Module:Date
Revision as of 04:58, 7 March 2016 by imported>Johnuniq (major refactor, mostly working now; add/subtract with a date; remove template handling which will be in Module:Age)
Documentation for this module may be created at Module:Date/doc
-- Date functions for implementing templates and for use by other modules.
-- I18N and time zones are not supported.
local MINUS = '−' -- Unicode U+2212 MINUS SIGN
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 = function (self, sep)
return table.concat(self, sep)
end,
}
end
local function strip_to_nil(text)
-- If text is a string, return its trimmed content, or nil.
-- Otherwise return text (convenient when Date fields are provided from
-- another module which is able to pass, for example, a number).
if type(text) == 'string' then
text = text:match('(%S.-)%s*$')
end
return text
end
local function number_name(number, singular, plural, sep)
-- Return the given number, converted to a string, with the
-- separator (default space) and singular or plural name appended.
plural = plural or (singular .. 's')
sep = sep or ' '
return tostring(number) .. sep .. ((number == 1) and singular or plural)
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).
local month_days = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
if month == 2 and is_leap_year(year, calname) then
return 29
end
return month_days[month]
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 floor = math.floor
local offset
local a = floor((14 - date.month)/12)
local y = date.year + 4800 - a
if date.calname == '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 + (date.hour + (date.minute + date.second / 60) /60) / 24 - 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 floor = math.floor
local calname = date.calname
local jd = date.jd
local limits -- min/max limits for date ranges −9999-01-01 to 9999-12-31
if calname == 'Julian' then
limits = { -1931076.5, 5373557.49999 }
elseif calname == 'Gregorian' then
limits = { -1930999.5, 5373484.49999 }
else
limits = { 1, 0 } -- impossible
end
if not (limits[1] <= jd and jd <= limits[2]) then
return
end
local jdn = floor(jd)
if date.hastime then
local time = jd - jdn
local hour
if time >= 0.5 then
jdn = jdn + 1
time = time - 0.5
hour = 0
else
hour = 12
end
time = floor(time * 24 * 3600 + 0.5) -- number of seconds after hour
date.second = time % 60
time = floor(time / 60)
date.minute = time % 60
date.hour = hour + floor(time / 60)
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 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.y or numbers[1]
local m = numbers.m or numbers[2]
local d = numbers.d or numbers[3]
local H = numbers.H or numbers[4]
local M = numbers.M or numbers[5] or 0
local S = numbers.S or numbers[6] or 0
if not (y and m and d) then
return
end
if not (-9999 <= y and y <= 9999 and 1 <= m and m <= 12 and
1 <= d and d <= days_in_month(y, m, date.calname)) then
return
end
if H then
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
return
end
date.year = y -- -9999 to 9999 ('n BC' → year = 1 - n)
date.month = m -- 1 to 12
date.day = d -- 1 to 31
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' }) 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 options2 or defaults.
-- Valid option settings are:
-- am: 'am', 'a.m.', 'AM', 'A.M.'
-- 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.
-- 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 = {}
if type(options1) == 'table' then
result = options1
elseif type(options1) == 'string' then
-- Example: '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
result[k] = result[k] or options2[k] or v
end
return result
end
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 'BC'] or {})[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 = 'doy' },
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]
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.' },
})[amopt] or { 'am', 'pm' }
return (spaces == '' and '' or ' ') .. (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 ' ') .. 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, for example, if id 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 formatted string from given date.
if type(fmt) ~= 'string' then
fmt = '%-d %B %-Y %{era}'
if date.hastime then
if date.second > 0 then
fmt = '%H:%M:%S ' .. fmt
else
fmt = '%H:%M ' .. fmt
end
end
return strftime(date, fmt, options)
end
if fmt:find('%', 1, true) then
return strftime(date, fmt, options)
end
local t = collection()
for item in fmt:gmatch('%S+') do
local f
if item == 'hm' then
f = '%H:%M'
elseif item == 'hms' then
f = '%H:%M:%S'
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 '(invalid format)'
end
t:add(f)
end
return strftime(date, t:join(' '), 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 month_number(text)
if type(text) == 'string' then
local month_names = {
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,
oct = 10, october = 10,
nov = 11, november = 11,
dec = 12, december = 12
}
return month_names[text:lower()]
end
end
-- A table to get the current year/month/day (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(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, 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 ambiguous.
local date, options = {}, {}
local function extract_ymd(item)
local ystr, mstr, dstr = item:match('^(%d%d%d%d)-(%w+)-(%d%d?)$')
if ystr then
local m
if mstr:match('^%d%d?$') then
m = tonumber(mstr)
else
m = month_number(mstr)
end
if m then
date.y = tonumber(ystr)
date.m = m
date.d = tonumber(dstr)
return true
end
end
end
local function extract_month(item)
-- A month must be given as a name or abbreviation; a number would be ambiguous.
local m = month_number(item)
if m then
date.m = m
return true
end
end
local function extract_time(item)
local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')
if date.H or not h then
return
end
if s ~= '' then
s = s:match('^:(%d%d)$')
if not s then
return
end
end
date.H = tonumber(h)
date.M = tonumber(m)
date.S = tonumber(s) -- nil if empty string
return true
end
local ampm_options = {
['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 item_count = 0
local index_time
local function set_ampm(item)
local H = date.H
if H and not options.am and index_time + 1 == item_count then
options.am = ampm_options[item]
if item:match('^[Aa]') then
if not (1 <= H and H <= 12) then
return
end
if H == 12 then
date.H = 0
end
else
if not (1 <= H and H <= 23) then
return
end
if H <= 11 then
date.H = H + 12
end
end
return true
end
end
for item in text:gsub(',', ' '):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.d and date.m then
if date.y then
return -- should be nothing more so item is invalid
end
if not item:match('^(%d%d?%d?%d?)$') then
return
end
date.y = tonumber(item)
elseif date.d then
if not extract_month(item) then
return
end
elseif date.m then
if not item:match('^(%d%d?)$') then
return
end
date.d = tonumber(item)
elseif not extract_ymd(item) then
if item:match('^(%d%d?)$') then
date.d = tonumber(item)
elseif not extract_month(item) then
return
end
end
end
if not date.y or date.y == 0 then
return
end
local era = era_text[options.era]
if era and era.isbc then
date.y = 1 - date.y
end
return date, options
end
local Date, DateDiff, datemt -- forward declarations
local function is_date(t)
return type(t) == 'table' and getmetatable(t) == datemt
end
local function date_add_sub(lhs, rhs, is_sub)
-- Return a new date from calculating (lhs + rhs) or (lhs - rhs),
-- or return nothing if invalid.
-- Caller ensures that lhs is a date; its properties are copied for the new date.
local function is_prefix(text, word, minlen)
local n = #text
return (minlen or 1) <= n and n <= #word and text == word:sub(1, n)
end
local function do_days(n)
if is_sub then
n = -n
end
return Date(lhs, 'juliandate', lhs.jd + n)
end
if type(rhs) == 'number' then
-- Add days, including fractional days.
return do_days(rhs)
end
if type(rhs) == 'string' then
-- rhs is a single component like '26m' or '26 months' (unsigned integer only).
local num, id = rhs:match('^%s*(%d+)%s*(%a+)$')
if num then
local y, m
num = tonumber(num)
id = id:lower()
if is_prefix(id, 'years') then
y = num
m = 0
elseif is_prefix(id, 'months') then
y = math.floor(num / 12)
m = num % 12
elseif is_prefix(id, 'weeks') then
return do_days(num * 7)
elseif is_prefix(id, 'days') then
return do_days(num)
elseif is_prefix(id, 'hours') then
return do_days(num / 24)
elseif is_prefix(id, 'minutes', 3) then
return do_days(num / (24 * 60))
elseif is_prefix(id, 'seconds') then
return do_days(num / (24 * 3600))
else
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.calname))
return Date(lhs, y, m, d)
end
end
end
-- Metatable for some operations on dates.
datemt = { -- for forward declaration above
__add = function (lhs, rhs)
if not is_date(lhs) then
lhs, rhs = rhs, lhs -- put date on left (it must be a date for this to have been called)
end
return date_add_sub(lhs, rhs)
end,
__sub = function (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,
__concat = function (lhs, rhs)
return tostring(lhs) .. tostring(rhs)
end,
__tostring = function (self)
return self:text()
end,
__eq = function (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 only called if lhs and rhs have the same metatable.
return lhs.jdz == rhs.jdz
end,
__lt = function (lhs, rhs)
-- Return true if lhs < rhs, for example,
-- Date('1 Jan 2016') < Date('06:00 1 Jan 2016') is true.
-- This is only called if lhs and rhs have the same metatable.
return lhs.jdz < rhs.jdz
end,
__index = function (self, key)
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.jd + 1) % 7 -- day-of-week 0=Sun to 6=Sat
elseif key == 'dowiso' then
value = (self.jd % 7) + 1 -- ISO day-of-week 1=Mon to 7=Sun
elseif key == 'doy' then
local first = Date(self.year, 1, 1, self.calname).jd
value = self.jd - first + 1 -- day-of-year 1 to 366
elseif key == 'era' then
-- Era text (not a negative sign) from year and options.
value = get_era_for_year(self.options.era, self.year)
elseif key == 'gsd' then
-- GSD = 1 from 00:00:00 to 23:59:59 on 1 January 1 AD Gregorian calendar,
-- which is JDN = 1721426, and is from jd 1721425.5 to 1721426.49999.
value = math.floor(self.jd - 1721424.5)
elseif key == 'jd' or key == 'jdz' then
local jd, jdz = julian_date(self)
rawset(self, 'jd', jd)
rawset(self, 'jdz', jdz)
return key == 'jd' and jd or jdz
elseif key == 'is_leap_year' then
value = is_leap_year(self.year, self.calname)
elseif key == 'monthabbr' then
value = month_info[self.month][1]
elseif key == 'monthname' then
value = month_info[self.month][2]
end
if value ~= nil then
rawset(self, key, value)
return value
end
end,
}
local function _month_days(date, month)
return days_in_month(date.year, month, date.calname)
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
LATER: Following is not yet implemented:
Date('currentdate', H, M, S) current date with given time
]]
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.
local is_copy
local calendars = { julian = 'Julian', gregorian = 'Gregorian' }
local result = {
calname = '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,
month_days = _month_days,
options = make_option_table(),
text = _date_text,
}
local argtype, datetext
local numbers = collection()
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
result.calname = calendars[vlower]
elseif is_date(v) then
-- Copy existing date (items can be overridden by other arguments).
if is_copy then
return
end
is_copy = true
result.calname = v.calname
result.hastime = v.hastime
result.options = v.options
result.year = v.year
result.month = v.month
result.day = v.day
result.hour = v.hour
result.minute = v.minute
result.second = v.second
else
local num = tonumber(v)
if not num and argtype == 'setdate' and numbers.n == 1 then
num = month_number(v)
end
if num then
if not argtype then
argtype = 'setdate'
end
numbers:add(num)
if argtype == 'juliandate' then
if type(v) == 'string' then
if v:find('.', 1, true) then
result.hastime = true
end
elseif num ~= math.floor(num) then
-- The given value was a number. The time will be used
-- if the fractional part is nonzero.
result.hastime = true
end
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 not (numbers.n == 0 and
set_date_from_numbers(result,
extract_date(datetext))) then
return
end
elseif argtype == 'juliandate' then
result.jd = numbers[1]
if not (numbers.n == 1 and set_date_from_jd(result)) then
return
end
elseif argtype == 'currentdate' or argtype == 'currentdatetime' then
result.year = current.year
result.month = current.month
result.day = current.day
if argtype == 'currentdatetime' then
result.hour = current.hour
result.minute = current.minute
result.second = current.second
result.hastime = true
end
result.calname = 'Gregorian' -- ignore any given calendar name
elseif argtype == 'setdate' then
if not set_date_from_numbers(result, numbers) then
return
end
elseif not is_copy then
return
end
return setmetatable(result, datemt)
end
function DateDiff(date1, date2) -- for forward declaration above
-- Return a table with the difference between the two dates (date1 - date2).
-- The difference is negative if date2 is more recent than date1.
-- Return nothing if invalid.
if not (date1 and date2 and date1.calname == date2.calname) then
return
end
local isnegative
if date1 < date2 then
isnegative = true
date1, date2 = date2, date1
end
-- It is known that date1 >= date2.
local y1, m1 = date1.year, date1.month
local y2, m2 = date2.year, date2.month
local years, months, days = y1 - y2, m1 - m2, date1.day - date2.day
if days < 0 then
days = days + days_in_month(y2, m2, date2.calname)
months = months - 1
end
if months < 0 then
months = months + 12
years = years - 1
end
return {
years = years,
months = months,
days = days,
isnegative = isnegative,
age_ym = function (self)
-- Return text specifying difference in years, months.
local sign = self.isnegative and MINUS or ''
local mtext = number_name(self.months, 'month')
local result
if self.years > 0 then
local ytext = number_name(self.years, 'year')
if self.months == 0 then
result = ytext
else
result = ytext .. ', ' .. mtext
end
else
if self.months == 0 then
sign = ''
end
result = mtext
end
return sign .. result
end,
}
end
return {
_current = current,
_Date = Date,
_DateDiff = DateDiff,
_days_in_month = days_in_month,
}
