indexing
	description: "Durations of date"
	legal: "See notice at end of class."
	status: "See notice at end of class."
	date: "$Date: 2006-01-22 18:25:44 -0800 (Sun, 22 Jan 2006) $"
	revision: "$Revision: 56675 $"
	access: date

class interface
	DATE_DURATION

create 
	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 -- 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

	date_default_format_string: STRING_8
			-- Default output format for dates
			-- (from DATE_CONSTANTS)

	date_time_tools: DATE_TIME_TOOLS
			-- Tools for outputting dates and times in different formats
			-- (from TIME_UTILITY)

	days_in_i_th_month (i, y: INTEGER_32): INTEGER_32
			-- Number of days in the `i' th month at year `y' 
			-- (from DATE_CONSTANTS)
		require -- from DATE_CONSTANTS
			i_large_enough: i >= 1
			i_small_enough: i <= months_in_year

	days_in_leap_year: INTEGER_32 is 366
			-- Number of days in a leap year 
			-- (from DATE_CONSTANTS)

	days_in_non_leap_year: INTEGER_32 is 365
			-- Number of days in a non-leap year
			-- (from DATE_CONSTANTS)

	days_in_week: INTEGER_32 is 7
			-- Number of days in a week
			-- (from DATE_CONSTANTS)

	days_text: ARRAY [STRING_8]
			-- Short text representation of days
			-- (from DATE_CONSTANTS)

	default_format_string: STRING_8
			-- Default output format string
			-- (from TIME_UTILITY)

	generating_type: STRING_8
			-- Name of current object's generating type
			-- (type of which it is a direct instance)
			-- (from ANY)

	generator: STRING_8
			-- Name of current object's generating class
			-- (base class of the type of which it is a direct instance)
			-- (from ANY)

	long_days_text: ARRAY [STRING_8]
			-- Long text representation of days
			-- (from DATE_CONSTANTS)

	long_months_text: ARRAY [STRING_8]
			-- Long text representation of months
			-- (from DATE_CONSTANTS)

	max_weeks_in_year: INTEGER_32 is 53
			-- Maximun number of weeks in a year 
			-- (from DATE_CONSTANTS)

	months_in_year: INTEGER_32 is 12
			-- Number of months in year
			-- (from DATE_CONSTANTS)

	months_text: ARRAY [STRING_8]
			-- Short text representation of months
			-- (from DATE_CONSTANTS)

	zero: DATE_DURATION
			-- Neutral element for "+" and "-"
		require -- from  GROUP_ELEMENT
			True
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
		ensure then
			definite: Result.definite
	
feature -- Comparison

	frozen deep_equal (some: ANY; other: like arg #1): BOOLEAN
			-- Are `some' and `other' either both void
			-- or attached to isomorphic object structures?
			-- (from ANY)
		ensure -- from ANY
			shallow_implies_deep: standard_equal (some, other) implies Result
			both_or_none_void: (some = Void) implies (Result = (other = Void))
			same_type: (Result and (some /= Void)) implies some.same_type (other)
			symmetric: Result implies deep_equal (other, some)

	frozen equal (some: ANY; other: like arg #1): BOOLEAN
			-- Are `some' and `other' either both void or attached
			-- to objects considered equal?
			-- (from ANY)
		ensure -- from ANY
			definition: Result = (some = Void and other = Void) or else ((some /= Void and other /= Void) and then some.is_equal (other))

	is_equal (other: like Current): BOOLEAN
			-- Are the current object and `other' equal?
		require -- from ANY
			other_not_void: other /= Void
		ensure -- from ANY
			symmetric: Result implies other.is_equal (Current)
			consistent: standard_is_equal (other) implies Result
		ensure then
			result_definition: Result = (year = other.year and then month = other.month and then day = other.day)

	frozen standard_equal (some: ANY; other: like arg #1): BOOLEAN
			-- Are `some' and `other' either both void or attached to
			-- field-by-field identical objects of the same type?
			-- Always uses default object comparison criterion.
			-- (from ANY)
		ensure -- from ANY
			definition: Result = (some = Void and other = Void) or else ((some /= Void and other /= Void) and then some.standard_is_equal (other))

	frozen standard_is_equal (other: like Current): BOOLEAN
			-- Is `other' attached to an object of the same type
			-- as current object, and field-by-field identical to it?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		ensure -- from ANY
			same_type: Result implies same_type (other)
			symmetric: Result implies other.standard_is_equal (Current)

	infix "<" (other: like Current): BOOLEAN
			-- Is the current object smaller than `other'?
			-- It is impossible to compare not definite duration.
		require -- from PART_COMPARABLE
			other_exists: other /= Void
		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 Result = False

	infix "<=" (other: like Current): BOOLEAN
			-- Is current object less than or equal to `other'?
			-- (from PART_COMPARABLE)
		require -- from PART_COMPARABLE
			other_exists: other /= Void

	infix ">" (other: like Current): BOOLEAN
			-- Is current object greater than `other'?
			-- (from PART_COMPARABLE)
		require -- from PART_COMPARABLE
			other_exists: other /= Void

	infix ">=" (other: like Current): BOOLEAN
			-- Is current object greater than or equal to `other'?
			-- (from PART_COMPARABLE)
		require -- from PART_COMPARABLE
			other_exists: other /= Void
	
feature -- Status report

	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

	conforms_to (other: ANY): BOOLEAN
			-- Does type of current object conform to type
			-- of `other' (as per Eiffel: The Language, chapter 13)?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void

	definite: BOOLEAN
			-- Is the duration is independant 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))

	has_origin_date: BOOLEAN
			-- Has `origin date' been set?

	is_leap_year (y: INTEGER_32): BOOLEAN
			-- Is year `y' a leap year? 
			-- (from DATE_CONSTANTS)

	is_negative: BOOLEAN
			-- Is duration negative?
			-- (from DURATION)

	is_positive: BOOLEAN
			-- Is duration positive?

	is_zero: BOOLEAN
			-- Is duration zero?
			-- (from DURATION)

	same_type (other: ANY): BOOLEAN
			-- Is type of current object identical to type of `other'?
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		ensure -- from ANY
			definition: Result = (conforms_to (other) and other.conforms_to (Current))
	
feature -- Status setting

	set_origin_date (d: DATE)
			-- Set origin_date to `d'.
		ensure
			origin_date_set: origin_date = d
	
feature -- Element change

	prefix "+": like Current
			-- Unary plus
			-- (from DURATION)
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
			result_definition: Result.is_equal (Current)

	infix "-" (other: like Current): like Current
			-- Difference with `other'
			-- (from DURATION)
		require -- from GROUP_ELEMENT
			other_exists: other /= Void
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
	
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_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

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

	copy (other: like Current)
			-- Update current object using fields of object attached
			-- to `other', so as to yield equal objects.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		ensure -- from ANY
			is_equal: is_equal (other)

	frozen deep_copy (other: like Current)
			-- Effect equivalent to that of:
			--		copy (`other' . deep_twin)
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
		ensure -- from ANY
			deep_equal: deep_equal (Current, other)

	frozen deep_twin: like Current
			-- New object structure recursively duplicated from Current.
			-- (from ANY)
		ensure -- from ANY
			deep_equal: deep_equal (Current, Result)

	frozen standard_copy (other: like Current)
			-- Copy every field of `other' onto corresponding field
			-- of current object.
			-- (from ANY)
		require -- from ANY
			other_not_void: other /= Void
			type_identity: same_type (other)
		ensure -- from ANY
			is_standard_equal: standard_is_equal (other)

	frozen standard_twin: like Current
			-- New object field-by-field identical to `other'.
			-- Always uses default copying semantics.
			-- (from ANY)
		ensure -- from ANY
			standard_twin_not_void: Result /= Void
			equal: standard_equal (Result, Current)

	frozen twin: like Current
			-- New object equal to `Current'
			-- twin calls copy; to change copying/twining semantics, redefine copy.
			-- (from ANY)
		ensure -- from ANY
			twin_not_void: Result /= Void
			is_equal: Result.is_equal (Current)
	
feature -- Basic operations

	frozen default: like Current
			-- Default value of object's type
			-- (from ANY)

	frozen default_pointer: POINTER
			-- Default value of type `POINTER'
			-- (Avoid the need to write `p'.default for
			-- some `p' of type `POINTER'.)
			-- (from ANY)

	default_rescue
			-- Process exception for routines with no Rescue clause.
			-- (Default: do nothing.)
			-- (from ANY)

	frozen do_nothing
			-- Execute a null action.
			-- (from ANY)

	infix "+" (other: like Current): like Current
			-- Sum of current object with `other'
		require -- from GROUP_ELEMENT
			other_exists: other /= Void
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
			commutative: Result.is_equal (other + Current)
		ensure then
			origin_equal: equal (origin_date, Result.origin_date)

	prefix "-": like Current
			-- Unary minus
		require -- from  GROUP_ELEMENT
			True
		ensure -- from GROUP_ELEMENT
			result_exists: Result /= Void
			result_definition: (Result + Current).is_equal (zero)
		ensure then
			origin_equal: equal (origin_date, Result.origin_date)
	
feature -- Attribute

	day: INTEGER_32

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

	month: INTEGER_32

	origin_date: DATE
			-- Origin date of duration

	year: INTEGER_32
	
feature -- Element Change

	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

	set_date (y, m, d: INTEGER_32)
			-- Set year with `y', month with `m' and day with `d'.
		require -- from DATE_MEASUREMENT
			d_large_enough: d >= 1
			m_large_enough: m >= 1
			m_small_enough: m <= months_in_year
			d_small_enough: d <= days_in_i_th_month (m, y)
		ensure -- from DATE_MEASUREMENT
			day_set: day = d
			month_set: month = m
			year_set: year = y

	set_day (d: INTEGER_32)
			-- Set day to `d'.
		require -- from DATE_MEASUREMENT
			d_large_enough: d >= 1
			d_small_enough: d <= days_in_month
		ensure -- from DATE_MEASUREMENT
			day_set: day = d

	set_month (m: INTEGER_32)
			-- Set month to `m'.
		require -- from DATE_MEASUREMENT
			m_large_enough: m >= 1
			m_small_enough: m <= months_in_year
			d_small_enough: day <= days_in_i_th_month (m, year)
		ensure -- from DATE_MEASUREMENT
			month_set: month = m

	set_year (y: INTEGER_32)
			-- Set year to `y'.
		require -- from DATE_MEASUREMENT
			can_not_cut_29th_feb: day <= days_in_i_th_month (month, y)
		ensure -- from DATE_MEASUREMENT
			year_set: year = y

	year_add (y: INTEGER_32)
			-- Add `y' years to `Current'.
		ensure
			year_set: year = old year + y
	
feature -- Output

	io: STD_FILES
			-- Handle to standard file setup
			-- (from ANY)

	out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- Was declared in ANY as synonym of tagged_out.
			-- (from ANY)

	print (some: ANY)
			-- Write terse external representation of `some'
			-- on standard output.
			-- (from ANY)

	frozen tagged_out: STRING_8
			-- New string containing terse printable representation
			-- of current object
			-- Was declared in ANY as synonym of out.
			-- (from ANY)
	
feature -- Platform

	operating_environment: OPERATING_ENVIRONMENT
			-- Objects available from the operating system
			-- (from ANY)
	
feature -- Status Report

	days_in_month: INTEGER_32
			-- Number of days in month 'month'.
			-- (from DATE_MEASUREMENT)
		ensure -- from DATE_MEASUREMENT
			positive_result: Result > 0
	
invariant
	equal_signs: (has_origin_date and then canonical (origin_date)) implies (day >= 0 and month >= 0 and year >= 0) or (day <= 0 and month <= 0 and year <= 0)

		-- from DURATION
	sign_correctness: is_positive xor is_negative xor is_zero

		-- from ANY
	reflexive_equality: standard_is_equal (Current)
	reflexive_conformance: conforms_to (Current)

		-- from GROUP_ELEMENT
	neutral_addition: Current.is_equal (Current + zero)
	self_subtraction: zero.is_equal (Current - Current)

indexing
	copyright: "Copyright (c) 1984-2006, Eiffel Software and others"
	license: "Eiffel Forum License v2 (see http://www.eiffel.com/licensing/forum.txt)"
	source: "[
		Eiffel Software
		356 Storke Road, 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