Golang calculating max time

main.go

package main

import (
	"fmt"
	"time"
)

// hoursSince returns how many hours passed from given date.
// for Time 0 (time.Time{}), it returns 0.
func hoursSince(d time.Time) int {
	// Get current year
	y, _, _ := d.Date()

	// Golang time starts from 1
	y = y - 1

	// Hours in non-leap years
	normalHours := y * 365 * 24

	// Hours in leap years
	leapHours := (y / 4) * 24

	// Calculate remaining hours since beginning of the year and remove hours in Time 0.
	remainingHours := int(d.Sub(time.Date(y, 0, 0, 0, 0, 0, 0, time.UTC)).Round(time.Hour).Hours()) - int(time.Time{}.Sub(time.Date(0, 0, 0, 0, 0, 0, 0, time.UTC)).Round(time.Hour).Hours())

	return normalHours + leapHours + remainingHours
}

func main() {
	// Snapshot current time
	t := time.Now()

	// Max golang date before it overflows
	// Calculate max date golang can handle. AddDate is easier to use than time.Date() since we don't have to calculate number of months
	tMax := time.Time{}.AddDate(292277026853, 0, 312).Add((time.Duration(7) * time.Hour) + (time.Duration(15) * time.Second) + (time.Duration(999) * time.Millisecond) + (time.Duration(999) * time.Microsecond) + (time.Duration(999) * time.Nanosecond))

	// h represents max number of hours we can add to a current time before it overflows
	h := hoursSince(tMax) - hoursSince(t) - 3 // +1

	// If hours now + added hours are bigged than max time, panic
	if hoursSince(t)+h > hoursSince(tMax)-3 {
		panic(fmt.Sprintf("Added time overflows the universe, max value possible to add is %d", hoursSince(tMax)-2))
	}

	fmt.Printf("Now is %s\n", t)
	fmt.Println()

	fmt.Printf("Attempting to add %d hours\n", h)
	fmt.Println()

	// First, calculate how many days we have to add
	days := h / 24
	fmt.Printf("%d days to add\n", days)

	// Calculate how many years we have in calculated days, this considers leap years as well
	years := (days / ((365 * 4) + 1)) * 4

	// Since we have years now, get remaining days we have left
	days = days % ((365 * 4) + 1)
	fmt.Printf("Adding %d years, %d days\n", years, days)

	// Add calculated years and days to current date
	t = t.AddDate(years, 0, days)
	fmt.Printf("Now is %s\n", t)
	fmt.Println()

	// There are some hours left to add after /24 division, get them with module and add as well
	h = h % 24
	fmt.Printf("%d hours remaining to add\n", h)
	fmt.Println()

	fmt.Printf("Adding %d hours\n", h)
	// We can't simply put entire h into time.Duration() as time.Duration overflows only after 290 years
	t = t.Add(time.Duration(h) * time.Hour)
	fmt.Printf("Now is %s\n", t)
}