# 12-Dates-And-Times

在本章，我们将讨论下 **Go** 处理日期和时间的方法，以及优化 User 及 Post 对象中的时间对象

*本章的GitHub链接为：* [Source](https://github.com/bonfy/go-mega-code/tree/12-Dates-And-Times), [Diff](https://github.com/bonfy/go-mega-code/compare/11-Facelift...12-Dates-And-Times), [Zip](https://github.com/bonfy/go-mega-code/archive/v1.2.zip)

## 优化 User 的 LastSeen

Flask-Mega 主要是用了它灵活的模板功能，以及 Moment.js 来在前端实现了时间日期的优化，与之不同，我们主要采用的是后端来实现同样的功能

model/user.go

```go
...
// FormattedLastSeen func
func (u *User) FormattedLastSeen() string {
    return u.LastSeen.Format("2006-01-02 15:04:05")
}
...
```

templates/content/profile.html

```markup
...
    <p>Last seen on: {{ .ProfileUser.FormattedLastSeen }}</p>
...
```

> Notice: 虽然我也比较喜欢其他语言的 %Y-%m-%d %H:%M:%S" layout 形式，但是无奈 Go 就是 "2006-01-02 15:04:05" 这样的layout，没有道理可讲，我有时候甚至怕它搞错 01 和 02 哪个是月 哪个表示 日

![12-01](/files/-LOzPnWhWVqQvkN4gWZ7)

> 本小节 [Diff](https://github.com/bonfy/go-mega-code/commit/01611b3d27f6c78ca6c53878502f539695d1170b)

## 优化 Post 的 Timestamp

我们目标是显示成 `user said 35 minutes ago: post message` 这样的形式，这就需要我们对时间日期进行转换

简单点，我们就在 utils.go 中实现一个 `FromTime` 函数

model/utils.go

```go
...

const (
    minute  = 1
    hour    = minute * 60
    day     = hour * 24
    month   = day * 30
    year    = day * 365
    quarter = year / 4
)

// FromDuration returns a friendly string representing an approximation of the
// given duration
func FromDuration(d time.Duration) string {
    seconds := round(d.Seconds())

    if seconds < 30 {
        return "less than a minute"
    }

    if seconds < 90 {
        return "1 minute"
    }

    minutes := div(seconds, 60)

    if minutes < 45 {
        return fmt.Sprintf("%0d minutes", minutes)
    }

    hours := div(minutes, 60)

    if minutes < day {
        return fmt.Sprintf("about %s", pluralize(hours, "hour"))
    }

    if minutes < (42 * hour) {
        return "1 day"
    }

    days := div(hours, 24)

    if minutes < (30 * day) {
        return pluralize(days, "day")
    }

    months := div(days, 30)

    if minutes < (45 * day) {
        return "about 1 month"
    }

    if minutes < (60 * day) {
        return "about 2 months"
    }

    if minutes < year {
        return pluralize(months, "month")
    }

    rem := minutes % year
    years := minutes / year

    if rem < (3 * month) {
        return fmt.Sprintf("about %s", pluralize(years, "year"))
    }
    if rem < (9 * month) {
        return fmt.Sprintf("over %s", pluralize(years, "year"))
    }

    years++
    return fmt.Sprintf("almost %s", pluralize(years, "year"))
}

// FromTime returns a friendly string representing the approximate difference
// from the given time and time.Now()
func FromTime(t time.Time) string {
    now := time.Now()

    var d time.Duration
    var suffix string

    if t.Before(now) {
        d = now.Sub(t)
        suffix = "ago"
    } else {
        d = t.Sub(now)
        suffix = "from now"
    }

    return fmt.Sprintf("%s %s", FromDuration(d), suffix)
}

func pluralize(i int, s string) string {
    var buf bytes.Buffer
    buf.WriteString(fmt.Sprintf("%d %s", i, s))
    if i != 1 {
        buf.WriteString("s")
    }
    return buf.String()
}

func round(f float64) int {
    return int(math.Floor(f + .50))
}

func div(numerator int, denominator int) int {
    rem := numerator % denominator
    result := numerator / denominator

    if rem >= (denominator / 2) {
        result++
    }

    return result
}
```

现在我们可以使用 `FromTime` 函数实现我们的功能了

model/post.go

```go
...
// FormattedTimeAgo func
func (p *Post) FormattedTimeAgo() string {
    return FromTime(*p.Timestamp)
}
...
```

templates/content/index.html & profile.html & explore.html

```markup
...
    {{range .Posts}}
        <table class="table table-hover">
            <tr valign="top">
                <td width="36px"><img src="{{.User.Avatar}}&s=36"></td>
                <td><a href="/user/{{.User.Username}}">{{ .User.Username }}</a> said {{.FormattedTimeAgo}}:<br>{{ .Body }}</td>
            </tr>
        </table>
    {{end}}
...
```

![12-02](/files/-LOzPnWnABdwki6KRUOu)

> 本小节 [Diff](https://github.com/bonfy/go-mega-code/commit/b5cdcf1fec212a012486928d2bc0ad3052d37d51)
>
> 写在最后: 突然发现模板可以使用 类的 Function, 所以前面 User 的 Avatar 字段貌似就没有那么必要了，直接用个function来实现，而且好处是不用去关心更改邮箱后的 SetAvatar,不过我任性，就不改了，我也是才发现 Go 模板还有这个妙用的

## Links

* [目录](/master.md)
* 上一节: [11-Facelift](/11-facelift.md)
* 下一节: [13-Javascript-Magic](/13-javascript-magic.md)


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