    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