gramps/src/gen/lib/date.py

#
# Gramps - a GTK+/GNOME based genealogy program
#
# Copyright (C) 2000-2007  Donald N. Allingham
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, 
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#

# $Id$

"""Support for dates."""

#------------------------------------------------------------------------
#
# Python modules
#
#------------------------------------------------------------------------
from gettext import gettext as _

#------------------------------------------------------------------------
#
# Set up logging
#
#------------------------------------------------------------------------
import logging
log = logging.getLogger(".Date")

#-------------------------------------------------------------------------
#
# Gnome/GTK modules
#
#-------------------------------------------------------------------------


#------------------------------------------------------------------------
#
# Gramps modules
#
#------------------------------------------------------------------------
from gen.lib.calendar import (gregorian_sdn, julian_sdn, hebrew_sdn, 
                              french_sdn, persian_sdn, islamic_sdn, 
                              gregorian_ymd, julian_ymd, hebrew_ymd, 
                              french_ymd, persian_ymd, islamic_ymd)
import Config

#-------------------------------------------------------------------------
#
# DateError exception
#
#-------------------------------------------------------------------------
class DateError(Exception):
    """Error used to report Date errors."""
    def __init__(self, value=""):
        Exception.__init__(self)
        self.value = value

    def __str__(self):
        return self.value

class Span:
    """ Class used in date differences """
    def __init__(self, *diff_tuple):
        self.diff_tuple = diff_tuple

    def __getitem__(self, pos):
        return self.diff_tuple[pos]

    def __repr__(self):
        if self.diff_tuple[1] != 0:
            retval = ((_("%d years") % self.diff_tuple[0])+ ", " +
                      (_("%d months") % self.diff_tuple[1]))
        else:
            retval = (_("%d years") % self.diff_tuple[0])
        return retval

    def __int__(self):
        return int(self.diff_tuple[0] * 12 + 
                   self.diff_tuple[1]
                   ) # number of months, for sorting

    def __float__(self):
        return float(self.diff_tuple[0] * 12 + 
                     self.diff_tuple[1] +
                     self.diff_tuple[2]/31.0 
                     ) # number of months, for sorting
    
    def __eq__(self, other):
        if other == None:
            return False
        return self.diff_tuple == other.diff_tuple

#-------------------------------------------------------------------------
#
# Date class
#
#-------------------------------------------------------------------------
class Date:
    """
    The core date handling class for GRAMPs. 
    
    Supports partial dates, compound dates and alternate calendars.
    """
    MOD_NONE       = 0  # CODE
    MOD_BEFORE     = 1
    MOD_AFTER      = 2
    MOD_ABOUT      = 3
    MOD_RANGE      = 4
    MOD_SPAN       = 5
    MOD_TEXTONLY   = 6

    QUAL_NONE        = 0 # BITWISE
    QUAL_ESTIMATED   = 1
    QUAL_CALCULATED  = 2
    QUAL_INTERPRETED = 4

    CAL_GREGORIAN  = 0 # CODE
    CAL_JULIAN     = 1
    CAL_HEBREW     = 2
    CAL_FRENCH     = 3
    CAL_PERSIAN    = 4
    CAL_ISLAMIC    = 5

    NEWYEAR_JAN1   = 0 # CODE
    NEWYEAR_MAR1   = 1
    NEWYEAR_MAR25  = 2
    NEWYEAR_SEP1   = 3

    EMPTY = (0, 0, 0, False)

    _POS_DAY  = 0
    _POS_MON  = 1
    _POS_YR   = 2
    _POS_SL   = 3
    _POS_RDAY = 4
    _POS_RMON = 5
    _POS_RYR  = 6
    _POS_RSL  = 7

    _calendar_convert = [
        gregorian_sdn, 
        julian_sdn, 
        hebrew_sdn, 
        french_sdn, 
        persian_sdn, 
        islamic_sdn, 
        ]

    _calendar_change = [
        gregorian_ymd, 
        julian_ymd, 
        hebrew_ymd, 
        french_ymd, 
        persian_ymd, 
        islamic_ymd, 
        ]

    calendar_names = ["Gregorian", 
                      "Julian", 
                      "Hebrew", 
                      "French Republican", 
                      "Persian", 
                      "Islamic"]


    ui_calendar_names = [_("Gregorian"), 
                         _("Julian"), 
                         _("Hebrew"), 
                         _("French Republican"), 
                         _("Persian"), 
                         _("Islamic")]

    def __init__(self, *source, **kwargs):
        """
        Create a new Date instance.
        """
        calendar = kwargs.get("calendar", None)
        modifier = kwargs.get("modifier", None)
        quality = kwargs.get("quality", None)
        #### setup None, Date, or numbers
        if len(source) == 0:
            source = None
        elif len(source) == 1:
            if isinstance(source[0], int):
                source = (source[0], 0, 0)
            else:
                source = source[0]
        elif len(source) == 2:
            source = (source[0], source[1], 0)
        elif len(source) == 3:
            pass # source is ok
        else:
            raise AttributeError, "invalid args to Date: %s" % source
        #### ok, process either date or tuple
        if isinstance(source, tuple):
            if calendar == None:
                self.calendar = Date.CAL_GREGORIAN
            else:
                self.calendar = self.lookup_calendar(calendar)
            if modifier == None:
                self.modifier = Date.MOD_NONE
            else:
                self.modifier = self.lookup_modifier(modifier)
            if quality == None:
                self.quality  = Date.QUAL_NONE
            else:
                self.quality = self.lookup_quality(quality)
            self.dateval  = Date.EMPTY
            self.text     = u""
            self.sortval  = 0
            self.newyear = 0
            self.set_yr_mon_day(*source)
        elif isinstance(source, str) and source != "":
            if (calendar != None or 
                modifier != None or 
                quality != None):
                raise AttributeError("can't set calendar, modifier, or "
                                     "quality with string date")
            import DateHandler
            source = DateHandler.parser.parse(source)
            self.calendar = source.calendar
            self.modifier = source.modifier
            self.quality  = source.quality
            self.dateval  = source.dateval
            self.text     = source.text
            self.sortval  = source.sortval
            self.newyear  = source.newyear
        elif source:
            self.calendar = source.calendar
            self.modifier = source.modifier
            self.quality  = source.quality
            self.dateval  = source.dateval
            self.text     = source.text
            self.sortval  = source.sortval
            self.newyear  = source.newyear
        else:
            self.calendar = Date.CAL_GREGORIAN
            self.modifier = Date.MOD_NONE
            self.quality  = Date.QUAL_NONE
            self.dateval  = Date.EMPTY
            self.text     = u""
            self.sortval  = 0
            self.newyear  = Date.NEWYEAR_JAN1

    def serialize(self, no_text_date=False):
        """
        Convert to a series of tuples for data storage.
        """
        if no_text_date:
            text = u''
        else:
            text = self.text
        
        return (self.calendar, self.modifier, self.quality, 
                self.dateval, text, self.sortval, self.newyear)

    def unserialize(self, data):
        """
        Load from the format created by serialize.
        """
        (self.calendar, self.modifier, self.quality, 
         self.dateval, self.text, self.sortval, self.newyear) = data
        return self

    def copy(self, source):
        """
        Copy all the attributes of the given Date instance to the present 
        instance, without creating a new object.
        """
        self.calendar = source.calendar
        self.modifier = source.modifier
        self.quality  = source.quality
        self.dateval  = source.dateval
        self.text     = source.text
        self.sortval  = source.sortval
        self.newyear  = source.newyear

    def __cmp__(self, other):
        """
        Compare two dates.
        
        Comparison function. Allows the usage of equality tests.
        This allows you do run statements like 'date1 <= date2'
        """
        if isinstance(other, Date):
            return cmp(self.sortval, other.sortval)
        else:
            return -1

    def __add__(self, other):
        """
        Date arithmetic: Date() + years, or Date() + (years, [months, [days]]).
        """
        if isinstance(other, int):
            return self.copy_offset_ymd(other)
        elif isinstance(other, (tuple, list)):
            return self.copy_offset_ymd(*other)
        else:
            raise AttributeError, "unknown date add type: %s " % type(other)

    def __radd__(self, other):
        """
        Add a number + Date() or (years, months, days) + Date().
        """
        return self + other

    def __sub__(self, other):
        """
        Date arithmetic: Date() - years, Date - (y,m,d), or Date() - Date().
        """
        if isinstance(other, int):                # Date - value -> Date
            return self.copy_offset_ymd(-other)
        elif isinstance(other, (tuple, list)):    # Date - (y, m, d) -> Date
            return self.copy_offset_ymd(*map(lambda x: -x, other))
        elif isinstance(other, self):             # Date1 - Date2 -> tuple
            # We should make sure that Date2 + tuple -> Date1 and
            #                          Date1 - tuple -> Date2
            d1 = map(lambda i: i or 1, self.get_ymd())
            d2 = map(lambda i: i or 1, other.get_ymd())
            date1 = self
            date2 = other
            if d1 < d2:
                d1, d2 = d2, d1
                date1, date2 = date2, date1
            # d1 - d2 (1998, 12, 32) - (1982, 12, 15)
            if date1.calendar != date2.calendar:
                diff = date1.sortval - date2.sortval
                return Span(diff/365, (diff % 365)/30, (diff % 365) % 30)
            # days:
            if d2[2] > d1[2]:
                # months:
                if d2[1] > d1[1]:
                    d1[0] -= 1
                    d1[1] += 12
                d1[1] -= 1
                d1[2] += 31
            # months:
            if d2[1] > d1[1]:
                d1[0] -= 1  # from years
                d1[1] += 12 # to months
            days = d1[2] - d2[2]
            months = d1[1] - d2[1]
            years = d1[0] - d2[0]
            if days > 31: 
                months += days / 31
                days = days % 31
            if months > 12:
                years += months / 12
                months = months % 12
            # estimate: (years, months, days)
            # Check transitivity:
            eDate = date1 - (years, months, days)
            if eDate < date2: # too small, strictly less than
                diff = 0
                while eDate << date2 and diff < 60:
                    diff += 1
                    eDate = eDate + (0, 0, diff)
                if diff == 60:
                    return Span(-1, -1, -1)
                return Span(years, months, days - diff)
            elif eDate > date2:
                diff = 0
                while eDate >> date2 and diff > -60:
                    diff -= 1
                    eDate = eDate - (0, 0, abs(diff))
                if diff == -60:
                    return Span(-1, -1, -1)
                return Span(years, months, days + diff)
            else:
                return Span(years, months, days)
        else:
            raise AttributeError, "unknown date sub type: %s " % type(other)

    # Can't use this (as is) as this breaks comparing dates to None
    #def __eq__(self, other):
    #    return self.sortval == other.sortval

    def __contains__(self, string):
        """
        For use with "x in Date" syntax.
        """
        return (str(string) in self.text)

    def __lshift__(self, other):
        """
        Comparison for strictly less than.
        """
        return self.match(other, comparison="<<")

    def __lt__(self, other):
        """
        Comparison for less than.
        """
        return self.match(other, comparison="<")

    def __rshift__(self, other):
        """
        Comparison for strictly greater than.
        """
        return self.match(other, comparison=">>")

    def __gt__(self, other):
        """
        Comparison for greater than.
        """
        return self.match(other, comparison=">")

    def is_equal(self, other):
        """
        Return 1 if the given Date instance is the same as the present
        instance IN ALL REGARDS. 
        
        Needed, because the __cmp__ only looks at the sorting value, and 
        ignores the modifiers/comments.
        """
        if self.modifier == other.modifier \
               and self.modifier == Date.MOD_TEXTONLY:
            value = self.text == other.text
        else:
            value = (self.calendar == other.calendar and 
                     self.modifier == other.modifier and 
                     self.quality == other.quality and 
                     self.dateval == other.dateval)
        return value

    def get_start_stop_range(self):
        """
        Return the minimal start_date, and a maximal stop_date corresponding 
        to this date, given in Gregorian calendar.
        
        Useful in doing range overlap comparisons between different dates.

        Note that we stay in (YR,MON,DAY) 
        """
        
        def yr_mon_day(dateval):
            """
            Local function to swap order for easy comparisons, and correct 
            year of slash date.
            
            Slash date is given as year1/year2, where year1 is Julian year, 
            and year2=year1+1 the Gregorian year.

            Slash date is already taken care of.
            """
            return (dateval[Date._POS_YR], dateval[Date._POS_MON], 
                    dateval[Date._POS_DAY])
        def date_offset(dateval, offset):
            """
            Local function to do date arithmetic: add the offset, return 
            (year,month,day) in the Gregorian calendar.
            """
            new_date = Date()
            new_date.set_yr_mon_day(dateval[0], dateval[1], dateval[2])
            return new_date.offset(offset)
        
        datecopy = Date(self)
        #we do all calculation in Gregorian calendar
        datecopy.convert_calendar(Date.CAL_GREGORIAN)
        start     = yr_mon_day(datecopy.get_start_date())
        stop      = yr_mon_day(datecopy.get_stop_date())

        if stop == (0, 0, 0):
            stop = start
            
        stopmax  = list(stop)
        if stopmax[0] == 0: # then use start_year, if one
            stopmax[0] = start[Date._POS_YR]
        if stopmax[1] == 0:
            stopmax[1] = 12
        if stopmax[2] == 0: 
            stopmax[2] = 31
        startmin  = list(start)
        if startmin[1] == 0:
            startmin[1] = 1
        if startmin[2] == 0:
            startmin[2] = 1
        # if BEFORE, AFTER, or ABOUT/EST, adjust:
        if self.modifier == Date.MOD_BEFORE:
            stopmax = date_offset(startmin, -1)
            fdiff = Config.get(Config.DATE_BEFORE_RANGE)
            startmin = (stopmax[0] - fdiff, stopmax[1], stopmax[2])
        elif self.modifier == Date.MOD_AFTER:
            startmin = date_offset(stopmax, 1)
            fdiff = Config.get(Config.DATE_AFTER_RANGE)
            stopmax = (startmin[0] + fdiff, startmin[1], startmin[2])
        elif (self.modifier == Date.MOD_ABOUT or
              self.quality == Date.QUAL_ESTIMATED):
            fdiff = Config.get(Config.DATE_ABOUT_RANGE)
            startmin = (startmin[0] - fdiff, startmin[1], startmin[2])
            stopmax = (stopmax[0] + fdiff, stopmax[1], stopmax[2])
        # return tuples not lists, for comparisons
        return (tuple(startmin), tuple(stopmax))
        
    def match(self, other_date, comparison="="):
        """
        Compare two dates using sophisticated techniques looking for any match 
        between two possible dates, date spans and qualities.
        
        The other comparisons for Date (is_equal() and __cmp() don't actually 
        look for anything other than a straight match, or a simple comparison 
        of the sortval.

        comparison =,== :
            Returns True if any part of other_date matches any part of self
        comparison < :
            Returns True if any part of other_date < any part of self
        comparison << :
            Returns True if all parts of other_date < all parts of self
        comparison > :
            Returns True if any part of other_date > any part of self
        comparison >> :
            Returns True if all parts of other_date > all parts of self
        """
        if (other_date.modifier == Date.MOD_TEXTONLY or
            self.modifier == Date.MOD_TEXTONLY):
            if comparison in ["=", "=="]:
                return (self.text.upper().find(other_date.text.upper()) != -1)
            else:
                return False
        if (self.sortval == 0 or other_date.sortval == 0):
            return False

        # Obtain minimal start and maximal stop in Gregorian calendar
        other_start, other_stop = other_date.get_start_stop_range()
        self_start,  self_stop  = self.get_start_stop_range()

        if comparison in ["=", "=="]:
            # If some overlap then match is True, otherwise False.
            return ((self_start <= other_start <= self_stop) or
                    (self_start <= other_stop <= self_stop) or 
                    (other_start <= self_start <= other_stop) or 
                    (other_start <= self_stop <= other_stop))
        elif comparison == "<":
            # If any < any
            return self_start < other_stop
        elif comparison == "<<":
            # If all < all
            return self_stop < other_start
        elif comparison == ">":
            # If any > any
            return self_stop > other_start
        elif comparison == ">>":
            # If all > all
            return self_start > other_stop
        else:
            raise AttributeError, ("invalid match comparison operator: '%s'" % 
                                   comparison)
            
    def __str__(self):
        """
        Produce a string representation of the Date object. 
        
        If the date is not valid, the text representation is displayed. If
        the date is a range or a span, a string in the form of
        'YYYY-MM-DD - YYYY-MM-DD' is returned. Otherwise, a string in
        the form of 'YYYY-MM-DD' is returned.
        """
        if self.quality == Date.QUAL_ESTIMATED:
            qual = "est "
        elif self.quality == Date.QUAL_CALCULATED:
            qual = "calc "
        else:
            qual = ""

        if self.modifier == Date.MOD_BEFORE:
            pref = "bef "
        elif self.modifier == Date.MOD_AFTER:
            pref = "aft "
        elif self.modifier == Date.MOD_ABOUT:
            pref = "abt "
        else:
            pref = ""

        if self.calendar != Date.CAL_GREGORIAN:
            cal = " (%s)" % Date.calendar_names[self.calendar]
        else:
            cal = ""
            
        if self.modifier == Date.MOD_TEXTONLY:
            val = self.text
        elif self.get_slash():
            val = "%04d/%d-%02d-%02d" % (
                self.dateval[Date._POS_YR] - 1, 
                (self.dateval[Date._POS_YR]) % 10, 
                self.dateval[Date._POS_MON], 
                self.dateval[Date._POS_DAY])
        elif self.modifier == Date.MOD_RANGE or self.modifier == Date.MOD_SPAN:
            val = "%04d-%02d-%02d - %04d-%02d-%02d" % (
                self.dateval[Date._POS_YR], self.dateval[Date._POS_MON], 
                self.dateval[Date._POS_DAY], self.dateval[Date._POS_RYR], 
                self.dateval[Date._POS_RMON], self.dateval[Date._POS_RDAY])
        else:
            val = "%04d-%02d-%02d" % (
                self.dateval[Date._POS_YR], self.dateval[Date._POS_MON], 
                self.dateval[Date._POS_DAY])
        return "%s%s%s%s" % (qual, pref, val, cal)

    def get_sort_value(self):
        """
        Return the sort value of Date object. 
        
        If the value is a text string, 0 is returned. Otherwise, the 
        calculated sort date is returned. The sort date is rebuilt on every 
        assignment.

        The sort value is an integer representing the value. The sortval is 
        the integer number of days that have elapsed since Monday, January 1, 
        4713 BC in the proleptic Julian calendar. 
        See http://en.wikipedia.org/wiki/Julian_day
        """
        return self.sortval

    def get_modifier(self):
        """
        Return an integer indicating the calendar selected. 
        
        The valid values are::
        
           MOD_NONE       = no modifier (default)
           MOD_BEFORE     = before
           MOD_AFTER      = after
           MOD_ABOUT      = about
           MOD_RANGE      = date range
           MOD_SPAN       = date span
           MOD_TEXTONLY   = text only
        """
        return self.modifier

    def set_modifier(self, val):
        """
        Set the modifier for the date.
        """
        if val not in (Date.MOD_NONE, Date.MOD_BEFORE, Date.MOD_AFTER, 
                       Date.MOD_ABOUT, Date.MOD_RANGE, Date.MOD_SPAN, 
                       Date.MOD_TEXTONLY):
            raise DateError("Invalid modifier")
        self.modifier = val

    def get_quality(self):
        """
        Return an integer indicating the calendar selected. 
        
        The valid values are::
        
           QUAL_NONE       = normal (default)
           QUAL_ESTIMATED  = estimated
           QUAL_CALCULATED = calculated
        """
        return self.quality

    def set_quality(self, val):
        """
        Set the quality selected for the date.
        """
        if val not in (Date.QUAL_NONE, Date.QUAL_ESTIMATED, 
                       Date.QUAL_CALCULATED):
            raise DateError("Invalid quality")
        self.quality = val
    
    def get_calendar(self):
        """
        Return an integer indicating the calendar selected. 
        
        The valid values are::

           CAL_GREGORIAN  - Gregorian calendar
           CAL_JULIAN     - Julian calendar
           CAL_HEBREW     - Hebrew (Jewish) calendar
           CAL_FRENCH     - French Republican calendar
           CAL_PERSIAN    - Persian calendar
           CAL_ISLAMIC    - Islamic calendar
        """
        return self.calendar

    def set_calendar(self, val):
        """
        Set the calendar selected for the date.
        """
        if val not in (Date.CAL_GREGORIAN, Date.CAL_JULIAN, Date.CAL_HEBREW, 
                       Date.CAL_FRENCH, Date.CAL_PERSIAN, Date.CAL_ISLAMIC):
            raise DateError("Invalid calendar")
        self.calendar = val

    def get_start_date(self):
        """
        Return a tuple representing the start date. 
        
        If the date is a compound date (range or a span), it is the first part 
        of the compound date. If the date is a text string, a tuple of
        (0, 0, 0, False) is returned. Otherwise, a date of (DD, MM, YY, slash)
        is returned. If slash is True, then the date is in the form of 1530/1.
        """
        if self.modifier == Date.MOD_TEXTONLY:
            val = Date.EMPTY
        else:
            val = self.dateval[0:4]
        return val

    def get_stop_date(self):
        """
        Return a tuple representing the second half of a compound date. 
        
        If the date is not a compound date, (including text strings) a tuple
        of (0, 0, 0, False) is returned. Otherwise, a date of (DD, MM, YY, slash)
        is returned. If slash is True, then the date is in the form of 1530/1.
        """
        if self.modifier == Date.MOD_RANGE or self.modifier == Date.MOD_SPAN:
            val = self.dateval[4:8]
        else:
            val = Date.EMPTY
        return val

    def _get_low_item(self, index):
        """
        Return the item specified.
        """
        if self.modifier == Date.MOD_TEXTONLY:
            val = 0
        else:
            val = self.dateval[index]
        return val

    def _get_low_item_valid(self, index):
        """
        Determine if the item specified is valid.
        """
        if self.modifier == Date.MOD_TEXTONLY:
            val = False
        else:
            val = self.dateval[index] != 0
        return val
        
    def _get_high_item(self, index):
        """
        Return the item specified.
        """
        if self.modifier == Date.MOD_SPAN or self.modifier == Date.MOD_RANGE:
            val = self.dateval[index]
        else:
            val = 0
        return val

    def get_year(self):
        """
        Return the year associated with the date. 
        
        If the year is not defined, a zero is returned. If the date is a 
        compound date, the lower date year is returned.
        """
        return self._get_low_item(Date._POS_YR)

    def set_yr_mon_day(self, year, month, day):
        """
        Set the year, month, and day values.
        """
        dv = list(self.dateval)
        dv[Date._POS_YR] = year
        dv[Date._POS_MON] = month
        dv[Date._POS_DAY] = day
        self.dateval = tuple(dv)
        self._calc_sort_value()

    def set_yr_mon_day_offset(self, year=0, month=0, day=0):
        """
        Set the year, month, and day values by offset.
        """
        dv = list(self.dateval)
        if dv[Date._POS_YR]:
            dv[Date._POS_YR] += year
        elif year:
            dv[Date._POS_YR] = year
        if dv[Date._POS_MON]:
            dv[Date._POS_MON] += month
        elif month:
            if month < 0:
                dv[Date._POS_MON] = 1 + month
            else:
                dv[Date._POS_MON] = month
        # Fix if month out of bounds:
        if month != 0: # only check if changed
            if dv[Date._POS_MON] == 0: # subtraction
                dv[Date._POS_MON] = 12
                dv[Date._POS_YR] -= 1
            elif dv[Date._POS_MON] < 0: # subtraction
                dv[Date._POS_YR] -= int((-dv[Date._POS_MON]) / 12) + 1
                dv[Date._POS_MON] = (dv[Date._POS_MON] % 12)
            elif dv[Date._POS_MON] > 12 or dv[Date._POS_MON] < 1:
                dv[Date._POS_YR] += int(dv[Date._POS_MON] / 12)
                dv[Date._POS_MON] = dv[Date._POS_MON] % 12
        self.dateval = tuple(dv)
        self._calc_sort_value()
        if day != 0 or dv[Date._POS_DAY] > 28:
            self.set_yr_mon_day(*self.offset(day))

    def copy_offset_ymd(self, year=0, month=0, day=0):
        """
        Return a Date copy based on year, month, and day offset.
        """
        orig_cal = self.calendar
        if self.calendar != 0:
            new_date = self.to_calendar("gregorian")
        else:
            new_date = self
        retval = Date(new_date)
        retval.set_yr_mon_day_offset(year, month, day)
        if orig_cal == 0:
            return retval
        else:
            retval.convert_calendar(orig_cal)
            return retval

    def copy_ymd(self, year=0, month=0, day=0):
        """
        Return a Date copy with year, month, and day set.
        """
        retval = Date(self)
        retval.set_yr_mon_day(year, month, day)
        return retval

    def set_year(self, year):
        """
        Set the year value.
        """
        self.dateval = self.dateval[0:2] + (year, ) + self.dateval[3:]
        self._calc_sort_value()

    def get_year_valid(self):
        """
        Return true if the year is valid.
        """
        return self._get_low_item_valid(Date._POS_YR)

    def get_month(self):
        """
        Return the month associated with the date. 
        
        If the month is not defined, a zero is returned. If the date is a 
        compound date, the lower date month is returned.
        """
        return self._get_low_item(Date._POS_MON)

    def get_month_valid(self):
        """
        Return true if the month is valid
        """
        return self._get_low_item_valid(Date._POS_MON)

    def get_day(self):
        """
        Return the day of the month associated with the date. 
        
        If the day is not defined, a zero is returned. If the date is a 
        compound date, the lower date day is returned.
        """
        return self._get_low_item(Date._POS_DAY)

    def get_day_valid(self):
        """
        Return true if the day is valid.
        """
        return self._get_low_item_valid(Date._POS_DAY)

    def get_valid(self):
        """ 
        Return true if any part of the date is valid.
        """
        return self.modifier != Date.MOD_TEXTONLY

    def get_stop_year(self):
        """
        Return the day of the year associated with the second part of a 
        compound date. 
        
        If the year is not defined, a zero is returned. 
        """
        return self._get_high_item(Date._POS_RYR)

    def get_stop_month(self):
        """
        Return the month of the month associated with the second part of a 
        compound date. 
        
        If the month is not defined, a zero is returned. 
        """
        return self._get_high_item(Date._POS_RMON)

    def get_stop_day(self):
        """
        Return the day of the month associated with the second part of a 
        compound date. 
        
        If the day is not defined, a zero is returned. 
        """
        return self._get_high_item(Date._POS_RDAY)

    def get_high_year(self):
        """
        Return the high year estimate. 
        
        For compound dates with non-zero stop year, the stop year is returned. 
        Otherwise, the start year is returned.
        """
        if self.is_compound():
            ret = self.get_stop_year()
            if ret:
                return ret
        else:
            return self.get_year()

    def get_text(self):
        """
        Return the text value associated with an invalid date.
        """
        return self.text

    def set(self, quality, modifier, calendar, value, text=None):
        """
        Set the date to the specified value. 
        
        Parameters are::

          quality  - The date quality for the date (see get_quality
                     for more information)
          modified - The date modifier for the date (see get_modifier
                     for more information)
          calendar - The calendar associated with the date (see
                     get_calendar for more information).
          value    - A tuple representing the date information. For a
                     non-compound date, the format is (DD, MM, YY, slash)
                     and for a compound date the tuple stores data as
                     (DD, MM, YY, slash1, DD, MM, YY, slash2)
          text     - A text string holding either the verbatim user input
                     or a comment relating to the date.

        The sort value is recalculated.
        """
        
        if modifier in (Date.MOD_NONE, Date.MOD_BEFORE, 
                        Date.MOD_AFTER, Date.MOD_ABOUT) and len(value) < 4:
            raise DateError("Invalid value. Should be: (DD, MM, YY, slash)")
        if modifier in (Date.MOD_RANGE, Date.MOD_SPAN) and len(value) < 8:
            raise DateError("Invalid value. Should be: (DD, MM, "
                            "YY, slash1, DD, MM, YY, slash2)")
        if modifier not in (Date.MOD_NONE, Date.MOD_BEFORE, Date.MOD_AFTER, 
                            Date.MOD_ABOUT, Date.MOD_RANGE, Date.MOD_SPAN, 
                            Date.MOD_TEXTONLY):
            raise DateError("Invalid modifier")
        if quality not in (Date.QUAL_NONE, Date.QUAL_ESTIMATED, 
                           Date.QUAL_CALCULATED):
            raise DateError("Invalid quality")
        if calendar not in (Date.CAL_GREGORIAN, Date.CAL_JULIAN,
                            Date.CAL_HEBREW, Date.CAL_FRENCH,
                            Date.CAL_PERSIAN, Date.CAL_ISLAMIC):
            raise DateError("Invalid calendar")

        self.quality = quality
        self.modifier = modifier
        self.calendar = calendar
        self.dateval = value
        year = max(value[Date._POS_YR], 1)
        month = max(value[Date._POS_MON], 1)
        day = max(value[Date._POS_DAY], 1)
        if year == 0 and month == 0 and day == 0:
            self.sortval = 0
        else:
            func = Date._calendar_convert[calendar]
            self.sortval = func(year, month, day)
        if text:
            self.text = text

    def recalc_sort_value(self):
        """
        Recalculates the numerical sort value associated with the date
        and returns it. Public method.
        """
        self._calc_sort_value()
        return self.sortval

    def _calc_sort_value(self):
        """
        Calculate the numerical sort value associated with the date.
        """
        year = max(self.dateval[Date._POS_YR], 1)
        month = max(self.dateval[Date._POS_MON], 1)
        day = max(self.dateval[Date._POS_DAY], 1)
        if year == 0 and month == 0 and day == 0:
            self.sortval = 0
        else:
            func = Date._calendar_convert[self.calendar]
            self.sortval = func(year, month, day)

    def convert_calendar(self, calendar):
        """
        Convert the date from the current calendar to the specified calendar.
        """
        if calendar == self.calendar:
            return
        (year, month, day) = Date._calendar_change[calendar](self.sortval)
        if self.is_compound():
            ryear = max(self.dateval[Date._POS_RYR], 1)
            rmonth = max(self.dateval[Date._POS_RMON], 1)
            rday = max(self.dateval[Date._POS_RDAY], 1)
            sdn = Date._calendar_convert[self.calendar](ryear, rmonth, rday)
            (nyear, nmonth, nday) = Date._calendar_change[calendar](sdn)
            self.dateval = (day, month, year, self.dateval[Date._POS_SL], 
                            nday, nmonth, nyear, self.dateval[Date._POS_RSL])
        else:
            self.dateval = (day, month, year, self.dateval[Date._POS_SL])
        self.calendar = calendar

    def set_as_text(self, text):
        """
        Set the day to a text string, and assign the sort value to zero.
        """
        self.modifier = Date.MOD_TEXTONLY
        self.text = text
        self.sortval = 0

    def set_text_value(self, text):
        """
        Set the text string to a given text.
        """
        self.text = text

    def is_empty(self):
        """
        Return True if the date contains no information (empty text).
        """
        return (self.modifier == Date.MOD_TEXTONLY and not self.text) or \
               (self.get_start_date()==Date.EMPTY
                and self.get_stop_date()==Date.EMPTY)
        
    def is_compound(self):
        """
        Return True if the date is a date range or a date span.
        """
        return self.modifier == Date.MOD_RANGE \
               or self.modifier == Date.MOD_SPAN

    def is_regular(self):
        """
        Return True if the date is a regular date.
        
        The regular date is a single exact date, i.e. not text-only, not 
        a range or a span, not estimated/calculated, not about/before/after 
        date, and having year, month, and day all non-zero.
        """
        return self.modifier == Date.MOD_NONE \
               and self.quality == Date.QUAL_NONE \
               and self.get_year_valid() and self.get_month_valid() \
               and self.get_day_valid()

    def get_ymd(self):
        """
        Return (year, month, day).
        """
        return (self.get_year(), self.get_month(), self.get_day())

    def offset(self, value):
        """
        Return (year, month, day) of this date +- value.
        """
        return Date._calendar_change[Date.CAL_GREGORIAN](self.sortval + value)

    def offset_date(self, value):
        """
        Return (year, month, day) of this date +- value.
        """
        return Date(Date._calendar_change[Date.CAL_GREGORIAN](self.sortval + value))

    def lookup_calendar(self, calendar):
        """
        Lookup calendar name in the list of known calendars, even if translated.
        """
        calendar_lower = [n.lower() for n in Date.calendar_names]
        ui_lower = [n.lower() for n in Date.ui_calendar_names]
        if calendar.lower() in calendar_lower:
            return calendar_lower.index(calendar.lower())
        elif calendar.lower() in ui_lower:
            return ui_lower.index(calendar.lower())
        else:
            raise AttributeError("invalid calendar: '%s'" % calendar)

    def lookup_quality(self, quality):
        """
        Lookup date quality keyword, even if translated.
        """
        qualities = ["none", "estimated", "calculated"]
        ui_qualities = [_("none"), _("estimated"), _("calculated")]
        if quality.lower() in qualities:
            return qualities.index(quality.lower())
        elif quality.lower() in ui_qualities:
            return ui_qualities.index(quality.lower())
        else:
            raise AttributeError("invalid quality: '%s'" % quality)

    def lookup_modifier(self, modifier):
        """
        Lookup date modifier keyword, even if translated.
        """
        mods = ["none", "before", "after", "about", 
                "range", "span", "textonly"]
        ui_mods = [_("none"), _("before"), _("after"), _("about"), 
                   _("range"), _("span"), _("textonly")]
        if modifier.lower() in mods:
            return mods.index(modifier.lower())
        elif modifier.lower() in ui_mods:
            return ui_mods.index(modifier.lower())
        else:
            raise AttributeError("invalid modifier: '%s'" % modifier)
    
    def to_calendar(self, calendar_name):
        """
        Return a new Date object in the calendar calendar_name.
        
        >>> Date("Jan 1 1591").to_calendar("julian")
        1590-12-22 (Julian)
        """
        cal = self.lookup_calendar(calendar_name)
        retval = Date(self)
        retval.convert_calendar(cal)
        return retval

    def get_slash(self):
        """
        Return true if the date is a slash-date.
        """
        return self._get_low_item_valid(Date._POS_SL)