package main

import (
    "errors"
    "fmt"
    "time"
)

const (
    BINano  = "2006-01-02 15:04:05.000000000"
    BIMicro = "2006-01-02 15:04:05.000000"
    BIMil   = "2006-01-02 15:04:05.000"
    BISec   = "2006-01-02 15:04:05"
    BICST   = "2006-01-02 15:04:05 +0800 CST"
    BIUTC   = "2006-01-02 15:04:05 +0000 UTC"
    BIDate  = "2006-01-02"
    BITime  = "15:04:05"
)

func main() {

    // snapchatAPI 获取到的时间格式是这种格式的字符串：2020-08-21T10:59:53.850Z
    timeStr := "2020-08-21T10:59:53.850Z"
    // 字符串转时间 得到的是CST 中国标准时间
    ret1,_ := Timestr2Time(timeStr)
    fmt.Printf("ret1>>>  %v, %T \n",ret1,ret1) // 2020-08-21 10:59:53 +0800 CST, time.Time
    // 字符串转时间戳
    ret2, _ := Timestr2Timestamp(timeStr)
    fmt.Printf("ret2>>> %v, %T \n", ret2,ret2) //1597978793, int64

    // 时间戳转时间
    ret3 := Timestamp2TimeSec(1597978793)
    fmt.Printf("ret3>>> %v, %T \n",ret3, ret3) //2020-08-21 10:59:53 +0800 CST, time.Time

    // 时间转字符串 —— ret1 是CST格式的时间
    ret4 := ret1.Format(BICST)
    fmt.Printf("ret4>>> %v, %T \n",ret4, ret4) //2020-08-21 10:59:53 +0800 CST, string
}

// 时间字符串转时间
func Timestr2Time(str string) (time.Time, error) {
    return Timestr2TimeBasic(str, "", nil)
}

// 时间字符串转时间戳
func Timestr2Timestamp(str string) (int64, error) {
    return Timestr2TimestampBasic(str, "", nil)
}

// 时间戳转时间 秒
func Timestamp2TimeSec(stamp int64) time.Time {
    return Timestamp2Time(stamp, 0)
}

// base...
func Timestr2TimeBasic(value string, resultFormat string, resultLoc *time.Location) (time.Time, error) {
    /**
    - params
        value:             转换内容字符串
        resultFormat:    结果时间格式
        resultLoc:        结果时区
    */
    resultLoc = getLocationDefault(resultLoc)
    useFormat := []string{ // 可能的转换格式
        BINano, BIMicro, BIMil, BISec, BICST, BIUTC, BIDate, BITime,
        time.RFC3339,
        time.RFC3339Nano,
    }
    var t time.Time
    for _, usef := range useFormat {
        tt, error := time.ParseInLocation(usef, value, resultLoc)
        t = tt
        if error != nil {
            continue
        }
        break
    }
    if t == getTimeDefault(resultLoc) {
        return t, errors.New("时间字符串格式错误")
    }

    if resultFormat == "" {
        resultFormat = "2006-01-02 15:04:05"
    }
    st := t.Format(resultFormat)
    fixedt, _ := time.ParseInLocation(resultFormat, st, resultLoc)

    return fixedt, nil
}

func Timestr2TimestampBasic(str string, format string, loc *time.Location) (int64, error) {
    t, err := Timestr2TimeBasic(str, format, loc)
    if err != nil {
        return -1., err
    }
    return (int64(t.UnixNano()) * 1) / 1e9, nil
}

func Timestamp2Time(stamp int64, nsec int64) time.Time {
    return time.Unix(stamp, nsec)
}

// 获取time默认值, 造一个错误
func getTimeDefault(loc *time.Location) time.Time {
    loc = getLocationDefault(loc)
    t, _ := time.ParseInLocation("2006-01-02 15:04:05", "", loc)
    return t
}

func getLocationDefault(loc *time.Location) *time.Location {
    if loc == nil {
        loc, _ = time.LoadLocation("Local")
    }
    return loc
}