note
	description: "Durations of date"
	legal: "See notice at end of class."
	status: "See notice at end of class."
	date: "$Date: 2017-03-29 12:26:46 +0000 (Wed, 29 Mar 2017) $"
	revision: "$Revision: 100065 $"
	access: date

class interface
	DATE_DURATION

create 
	make,
	make_by_days

feature -- Initialization

	make (y, m, d: INTEGER_32)
			-- Set year, month and day to y, m and d respectively.
		ensure
			year_set: year = y
			month_set: month = m
			day_set: day = d

	make_by_days (d: INTEGER_32)
			-- Set day to d.
			-- The duration is definite
		ensure
			day_set: day = d
			definite_duration: definite
	
feature -- Access

	zero: like Current
			-- Neutral element for "+" and "-"
		ensure then
			definite: Result.definite
	
feature -- Attribute

	day: INTEGER_32
			-- Number of days associated with current object

	month: INTEGER_32
			-- Number of monthes associated with current object

	year: INTEGER_32
			-- Number of years associated with current object

	origin_date: detachable DATE
			-- Origin date of duration

	days_count: INTEGER_32
			-- Number of days in duration
		require
			origin_date_set: has_origin_date
	
feature -- Comparison

	is_less alias "<" (other: like Current): BOOLEAN
			-- Is the current object smaller than other?
			-- It is impossible to compare not definite duration.
		ensure then
			definite_duration: (definite and then other.definite) implies Result = (day < other.day)
			non_definite_duration: (not definite or else not other.definite) implies not Result

	is_equal (other: like Current): BOOLEAN
			-- Are the current object and other equal?
		ensure then
			result_definition: Result = (year = other.year and then month = other.month and then day = other.day)
	
feature -- Status report

	definite: BOOLEAN
			-- Is the duration is independent of the date
			-- on which it applies? (use of day only)?
			-- or not (use of year, month and day)?
		ensure
			result_definition: Result = ((year = 0) and then (month = 0))

	canonical (date: DATE): BOOLEAN
			-- Is duration expressed minimally for adding to date, i.e.
			-- 	If addition will yield a date after date, then:
			--		year positive,
			--		month between 0 and Months_in_year - 1,
			--		day between 0 and (number of days of the month before
			--		the yielded) - 1?
			-- 	If addition will yield a date before date, then:
			--		year negative,
			--		month between 1 - Months_in_year and 0,
			--		day between (number of days of the month before the
			--		yielded) and 0?
		require
			date_exist: date /= Void

	is_positive: BOOLEAN
			-- Is duration positive?

	has_origin_date: BOOLEAN
			-- Has origin date been set?
	
feature -- Status setting

	set_origin_date (d: detachable DATE)
			-- Set origin_date to d.
		ensure
			origin_date_set: origin_date = d
	
feature -- Element Change

	set_day (d: INTEGER_32)
			-- Set day to d.

	set_month (m: INTEGER_32)
			-- Set month to m.

	set_year (y: INTEGER_32)
			-- Set year to y.

	set_date (y, m, d: INTEGER_32)
			-- Set year with y, month with m and day with d.

	day_add (d: INTEGER_32)
			-- Add d days to Current.
		ensure
			day_set: day = old day + d

	month_add (m: INTEGER_32)
			-- Add m months to Current.
		ensure
			month_set: month = old month + m

	year_add (y: INTEGER_32)
			-- Add y years to Current.
		ensure
			year_set: year = old year + y
	
feature -- Basic operations

	plus alias "+" (other: like Current): like Current
			-- Sum of current object with other
		ensure then
			origin_equal: equal (origin_date, Result.origin_date)

	opposite alias "-": like Current
			-- Unary minus
		ensure then
			origin_equal: equal (origin_date, Result.origin_date)
	
feature -- Conversion

	to_canonical (start_date: DATE): like Current
			-- A new duration, equivalent to current one
			-- and canonical for date
		require
			start_date_not_void: start_date /= Void
		ensure
			canonical_result: Result.canonical (start_date)
			duration_not_changed: equal (start_date + Current, start_date + Result)

	to_definite (date: DATE)
			-- Make current duration definite.
		require
			date_exists: date /= Void
		ensure
			definite_result: definite

	to_date_time: DATE_TIME_DURATION
			-- Date-time version, with a zero time component
		ensure
			result_exists: Result /= Void
			year_set: Result.year = year
			month_set: Result.month = month
			day_set: Result.day = day
	
invariant
	equal_signs: (has_origin_date and then attached origin_date as l_origin_date and then canonical (l_origin_date)) implies (day >= 0 and month >= 0 and year >= 0) or (day <= 0 and month <= 0 and year <= 0)

note
	copyright: "Copyright (c) 1984-2017, Eiffel Software and others"
	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
	source: "[
		Eiffel Software
		5949 Hollister Ave., Goleta, CA 93117 USA
		Telephone 805-685-1006, Fax 805-685-6869
		Website http://www.eiffel.com
		Customer support http://support.eiffel.com
	]"

end -- class DATE_DURATION

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