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Module:Date: Difference between revisions

Module:Date (edit)

Revision as of 10:31, 20 March 2016

4,849 bytes added ,  8 years ago
major refactor with fixes; force Date to be read-only (error on write); list of dates in a month on a particular day of week
(clean up and some aliases)
(major refactor with fixes; force Date to be read-only (error on write); list of dates in a month on a particular day of week)
Line 4: Line 4:
local MINUS = '−'  -- Unicode U+2212 MINUS SIGN
local MINUS = '−'  -- Unicode U+2212 MINUS SIGN


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


local function is_date(t)
local function is_date(t)
return type(t) == 'table' and getmetatable(t) == datemt
-- 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
end


Line 18: Line 29:
self[self.n] = item
self[self.n] = item
end,
end,
join = function (self, sep)
join = _list_join,
return table.concat(self, sep)
end,
}
}
end
end
Line 93: Line 102:
local floor = math.floor
local floor = math.floor
local calname = date.calname
local calname = date.calname
local jd = date.jd
local limits  -- min/max limits for date ranges −9999-01-01 to 9999-12-31
local limits  -- min/max limits for date ranges −9999-01-01 to 9999-12-31
if calname == 'Julian' then
if calname == 'Julian' then
Line 100: Line 108:
limits = { -1930999.5, 5373484.49999 }
limits = { -1930999.5, 5373484.49999 }
else
else
limits = { 1, 0 }  -- impossible
return
end
end
if not (limits[1] <= jd and jd <= limits[2]) then
local jd = date.jd
if not (type(jd) == 'number' and limits[1] <= jd and jd <= limits[2]) then
return
return
end
end
Line 150: Line 159:
return
return
end
end
local y = numbers.y or numbers[1]
local y = numbers.year  or date.year
local m = numbers.m or numbers[2]
local m = numbers.month  or date.month
local d = numbers.d or numbers[3]
local d = numbers.day    or date.day
local H = numbers.H or numbers[4]
local H = numbers.hour
local M = numbers.M or numbers[5] or 0
local M = numbers.minute or date.minute or 0
local S = numbers.S or numbers[6] or 0
local S = numbers.second or date.second or 0
if not (y and m and d) then
if not (y and m and d) or not
return
(-9999 <= y and y <= 9999 and
end
1 <= m and m <= 12 and
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
1 <= d and d <= days_in_month(y, m, date.calname)) then
return
return
end
end
Line 166: Line 174:
date.hastime = true
date.hastime = true
else
else
H = 0
H = date.hour or 0
end
end
if not (0 <= H and H <= 23 and
if not (0 <= H and H <= 23 and
Line 206: Line 214:
-- Example: 'am:AM era:BC'
-- Example: 'am:AM era:BC'
for item in options1:gmatch('%S+') do
for item in options1:gmatch('%S+') do
local lhs, rhs = item:match('^(%w+):(.+)$')
local lhs, rhs = item:match('^(%w+)[:=](.+)$')
if lhs then
if lhs then
result[lhs] = rhs
result[lhs] = rhs
Line 339: Line 347:
:gsub('%%%%', PERCENT)
:gsub('%%%%', PERCENT)
:gsub('(%s*)%%{(%w+)}', replace_property)
:gsub('(%s*)%%{(%w+)}', replace_property)
:gsub('(%s*)%%(-?)(%a)', replace_code)
:gsub('(%s*)%%(%-?)(%a)', replace_code)
:gsub(PERCENT, '%%')
:gsub(PERCENT, '%%')
)
)
Line 345: Line 353:


local function _date_text(date, fmt, options)
local function _date_text(date, fmt, options)
-- Return formatted string from given date.
-- Return a formatted string representing the given date.
if not is_date(date) then
if not is_date(date) then
return 'Need a date (use "date:text()" with a colon).'
return 'Need a date (use "date:text()" with a colon).'
Line 410: Line 418:
{ 'Dec', 'December' },
{ '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)
local function month_number(text)
if type(text) == 'string' then
return name_to_number(text, {
local month_names = {
jan = 1, january = 1,
jan = 1, january = 1,
feb = 2, february = 2,
feb = 2, february = 2,
mar = 3, march = 3,
mar = 3, march = 3,
apr = 4, april = 4,
apr = 4, april = 4,
may = 5,
may = 5,
jun = 6, june = 6,
jun = 6, june = 6,
jul = 7, july = 7,
jul = 7, july = 7,
aug = 8, august = 8,
aug = 8, august = 8,
sep = 9, september = 9,
sep = 9, september = 9,
oct = 10, october = 10,
oct = 10, october = 10,
nov = 11, november = 11,
nov = 11, november = 11,
dec = 12, december = 12,
dec = 12, december = 12
})
}
end
return month_names[text:lower()]
 
local function _list_text(list, fmt)
-- Return a list of formatted strings from a list of dates.
if not type(list) == 'table' then
return 'Need "list:text()" with a colon.'
end
local result = { join = _list_join }
for i, date in ipairs(list) do
result[i] = date:text(fmt)
end
return result
end
 
local function _make_list(date, spec)
-- Return a possibly empty numbered table of dates meeting the specification.
-- The spec should be a string like "Tue >=" meaning that the list will
-- hold dates for all Tuesdays on or after date, and in date's month.
if not is_date(date) then
return 'Need a date (use "date:list()" with a colon).'
end
local want_dow, op
local ops = {
['>='] = { before = false, include = true  },
['>']  = { before = false, include = false },
['<='] = { before = true , include = true  },
['<']  = { before = true , include = false },
}
if spec then
if type(spec) ~= 'string' then
return {}
end
for item in spec:gmatch('%S+') do
if ops[item] then
if op then
return {}
end
op = ops[item]
else
local dow = day_number(item)
if dow then
if want_dow then
-- LATER Could handle more than one day, but probably not needed.
return {}
end
want_dow = dow
else
return {}
end
end
end
end
local offset = want_dow and want_dow - date.dow or 0
op = op or ops['>=']
local first, last
if op.before then
if offset >= 0 and not (op.include and offset == 0) then
offset = offset - 7
end
last = date.day + offset
first = last % 7
if first == 0 then
first = 7
end
else
if offset < 0 or (not op.include and offset == 0) then
offset = offset + 7
end
first = date.day + offset
last = date.monthdays
end
local list = { text = _list_text }
local count = math.floor((last - first)/7) + 1
for i = 1, count do
list[i] = Date(date, {day = first})
first = first + 7
end
end
return list
end
end


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


local function extract_date(text)
local function extract_date(text)
Line 458: Line 560:
local date, options = {}, {}
local date, options = {}, {}
local function extract_ymd(item)
local function extract_ymd(item)
local ystr, mstr, dstr = item:match('^(%d%d%d%d)-(%w+)-(%d%d?)$')
local ystr, mstr, dstr = item:match('^(%d%d%d%d)%-(%w+)%-(%d%d?)$')
if ystr then
if ystr then
local m
local m
Line 467: Line 569:
end
end
if m then
if m then
date.y = tonumber(ystr)
date.year = tonumber(ystr)
date.m = m
date.month = m
date.d = tonumber(dstr)
date.day = tonumber(dstr)
return true
return true
end
end
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local m = month_number(item)
local m = month_number(item)
if m then
if m then
date.m = m
date.month = m
return true
return true
end
end
Line 484: Line 586:
local function extract_time(item)
local function extract_time(item)
local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')
local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')
if date.H or not h then
if date.hour or not h then
return
return
end
end
Line 493: Line 595:
end
end
end
end
date.H = tonumber(h)
date.hour = tonumber(h)
date.M = tonumber(m)
date.minute = tonumber(m)
date.S = tonumber(s)  -- nil if empty string
date.second = tonumber(s)  -- nil if empty string
return true
return true
end
end
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local index_time
local index_time
local function set_ampm(item)
local function set_ampm(item)
local H = date.H
local H = date.hour
if H and not options.am and index_time + 1 == item_count then
if H and not options.am and index_time + 1 == item_count then
options.am = ampm_options[item]
options.am = ampm_options[item]
Line 519: Line 621:
end
end
if H == 12 then
if H == 12 then
date.H = 0
date.hour = 0
end
end
else
else
Line 526: Line 628:
end
end
if H <= 11 then
if H <= 11 then
date.H = H + 12
date.hour = H + 12
end
end
end
end
Line 549: Line 651:
end
end
index_time = item_count
index_time = item_count
elseif date.d and date.m then
elseif date.day and date.month then
if date.y then
if date.year then
return  -- should be nothing more so item is invalid
return  -- should be nothing more so item is invalid
end
end
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return
return
end
end
date.y = tonumber(item)
date.year = tonumber(item)
elseif date.d then
elseif date.day then
if not extract_month(item) then
if not extract_month(item) then
return
return
end
end
elseif date.m then
elseif date.month then
if not item:match('^(%d%d?)$') then
if not item:match('^(%d%d?)$') then
return
return
end
end
date.d = tonumber(item)
date.day = tonumber(item)
elseif not extract_ymd(item) then
elseif not extract_ymd(item) then
if item:match('^(%d%d?)$') then
if item:match('^(%d%d?)$') then
date.d = tonumber(item)
date.day = tonumber(item)
elseif not extract_month(item) then
elseif not extract_month(item) then
return
return
Line 574: Line 676:
end
end
end
end
if not date.y or date.y == 0 then
if not date.year or date.year == 0 then
return
return
end
end
local era = era_text[options.era]
local era = era_text[options.era]
if era and era.isbc then
if era and era.isbc then
date.y = 1 - date.y
date.year = 1 - date.year
end
end
return date, options
return date, options
Line 587: Line 689:
-- Return a new date from calculating (lhs + rhs) or (lhs - rhs),
-- Return a new date from calculating (lhs + rhs) or (lhs - rhs),
-- or return nothing if invalid.
-- 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.
-- Caller ensures that lhs is a date; its properties are copied for the new date.
local function is_prefix(text, word, minlen)
local function is_prefix(text, word, minlen)
Line 593: Line 696:
end
end
local function do_days(n)
local function do_days(n)
if is_sub then
local forcetime, jd
n = -n
if math.floor(n) == n then
jd = lhs.jd
else
forcetime = not lhs.hastime
jd = lhs.jdz
end
end
return Date(lhs, 'juliandate', lhs.jd + n)
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
end
if type(rhs) == 'number' then
if type(rhs) == 'number' then
-- Add days, including fractional days.
-- Add/subtract days, including fractional days.
return do_days(rhs)
return do_days(rhs)
end
end
Line 648: Line 762:
end
end


-- Metatable for some operations on dates.
-- Metatable for a date's calculated fields.
datemt = {  -- for forward declaration above
local datemt = {
__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)
__index = function (self, key)
local value
local value
Line 689: Line 771:
value = day_info[self.dow][2]
value = day_info[self.dow][2]
elseif key == 'dow' then
elseif key == 'dow' then
value = (self.jd + 1) % 7  -- day-of-week 0=Sun to 6=Sat
value = (self.jdnoon + 1) % 7  -- day-of-week 0=Sun to 6=Sat
elseif key == 'dayofweek' then
elseif key == 'dayofweek' then
value = self.dow
value = self.dow
elseif key == 'dowiso' then
elseif key == 'dowiso' then
value = (self.jd % 7) + 1  -- ISO day-of-week 1=Mon to 7=Sun
value = (self.jdnoon % 7) + 1  -- ISO day-of-week 1=Mon to 7=Sun
elseif key == 'dayofweekiso' then
elseif key == 'dayofweekiso' then
value = self.dowiso
value = self.dowiso
elseif key == 'doy' then
elseif key == 'doy' then
local first = Date(self.year, 1, 1, self.calname).jd
local first = Date(self.year, 1, 1, self.calname).jdnoon
value = self.jd - first + 1  -- day-of-year 1 to 366
value = self.jdnoon - first + 1  -- day-of-year 1 to 366
elseif key == 'dayofyear' then
elseif key == 'dayofyear' then
value = self.doy
value = self.doy
Line 706: Line 788:
elseif key == 'gsd' then
elseif key == 'gsd' then
-- GSD = 1 from 00:00:00 to 23:59:59 on 1 January 1 AD Gregorian calendar,
-- 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.
-- which is from jd 1721425.5 to 1721426.49999.
value = math.floor(self.jd - 1721424.5)
value = math.floor(self.jd - 1721424.5)
elseif key == 'juliandate' or key == 'jd' or key == 'jdz' then
elseif key == 'juliandate' or key == 'jd' or key == 'jdz' then
Line 714: Line 796:
rawset(self, 'jdz', jdz)
rawset(self, 'jdz', jdz)
return key == 'jdz' and jdz or jd
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 = math.floor(self.jd + 0.5)
elseif key == 'isleapyear' then
elseif key == 'isleapyear' then
value = is_leap_year(self.year, self.calname)
value = is_leap_year(self.year, self.calname)
Line 729: Line 814:
end,
end,
}
}
-- Date operators.
local function mt_date_add(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
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 only called if lhs and rhs have the same metatable.
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 only called if lhs and rhs have the same metatable.
return lhs.jdz < rhs.jdz
end


--[[ Examples of syntax to construct a date:
--[[ Examples of syntax to construct a date:
Line 740: Line 864:
Date('04:30:59 1 April 1995', 'julian')
Date('04:30:59 1 April 1995', 'julian')
Date(date)                          copy of an existing date
Date(date)                          copy of an existing date
LATER: Following is not yet implemented:
Date(date, t)                      same, updated with y,m,d,H,M,S fields from table t
Date('currentdate', H, M, S)       current date with given time
Date(t)                       date with y,m,d,H,M,S fields from table t
]]
]]
function Date(...)  -- for forward declaration above
function Date(...)  -- for forward declaration above
Line 747: Line 871:
-- (proleptic Gregorian calendar or proleptic Julian calendar), or
-- (proleptic Gregorian calendar or proleptic Julian calendar), or
-- return nothing if date is invalid.
-- return nothing if date is invalid.
local is_copy
local calendars = { julian = 'Julian', gregorian = 'Gregorian' }
local calendars = { julian = 'Julian', gregorian = 'Gregorian' }
local result = {
local newdate = {
_id = uniq,
calname = 'Gregorian',  -- default is Gregorian calendar
calname = 'Gregorian',  -- default is Gregorian calendar
hastime = false,  -- true if input sets a time
hastime = false,  -- true if input sets a time
Line 756: Line 880:
second = 0,
second = 0,
options = make_option_table(),
options = make_option_table(),
list = _make_list,
text = _date_text,
text = _date_text,
}
}
local argtype, datetext
local argtype, datetext, is_copy, jd_number, tnums
local numbers = collection()
local numindex = 0
local numfields = { 'year', 'month', 'day', 'hour', 'minute', 'second' }
local numbers = {}
for _, v in ipairs({...}) do
for _, v in ipairs({...}) do
v = strip_to_nil(v)
v = strip_to_nil(v)
Line 766: Line 893:
-- Ignore empty arguments after stripping so modules can directly pass template parameters.
-- Ignore empty arguments after stripping so modules can directly pass template parameters.
elseif calendars[vlower] then
elseif calendars[vlower] then
result.calname = calendars[vlower]
newdate.calname = calendars[vlower]
elseif is_date(v) then
elseif is_date(v) then
-- Copy existing date (items can be overridden by other arguments).
-- Copy existing date (items can be overridden by other arguments).
if is_copy then
if is_copy or tnums then
return
return
end
end
is_copy = true
is_copy = true
result.calname = v.calname
newdate.calname = v.calname
result.hastime = v.hastime
newdate.hastime = v.hastime
result.options = v.options
newdate.options = v.options
result.year = v.year
newdate.year = v.year
result.month = v.month
newdate.month = v.month
result.day = v.day
newdate.day = v.day
result.hour = v.hour
newdate.hour = v.hour
result.minute = v.minute
newdate.minute = v.minute
result.second = v.second
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
else
local num = tonumber(v)
local num = tonumber(v)
if not num and argtype == 'setdate' and numbers.n == 1 then
if not num and argtype == 'setdate' and numindex == 1 then
num = month_number(v)
num = month_number(v)
end
end
Line 791: Line 932:
argtype = 'setdate'
argtype = 'setdate'
end
end
numbers:add(num)
if argtype == 'setdate' and numindex < 6 then
if argtype == 'juliandate' 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 type(v) == 'string' then
if v:find('.', 1, true) then
if v:find('.', 1, true) then
result.hastime = true
newdate.hastime = true
end
end
elseif num ~= math.floor(num) then
elseif num ~= math.floor(num) then
-- The given value was a number. The time will be used
-- The given value was a number. The time will be used
-- if the fractional part is nonzero.
-- if the fractional part is nonzero.
result.hastime = true
newdate.hastime = true
end
end
else
return
end
end
elseif argtype then
elseif argtype then
Line 818: Line 964:
end
end
if argtype == 'datetext' then
if argtype == 'datetext' then
if not (numbers.n == 0 and
if tnums or not set_date_from_numbers(newdate, extract_date(datetext)) then
set_date_from_numbers(result,
extract_date(datetext))) then
return
return
end
end
elseif argtype == 'juliandate' then
elseif argtype == 'juliandate' then
result.jd = numbers[1]
newdate.jd = jd_number
if not (numbers.n == 1 and set_date_from_jd(result)) then
if not set_date_from_jd(newdate) then
return
return
end
end
elseif argtype == 'currentdate' or argtype == 'currentdatetime' then
elseif argtype == 'currentdate' or argtype == 'currentdatetime' then
result.year = current.year
newdate.year = current.year
result.month = current.month
newdate.month = current.month
result.day = current.day
newdate.day = current.day
if argtype == 'currentdatetime' then
if argtype == 'currentdatetime' then
result.hour = current.hour
newdate.hour = current.hour
result.minute = current.minute
newdate.minute = current.minute
result.second = current.second
newdate.second = current.second
result.hastime = true
newdate.hastime = true
end
end
result.calname = 'Gregorian'  -- ignore any given calendar name
newdate.calname = 'Gregorian'  -- ignore any given calendar name
elseif argtype == 'setdate' then
elseif argtype == 'setdate' then
if not set_date_from_numbers(result, numbers) then
if tnums or not set_date_from_numbers(newdate, numbers) then
return
return
end
end
elseif not is_copy then
elseif not (is_copy or tnums) then
return
return
end
end
return setmetatable(result, datemt)
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
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
end
local function _age_ym(diff)
-- Return text specifying date difference in years, months.
local sign = diff.isnegative and MINUS or ''
local mtext = number_name(diff.months, 'month')
local result
if diff.years > 0 then
local ytext = number_name(diff.years, 'year')
if diff.months == 0 then
result = ytext
else
result = ytext .. ',&nbsp;' .. mtext
end
else
if diff.months == 0 then
sign = ''
end
result = mtext
end
return sign .. result
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.daystotal)
end,
__index = function (self, key)
local value
if key == 'age_ym' then
value = _age_ym(self)
elseif key == 'daystotal' then
value = self.date1.jdz - self.date2.jdz
end
if value ~= nil then
rawset(self, key, value)
return value
end
end,
}


function DateDiff(date1, date2)  -- for forward declaration above
function DateDiff(date1, date2)  -- for forward declaration above
-- Return a table with the difference between the two dates (date1 - date2).
-- Return a table with the difference between the two dates (date1 - date2).
-- The difference is negative if date2 is more recent than date1.
-- The difference is negative if date1 is older than date2.
-- Return nothing if invalid.
-- Return nothing if invalid.
if not (is_date(date1) and is_date(date2) and date1.calname == date2.calname) then
if not (is_date(date1) and is_date(date2) and date1.calname == date2.calname) then
return
return
end
end
local isnegative
local isnegative = false
if date1 < date2 then
if date1 < date2 then
isnegative = true
isnegative = true
Line 873: Line 1,078:
years = years - 1
years = years - 1
end
end
return {
return setmetatable({
date1 = date1,
date2 = date2,
years = years,
years = years,
months = months,
months = months,
days = days,
days = days,
isnegative = isnegative,
isnegative = isnegative,
age_ym = function (self)
}, diffmt)
-- 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 .. ',&nbsp;' .. mtext
end
else
if self.months == 0 then
sign = ''
end
result = mtext
end
return sign .. result
end,
}
end
end


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Retrieved from "https://nonbinary.wiki/wiki/Special:MobileDiff/30259"
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