Class DT_DATE |

    note

>     description:

>         "Dates (Gregorian calendar)"

>     library:    "Gobo Eiffel Time Library"
>     author:     "Eric Bezault <ericb@gobosoft.com>"
>     copyright:  "Copyright (c) 2000-2001, Eric Bezault and others"
>     license:    "MIT License"

    class interface

>     DT_DATE

    inherit

>     DT_ABSOLUTE_TIME
>         COMPARABLE
>         HASHABLE
>     DT_DATE_VALUE
>     DT_GREGORIAN_CALENDAR

    create

>     make (y, m, d: INTEGER)
>             -- Create a new date.
>         require
>             m_large_enough: m >= January
>             m_small_enough: m <= December
>             d_large_enough: d >= 1
>             d_small_enough: d <= days_in_month (m, y)
>         ensure
>             year_set: year = y
>             month_set: month = m
>             day_set: day = d

>     make_from_day_count (d: INTEGER)
>             -- Create a new date from the number
>             -- of days since epoch (1 Jan 1970).
>         ensure
>             day_count_set: day_count = d

    feature -- Access

>     year: INTEGER
>             -- Year
>             -- (From DT_DATE_VALUE.)

>     month: INTEGER
>             -- Month
>             -- (From DT_DATE_VALUE.)
>         ensure
>             month_large_enough: Result >= January
>             month_small_enough: Result <= December

>     day: INTEGER
>             -- Day
>             -- (From DT_DATE_VALUE.)
>         ensure
>             day_large_enough: Result >= 1
>             day_small_enough: Result <= days_in_month (month, year)

>     year_day: INTEGER
>             -- Day in current year
>         ensure
>             non_leap_year: not is_leap_year implies (Result >= 1 and Result <= Days_in_year)
>             leap_year: is_leap_year implies (Result >= 1 and Result <= Days_in_leap_year)

>     week_day: INTEGER
>             -- Day in current week
>         ensure
>             valid_day: Result >= Sunday and Result <= Saturday

>     infix "-" (other: like Current): like duration
>             -- Duration between other and Current
>             -- (From DT_ABSOLUTE_TIME.)
>         require
>             other_not_void: other /= Void
>         ensure
>             duration_not_void: Result /= Void
>             definition: (other + Result).is_equal (Current)

>     infix "+" (a_duration: like duration): like Current
>             -- Addition of a_duration to Current
>             -- (Create a new object at each call.)
>             -- (From DT_ABSOLUTE_TIME.)
>         require
>             a_duration_not_void: a_duration /= Void
>         ensure
>             addition_not_void: Result /= Void

>     infix "&d" (a_duration: like date_duration): like Current
>             -- Addition of a_duration to current date
>             -- (Create a new object at each call.)
>         require
>             a_duration_not_void: a_duration /= Void
>         ensure
>             addition_not_void: Result /= Void

>     duration (other: like Current): DT_DATE_DURATION
>             -- Duration between other and curent date
>             -- (From DT_ABSOLUTE_TIME.)
>         require
>             other_not_void: other /= Void
>         ensure
>             duration_not_void: Result /= Void
>             definition: (other + Result).is_equal (Current)
>             definite_duration: Result.is_definite

>     canonical_duration (other: like Current): like duration
>             -- Canonical duration between other and current date
>         require
>             other_not_void: other /= Void
>         ensure
>             duration_not_void: Result /= Void
>             canonical_duration: Result.is_canonical (other)
>             definition: (other + Result).is_equal (Current)

>     date_duration (other: like Current): DT_DATE_DURATION
>             -- Duration between other and current date
>         require
>             other_not_void: other /= Void
>         ensure
>             date_duration_not_void: Result /= Void
>             definite_duration: Result.is_definite
>             definition: (other &d Result).is_equal (Current)

>     day_count: INTEGER
>             -- Number of days since epoch (1 Jan 1970)

>     days_in_current_month: INTEGER
>             -- Number of days in current month
>         ensure
>             at_least_one: Result >= 1
>             max_days_in_month: Result <= Max_days_in_month

>     days_in_previous_month: INTEGER
>             -- Number of days in previous month
>         ensure
>             at_least_one: Result >= 1
>             max_days_in_month: Result <= Max_days_in_month

>     hash_code: INTEGER
>             -- Hash code value
>             -- (From HASHABLE.)
>         ensure
>             good_hash_value: Result >= 0

    feature -- Status report

>     is_leap_year: BOOLEAN
>             -- Is year a leap year?

    feature -- Comparison

>     infix "<" (other: like Current): BOOLEAN
>             -- Is current date before other on the time axis?
>             -- (From COMPARABLE.)
>         require
>             other_exists: other /= Void
>         ensure
>             asymmetric: Result implies not (other < Current)

>     infix "<=" (other: like Current): BOOLEAN
>             -- Is current object less than or equal to other?
>             -- (From COMPARABLE.)
>         require
>             other_exists: other /= Void
>         ensure
>             definition: Result = ((Current < other) or is_equal (other))

>     infix ">=" (other: like Current): BOOLEAN
>             -- Is current object greater than or equal to other?
>             -- (From COMPARABLE.)
>         require
>             other_exists: other /= Void
>         ensure
>             definition: Result = (other <= Current)

>     infix ">" (other: like Current): BOOLEAN
>             -- Is current object greater than other?
>             -- (From COMPARABLE.)
>         require
>             other_exists: other /= Void
>         ensure
>             definition: Result = (other < Current)

>     is_equal (other: like Current): BOOLEAN
>             -- Is other attached to an object considered equal
>             -- to current object?
>             -- (From GENERAL.)
>         require
>             other_not_void: other /= Void
>         ensure
>             symmetric: Result implies other.is_equal (Current)
>             consistent: standard_is_equal (other) implies Result
>             trichotomy: Result = (not (Current < other) and not (other < Current))

>     max (other: like Current): like Current
>             -- The greater of current object and other
>             -- (From COMPARABLE.)
>         require
>             other_exists: other /= Void
>         ensure
>             current_if_not_smaller: (Current >= other) implies (Result = Current)
>             other_if_smaller: (Current < other) implies (Result = other)

>     min (other: like Current): like Current
>             -- The smaller of current object and other
>             -- (From COMPARABLE.)
>         require
>             other_exists: other /= Void
>         ensure
>             current_if_not_greater: (Current <= other) implies (Result = Current)
>             other_if_greater: (Current > other) implies (Result = other)

>     three_way_comparison (other: like Current): INTEGER
>             -- If current object equal to other, 0; if smaller,
>             -- -1; if greater, 1.
>             -- (From COMPARABLE.)
>         require
>             other_exists: other /= Void
>         ensure
>             equal_zero: (Result = 0) = is_equal (other)
>             smaller_negative: (Result = -1) = (Current < other)
>             greater_positive: (Result = 1) = (Current > other)

    feature -- Duplication

>     copy (other: like Current)
>             -- Copy other to current date.
>             -- (From GENERAL.)
>         require
>             other_not_void: other /= Void
>             type_identity: same_type (other)
>         ensure
>             is_equal: is_equal (other)

    feature -- Setting

>     set_date (a_date: DT_DATE)
>             -- Set year, month and day from a_date.
>         require
>             a_date_not_void: a_date /= Void
>         ensure
>             year_set: year = a_date.year
>             month_set: month = a_date.month
>             day_set: day = a_date.day

>     set_year_month_day (y, m, d: INTEGER)
>             -- Set year to y, month to m and day to d.
>         require
>             m_large_enough: m >= January
>             m_small_enough: m <= December
>             d_large_enough: d >= 1
>             d_small_enough: d <= days_in_month (m, y)
>         ensure
>             year_set: year = y
>             month_set: month = m
>             day_set: day = d

>     set_year (y: INTEGER)
>             -- Set year to y.
>         require
>             leap_year_aware: day <= days_in_month (month, y)
>         ensure
>             year_set: year = y
>             same_month: month = old month
>             same_day: day = old day

>     set_month (m: INTEGER)
>             -- Set month to m.
>         require
>             m_large_enough: m >= January
>             m_small_enough: m <= December
>             leap_year_aware: day <= days_in_month (m, year)
>         ensure
>             month_set: month = m
>             same_year: year = old year
>             same_day: day = old day

>     set_day (d: INTEGER)
>             -- Set day to d.
>         require
>             d_large_enough: d >= 1
>             d_small_enough: d <= days_in_month (month, year)
>         ensure
>             day_set: day = d
>             same_year: year = old year
>             same_month: month = old month

>     set_day_count (d: INTEGER)
>             -- Set day_count to d.
>         ensure
>             day_count_set: day_count = d

    feature -- Element change

>     add_duration (a_duration: like duration)
>             -- Add a_duration to current date.
>             -- (Add a_duration.year and a_duration.month first, then
>             -- set day to day.min (days_in_month (new_month, new_year))
>             -- and finally add a_duration.day.)
>             -- (From DT_ABSOLUTE_TIME.)
>         require
>             a_duration_not_void: a_duration /= Void

>     add_date_duration (a_duration: like date_duration)
>             -- Add a_duration to current date.
>             -- (Add a_duration.year and a_duration.month first, then
>             -- set day to day.min (days_in_month (new_month, new_year))
>             -- and finally add a_duration.day.)
>         require
>             a_duration_not_void: a_duration /= Void

>     add_years_months_days (y, m, d: INTEGER)
>             -- Add y years, m months and d days to current date.
>             -- (Add y and m first, then set day to
>             -- day.min (days_in_month (new_month, new_year))
>             -- and finally add d.)

>     add_years (y: INTEGER)
>             -- Add y years to current date.
>         ensure
>             day_adjusted: day = (old day).min (days_in_month (month, year))

>     add_months (m: INTEGER)
>             -- Add m months to current date.
>         ensure
>             day_adjusted: day = (old day).min (days_in_month (month, year))

>     add_days (d: INTEGER)
>             -- Add d days to current date.

    feature -- Output

>     out: STRING
>             -- Printable representation (yyyy/mm/dd)
>             -- (From GENERAL.)
>         ensure
>             out_not_void: Result /= Void

>     date_out: STRING
>             -- Printable representation (yyyy/mm/dd)
>             -- (From DT_DATE_VALUE.)
>         ensure
>             date_out_not_void: Result /= Void

>     append_to_string (a_string: STRING)
>             -- Append printable representation
>             -- (yyyy/mm/dd) to a_string.
>             -- (From DT_DATE_VALUE.)
>         require
>             a_string_not_void: a_string /= Void

>     append_date_to_string (a_string: STRING)
>             -- Append printable representation
>             -- (yyyy/mm/dd) to a_string.
>             -- (From DT_DATE_VALUE.)
>         require
>             a_string_not_void: a_string /= Void

    feature -- Year

>     leap_year (y: INTEGER): BOOLEAN
>             -- Is y a leap year?
>             -- (From DT_GREGORIAN_CALENDAR.)

>     Months_in_year: INTEGER
>             -- Number of months in a year
>             -- (From DT_GREGORIAN_CALENDAR.)
>         ensure
>             definition: Result = (December - Januray + 1)

>     Days_in_year: INTEGER
>     Days_in_leap_year: INTEGER
>             -- Number of days in a (leap) year
>             -- (From DT_GREGORIAN_CALENDAR.)

>     Days_in_400_years: INTEGER
>     Days_in_100_years: INTEGER
>     Days_in_4_years: INTEGER
>     Days_in_3_years: INTEGER
>     Days_in_3_leap_years: INTEGER
>     Days_in_2_years: INTEGER
>     Days_in_2_leap_years: INTEGER
>             -- Number of days in multiple years
>             -- (From DT_GREGORIAN_CALENDAR.)

    feature -- Month

>     January: INTEGER
>     February: INTEGER
>     March: INTEGER
>     April: INTEGER
>     May: INTEGER
>     June: INTEGER
>     July: INTEGER
>     August: INTEGER
>     September: INTEGER
>     October: INTEGER
>     November: INTEGER
>     December: INTEGER
>             -- Months
>             -- (From DT_GREGORIAN_CALENDAR.)

>     days_in_month (m, y: INTEGER): INTEGER
>             -- Number of days in month m of year y
>             -- (From DT_GREGORIAN_CALENDAR.)
>         require
>             m_large_enough: m >= January
>             m_small_enough: m <= December
>         ensure
>             at_least_one: Result >= 1
>             max_days_in_month: Result <= Max_days_in_month

>     Max_days_in_month: INTEGER
>             -- Maximum number of days in a month
>             -- (From DT_GREGORIAN_CALENDAR.)

>     days_at_month (m, y: INTEGER): INTEGER
>             -- Number of days from beginning of year
>             -- y until beginning of month m
>             -- (From DT_GREGORIAN_CALENDAR.)
>         require
>             m_large_enough: m >= January
>             m_small_enough: m <= December
>         ensure
>             days_positive: Result >= 0

    feature -- Week day

>     Sunday: INTEGER
>     Monday: INTEGER
>     Tuesday: INTEGER
>     Wednesday: INTEGER
>     Thursday: INTEGER
>     Friday: INTEGER
>     Saturday: INTEGER
>             -- Week days
>             -- (From DT_GREGORIAN_CALENDAR.)

>     Days_in_week: INTEGER
>             -- Number of days in a week
>             -- (From DT_GREGORIAN_CALENDAR.)
>         ensure
>             definition: Result = (Saturday - Sunday + 1)

>     next_day (d: INTEGER): INTEGER
>             -- Week day after d
>             -- (From DT_GREGORIAN_CALENDAR.)
>         require
>             d_large_enough: d >= Sunday
>             d_small_enough: d <= Saturday
>         ensure
>             sunday_definition: (d = Sunday) implies (Result = Monday)
>             monday_definition: (d = Monday) implies (Result = Tuesday)
>             tuesday_definition: (d = Tuesday) implies (Result = Wednesday)
>             wednesday_definition: (d = Wednesday) implies (Result = Thursday)
>             thursday_definition: (d = Thursday) implies (Result= Friday)
>             friday_definition: (d = Friday) implies (Result = Saturday)
>             saturday_definition: (d = Saturday) implies (Result = Sunday)

>     previous_day (d: INTEGER): INTEGER
>             -- Week day before d
>             -- (From DT_GREGORIAN_CALENDAR.)
>         require
>             d_large_enough: d >= Sunday
>             d_small_enough: d <= Saturday
>         ensure
>             sunday_definition: (d = Sunday) implies (Result = Saturday)
>             monday_definition: (d = Monday) implies (Result = Sunday)
>             tuesday_definition: (d = Tuesday) implies (Result = Monday)
>             wednesday_definition: (d = Wednesday) implies (Result = Tuesday)
>             thursday_definition: (d = Thursday) implies (Result= Wednesday)
>             friday_definition: (d = Friday) implies (Result = Thursday)
>             saturday_definition: (d = Saturday) implies (Result = Friday)

    feature -- Time

>     Seconds_in_minute: INTEGER
>             -- Number of seconds in a minute
>             -- (From DT_GREGORIAN_CALENDAR.)

>     Seconds_in_hour: INTEGER
>             -- Number of seconds in an hour
>             -- (From DT_GREGORIAN_CALENDAR.)

>     Seconds_in_day: INTEGER
>             -- Number of seconds in a day
>             -- (From DT_GREGORIAN_CALENDAR.)

>     Milliseconds_in_day: INTEGER
>             -- Number of milliseconds in a day
>             -- (From DT_GREGORIAN_CALENDAR.)

>     Minutes_in_hour: INTEGER
>             -- Number of minutes in an hour
>             -- (From DT_GREGORIAN_CALENDAR.)

>     Hours_in_day: INTEGER
>             -- Number of hours in a day
>             -- (From DT_GREGORIAN_CALENDAR.)

    feature -- Epoch

>     Epoch_year: INTEGER
>     Epoch_month: INTEGER
>     Epoch_day: INTEGER
>             -- Epoch date (1 Jan 1970)
>             -- (From DT_GREGORIAN_CALENDAR.)

>     epoch_days (y, m, d: INTEGER): INTEGER
>             -- Number of days since epoch date (1 Jan 1970)
>             -- (From DT_GREGORIAN_CALENDAR.)
>         require
>             m_large_enough: m >= January
>             m_small_enough: m <= December
>             d_large_enough: d >= 1
>             d_small_enough: d <= days_in_month (m, y)

    invariant

>     irreflexive_comparison: not (Current < Current)
>         -- (From COMPARABLE.)

    end -- class DT_DATE