package main

import (
    "bytes"
    "fmt"
    "log"
    "reflect"
)

func CamelCase(s string) string {
    if s == "" {
        return ""
    }
    t := make([]byte, 0, 32)
    i := 0
    if s[0] == '_' {
        t = append(t, 'X')
        i++
    }
    for ; i < len(s); i++ {
        c := s[i]
        if c == '_' && i+1 < len(s) && isASCIIUpper(s[i+1]) {
            continue
        }
        if isASCIIDigit(c) {
            t = append(t, c)
            continue
        }

        if isASCIIUpper(c) {
            c ^= ' '
        }
        t = append(t, c)

        for i+1 < len(s) && isASCIIUpper(s[i+1]) {
            i++
            t = append(t, '_')
            t = append(t, bytes.ToLower([]byte{s[i]})[0])
        }
    }
    return string(t)
}
func isASCIIUpper(c byte) bool {
    return 'A' <= c && c <= 'Z'
}


func isASCIIDigit(c byte) bool {
    return '0' <= c && c <= '9'
}

type User struct {
    Id int
    UserName string
    Password string
    Avatar string
    Birthday string
}
func main(){
    // 1. 普通使用
    log.Println(CamelCase("AAAA"))
    log.Println(CamelCase("IconUrl"))
    log.Println(CamelCase("iconUrl"))
    log.Println(CamelCase("parentId"))
    log.Println(CamelCase("a9b9Ba"))
    log.Println(CamelCase("_An"))
    // s输出
    //2019/03/20 16:34:25 a_a_a_a
    //2019/03/20 16:34:25 icon_url
    //2019/03/20 16:34:25 icon_url
    //2019/03/20 16:34:25 parent_id
    //2019/03/20 16:34:25 a9b9ba
    //2019/03/20 16:34:25 Xan

    // 2. 比如数据库 User 表, 仅修改Birthday Avatar列,
    // 反射遍历字段 然后修改 拼装sql语句
    user := &User{ Id:10,UserName:"track",Password:"123456",Avatar:"http://baidu.com",Birthday:"1999-09-09"}
    rt := reflect.ValueOf(user)
    sql := "UPDATE user SET"
    for i := 0; i < rt.Elem().NumField(); i++ {
        fieldValue := rt.Elem().Field(i)
        fieldType := rt.Elem().Type().Field(i)
        fieldName := CamelCase(fieldType.Name)
        if fieldName == "id" {
            continue
        }
        sql+= fmt.Sprintf(" %s = %s ,",fieldName,fieldValue)
    }
    sql+= " "+ fmt.Sprintf("WHERE id = %d",user.Id)

    // 当然 还是有问题的. 简单举个栗子
    log.Println("SQL语句组装为:",sql)
    // SQL语句组装为: UPDATE user SET user_name = track , password = 123456 , avatar = http://baidu.com , birthday = 1999-09-09 , WHERE id = 10
}