package timeext

import "time"

// YearDifference calculates the difference between two timestamps in years.
// = t1 - t2
// returns a float value
func YearDifference(t1 time.Time, t2 time.Time, tz *time.Location) float64 {

	yDelta := float64(t1.Year() - t2.Year())

	processT1 := float64(t1.Sub(TimeToYearStart(t1, tz))) / float64(TimeToYearEnd(t1, tz).Sub(TimeToYearStart(t1, tz)))
	processT2 := float64(t2.Sub(TimeToYearStart(t2, tz))) / float64(TimeToYearEnd(t2, tz).Sub(TimeToYearStart(t2, tz)))

	return yDelta + (processT1 - processT2)
}

// MonthDifference calculates the difference between two timestamps in months.
// = t1 - t2
// returns a float value
func MonthDifference(t1 time.Time, t2 time.Time) float64 {

	yDelta := float64(t1.Year() - t2.Year())
	mDelta := float64(t1.Month() - t2.Month())

	dDelta := float64(0)

	t1MonthDays := DaysInMonth(t1)
	t2MonthDays := DaysInMonth(t2)

	if t2.Year() > t1.Year() || (t2.Year() == t1.Year() && t2.Month() > t1.Month()) {
		dDelta -= 1
		dDelta += float64(t1MonthDays-t1.Day()) / float64(t1MonthDays)
		dDelta += float64(t2.Day()) / float64(t2MonthDays)
	} else if t2.Year() < t1.Year() || (t2.Year() == t1.Year() && t2.Month() < t1.Month()) {
		dDelta -= 1
		dDelta += float64(t1.Day()) / float64(t1MonthDays)
		dDelta += float64(t2MonthDays-t2.Day()) / float64(t2MonthDays)
	} else {
		dDelta += float64(t1.Day()-t2.Day()) / float64(t1MonthDays)
	}

	return yDelta*12 + mDelta + dDelta
}