# Module:Date

-- Date functions for use by other modules.  
-- I18N and time zones are not supported.  

local MINUS = '−' -- Unicode U+2212 MINUS SIGN  
local floor = math.floor  

local Date, DateDiff, diffmt -- forward declarations  
local uniq = { 'unique identifier' }  

local function is_date(t)  
-- The system used to make a date read-only means there is no unique  
-- metatable that is conveniently accessible to check.  
return type(t) == 'table' and t._id == uniq  
end  

local function is_diff(t)  
return type(t) == 'table' and getmetatable(t) == diffmt  
end  

local function _list_join(list, sep)  
return table.concat(list, sep)  
end  

local function collection  
-- Return a table to hold items.  
return {  
n = 0,  
add = function (self, item)  
self.n = self.n + 1  
self[self.n] = item  
end,  
join = _list_join,  
}  
end  

local function strip_to_nil(text)  
-- If text is a string, return its trimmed content, or nil if empty.  
-- Otherwise return text (convenient when Date fields are provided from  
-- another module which may pass a string, a number, or another type).  
if type(text) == 'string' then  
text = text:match('(%S.-)%s*$')  
end  
return text  
end  

local function is_leap_year(year, calname)  
-- Return true if year is a leap year.  
if calname == 'Julian' then  
return year % 4 == 0  
end  
return (year % 4 == 0 and year % 100 ~= 0) or year % 400 == 0  
end  

local function days_in_month(year, month, calname)  
-- Return number of days (1..31) in given month (1..12).  
if month == 2 and is_leap_year(year, calname) then  
return 29  
end  
return ({ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 })[month]  
end  

local function h_m_s(time)  
-- Return hour, minute, second extracted from fraction of a day.  
time = floor(time * 24 * 3600 + 0.5) -- number of seconds  
local second = time % 60  
time = floor(time / 60)  
return floor(time / 60), time % 60, second  
end  

local function hms(date)  
-- Return fraction of a day from date's time, where (0 <= fraction < 1)  
-- if the values are valid, but could be anything if outside range.  
return (date.hour + (date.minute + date.second / 60) / 60) / 24  
end  

local function julian_date(date)  
-- Return jd, jdz from a Julian or Gregorian calendar date where  
-- jd = Julian date and its fractional part is zero at noon  
-- jdz = same, but assume time is 00:00:00 if no time given  
-- http://www.tondering.dk/claus/cal/julperiod.php#formula  
-- Testing shows this works for all dates from year -9999 to 9999!  
-- JDN 0 is the 24-hour period starting at noon UTC on Monday  
-- 1 January 4713 BC = (-4712, 1, 1) Julian calendar  
-- 24 November 4714 BC = (-4713, 11, 24) Gregorian calendar  
local offset  
local a = floor((14 - date.month)/12)  
local y = date.year + 4800 - a  
if date.calendar == 'Julian' then  
offset = floor(y/4) - 32083  
else  
offset = floor(y/4) - floor(y/100) + floor(y/400) - 32045  
end  
local m = date.month + 12*a - 3  
local jd = date.day + floor((153*m + 2)/5) + 365*y + offset  
if date.hastime then  
jd = jd + hms(date) - 0.5  
return jd, jd  
end  
return jd, jd - 0.5  
end  

local function set_date_from_jd(date)  
-- Set the fields of table date from its Julian date field.  
-- Return true if date is valid.  
-- http://www.tondering.dk/claus/cal/julperiod.php#formula  
-- This handles the proleptic Julian and Gregorian calendars.  
-- Negative Julian dates are not defined but they work.  
local calname = date.calendar  
local low, high -- min/max limits for date ranges −9999-01-01 to 9999-12-31  
if calname == 'Gregorian' then  
low, high = -1930999.5, 5373484.49999  
elseif calname == 'Julian' then  
low, high = -1931076.5, 5373557.49999  
else  
return  
end  
local jd = date.jd  
if not (type(jd) == 'number' and low <= jd and jd <= high) then  
return  
end  
local jdn = floor(jd)  
if date.hastime then  
local time = jd - jdn -- 0 <= time < 1  
if time >= 0.5 then -- if at or after midnight of next day  
jdn = jdn + 1  
time = time - 0.5  
else  
time = time + 0.5  
end  
date.hour, date.minute, date.second = h_m_s(time)  
else  
date.second = 0  
date.minute = 0  
date.hour = 0  
end  
local b, c  
if calname == 'Julian' then  
b = 0  
c = jdn + 32082  
else -- Gregorian  
local a = jdn + 32044  
b = floor((4*a + 3)/146097)  
c = a - floor(146097*b/4)  
end  
local d = floor((4*c + 3)/1461)  
local e = c - floor(1461*d/4)  
local m = floor((5*e + 2)/153)  
date.day = e - floor((153*m + 2)/5) + 1  
date.month = m + 3 - 12*floor(m/10)  
date.year = 100*b + d - 4800 + floor(m/10)  
return true  
end  

local function fix_numbers(numbers, y, m, d, H, M, S, partial, hastime, calendar)  
-- Put the result of normalizing the given values in table numbers.  
-- The result will have valid m, d values if y is valid; caller checks y.  
-- The logic of PHP mktime is followed where m or d can be zero to mean  
-- the previous unit, and -1 is the one before that, etc.  
-- Positive values carry forward.  
local date  
if not (1 <= m and m <= 12) then  
date = Date(y, 1, 1)  
if not date then return end  
date = date + ((m - 1) .. 'm')  
y, m = date.year, date.month  
end  
local days_hms  
if not partial then  
if hastime and H and M and S then  
if not (0 <= H and H <= 23 and  
0 <= M and M <= 59 and  
0 <= S and S <= 59) then  
days_hms = hms({ hour = H, minute = M, second = S })  
end  
end  
if days_hms or not (1 <= d and d <= days_in_month(y, m, calendar)) then  
date = date or Date(y, m, 1)  
if not date then return end  
date = date + (d - 1 + (days_hms or 0))  
y, m, d = date.year, date.month, date.day  
if days_hms then  
H, M, S = date.hour, date.minute, date.second  
end  
end  
end  
numbers.year = y  
numbers.month = m  
numbers.day = d  
if days_hms then  
-- Don't set H unless it was valid because a valid H will set hastime.  
numbers.hour = H  
numbers.minute = M  
numbers.second = S  
end  
end  

local function set_date_from_numbers(date, numbers, options)  
-- Set the fields of table date from numeric values.  
-- Return true if date is valid.  
if type(numbers) ~= 'table' then  
return  
end  
local y = numbers.year or date.year  
local m = numbers.month or date.month  
local d = numbers.day or date.day  
local H = numbers.hour  
local M = numbers.minute or date.minute or 0  
local S = numbers.second or date.second or 0  
local need_fix  
if y and m and d then  
date.partial = nil  
if not (-9999 <= y and y <= 9999 and  
1 <= m and m <= 12 and  
1 <= d and d <= days_in_month(y, m, date.calendar)) then  
if not date.want_fix then  
return  
end  
need_fix = true  
end  
elseif y and date.partial then  
if d or not (-9999 <= y and y <= 9999) then  
return  
end  
if m and not (1 <= m and m <= 12) then  
if not date.want_fix then  
return  
end  
need_fix = true  
end  
else  
return  
end  
if date.partial then  
H = nil -- ignore any time  
M = nil  
S = nil  
else  
if H then  
-- It is not possible to set M or S without also setting H.  
date.hastime = true  
else  
H = 0  
end  
if not (0 <= H and H <= 23 and  
0 <= M and M <= 59 and  
0 <= S and S <= 59) then  
if date.want_fix then  
need_fix = true  
else  
return  
end  
end  
end  
date.want_fix = nil  
if need_fix then  
fix_numbers(numbers, y, m, d, H, M, S, date.partial, date.hastime, date.calendar)  
return set_date_from_numbers(date, numbers, options)  
end  
date.year = y -- -9999 to 9999 ('n BC' → year = 1 - n)  
date.month = m -- 1 to 12 (may be nil if partial)  
date.day = d -- 1 to 31 (* = nil if partial)  
date.hour = H -- 0 to 59 (*)  
date.minute = M -- 0 to 59 (*)  
date.second = S -- 0 to 59 (*)  
if type(options) == 'table' then  
for _, k in ipairs({ 'am', 'era', 'format' }) do  
if options[k] then  
date.options[k] = options[k]  
end  
end  
end  
return true  
end  

local function make_option_table(options1, options2)  
-- If options1 is a string, return a table with its settings, or  
-- if it is a table, use its settings.  
-- Missing options are set from table options2 or defaults.  
-- If a default is used, a flag is set so caller knows the value was not intentionally set.  
-- Valid option settings are:  
-- am: 'am', 'a.m.', 'AM', 'A.M.'  
-- 'pm', 'p.m.', 'PM', 'P.M.' (each has same meaning as corresponding item above)  
-- era: 'BCMINUS', 'BCNEGATIVE', 'BC', 'B.C.', 'BCE', 'B.C.E.', 'AD', 'A.D.', 'CE', 'C.E.'  
-- Option am = 'am' does not mean the hour is AM; it means 'am' or 'pm' is used, depending on the hour,  
-- and am = 'pm' has the same meaning.  
-- Similarly, era = 'BC' means 'BC' is used if year <= 0.  
-- BCMINUS displays a MINUS if year < 0 and the display format does not include %{era}.  
-- BCNEGATIVE is similar but displays a hyphen.  
local result = { bydefault = {} }  
if type(options1) == 'table' then  
result.am = options1.am  
result.era = options1.era  
elseif type(options1) == 'string' then  
-- Example: 'am:AM era:BC' or 'am=AM era=BC'.  
for item in options1:gmatch('%S+') do  
local lhs, rhs = item:match('^(%w+)[:=](.+)$')  
if lhs then  
result[lhs] = rhs  
end  
end  
end  
options2 = type(options2) == 'table' and options2 or {}  
local defaults = { am = 'am', era = 'BC' }  
for k, v in pairs(defaults) do  
if not result[k] then  
if options2[k] then  
result[k] = options2[k]  
else  
result[k] = v  
result.bydefault[k] = true  
end  
end  
end  
return result  
end  

local ampm_options = {  
-- lhs = input text accepted as an am/pm option  
-- rhs = code used internally  
['am'] = 'am',  
['AM'] = 'AM',  
['a.m.'] = 'a.m.',  
['A.M.'] = 'A.M.',  
['pm'] = 'am', -- same as am  
['PM'] = 'AM',  
['p.m.'] = 'a.m.',  
['P.M.'] = 'A.M.',  
}  

local era_text = {  
-- Text for displaying an era with a positive year (after adjusting  
-- by replacing year with 1 - year if date.year <= 0).  
-- options.era = { year<=0 , year>0 }  
['BCMINUS'] = { 'BC' , '' , isbc = true, sign = MINUS },  
['BCNEGATIVE'] = { 'BC' , '' , isbc = true, sign = '-' },  
['BC'] = { 'BC' , '' , isbc = true },  
['B.C.'] = { 'B.C.' , '' , isbc = true },  
['BCE'] = { 'BCE' , '' , isbc = true },  
['B.C.E.'] = { 'B.C.E.', '' , isbc = true },  
['AD'] = { 'BC' , 'AD' },  
['A.D.'] = { 'B.C.' , 'A.D.' },  
['CE'] = { 'BCE' , 'CE' },  
['C.E.'] = { 'B.C.E.', 'C.E.' },  
}  

local function get_era_for_year(era, year)  
return (era_text[era] or era_text['BC'])[year > 0 and 2 or 1] or ''  
end  

local function strftime(date, format, options)  
-- Return date formatted as a string using codes similar to those  
-- in the C strftime library function.  
local sformat = string.format  
local shortcuts = {  
['%c'] = '%-I:%M %p %-d %B %-Y %{era}', -- date and time: 2:30 pm 1 April 2016  
['%x'] = '%-d %B %-Y %{era}', -- date: 1 April 2016  
['%X'] = '%-I:%M %p', -- time: 2:30 pm  
}  
if shortcuts[format] then  
format = shortcuts[format]  
end  
local codes = {  
a = { field = 'dayabbr' },  
A = { field = 'dayname' },  
b = { field = 'monthabbr' },  
B = { field = 'monthname' },  
u = { fmt = '%d' , field = 'dowiso' },  
w = { fmt = '%d' , field = 'dow' },  
d = { fmt = '%02d', fmt2 = '%d', field = 'day' },  
m = { fmt = '%02d', fmt2 = '%d', field = 'month' },  
Y = { fmt = '%04d', fmt2 = '%d', field = 'year' },  
H = { fmt = '%02d', fmt2 = '%d', field = 'hour' },  
M = { fmt = '%02d', fmt2 = '%d', field = 'minute' },  
S = { fmt = '%02d', fmt2 = '%d', field = 'second' },  
j = { fmt = '%03d', fmt2 = '%d', field = 'dayofyear' },  
I = { fmt = '%02d', fmt2 = '%d', field = 'hour', special = 'hour12' },  
p = { field = 'hour', special = 'am' },  
}  
options = make_option_table(options, date.options)  
local amopt = options.am  
local eraopt = options.era  
local function replace_code(spaces, modifier, id)  
local code = codes[id]  
if code then  
local fmt = code.fmt  
if modifier == '-' and code.fmt2 then  
fmt = code.fmt2  
end  
local value = date[code.field]  
if not value then  
return nil -- an undefined field in a partial date  
end  
local special = code.special  
if special then  
if special == 'hour12' then  
value = value % 12  
value = value == 0 and 12 or value  
elseif special == 'am' then  
local ap = ({  
['a.m.'] = { 'a.m.', 'p.m.' },  
['AM'] = { 'AM', 'PM' },  
['A.M.'] = { 'A.M.', 'P.M.' },  
})[ampm_options[amopt]] or { 'am', 'pm' }  
return (spaces == * and * or '&nbsp;') .. (value < 12 and ap[1] or ap[2])  
end  
end  
if code.field == 'year' then  
local sign = (era_text[eraopt] or {}).sign  
if not sign or format:find('%{era}', 1, true) then  
sign = ''  
if value <= 0 then  
value = 1 - value  
end  
else  
if value >= 0 then  
sign = ''  
else  
value = -value  
end  
end  
return spaces .. sign .. sformat(fmt, value)  
end  
return spaces .. (fmt and sformat(fmt, value) or value)  
end  
end  
local function replace_property(spaces, id)  
if id == 'era' then  
-- Special case so can use local era option.  
local result = get_era_for_year(eraopt, date.year)  
if result == '' then  
return ''  
end  
return (spaces == * and * or '&nbsp;') .. result  
end  
local result = date[id]  
if type(result) == 'string' then  
return spaces .. result  
end  
if type(result) == 'number' then  
return spaces .. tostring(result)  
end  
if type(result) == 'boolean' then  
return spaces .. (result and '1' or '0')  
end  
-- This occurs if id is an undefined field in a partial date, or is the name of a function.  
return nil  
end  
local PERCENT = '\127PERCENT\127'  
return (format  
:gsub('%%%%', PERCENT)  
:gsub('(%s*)%%{(%w+)}', replace_property)  
:gsub('(%s*)%%(%-?)(%a)', replace_code)  
:gsub(PERCENT, '%%')  
end  

local function _date_text(date, fmt, options)  
-- Return a formatted string representing the given date.  
if not is_date(date) then  
error('date:text: need a date (use "date:text" with a colon)', 2)  
end  
if type(fmt) == 'string' and fmt:match('%S') then  
if fmt:find('%', 1, true) then  
return strftime(date, fmt, options)  
end  
elseif date.partial then  
fmt = date.month and 'my' or 'y'  
else  
fmt = 'dmy'  
if date.hastime then  
fmt = (date.second > 0 and 'hms ' or 'hm ') .. fmt  
end  
end  
local function bad_format  
-- For consistency with other format processing, return given format  
-- (or cleaned format if original was not a string) if invalid.  
return mw.text.nowiki(fmt)  
end  
if date.partial then  
-- Ignore days in standard formats like 'ymd'.  
if fmt == 'ym' or fmt == 'ymd' then  
fmt = date.month and '%Y-%m %{era}' or '%Y %{era}'  
elseif fmt == 'my' or fmt == 'dmy' or fmt == 'mdy' then  
fmt = date.month and '%B %-Y %{era}' or '%-Y %{era}'  
elseif fmt == 'y' then  
fmt = date.month and '%-Y %{era}' or '%-Y %{era}'  
else  
return bad_format  
end  
return strftime(date, fmt, options)  
end  
local function hm_fmt  
local plain = make_option_table(options, date.options).bydefault.am  
return plain and '%H:%M' or '%-I:%M %p'  
end  
local need_time = date.hastime  
local t = collection  
for item in fmt:gmatch('%S+') do  
local f  
if item == 'hm' then  
f = hm_fmt  
need_time = false  
elseif item == 'hms' then  
f = '%H:%M:%S'  
need_time = false  
elseif item == 'ymd' then  
f = '%Y-%m-%d %{era}'  
elseif item == 'mdy' then  
f = '%B %-d, %-Y %{era}'  
elseif item == 'dmy' then  
f = '%-d %B %-Y %{era}'  
else  
return bad_format  
end  
t:add(f)  
end  
fmt = t:join(' ')  
if need_time then  
fmt = hm_fmt .. ' ' .. fmt  
end  
return strftime(date, fmt, options)  
end  

local day_info = {  
-- 0=Sun to 6=Sat  
[0] = { 'Sun', 'Sunday' },  
{ 'Mon', 'Monday' },  
{ 'Tue', 'Tuesday' },  
{ 'Wed', 'Wednesday' },  
{ 'Thu', 'Thursday' },  
{ 'Fri', 'Friday' },  
{ 'Sat', 'Saturday' },  
}  

local month_info = {  
-- 1=Jan to 12=Dec  
{ 'Jan', 'January' },  
{ 'Feb', 'February' },  
{ 'Mar', 'March' },  
{ 'Apr', 'April' },  
{ 'May', 'May' },  
{ 'Jun', 'June' },  
{ 'Jul', 'July' },  
{ 'Aug', 'August' },  
{ 'Sep', 'September' },  
{ 'Oct', 'October' },  
{ 'Nov', 'November' },  
{ 'Dec', 'December' },  
}  

local function name_to_number(text, translate)  
if type(text) == 'string' then  
return translate[text:lower]  
end  
end  

local function day_number(text)  
return name_to_number(text, {  
sun = 0, sunday = 0,  
mon = 1, monday = 1,  
tue = 2, tuesday = 2,  
wed = 3, wednesday = 3,  
thu = 4, thursday = 4,  
fri = 5, friday = 5,  
sat = 6, saturday = 6,  
})  
end  

local function month_number(text)  
return name_to_number(text, {  
jan = 1, january = 1,  
feb = 2, february = 2,  
mar = 3, march = 3,  
apr = 4, april = 4,  
may = 5,  
jun = 6, june = 6,  
jul = 7, july = 7,  
aug = 8, august = 8,  
sep = 9, september = 9, sept = 9,  
oct = 10, october = 10,  
nov = 11, november = 11,  
dec = 12, december = 12,  
})  
end  

local function _list_text(list, fmt)  
-- Return a list of formatted strings from a list of dates.  
if not type(list) == 'table' then  
error('date:list:text: need "list:text" with a colon', 2)  
end  
local result = { join = _list_join }  
for i, date in ipairs(list) do  
result[i] = date:text(fmt)  
end  
return result  
end  

local function _date_list(date, spec)  
-- Return a possibly empty numbered table of dates meeting the specification.  
-- Dates in the list are in ascending order (oldest date first).  
-- The spec should be a string of form "<count> <day> <op>"  
-- where each item is optional and  
-- count = number of items wanted in list  
-- day = abbreviation or name such as Mon or Monday  
-- op = >, >=, <, <= (default is > meaning after date)  
-- If no count is given, the list is for the specified days in date's month.  
-- The default day is date's day.  
-- The spec can also be a positive or negative number:  
-- -5 is equivalent to '5 <'  
-- 5 is equivalent to '5' which is '5 >'  
if not is_date(date) then  
error('date:list: need a date (use "date:list" with a colon)', 2)  
end  
local list = { text = _list_text }  
if date.partial then  
return list  
end  
local count, offset, operation  
local ops = {  
['>='] = { before = false, include = true },  
['>'] = { before = false, include = false },  
['<='] = { before = true , include = true },  
['<'] = { before = true , include = false },  
}  
if spec then  
if type(spec) == 'number' then  
count = floor(spec + 0.5)  
if count < 0 then  
count = -count  
operation = ops['<']  
end  
elseif type(spec) == 'string' then  
local num, day, op = spec:match('^%s*(%d*)%s*(%a*)%s*([<>=]*)%s*$')  
if not num then  
return list  
end  
if num ~= '' then  
count = tonumber(num)  
end  
if day ~= '' then  
local dow = day_number(day:gsub('[sS]$', '')) -- accept plural days  
if not dow then  
return list  
end  
offset = dow - date.dow  
end  
operation = ops[op]  
else  
return list  
end  
end  
offset = offset or 0  
operation = operation or ops['>']  
local datefrom, dayfirst, daylast  
if operation.before then  
if offset > 0 or (offset == 0 and not operation.include) then  
offset = offset - 7  
end  
if count then  
if count > 1 then  
offset = offset - 7*(count - 1)  
end  
datefrom = date + offset  
else  
daylast = date.day + offset  
dayfirst = daylast % 7  
if dayfirst == 0 then  
dayfirst = 7  
end  
end  
else  
if offset < 0 or (offset == 0 and not operation.include) then  
offset = offset + 7  
end  
if count then  
datefrom = date + offset  
else  
dayfirst = date.day + offset  
daylast = date.monthdays  
end  
end  
if not count then  
if daylast < dayfirst then  
return list  
end  
count = floor((daylast - dayfirst)/7) + 1  
datefrom = Date(date, {day = dayfirst})  
end  
for i = 1, count do  
if not datefrom then break end -- exceeds date limits  
list[i] = datefrom  
datefrom = datefrom + 7  
end  
return list  
end  

-- A table to get the current date/time (UTC), but only if needed.  
local current = setmetatable({}, {  
__index = function (self, key)  
local d = os.date('!*t')  
self.year = d.year  
self.month = d.month  
self.day = d.day  
self.hour = d.hour  
self.minute = d.min  
self.second = d.sec  
return rawget(self, key)  
end })  

local function extract_date(newdate, text)  
-- Parse the date/time in text and return n, o where  
-- n = table of numbers with date/time fields  
-- o = table of options for AM/PM or AD/BC or format, if any  
-- or return nothing if date is known to be invalid.  
-- Caller determines if the values in n are valid.  
-- A year must be positive ('1' to '9999'); use 'BC' for BC.  
-- In a y-m-d string, the year must be four digits to avoid ambiguity  
-- ('0001' to '9999'). The only way to enter year <= 0 is by specifying  
-- the date as three numeric parameters like ymd Date(-1, 1, 1).  
-- Dates of form d/m/y, m/d/y, y/m/d are rejected as potentially ambiguous.  
local date, options = {}, {}  
if text:sub(-1) == 'Z' then  
-- Extract date/time from a Wikidata timestamp.  
-- The year can be 1 to 16 digits but this module handles 1 to 4 digits only.  
-- Examples: '+2016-06-21T14:30:00Z', '-0000000180-00-00T00:00:00Z'.  
local sign, y, m, d, H, M, S = text:match('^([+%-])(%d+)%-(%d%d)%-(%d%d)T(%d%d):(%d%d):(%d%d)Z$')  
if sign then  
y = tonumber(y)  
if sign == '-' and y > 0 then  
y = -y  
end  
if y <= 0 then  
options.era = 'BCE'  
end  
date.year = y  
m = tonumber(m)  
d = tonumber(d)  
H = tonumber(H)  
M = tonumber(M)  
S = tonumber(S)  
if m == 0 then  
newdate.partial = true  
return date, options  
end  
date.month = m  
if d == 0 then  
newdate.partial = true  
return date, options  
end  
date.day = d  
if H > 0 or M > 0 or S > 0 then  
date.hour = H  
date.minute = M  
date.second = S  
end  
return date, options  
end  
return  
end  
local function extract_ymd(item)  
-- Called when no day or month has been set.  
local y, m, d = item:match('^(%d%d%d%d)%-(%w+)%-(%d%d?)$')  
if y then  
if date.year then  
return  
end  
if m:match('^%d%d?$') then  
m = tonumber(m)  
else  
m = month_number(m)  
end  
if m then  
date.year = tonumber(y)  
date.month = m  
date.day = tonumber(d)  
return true  
end  
end  
end  
local function extract_day_or_year(item)  
-- Called when a day would be valid, or  
-- when a year would be valid if no year has been set and partial is set.  
local number, suffix = item:match('^(%d%d?%d?%d?)(.*)$')  
if number then  
local n = tonumber(number)  
if #number <= 2 and n <= 31 then  
suffix = suffix:lower  
if suffix == '' or suffix == 'st' or suffix == 'nd' or suffix == 'rd' or suffix == 'th' then  
date.day = n  
return true  
end  
elseif suffix == '' and newdate.partial and not date.year then  
date.year = n  
return true  
end  
end  
end  
local function extract_month(item)  
-- A month must be given as a name or abbreviation; a number could be ambiguous.  
local m = month_number(item)  
if m then  
date.month = m  
return true  
end  
end  
local function extract_time(item)  
local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')  
if date.hour or not h then  
return  
end  
if s ~= '' then  
s = s:match('^:(%d%d)$')  
if not s then  
return  
end  
end  
date.hour = tonumber(h)  
date.minute = tonumber(m)  
date.second = tonumber(s) -- nil if empty string  
return true  
end  
local item_count = 0  
local index_time  
local function set_ampm(item)  
local H = date.hour  
if H and not options.am and index_time + 1 == item_count then  
options.am = ampm_options[item] -- caller checked this is not nil  
if item:match('^[Aa]') then  
if not (1 <= H and H <= 12) then  
return  
end  
if H == 12 then  
date.hour = 0  
end  
else  
if not (1 <= H and H <= 23) then  
return  
end  
if H <= 11 then  
date.hour = H + 12  
end  
end  
return true  
end  
end  
for item in text:gsub(',', ' '):gsub('&nbsp;', ' '):gmatch('%S+') do  
item_count = item_count + 1  
if era_text[item] then  
-- Era is accepted in peculiar places.  
if options.era then  
return  
end  
options.era = item  
elseif ampm_options[item] then  
if not set_ampm(item) then  
return  
end  
elseif item:find(':', 1, true) then  
if not extract_time(item) then  
return  
end  
index_time = item_count  
elseif date.day and date.month then  
if date.year then  
return -- should be nothing more so item is invalid  
end  
if not item:match('^(%d%d?%d?%d?)$') then  
return  
end  
date.year = tonumber(item)  
elseif date.day then  
if not extract_month(item) then  
return  
end  
elseif date.month then  
if not extract_day_or_year(item) then  
return  
end  
elseif extract_month(item) then  
options.format = 'mdy'  
elseif extract_ymd(item) then  
options.format = 'ymd'  
elseif extract_day_or_year(item) then  
if date.day then  
options.format = 'dmy'  
end  
else  
return  
end  
end  
if not date.year or date.year == 0 then  
return  
end  
local era = era_text[options.era]  
if era and era.isbc then  
date.year = 1 - date.year  
end  
return date, options  
end  

local function autofill(date1, date2)  
-- Fill any missing month or day in each date using the  
-- corresponding component from the other date, if present,  
-- or with 1 if both dates are missing the month or day.  
-- This gives a good result for calculating the difference  
-- between two partial dates when no range is wanted.  
-- Return filled date1, date2 (two full dates).  
local function filled(a, b)  
-- Return date a filled, if necessary, with month and/or day from date b.  
-- The filled day is truncated to fit the number of days in the month.  
local fillmonth, fillday  
if not a.month then  
fillmonth = b.month or 1  
end  
if not a.day then  
fillday = b.day or 1  
end  
if fillmonth or fillday then -- need to create a new date  
a = Date(a, {  
month = fillmonth,  
day = math.min(fillday or a.day, days_in_month(a.year, fillmonth or a.month, a.calendar))  
})  
end  
return a  
end  
return filled(date1, date2), filled(date2, date1)  
end  

local function date_add_sub(lhs, rhs, is_sub)  
-- Return a new date from calculating (lhs + rhs) or (lhs - rhs),  
-- or return nothing if invalid.  
-- The result is nil if the calculated date exceeds allowable limits.  
-- Caller ensures that lhs is a date; its properties are copied for the new date.  
if lhs.partial then  
-- Adding to a partial is not supported.  
-- Can subtract a date or partial from a partial, but this is not called for that.  
return  
end  
local function is_prefix(text, word, minlen)  
local n = #text  
return (minlen or 1) <= n and n <= #word and text == word:sub(1, n)  
end  
local function do_days(n)  
local forcetime, jd  
if floor(n) == n then  
jd = lhs.jd  
else  
forcetime = not lhs.hastime  
jd = lhs.jdz  
end  
jd = jd + (is_sub and -n or n)  
if forcetime then  
jd = tostring(jd)  
if not jd:find('.', 1, true) then  
jd = jd .. '.0'  
end  
end  
return Date(lhs, 'juliandate', jd)  
end  
if type(rhs) == 'number' then  
-- Add/subtract days, including fractional days.  
return do_days(rhs)  
end  
if type(rhs) == 'string' then  
-- rhs is a single component like '26m' or '26 months' (with optional sign).  
-- Fractions like '3.25d' are accepted for the units which are handled as days.  
local sign, numstr, id = rhs:match('^%s*([+-]?)([%d%.]+)%s*(%a+)$')  
if sign then  
if sign == '-' then  
is_sub = not (is_sub and true or false)  
end  
local y, m, days  
local num = tonumber(numstr)  
if not num then  
return  
end  
id = id:lower  
if is_prefix(id, 'years') then  
y = num  
m = 0  
elseif is_prefix(id, 'months') then  
y = floor(num / 12)  
m = num % 12  
elseif is_prefix(id, 'weeks') then  
days = num * 7  
elseif is_prefix(id, 'days') then  
days = num  
elseif is_prefix(id, 'hours') then  
days = num / 24  
elseif is_prefix(id, 'minutes', 3) then  
days = num / (24 * 60)  
elseif is_prefix(id, 'seconds') then  
days = num / (24 * 3600)  
else  
return  
end  
if days then  
return do_days(days)  
end  
if numstr:find('.', 1, true) then  
return  
end  
if is_sub then  
y = -y  
m = -m  
end  
assert(-11 <= m and m <= 11)  
y = lhs.year + y  
m = lhs.month + m  
if m > 12 then  
y = y + 1  
m = m - 12  
elseif m < 1 then  
y = y - 1  
m = m + 12  
end  
local d = math.min(lhs.day, days_in_month(y, m, lhs.calendar))  
return Date(lhs, y, m, d)  
end  
end  
if is_diff(rhs) then  
local days = rhs.age_days  
if (is_sub or false) ~= (rhs.isnegative or false) then  
days = -days  
end  
return lhs + days  
end  
end  

local full_date_only = {  
dayabbr = true,  
dayname = true,  
dow = true,  
dayofweek = true,  
dowiso = true,  
dayofweekiso = true,  
dayofyear = true,  
gsd = true,  
juliandate = true,  
jd = true,  
jdz = true,  
jdnoon = true,  
}  

-- Metatable for a date's calculated fields.  
local datemt = {  
__index = function (self, key)  
if rawget(self, 'partial') then  
if full_date_only[key] then return end  
if key == 'monthabbr' or key == 'monthdays' or key == 'monthname' then  
if not self.month then return end  
end  
end  
local value  
if key == 'dayabbr' then  
value = day_info[self.dow][1]  
elseif key == 'dayname' then  
value = day_info[self.dow][2]  
elseif key == 'dow' then  
value = (self.jdnoon + 1) % 7 -- day-of-week 0=Sun to 6=Sat  
elseif key == 'dayofweek' then  
value = self.dow  
elseif key == 'dowiso' then  
value = (self.jdnoon % 7) + 1 -- ISO day-of-week 1=Mon to 7=Sun  
elseif key == 'dayofweekiso' then  
value = self.dowiso  
elseif key == 'dayofyear' then  
local first = Date(self.year, 1, 1, self.calendar).jdnoon  
value = self.jdnoon - first + 1 -- day-of-year 1 to 366  
elseif key == 'era' then  
-- Era text (never a negative sign) from year and options.  
value = get_era_for_year(self.options.era, self.year)  
elseif key == 'format' then  
value = self.options.format or 'dmy'  
elseif key == 'gsd' then  
-- GSD = 1 from 00:00:00 to 23:59:59 on 1 January 1 AD Gregorian calendar,  
-- which is from jd 1721425.5 to 1721426.49999.  
value = floor(self.jd - 1721424.5)  
elseif key == 'juliandate' or key == 'jd' or key == 'jdz' then  
local jd, jdz = julian_date(self)  
rawset(self, 'juliandate', jd)  
rawset(self, 'jd', jd)  
rawset(self, 'jdz', jdz)  
return key == 'jdz' and jdz or jd  
elseif key == 'jdnoon' then  
-- Julian date at noon (an integer) on the calendar day when jd occurs.  
value = floor(self.jd + 0.5)  
elseif key == 'isleapyear' then  
value = is_leap_year(self.year, self.calendar)  
elseif key == 'monthabbr' then  
value = month_info[self.month][1]  
elseif key == 'monthdays' then  
value = days_in_month(self.year, self.month, self.calendar)  
elseif key == 'monthname' then  
value = month_info[self.month][2]  
end  
if value ~= nil then  
rawset(self, key, value)  
return value  
end  
end,  
}  

-- Date operators.  
local function mt_date_add(lhs, rhs)  
if not is_date(lhs) then  
lhs, rhs = rhs, lhs -- put date on (it must be a date for this to have been called)  
end  
return date_add_sub(lhs, rhs)  
end  

local function mt_date_sub(lhs, rhs)  
if is_date(lhs) then  
if is_date(rhs) then  
return DateDiff(lhs, rhs)  
end  
return date_add_sub(lhs, rhs, true)  
end  
end  

local function mt_date_concat(lhs, rhs)  
return tostring(lhs) .. tostring(rhs)  
end  

local function mt_date_tostring(self)  
return self:text  
end  

local function mt_date_eq(lhs, rhs)  
-- Return true if dates identify same date/time where, for example,  
-- Date(-4712, 1, 1, 'Julian') == Date(-4713, 11, 24, 'Gregorian') is true.  
-- This is called only if lhs and rhs have the same type and the same metamethod.  
if lhs.partial or rhs.partial then  
-- One date is partial; the other is a partial or a full date.  
-- The months may both be nil, but must be the same.  
return lhs.year == rhs.year and lhs.month == rhs.month and lhs.calendar == rhs.calendar  
end  
return lhs.jdz == rhs.jdz  
end  

local function mt_date_lt(lhs, rhs)  
-- Return true if lhs < rhs, for example,  
-- Date('1 Jan 2016') < Date('06:00 1 Jan 2016') is true.  
-- This is called only if lhs and rhs have the same type and the same metamethod.  
if lhs.partial or rhs.partial then  
-- One date is partial; the other is a partial or a full date.  
if lhs.calendar ~= rhs.calendar then  
return lhs.calendar == 'Julian'  
end  
if lhs.partial then  
lhs = lhs.partial.first  
end  
if rhs.partial then  
rhs = rhs.partial.first  
end  
end  
return lhs.jdz < rhs.jdz  
end  

-- Examples of syntax to construct a date:  
Date(y, m, d, 'julian') default calendar is 'gregorian'  
Date(y, m, d, H, M, S, 'julian')  
Date('juliandate', jd, 'julian') if jd contains "." text output includes H:M:S  
Date('currentdate')  
Date('currentdatetime')  
Date('1 April 1995', 'julian') parse date from text  
Date('1 April 1995 AD', 'julian') using an era sets a flag to do the same for output  
Date('04:30:59 1 April 1995', 'julian')  
Date(date) copy of an existing date  
Date(date, t) same, updated with y,m,d,H,M,S fields from table t  
Date(t) date with y,m,d,H,M,S fields from table t  

function Date(...) -- for forward declaration above  
-- Return a table holding a date assuming a uniform calendar always applies  
-- (proleptic Gregorian calendar or proleptic Julian calendar), or  
-- return nothing if date is invalid.  
-- A partial date has a valid year, however its month may be nil, and  
-- its day and time fields are nil.  
-- Field partial is set to false (if a full date) or a table (if a partial date).  
local calendars = { julian = 'Julian', gregorian = 'Gregorian' }  
local newdate = {  
_id = uniq,  
calendar = 'Gregorian', -- default is Gregorian calendar  
hastime = false, -- true if input sets a time  
hour = 0, -- always set hour/minute/second so don't have to handle nil  
minute = 0,  
second = 0,  
options = {},  
list = _date_list,  
subtract = function (self, rhs, options)  
return DateDiff(self, rhs, options)  
end,  
text = _date_text,  
}  
local argtype, datetext, is_copy, jd_number, tnums  
local numindex = 0  
local numfields = { 'year', 'month', 'day', 'hour', 'minute', 'second' }  
local numbers = {}  
for _, v in ipairs({...}) do  
v = strip_to_nil(v)  
local vlower = type(v) == 'string' and v:lower or nil  
if v == nil then  
-- Ignore empty arguments after stripping so modules can directly pass template parameters.  
elseif calendars[vlower] then  
newdate.calendar = calendars[vlower]  
elseif vlower == 'partial' then  
newdate.partial = true  
elseif vlower == 'fix' then  
newdate.want_fix = true  
elseif is_date(v) then  
-- Copy existing date (items can be overridden by other arguments).  
if is_copy or tnums then  
return  
end  
is_copy = true  
newdate.calendar = v.calendar  
newdate.partial = v.partial  
newdate.hastime = v.hastime  
newdate.options = v.options  
newdate.year = v.year  
newdate.month = v.month  
newdate.day = v.day  
newdate.hour = v.hour  
newdate.minute = v.minute  
newdate.second = v.second  
elseif type(v) == 'table' then  
if tnums then  
return  
end  
tnums = {}  
local tfields = { year=1, month=1, day=1, hour=2, minute=2, second=2 }  
for tk, tv in pairs(v) do  
if tfields[tk] then  
tnums[tk] = tonumber(tv)  
end  
if tfields[tk] == 2 then  
newdate.hastime = true  
end  
end  
else  
local num = tonumber(v)  
if not num and argtype == 'setdate' and numindex == 1 then  
num = month_number(v)  
end  
if num then  
if not argtype then  
argtype = 'setdate'  
end  
if argtype == 'setdate' and numindex < 6 then  
numindex = numindex + 1  
numbers[numfields[numindex]] = num  
elseif argtype == 'juliandate' and not jd_number then  
jd_number = num  
if type(v) == 'string' then  
if v:find('.', 1, true) then  
newdate.hastime = true  
end  
elseif num ~= floor(num) then  
-- The given value was a number. The time will be used  
-- if the fractional part is nonzero.  
newdate.hastime = true  
end  
else  
return  
end  
elseif argtype then  
return  
elseif type(v) == 'string' then  
if v == 'currentdate' or v == 'currentdatetime' or v == 'juliandate' then  
argtype = v  
else  
argtype = 'datetext'  
datetext = v  
end  
else  
return  
end  
end  
end  
if argtype == 'datetext' then  
if tnums or not set_date_from_numbers(newdate, extract_date(newdate, datetext)) then  
return  
end  
elseif argtype == 'juliandate' then  
newdate.partial = nil  
newdate.jd = jd_number  
if not set_date_from_jd(newdate) then  
return  
end  
elseif argtype == 'currentdate' or argtype == 'currentdatetime' then  
newdate.partial = nil  
newdate.year = current.year  
newdate.month = current.month  
newdate.day = current.day  
if argtype == 'currentdatetime' then  
newdate.hour = current.hour  
newdate.minute = current.minute  
newdate.second = current.second  
newdate.hastime = true  
end  
newdate.calendar = 'Gregorian' -- ignore any given calendar name  
elseif argtype == 'setdate' then  
if tnums or not set_date_from_numbers(newdate, numbers) then  
return  
end  
elseif not (is_copy or tnums) then  
return  
end  
if tnums then  
newdate.jd = nil -- force recalculation in case jd was set before changes from tnums  
if not set_date_from_numbers(newdate, tnums) then  
return  
end  
end  
if newdate.partial then  
local year = newdate.year  
local month = newdate.month  
local first = Date(year, month or 1, 1, newdate.calendar)  
month = month or 12  
local last = Date(year, month, days_in_month(year, month), newdate.calendar)  
newdate.partial = { first = first, last = last }  
else  
newdate.partial = false -- avoid index lookup  
end  
setmetatable(newdate, datemt)  
local readonly = {}  
local mt = {  
__index = newdate,  
__newindex = function(t, k, v) error('date.' .. tostring(k) .. ' is read-only', 2) end,  
__add = mt_date_add,  
__sub = mt_date_sub,  
__concat = mt_date_concat,  
__tostring = mt_date_tostring,  
__eq = mt_date_eq,  
__lt = mt_date_lt,  
}  
return setmetatable(readonly, mt)  
end  

local function _diff_age(diff, code, options)  
-- Return a tuple of integer values from diff as specified by code, except that  
-- each integer may be a list of two integers for a diff with a partial date, or  
-- return nil if the code is not supported.  
-- If want round, the least significant unit is rounded to nearest whole unit.  
-- For a duration, an extra day is added.  
local wantround, wantduration, wantrange  
if type(options) == 'table' then  
wantround = options.round  
wantduration = options.duration  
wantrange = options.range  
else  
wantround = options  
end  
if not is_diff(diff) then  
local f = wantduration and 'duration' or 'age'  
error(f .. ': need a date difference (use "diff:' .. f .. '" with a colon)', 2)  
end  
if diff.partial then  
-- Ignore wantround, wantduration.  
local function choose(v)  
if type(v) == 'table' then  
if not wantrange or v[1] == v[2] then  
-- Example: Date('partial', 2005) - Date('partial', 2001) gives  
-- diff.years = { 3, 4 } to show the range of possible results.  
-- If do not want a range, choose the second value as more expected.  
return v[2]  
end  
end  
return v  
end  
if code == 'ym' or code == 'ymd' then  
if not wantrange and diff.iszero then  
-- This avoids an unexpected result such as  
-- Date('partial', 2001) - Date('partial', 2001)  
-- giving diff = { years = 0, months = { 0, 11 } }  
-- which would be reported as 0 years and 11 months.  
return 0, 0  
end  
return choose(diff.partial.years), choose(diff.partial.months)  
end  
if code == 'y' then  
return choose(diff.partial.years)  
end  
if code == 'm' or code == 'w' or code == 'd' then  
return choose({ diff.partial.mindiff:age(code), diff.partial.maxdiff:age(code) })  
end  
return nil  
end  
local extra_days = wantduration and 1 or 0  
if code == 'wd' or code == 'w' or code == 'd' then  
local offset = wantround and 0.5 or 0  
local days = diff.age_days + extra_days  
if code == 'wd' or code == 'd' then  
days = floor(days + offset)  
if code == 'd' then  
return days  
end  
return floor(days/7), days % 7  
end  
return floor(days/7 + offset)  
end  
local H, M, S = diff.hours, diff.minutes, diff.seconds  
if code == 'dh' or code == 'dhm' or code == 'dhms' or code == 'h' or code == 'hm' or code == 'hms' or code == 'M' or code == 's' then  
local days = floor(diff.age_days + extra_days)  
local inc_hour  
if wantround then  
if code == 'dh' or code == 'h' then  
if M >= 30 then  
inc_hour = true  
end  
elseif code == 'dhm' or code == 'hm' then  
if S >= 30 then  
M = M + 1  
if M >= 60 then  
M = 0  
inc_hour = true  
end  
end  
elseif code == 'M' then  
if S >= 30 then  
M = M + 1  
end  
else  
-- Nothing needed because S is an integer.  
end  
if inc_hour then  
H = H + 1  
if H >= 24 then  
H = 0  
days = days + 1  
end  
end  
end  
if code == 'dh' or code == 'dhm' or code == 'dhms' then  
if code == 'dh' then  
return days, H  
elseif code == 'dhm' then  
return days, H, M  
else  
return days, H, M, S  
end  
end  
local hours = days * 24 + H  
if code == 'h' then  
return hours  
elseif code == 'hm' then  
return hours, M  
elseif code == 'M' or code == 's' then  
M = hours * 60 + M  
if code == 'M' then  
return M  
end  
return M * 60 + S  
end  
return hours, M, S  
end  
if wantround then  
local inc_hour  
if code == 'ymdh' or code == 'ymwdh' then  
if M >= 30 then  
inc_hour = true  
end  
elseif code == 'ymdhm' or code == 'ymwdhm' then  
if S >= 30 then  
M = M + 1  
if M >= 60 then  
M = 0  
inc_hour = true  
end  
end  
elseif code == 'ymd' or code == 'ymwd' or code == 'yd' or code == 'md' then  
if H >= 12 then  
extra_days = extra_days + 1  
end  
end  
if inc_hour then  
H = H + 1  
if H >= 24 then  
H = 0  
extra_days = extra_days + 1  
end  
end  
end  
local y, m, d = diff.years, diff.months, diff.days  
if extra_days > 0 then  
d = d + extra_days  
if d > 28 or code == 'yd' then  
-- Recalculate in case have passed a month.  
diff = diff.date1 + extra_days - diff.date2  
y, m, d = diff.years, diff.months, diff.days  
end  
end  
if code == 'ymd' then  
return y, m, d  
elseif code == 'yd' then  
if y > 0 then  
-- It is known that diff.date1 > diff.date2.  
diff = diff.date1 - (diff.date2 + (y .. 'y'))  
end  
return y, floor(diff.age_days)  
elseif code == 'md' then  
return y * 12 + m, d  
elseif code == 'ym' or code == 'm' then  
if wantround then  
if d >= 16 then  
m = m + 1  
if m >= 12 then  
m = 0  
y = y + 1  
end  
end  
end  
if code == 'ym' then  
return y, m  
end  
return y * 12 + m  
elseif code == 'ymw' then  
local weeks = floor(d/7)  
if wantround then  
local days = d % 7  
if days > 3 or (days == 3 and H >= 12) then  
weeks = weeks + 1  
end  
end  
return y, m, weeks  
elseif code == 'ymwd' then  
return y, m, floor(d/7), d % 7  
elseif code == 'ymdh' then  
return y, m, d, H  
elseif code == 'ymwdh' then  
return y, m, floor(d/7), d % 7, H  
elseif code == 'ymdhm' then  
return y, m, d, H, M  
elseif code == 'ymwdhm' then  
return y, m, floor(d/7), d % 7, H, M  
end  
if code == 'y' then  
if wantround and m >= 6 then  
y = y + 1  
end  
return y  
end  
return nil  
end  

local function _diff_duration(diff, code, options)  
if type(options) ~= 'table' then  
options = { round = options }  
end  
options.duration = true  
return _diff_age(diff, code, options)  
end  

-- Metatable for some operations on date differences.  
diffmt = { -- for forward declaration above  
__concat = function (lhs, rhs)  
return tostring(lhs) .. tostring(rhs)  
end,  
__tostring = function (self)  
return tostring(self.age_days)  
end,  
__index = function (self, key)  
local value  
if key == 'age_days' then  
if rawget(self, 'partial') then  
local function jdz(date)  
return (date.partial and date.partial.first or date).jdz  
end  
value = jdz(self.date1) - jdz(self.date2)  
else  
value = self.date1.jdz - self.date2.jdz  
end  
end  
if value ~= nil then  
rawset(self, key, value)  
return value  
end  
end,  
}  

function DateDiff(date1, date2, options) -- for forward declaration above  
-- Return a table with the difference between two dates (date1 - date2).  
-- The difference is negative if date1 is older than date2.  
-- Return nothing if invalid.  
-- If d = date1 - date2 then  
-- date1 = date2 + d  
-- If date1 >= date2 and the dates have no H:M:S time specified then  
-- date1 = date2 + (d.years..'y') + (d.months..'m') + d.days  
-- where the larger time units are added first.  
-- The result of Date(2015,1,x) + '1m' is Date(2015,2,28) for  
-- x = 28, 29, 30, 31. That means, for example,  
-- d = Date(2015,3,3) - Date(2015,1,31)  
-- gives d.years, d.months, d.days = 0, 1, 3 (excluding date1).  
if not (is_date(date1) and is_date(date2) and date1.calendar == date2.calendar) then  
return  
end  
local wantfill  
if type(options) == 'table' then  
wantfill = options.fill  
end  
local isnegative = false  
local iszero = false  
if date1 < date2 then  
isnegative = true  
date1, date2 = date2, date1  
elseif date1 == date2 then  
iszero = true  
end  
-- It is known that date1 >= date2 (period is from date2 to date1).  
if date1.partial or date2.partial then  
-- Two partial dates might have timelines:  
---------------------A=================B--- date1 is from A to B inclusive  
--------C=======D-------------------------- date2 is from C to D inclusive  
-- date1 > date2 iff A > C (date1.partial.first > date2.partial.first)  
-- The periods can overlap ('April 2001' - '2001'):  
-------------A===B------------------------- A=2001-04-01 B=2001-04-30  
--------C=====================D------------ C=2001-01-01 D=2001-12-31  
if wantfill then  
date1, date2 = autofill(date1, date2)  
else  
local function zdiff(date1, date2)  
local diff = date1 - date2  
if diff.isnegative then  
return date1 - date1 -- a valid diff in case we call its methods  
end  
return diff  
end  
local function getdate(date, which)  
return date.partial and date.partial[which] or date  
end  
local maxdiff = zdiff(getdate(date1, 'last'), getdate(date2, 'first'))  
local mindiff = zdiff(getdate(date1, 'first'), getdate(date2, 'last'))  
local years, months  
if maxdiff.years == mindiff.years then  
years = maxdiff.years  
if maxdiff.months == mindiff.months then  
months = maxdiff.months  
else  
months = { mindiff.months, maxdiff.months }  
end  
else  
years = { mindiff.years, maxdiff.years }  
end  
return setmetatable({  
date1 = date1,  
date2 = date2,  
partial = {  
years = years,  
months = months,  
maxdiff = maxdiff,  
mindiff = mindiff,  
},  
isnegative = isnegative,  
iszero = iszero,  
age = _diff_age,  
duration = _diff_duration,  
}, diffmt)  
end  
end  
local y1, m1 = date1.year, date1.month  
local y2, m2 = date2.year, date2.month  
local years = y1 - y2  
local months = m1 - m2  
local d1 = date1.day + hms(date1)  
local d2 = date2.day + hms(date2)  
local days, time  
if d1 >= d2 then  
days = d1 - d2  
else  
months = months - 1  
-- Get days in previous month (before the "to" date) given December has 31 days.  
local dpm = m1 > 1 and days_in_month(y1, m1 - 1, date1.calendar) or 31  
if d2 >= dpm then  
days = d1 - hms(date2)  
else  
days = dpm - d2 + d1  
end  
end  
if months < 0 then  
years = years - 1  
months = months + 12  
end  
days, time = math.modf(days)  
local H, M, S = h_m_s(time)  
return setmetatable({  
date1 = date1,  
date2 = date2,  
partial = false, -- avoid index lookup  
years = years,  
months = months,  
days = days,  
hours = H,  
minutes = M,  
seconds = S,  
isnegative = isnegative,  
iszero = iszero,  
age = _diff_age,  
duration = _diff_duration,  
}, diffmt)  
end  

return {  
_current = current,  
_Date = Date,  
_days_in_month = days_in_month,  
}