package main

import (
	"fmt"
	"gorm.io/driver/mysql"
	"gorm.io/gorm"
	"log"
)

type User struct {
	ID      uint   `gorm:"primaryKey"`
	Name    string `gorm:"size:100"`
	Balance int    // 賬戶余額
}

var db *gorm.DB

func initDB() {
	dsn := "root:123456@tcp(127.0.0.1:3306)/testdb?charset=utf8mb4&parseTime=True&loc=Local"
	var err error
	db, err = gorm.Open(mysql.Open(dsn), &gorm.Config{})
	if err != nil {
		log.Fatal("數(shù)據(jù)庫(kù)連接失敗:", err)
	}
	_ = db.AutoMigrate(&User{})
}

// Transfer 轉(zhuǎn)賬函數(shù)：fromID -> toID，金額 amount
func Transfer(fromID, toID uint, amount int) error {
	return db.Transaction(func(tx *gorm.DB) error {
		var from, to User

		// 查詢轉(zhuǎn)出賬戶
		if err := tx.First(&from, fromID).Error; err != nil {
			return err
		}
		if from.Balance < amount {
			return fmt.Errorf("余額不足")
		}

		// 扣減余額
		if err := tx.Model(&from).Update("balance", from.Balance-amount).Error; err != nil {
			return err
		}

		// 查詢轉(zhuǎn)入賬戶
		if err := tx.First(&to, toID).Error; err != nil {
			return err
		}

		// 增加余額
		if err := tx.Model(&to).Update("balance", to.Balance+amount).Error; err != nil {
			return err
		}

		// 所有操作成功 -> 提交事務(wù)
		return nil
	})
}

func main() {
	initDB()

	// 初始化兩位用戶
	db.Create(&User{Name: "Alice", Balance: 100})
	db.Create(&User{Name: "Bob", Balance: 50})

	// 轉(zhuǎn)賬：Alice -> Bob 30元
	err := Transfer(1, 2, 30)
	if err != nil {
		log.Println("轉(zhuǎn)賬失敗:", err)
	} else {
		log.Println("轉(zhuǎn)賬成功")
	}

	var users []User
	db.Find(&users)
	log.Println("當(dāng)前用戶余額:", users)
}