package common

import (
	"bytes"
	"encoding/json"
)

func FormatJson(data string) (string, error) {
	var out bytes.Buffer
	err := json.Indent(&out, []byte(data), "", "    ")
	return out.String(), err
}

func SubStr(str string, start int, length int) (result string) {
    s := []rune(str)
    total := len(s)
    if total == 0 {
        return
    }
    // 允许从尾部开始计算
    if start < 0 {
        start = total + start
        if start < 0 {
            return
        }
    }
    if start > total {
        return
    }
    // 到末尾
    if length < 0 {
        length = total
    }
 
    end := start + length
    if end > total {
        result = string(s[start:])
    } else {
        result = string(s[start:end])
    }
 
    return
}