# A date, composed by a `year`, a `month` and a `day`
class Date
	super Comparable
	redef type OTHER: Date

	# Year, ex: 1989
	var year: Int

	# Month as an integer, `1` for January, `2` for February, etc.
	var month: Int

	# Day of the month
	var day: Int

	# UTC time zone
	#
	# FIXME this value is not yet applied
	var time_zone = "Z"

	# The date of this day
	init today do
		var tm = new Tm.localtime
		init(1900 + tm.year, tm.mon + 1, tm.mday)
	end

	# `self` formatted according to ISO 8601
	redef fun to_s do return "{year}-{month}-{day}"

	# Difference in days between `self` and `other`
	fun diff_days(other: Date): Int
	do
		var y_out = year - other.year
		y_out = y_out * 365
		var m_out = month - other.month
		m_out = m_out * 30 # FIXME
		return day - other.day + m_out + y_out
	end

	# Difference in months between `self` and `other`
	fun diff_months(other: Date): Int
	do
		var y_out = year - other.year
		y_out = y_out * 12
		return month - other.month + y_out
	end

	# Difference in years between `self` and `other`
	fun diff_years(other: Date): Int do return year - other.year

	redef fun ==(d) do return d isa Date and self.diff_days(d) == 0

	redef fun hash do return year + month * 1024 + day * 2048

	redef fun <(d) do return self.diff_days(d) < 0

	# Is `self` is between the years of `a` and `b`?
	private fun is_between_years(a, b: Date): Bool
	do
		return (a.year > year and b.year < year) or (b.year > year and a.year < year) or (a.year == year or b.year == year)
	end

	# Is `self` is between the months of `a` and `b`?
	private fun is_between_months(a, b: Date) : Bool
	do
		if not self.is_between_years(a,b) then return false
		return (a.month > month and b.month < month) or (b.month > month and a.month < month) or (a.month == month or b.month == month)
	end

	# Is `self` between `a` and `b`?
	redef fun is_between(a, b)
	do
		if not self.is_between_months(a, b) then return false
		return (a.day > day and b.day < day) or (b.day > day and a.day < day) or (a.day == day or b.day == day)
	end
end