Calculating total number of Hours, Days, Minutes and Seconds between two dates in Golang

To get the number of days between two dates, we can calculate the number of days from the beginning 0/0/0000 to the first date and the second date and compute their difference.

Examples:

Input: 2020-04-27 23:35:00, 2018-5-12 12:43:23
Output: 716 days, 10 hours, 51 minutes, 37 seconds

Input: 2014-02-25 05:50:20, 2003-12-13 21:42:12
Output: 3726 days, 8 hours, 8 minutes, 8 seconds

To calculate the time difference, we can calculate hours2-hours1, minutes2-minutes1, seconds2-seconds1, and perform some operations (shown in the code from line 65 to line 80) to avoid negative values.

// Golang program for Calculating the total number
// of Hours, Days, Minutes and Seconds
// between two dates
package main

import (
    "fmt"
    "time"
)

// This function counts the
// number of leap years
// since the starting of time
// to the current year that
// is passed
func leapYears(date time.Time) (leaps int) {

    // returns year, month,
    // date of a time object
    y, m, _ := date.Date()

    if m <= 2 {
        y--
    }
    leaps = y/4 + y/400 - y/100
    return leaps
}

// The function calculates the
// difference between two dates and times
// and returns the days, hours, minutes,
// seconds between two dates

func getDifference(a, b time.Time) (days, hours, minutes, seconds int) {

    // month-wise days
    monthDays := [12]int{31, 28, 31, 30, 31,
                 30, 31, 31, 30, 31, 30, 31}

    // extracting years, months,
    // days of two dates
    y1, m1, d1 := a.Date()
    y2, m2, d2 := b.Date()

    // extracting hours, minutes,
    // seconds of two times
    h1, min1, s1 := a.Clock()
    h2, min2, s2 := b.Clock()

    // totalDays since the
    // beginning = year*365 + number_of_days
    totalDays1 := y1*365 + d1

    // adding days of the months
    // before the current month
    for i := 0; i < (int)(m1)-1; i++ {
        totalDays1 += monthDays[i]
    }

    // counting leap years since
    // beginning to the year "a"
    // and adding that many extra
    // days to the totaldays
    totalDays1 += leapYears(a)

    // Similar procedure for second date
    totalDays2 := y2*365 + d2

    for i := 0; i < (int)(m2)-1; i++ {
        totalDays2 += monthDays[i]
    }

    totalDays2 += leapYears(b)

    // Number of days between two days
    days = totalDays2 - totalDays1

    // calculating hour, minutes,
    // seconds differences
    hours = h2 - h1
    minutes = min2 - min1
    seconds = s2 - s1

    // if seconds difference goes below 0,
    // add 60 and decrement number of minutes
    if seconds < 0 {
        seconds += 60
        minutes--
    }

    // performing similar operations
    // on minutes and hours
    if minutes < 0 {
        minutes += 60
        hours--
    }

    // performing similar operations
    // on hours and days
    if hours < 0 {
        hours += 24
        days--
    }

    return days, hours, minutes, seconds

}

// Driver code

func main() {

    // Syntax for time date:
    // d := time.Date(year, month, days, hours,
    // minutes, seconds, nanoseconds, timeZone)

    date1 := time.Date(2020, 4, 27, 23, 35, 0, 0, time.UTC)
    date2 := time.Date(2018, 5, 12, 12, 43, 23, 0, time.UTC)

    // if date1 occurs after date2 then
    // swap days since absolute
    // difference is being calculated
    if date1.After(date2) {
        date1, date2 = date2, date1
    }
    // Calling function and getting
    // difference between two dates
    days, hours, minutes, seconds := getDifference(date1, date2)

    // Printing the difference
    fmt.Printf("%v days, %v hours, %v minutes, %v seconds",
                             days, hours, minutes, seconds)

}

Output:

716 days, 10 hours, 51 minutes, 37 seconds