Get real calendar days between two dates

Question

I'm trying to get amount of days between two dates in Go but as I'm getting the difference in time (hours) and then divided by the amount of time per day, I have an issue.

Problem: if dates are different (7 of May and 8 of May) but the time between then is lower than 24h, my code counts as there are no days in between.

What I want: count real days in between.

// Days
firstDay := firstDate.Unix()
lastDay := lastDate.Unix()
fmt.Println("firstDay: ", firstDay)
fmt.Println("lastDay: ", lastDay)

if firstDay > lastDay {
        fmt.Println("IS TO SMALL")
    return
}

// businessDays = 
businessDays := (lastDay - firstDay) / 86400
fmt.Println("businessDays: ", businessDays)

Thank you very much.

Answer 1

There are many things to worry about. For example, due to daylight saving time (DST), not all days are 24 hours. What if the times are in different time zones? And so on.

Here's a solution that addresses these issues.

package main

import (
    "fmt"
    "time"
)

// CalendarDays returns the calendar difference between times (t2 - t1) as days.
func CalendarDays(t2, t1 time.Time) int {
    y, m, d := t2.Date()
    u2 := time.Date(y, m, d, 0, 0, 0, 0, time.UTC)
    y, m, d = t1.In(t2.Location()).Date()
    u1 := time.Date(y, m, d, 0, 0, 0, 0, time.UTC)
    days := u2.Sub(u1) / (24 * time.Hour)
    return int(days)
}

func main() {
    first := time.Now().Round(0)
    end := first.Add(48 * time.Hour)
    for last := first; last.Before(end); last = last.Add(6 * time.Hour) {
        fmt.Println("Days:", CalendarDays(last, first), "Last:", last, "First:", first)
    }
}

Playground: https://play.golang.org/p/wKwQzgfKa8f

Output:

Days: 0 Last: 2018-02-05 17:38:15.623292254 -0500 EST First: 2018-02-05 17:38:15.623292254 -0500 EST
Days: 0 Last: 2018-02-05 23:38:15.623292254 -0500 EST First: 2018-02-05 17:38:15.623292254 -0500 EST
Days: 1 Last: 2018-02-06 05:38:15.623292254 -0500 EST First: 2018-02-05 17:38:15.623292254 -0500 EST
Days: 1 Last: 2018-02-06 11:38:15.623292254 -0500 EST First: 2018-02-05 17:38:15.623292254 -0500 EST
Days: 1 Last: 2018-02-06 17:38:15.623292254 -0500 EST First: 2018-02-05 17:38:15.623292254 -0500 EST
Days: 1 Last: 2018-02-06 23:38:15.623292254 -0500 EST First: 2018-02-05 17:38:15.623292254 -0500 EST
Days: 2 Last: 2018-02-07 05:38:15.623292254 -0500 EST First: 2018-02-05 17:38:15.623292254 -0500 EST
Days: 2 Last: 2018-02-07 11:38:15.623292254 -0500 EST First: 2018-02-05 17:38:15.623292254 -0500 EST

Answer 2

1. Use Duration.Hours() to get hours
2. Use math.Ceil() to find calendar days
3. Use Time.Truncate() to truncate hour and minute, only save day

The source code:

package main

import (
    "fmt"
    "math"
    "time"
)

func main() {
    d1, err := time.Parse("200601021504", "201801020001")
    if err != nil {
        panic(err)
    }
    d2, err := time.Parse("200601021504", "201801020002")
    if err != nil {
        panic(err)
    }

    newD1 := d1.Truncate(time.Hour * 24)
    newD2 := d2.Truncate(time.Hour * 24)

    fmt.Printf("days: %v\n", math.Ceil(newD2.Sub(newD1).Hours()/24))

}