {
			return
		}
		l.min = maxId
		l.max = maxId + step
		return
	})
	return txErr
}