package datetime

import (
	"math"
	"time"
)

// DiffInYears retourne (t1 - t2) exprimé en années.
func DiffInYears(t1, t2 time.Time) int64 {
	y1, m1, d1 := t1.Date()
	y2, m2, d2 := t2.Date()

	dy, dm, dd := y1-y2, m1-m2, d1-d2
	if dm < 0 || (dm == 0 && dd < 0) {
		dy--
	}
	if dy < 0 && (dd != 0 || dm != 0) {
		dy++
	}

	return int64(dy)
}

// DiffInMonths retourne (t1 - t2) exprimé en mois.
func DiffInMonths(t1, t2 time.Time) int64 {
	y1, m1, d1 := t1.Date()
	y2, m2, d2 := t2.Date()

	dy, dm, dd := y1-y2, m1-m2, d1-d2
	if dd < 0 {
		dm--
	}
	if dy == 0 && dm == 0 {
		return int64(dm)
	}
	if dy == 0 && dm != 0 && dd != 0 {
		dh := abs(DiffInHours(t1, t2))
		if int(dh) < DaysInMonth(t1)*HoursPerDay {
			return int64(0)
		}
		return int64(dm)
	}

	return int64(dy*MonthsPerYear + int(dm))
}

// DiffInWeeks retourne (t1 - t2) exprimé en semaines.
func DiffInWeeks(t1, t2 time.Time) int64 {
	return int64(math.Floor(float64(DiffInSeconds(t1, t2)) / float64(SecondsPerWeek)))
}

// DiffInDays retourne (t1 - t2) exprimé en jours.
func DiffInDays(t1, t2 time.Time) int64 {
	return int64(math.Floor(float64(DiffInSeconds(t1, t2)) / float64(SecondsPerDay)))
}

// DiffInHours retourne (t1 - t2) exprimé en heures.
func DiffInHours(t1, t2 time.Time) int64 {

	return DiffInSeconds(t1, t2) / SecondsPerHour
}

// DiffInMinutes retourne (t1 - t2) exprimé en minutes.
func DiffInMinutes(t1, t2 time.Time) int64 {

	return DiffInSeconds(t1, t2) / SecondsPerMinute
}

// DiffInSeconds retourne (t1 - t2) exprimé en secondes.
func DiffInSeconds(t1, t2 time.Time) int64 {
	return t1.Unix() - t2.Unix()
}