// demo_db.go

package main

import (
	"database/sql"
	"fmt"
	_ "github.com/go-sql-driver/mysql"
)

var (
	db *sql.DB
)

func check(err error) {
	if err != nil {
		fmt.Println(err)
	}
}

func InitDB(mydb *sql.DB) {
	db = mydb
}

func main() {
	mydb, err := sql.Open("mysql", "root:root@tcp(localhost:3306)/imooc")
	check(err)
	defer mydb.Close()

	InitDB(mydb)
	fmt.Println(db)
}

// demo_method.go

package main

import (
	"database/sql"
	"fmt"
	_ "github.com/go-sql-driver/mysql"
)

var (
	db *sql.DB
)

func check(err error) {
	if err != nil {
		fmt.Println(err)
	}
}

func InitDB(mydb *sql.DB) {
	db = mydb
}

func DemoExec() {
	sql_insert := "insert user set username=?"
	result, err := db.Exec(sql_insert, "xiaoming")
	check(err)
	rows, err := result.RowsAffected()
	check(err)
	fmt.Printf("rows affected: %d\n", rows)
}

func DemoQuery() {
	sql_query := "select acctid from account where money=?"
	rows, err := db.Query(sql_query, 2000)
	defer rows.Close()
	check(err)
	for rows.Next() {
		var id int
		if err := rows.Scan(&id); err != nil {
			fmt.Println(err)
		}
		fmt.Printf("id: %d\n", id)
	}
}

func DemoQueryRow() {
	var id int
	sql_query := "select acctid from account where money=?"
	row := db.QueryRow(sql_query, 2000)
	err := row.Scan(&id)
	check(err)
	fmt.Printf("id: %d\n", id)
}

func DemoPrepare() {
	stmt, err := db.Prepare("select username from user where userid=?")
	check(err)

	rows, err := stmt.Query(3)
	defer rows.Close()
	check(err)

	for rows.Next() {
		var username string
		if err := rows.Scan(&username); err != nil {
			fmt.Println(err)
		}
		fmt.Printf("username: %s\n", username)
	}
}

func main() {
	mydb, err := sql.Open("mysql", "root:root@tcp(localhost:3306)/imooc")
	check(err)
	defer mydb.Close()
	InitDB(mydb)

	DemoExec()
	DemoQuery()
	DemoQueryRow()
	DemoPrepare()
}

// demo_transaction.go

package main

import (
    "database/sql"
    _ "github.com/go-sql-driver/mysql"
    "fmt"
    "log"
)

var (
    db *sql.DB
    tx *sql.Tx
)

func check(err error) {
    if err != nil {
        fmt.Println(err)
    }
}

func InitDB(mydb *sql.DB) {
    db = mydb
}

func InitTx(mytx *sql.Tx) {
    tx = mytx
}

func CheckAccountAvaiable(acctid int) {
    sql := "select * from account where acctid=?"
    rows,err := tx.Query(sql, acctid)
    // 如果不调用rows.Close，conn无法回到 tx上
    defer rows.Close()
    if err != nil {
        log.Println(err)
        panic(fmt.Sprintf("查询错误，账号%d不可得!", acctid))
    }
    if !rows.Next() {
        panic(fmt.Sprintf("查询失败，账号%d不可得!", acctid))
    }
}

func HasEnoughMoney(acctid, money int) {
    sql := "select * from account where acctid=? and money>=?"
    rows,err := tx.Query(sql, acctid, money)
    defer rows.Close()
    if err != nil {
        log.Println(err)
        panic(fmt.Sprintf("用户%d余额查询失败！", acctid))
    }
    if !rows.Next() {
        panic(fmt.Sprintf("用户%d余额不足！", acctid))
    }
}

func ReduceMoney(acctid, money int) {
    sql := "update account set money = money-? where acctid = ?"
    _,err := tx.Exec(sql, money, acctid)
    if err != nil {
        log.Println(err)
        panic(fmt.Sprintf("用户%d减款失败！", acctid))
    }
}

func AddMoney(acctid, money int) {
    sql := "update account set money =money+? where acctid = ?"
    _,err := tx.Exec(sql, money, acctid)
    if err != nil {
        log.Println(err)
        panic(fmt.Sprintf("用户%d加款失败！", acctid))
    }
}

func Transfer(source_acctid, target_acctid, money int) {
    tx,err :=  db.Begin()
    check(err)
    InitTx(tx)

    defer func() {
        if err := recover(); err != sql.ErrTxDone && err != nil {
            fmt.Printf("出错了 ERR:%s\n", err)
            tx.Rollback()
        } else {
            tx.Commit()
            fmt.Printf("%d转给%d一共%d元, 转账成功！",source_acctid, target_acctid, money)
        }
    }()

    CheckAccountAvaiable(source_acctid)
    CheckAccountAvaiable(target_acctid)
    HasEnoughMoney(source_acctid, money)
    ReduceMoney(source_acctid, money)
    AddMoney(target_acctid, money)
}

func main() {
    mydb,err := sql.Open("mysql", "root:root@tcp(localhost:3306)/imooc")
    check(err)
    defer mydb.Close()

    InitDB(mydb)
    Transfer(4, 3, 500)
}