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restore new version: sorry, I forgot to update Template:Age in years and months last time
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(restore new version: sorry, I forgot to update Template:Age in years and months last time)
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--[[ Code for some date functions, including implementations of:
-- Implement various "age of" and other date-related templates.
        {{Age in days}}                age_days
        {{Age in years and months}}    age_ym
        {{Gregorian serial date}}      gsd_ymd
Calendar functions will be needed in many areas, so this may be superseded
by some other system, perhaps using PHP functions accessed via mediawiki.
]]


local MINUS = '' -- Unicode U+2212 MINUS SIGN
local _Date, _current_date
local function get_exports(frame)
-- Return objects exported from the date module or its sandbox.
if not _Date then
local sandbox = frame:getTitle():find('sandbox', 1, true) and '/sandbox' or ''
local datemod = require('Module:Date' .. sandbox)
_Date = datemod._Date
_current_date = datemod._current
end
return _Date, _current_date
end


local function number_name(number, singular, plural, sep)
local function collection()
    -- Return the given number, converted to a string, with the
-- Return a table to hold items.
    -- separator (default space) and singular or plural name appended.
return {
    plural = plural or (singular .. 's')
n = 0,
    sep = sep or ' '
add = function (self, item)
    return tostring(number) .. sep .. ((number == 1) and singular or plural)
self.n = self.n + 1
    -- this uses an interesting trick of Lua:
self[self.n] = item
    --  * and returns false if the first argument is false, and the second otherwise, so (number==1) and singular returns singular if its 1, returns false if it is only 1
end,
    --  * or returns the first argument if it is not false, and the second argument if the first is false
join = function (self, sep)
    --  * so, if number is 1, and evaluates (true and singular) returning (singular); or evaluates (singular or plural), finds singular non-false, and returns singular
return table.concat(self, sep)
    --  * but, if number is not 1, and evaluates (false and singular) returning (false); or evaluates (false or plural), and is forced to return plural
end,
}
end
end


local function strip_to_nil(text)
local function strip_to_nil(text)
    -- If text is a non-blank string, return its content with no leading
-- If text is a string, return its trimmed content, or nil if empty.
    -- or trailing whitespace.
-- Otherwise return text (which may, for example, be nil).
    -- Otherwise return nil (a nil or empty string argument gives a nil
if type(text) == 'string' then
    -- result, as does a string argument of only whitespace).
text = text:match('(%S.-)%s*$')
    if type(text) == 'string' then
end
        local result = text:match("^%s*(.-)%s*$")
return text
        if result ~= '' then
            return result
        end
    end
    return nil
end
end


local function is_leap_year(year)
local function yes(parameter)
    -- Return true if year is a leap year, assuming Gregorian calendar.
-- Return true if parameter should be interpreted as "yes".
    return year % 4 == 0 and (year % 100 ~= 0 or year % 400 == 0)
-- Do not want to accept mixed upper/lowercase unless done by current templates.
-- Need to accept "on" because "round=on" is wanted.
return ({ y = true, yes = true, on = true })[parameter]
end
end


local function days_in_month(year, month)
local function message(msg, nocat)
    -- Return number of days (1..31) in given month (1..12).
-- Return formatted message text for an error.
    local month_days = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
-- Can append "#FormattingError" to URL of a page with a problem to find it.
    if month == 2 and is_leap_year(year) then
local anchor = '<span id="FormattingError" />'
        return 29
local category
    end
if not nocat and mw.title.getCurrentTitle():inNamespaces(0, 10) then
    return month_days[month]
-- Category only in namespaces: 0=article, 10=template.
category = '[[Category:Age error]]'
else
category = ''
end
return anchor ..
'<strong class="error">Error: ' ..
mw.text.nowiki(msg) ..
'</strong>' ..
category
end
end


-- A table to get current year/month/day (UTC), but only if needed.
local function formatnumber(number)
local current = setmetatable({}, {
-- Return the given number formatted with commas as group separators,
        __index = function (self, key)
-- given that the number is an integer.
            local d = os.date('!*t')
local numstr = tostring(number)
            self.year = d.year
local length = #numstr
            self.month = d.month
local places = collection()
            self.day = d.day
local pos = 0
            return rawget(self, key)
repeat
        end
places:add(pos)
    })
pos = pos + 3
 
until pos >= length
local function date_component(named, positional, component)
places:add(length)
    -- Return the first of the two arguments that is not nil and is not empty.
local groups = collection()
    -- If both are nil, return the current date component, if specified.
for i = places.n, 2, -1 do
    -- The returned value is nil or is a number.
local p1 = length - places[i] + 1
    -- This translates empty arguments passed to the template to nil, and
local p2 = length - places[i - 1]
    -- optionally replaces a nil argument with a value from the current date.
groups:add(numstr:sub(p1, p2))
    named = strip_to_nil(named)
end
    if named then
return groups:join(',')
        return tonumber(named)
    end
    positional = strip_to_nil(positional)
    if positional then
        return tonumber(positional)
    end
    if component then
        return current[component]
    end
    return nil
end
end


local function gsd(year, month, day)
local function make_sort(value, sortable)
    -- Return the Gregorian serial day (an integer >= 1) for the given date,
-- Return a sort key in a span if specified.
    -- or return nil if the date is invalid (only check that year >= 1).
-- Assume value is a valid number which has not overflowed.
    -- This is the number of days from the start of 1 AD (there is no year 0).
if sortable == 'sortable_on' or sortable == 'sortable_debug' then
    -- This code implements the logic in [[Template:Gregorian serial date]].
local sortkey
    if year < 1 then
if value == 0 then
        return nil
sortkey = '5000000000000000000'
    end
else
    local floor = math.floor
local mag = math.floor(math.log10(math.abs(value)) + 1e-14)
    local days_this_year = (month - 1) * 30.5 + day
local prefix
    if month > 2 then
if value > 0 then
        if is_leap_year(year) then
prefix = 7000 + mag
            days_this_year = days_this_year - 1
else
        else
prefix = 2999 - mag
            days_this_year = days_this_year - 2
value = value + 10^(mag+1)
        end
end
        if month > 8 then
sortkey = string.format('%d', prefix) .. string.format('%015.0f', math.floor(value * 10^(14-mag)))
            days_this_year = days_this_year + 0.9
end
        end
local lhs = sortable == 'sortable_debug' and
    end
'<span style="border:1px solid;display:inline;" class="sortkey">' or
    days_this_year = floor(days_this_year + 0.5)
'<span style="display:none" class="sortkey">'
    year = year - 1
return lhs .. sortkey .. '♠</span>'
    local days_from_past_years = year * 365
end
        + floor(year / 4)
        - floor(year / 100)
        + floor(year / 400)
    return days_from_past_years + days_this_year
end
end


local Date = {
local translate_parameters = {
    -- A naive date that assumes the Gregorian calendar always applied.
abbr = {
    year = 0,   -- 1 to 9999 (0 if never set)
off = 'abbr_off',
    month = 1, -- 1 to 12
on = 'abbr_on',
    day = 1,   -- 1 to 31
},
    isvalid = false,
disp = {
    new = function (self, o)
age = 'disp_age',
        o = o or {}
raw = 'disp_raw',
        setmetatable(o, self)
},
        self.__index = self
format = {
        return o
raw = 'format_raw',
    end
commas = 'format_commas',
},
round = {
on = 'on',
yes = 'on',
months = 'ym',
weeks = 'ymw',
days = 'ymd',
hours = 'ymdh',
},
sep = {
comma = 'sep_comma',
[','] = 'sep_comma',
serialcomma = 'sep_serialcomma',
space = 'sep_space',
},
show = {
hide = { id = 'hide' },
y = { 'y', id = 'y' },
ym = { 'y', 'm', id = 'ym' },
ymd = { 'y', 'm', 'd', id = 'ymd' },
ymw = { 'y', 'm', 'w', id = 'ymw' },
ymwd = { 'y', 'm', 'w', 'd', id = 'ymwd' },
yd = { 'y', 'd', id = 'yd', keepzero = true },
m = { 'm', id = 'm' },
md = { 'm', 'd', id = 'md' },
w = { 'w', id = 'w' },
wd = { 'w', 'd', id = 'wd' },
d = { 'd', id = 'd' },
dh = { 'd', 'H', id = 'dh' },
dhm = { 'd', 'H', 'M', id = 'dhm' },
ymdh = { 'y', 'm', 'd', 'H', id = 'ymdh' },
ymdhm = { 'y', 'm', 'd', 'H', 'M', id = 'ymdhm' },
ymwdh = { 'y', 'm', 'w', 'd', 'H', id = 'ymwdh' },
ymwdhm = { 'y', 'm', 'w', 'd', 'H', 'M', id = 'ymwdhm' },
},
sortable = {
off = false,
on = 'sortable_on',
debug = 'sortable_debug',
},
}
}


function Date:__lt(rhs)
local function date_extract(frame)
    -- Return true if self < rhs.
-- Return part of a date after performing an optional operation.
    if self.year < rhs.year then
local Date = get_exports(frame)
        return true
local args = frame:getParent().args
    elseif self.year == rhs.year then
local parms = {}
        if self.month < rhs.month then
for i, v in ipairs(args) do
            return true
parms[i] = v
        elseif self.month == rhs.month then
end
            return self.day < rhs.day
if yes(args.fix) then
        end
table.insert(parms, 'fix')
    end
end
    return false
if yes(args.partial) then
    -- probably simplify to return (self.year < rhs.year) or ((self.year == rhs.year) and ((self.month < rhs.month) or ((self.month == rhs.month) and (self.day < rhs.day))))
table.insert(parms, 'partial')
    -- would be just as efficient, as lua does not evaluate second argument of (true or second_argument)
end
    -- or similarly return self.year < rhs.year ? true : self.year > rhs.year ? false : self.month < rhs.month ? true : self.month > rhs.month ? false : self.day < rhs.day
local date = Date(unpack(parms))
if not date then
return message('Need valid date')
end
local add = strip_to_nil(args.add)
if add then
for item in add:gmatch('%S+') do
date = date + item
if not date then
return message('Cannot add "' .. item .. '"')
end
end
end
local prefix, result
local sortable = translate_parameters.sortable[args.sortable]
if sortable then
local value = (date.partial and date.partial.first or date).jdz
prefix = make_sort(value, sortable)
end
local show = strip_to_nil(args.show) or 'dmy'
if show ~= 'hide' then
result = date[show]
if result == nil then
result = date:text(show)
elseif type(result) == 'boolean' then
result = result and '1' or '0'
else
result = tostring(result)
end
end
return (prefix or '') .. (result or '')
end
end


function Date:set_current()
local function make_text(values, components, names, options)
    -- Set date from current time (UTC) and return self.
-- Return wikitext representing an age or duration.
    self.year = current.year
local text = collection()
    self.month = current.month
local count = #values
    self.day = current.day
local sep = names.sep or ''
    self.isvalid = true
for i, v in ipairs(values) do
    return self
-- v is a number (say 4 for 4 years), or a table ({4,5} for 4 or 5 years).
local islist = type(v) == 'table'
if (islist or v > 0) or (text.n == 0 and i == count) or (text.n > 0 and components.keepzero) then
local fmt, vstr
if i == 1 and options.format == 'format_commas' then
-- Numbers after the first should be small and not need formatting.
fmt = formatnumber
else
fmt = tostring
end
if islist then
local join = options.range == 'dash' and '–' or '&nbsp;or '
vstr = fmt(v[1]) .. join .. fmt(v[2])
else
vstr = fmt(v)
end
local name = names[components[i]]
if name then
local plural = names.plural
if not plural or (islist and v[2] or v) == 1 then
plural = ''
end
text:add(vstr .. sep .. name .. plural)
else
text:add(vstr)
end
end
end
local first, last
if options.join == 'sep_space' then
first = ' '
last = ' '
elseif options.join == 'sep_comma' then
first = ', '
last = ', '
elseif options.join == 'sep_serialcomma' and text.n > 2 then
first = ', '
last = ', and '
else
first = ', '
last = ' and '
end
for i, v in ipairs(text) do
if i < text.n then
text[i] = v .. (i + 1 < text.n and first or last)
end
end
local sign = ''
if options.isnegative then
-- Do not display negative zero.
if text.n > 1 or (text.n == 1 and text[1]:sub(1, 1) ~= '0' ) then
if options.format == 'format_raw' then
sign = '-'  -- plain hyphen so result can be used in a calculation
else
sign = '−'  -- Unicode U+2212 MINUS SIGN
end
end
end
return
(options.prefix or '') ..
sign ..
text:join() ..
(options.suffix or '')
end
end


function Date:set_ymd(y, m, d)
local function date_difference(parms)
    -- Set date from year, month, day (strings or numbers) and return self.
-- Return a formatted date difference using the given parameters
    -- LATER: If m is a name like "March" or "mar", translate it to a month.
-- which have been validated.
    y = tonumber(y)
local names = {
    m = tonumber(m)
abbr_off = {
    d = tonumber(d)
plural = 's',
    if type(y) == 'number' and type(m) == 'number' and type(d) == 'number' then
sep = '&nbsp;',
        self.year = y
y = 'year',
        self.month = m
m = 'month',
        self.day = d
w = 'week',
        self.isvalid = (1 <= y and y <= 9999 and 1 <= m and m <= 12 and
d = 'day',
                        1 <= d and d <= days_in_month(y, m))
H = 'hour',
    end
M = 'minute',
    return self
},
abbr_on = {
y = 'y',
m = 'm',
w = 'w',
d = 'd',
H = 'h',
M = 'm',
},
abbr_infant = {      -- for {{age for infant}}
plural = 's',
sep = '&nbsp;',
y = 'yr',
m = 'mo',
w = 'wk',
d = 'day',
H = 'hr',
M = 'min',
},
abbr_raw = {},
}
local diff = parms.diff  -- must be a valid date difference
local show = parms.show  -- may be nil; default is set below
local abbr = parms.abbr or 'abbr_off'
local default_join
if abbr ~= 'abbr_off' then
default_join = 'sep_space'
end
if not show then
show = 'ymd'
if parms.disp == 'disp_age' then
if diff.years < 3 then
default_join = 'sep_space'
if diff.years >= 1 then
show = 'ym'
else
show = 'md'
end
else
show = 'y'
end
end
end
if type(show) ~= 'table' then
show = translate_parameters.show[show]
end
if parms.disp == 'disp_raw' then
default_join = 'sep_space'
abbr = 'abbr_raw'
elseif parms.want_sc then
default_join = 'sep_serialcomma'
end
local diff_options = {
round = parms.round,
duration = parms.want_duration,
range = parms.range and true or nil,
}
local prefix
if parms.sortable then
local value = diff.age_days + (parms.want_duration and 1 or 0)  -- days and fraction of a day
if diff.isnegative then
value = -value
end
prefix = make_sort(value, parms.sortable)
end
local text_options = {
prefix = prefix,
suffix = parms.suffix,  -- not currently used
format = parms.format,
join = parms.sep or default_join,
isnegative = diff.isnegative,
range = parms.range,
}
if show.id == 'hide' then
return prefix or ''
end
local values = { diff:age(show.id, diff_options) }
return make_text(values, show, names[abbr], text_options)
end
end


local DateDiff = {
local function get_dates(frame, getopt)
    -- Simple difference between two dates, assuming Gregorian calendar.
-- Parse template parameters and return one of:
    isnegative = false,  -- true if second date is before first
-- * date        (a date table, if single)
    years = 0,
-- * date1, date2 (two date tables, if not single)
    months = 0,
-- * text        (a string error message)
    days = 0,
-- A missing date is replaced with the current date.
    new = function (self, o)
-- If want_mixture is true, a missing date component is replaced
        o = o or {}
-- from the current date, so can get a bizarre mixture of
        setmetatable(o, self)
-- specified/current y/m/d as has been done by some "age" templates.
        self.__index = self
-- Some results may be placed in table getopt.
        return o
local Date, current_date = get_exports(frame)
    end
getopt = getopt or {}
}
local fix = getopt.fix and 'fix' or ''
 
local partial = getopt.range and 'partial' or ''
function DateDiff:set(date1, date2)
local args = frame:getParent().args
    -- Set difference between the two dates, and return self.
local fields = {}
    -- Difference is negative if the second date is older than the first.
local is_named = args.year or args.year1 or args.year2 or
    local isnegative
args.month or args.month1 or args.month2 or
    if date2 < date1 then
args.day or args.day1 or args.day2
        isnegative = true
if is_named then
        date1, date2 = date2, date1
fields[1] = args.year1 or args.year
    else
fields[2] = args.month1 or args.month
        isnegative = false
fields[3] = args.day1 or args.day
    end
fields[4] = args.year2
    -- It is known that date1 <= date2.
fields[5] = args.month2
    local y1, m1, d1 = date1.year, date1.month, date1.day
fields[6] = args.day2
    local y2, m2, d2 = date2.year, date2.month, date2.day
else
    local years, months, days = y2 - y1, m2 - m1, d2 - d1
for i = 1, 6 do
    if days < 0 then
fields[i] = args[i]
        days = days + days_in_month(y1, m1)
end
        months = months - 1
end
    end
local imax = 0
    if months < 0 then
for i = 1, 6 do
        months = months + 12
fields[i] = strip_to_nil(fields[i])
        years = years - 1
if fields[i] then
    end
imax = i
    self.years, self.months, self.days, self.isnegative = years, months, days, isnegative
end
    return self
end
local single = getopt.single
local dates = {}
if is_named or imax > 2 then
local nr_dates = single and 1 or 2
if getopt.want_mixture then
-- Cannot be partial since empty fields are set from current.
local components = { 'year', 'month', 'day' }
for i = 1, nr_dates * 3 do
fields[i] = fields[i] or current_date[components[i > 3 and i - 3 or i]]
end
for i = 1, nr_dates do
local index = i == 1 and 1 or 4
dates[i] = Date(fields[index], fields[index+1], fields[index+2])
end
else
for i = 1, nr_dates do
local index = i == 1 and 1 or 4
local y, m, d = fields[index], fields[index+1], fields[index+2]
if (partial and y) or (y and m and d) then
dates[i] = Date(fix, partial, y, m, d)
elseif not (y or m or d) then
dates[i] = Date('currentdate')
end
end
end
else
getopt.textdates = true
dates[1] = Date(fix, partial, fields[1] or 'currentdate')
if not single then
dates[2] = Date(fix, partial, fields[2] or 'currentdate')
end
end
if not dates[1] then
return message('Need valid year, month, day')
end
if single then
return dates[1]
end
if not dates[2] then
return message('Second date should be year, month, day')
end
return dates[1], dates[2]
end
end


function DateDiff:age_ym()
local function age_generic(frame)
    -- Return text specifying difference in years, months.
-- Return the result required by the specified template.
    local sign = self.isnegative and MINUS or ''
-- Can use sortable=x where x = on/off/debug in any supported template.
    local mtext = number_name(self.months, 'month')
-- Some templates default to sortable=on but can be overridden with sortable=off.
    local result
local name = frame.args.template
    if self.years > 0 then
if not name then
        local ytext = number_name(self.years, 'year')
return message('The template invoking this must have "|template=x" where x is the wanted operation')
        if self.months == 0 then
end
            result = ytext
local args = frame:getParent().args
        else
local specs = {
            result = ytext .. ',&nbsp;' .. mtext
age_days = {                -- {{age in days}}
        end
show = 'd',
    else
disp = 'disp_raw',
        if self.months == 0 then
},
            sign = ''
age_days_nts = {            -- {{age in days nts}}
        end
show = 'd',
        result = mtext
disp = 'disp_raw',
    end
format = 'format_commas',
    return sign .. result
sortable = 'on',
},
duration_days = {          -- {{duration in days}}
show = 'd',
disp = 'disp_raw',
duration = true,
},
duration_days_nts = {      -- {{duration in days nts}}
show = 'd',
disp = 'disp_raw',
format = 'format_commas',
sortable = 'on',
duration = true,
},
age_full_years = {          -- {{age}}
show = 'y',
abbr = 'abbr_raw',
},
age_full_years_nts = {      -- {{age nts}}
show = 'y',
abbr = 'abbr_raw',
format = 'format_commas',
sortable = 'on',
},
age_in_years = {            -- {{age in years}}
show = 'y',
abbr = 'abbr_raw',
negative = 'error',
range = 'dash',
},
age_in_years_nts = {        -- {{age in years nts}}
show = 'y',
abbr = 'abbr_raw',
negative = 'error',
range = 'dash',
format = 'format_commas',
sortable = 'on',
},
age_infant = {              -- {{age for infant}}
-- Do not set show because special processing is done later.
abbr = yes(args.abbr) and 'abbr_infant' or 'abbr_off',
disp = 'disp_age',
sep = 'sep_space',
sortable = 'on',
},
age_m = {                  -- {{age in months}}
show = 'm',
disp = 'disp_raw',
},
age_w = {                  -- {{age in weeks}}
show = 'w',
disp = 'disp_raw',
},
age_wd = {                  -- {{age in weeks and days}}
show = 'wd',
},
age_yd = {                  -- {{age in years and days}}
show = 'yd',
sep = args.sep ~= 'and' and 'sep_comma' or nil,
sortable = 'on',
},
age_ym = {                  -- {{age in years and months}}
show = 'ym',
sep = 'sep_comma',
},
age_ymd = {                -- {{age in years, months and days}}
show = 'ymd',
range = true,
},
age_ymwd = {                -- {{age in years, months, weeks and days}}
show = 'ymwd',
want_mixture = true,
},
}
local spec = specs[name]
if not spec then
return message('The specified template name is not valid')
end
if name == 'age_days' then
local su = strip_to_nil(args['show unit'])
if su then
if su == 'abbr' or su == 'full' then
spec.disp = nil
spec.abbr = su == 'abbr' and 'abbr_on' or nil
end
end
end
local range = spec.range or yes(args.range) or (args.range == 'dash' and 'dash' or nil)
local getopt = {
fix = yes(args.fix),
range = range,
want_mixture = spec.want_mixture,
}
local date1, date2 = get_dates(frame, getopt)
if type(date1) == 'string' then
return date1
end
local format = strip_to_nil(args.format)
if format then
format = 'format_' .. format
elseif name == 'age_days' and getopt.textdates then
format = 'format_commas'
end
local parms = {
diff = date2 - date1,
want_duration = spec.duration or yes(args.duration),
range = range,
want_sc = yes(args.sc),
show = args.show == 'hide' and 'hide' or spec.show,
abbr = spec.abbr,
disp = spec.disp,
format = format or spec.format,
round = yes(args.round),
sep = spec.sep,
sortable = translate_parameters.sortable[args.sortable or spec.sortable],
}
if (spec.negative or frame.args.negative) == 'error' and parms.diff.isnegative then
return message('The second date should not be before the first date')
end
return date_difference(parms)
end
end


local function error_wikitext(text)
local function date_to_gsd(frame)
    -- Return message for display when template parameters are invalid.
-- This implements {{gregorian serial date}}.
    local prefix = '[[Module talk:Age|Module error]]:'
-- Return Gregorian serial date of the given date, or the current date.
    local cat = '[[Category:Age error]]'
-- The returned value is negative for dates before 1 January 1 AD
    return '<span style="color:black; background-color:pink;">' ..
-- despite the fact that GSD is not defined for such dates.
            prefix .. ' ' .. text .. cat .. '</span>'
local date = get_dates(frame, { want_mixture=true, single=true })
if type(date) == 'string' then
return date
end
return tostring(date.gsd)
end
end


local function age_days(frame)
local function jd_to_date(frame)
    -- Return age in days between two given dates, or
-- Return formatted date from a Julian date.
    -- between given date and current date.
-- The result includes a time if the input includes a fraction.
    -- This code implements the logic in [[Template:Age in days]].
-- The word 'Julian' is accepted for the Julian calendar.
    -- Like {{Age in days}}, a missing argument is replaced from the current
local Date = get_exports(frame)
    -- date, so can get a bizarre mixture of specified/current y/m/d.
local args = frame:getParent().args
    local args = frame:getParent().args
local date = Date('juliandate', args[1], args[2])
    local year1  = date_component(args.year1 , args[1], 'year' )
if date then
    local month1 = date_component(args.month1, args[2], 'month')
return date:text()
    local day1  = date_component(args.day1  , args[3], 'day'  )
end
    local year2  = date_component(args.year2 , args[4], 'year' )
return message('Need valid Julian date number')
    local month2 = date_component(args.month2, args[5], 'month')
    local day2  = date_component(args.day2  , args[6], 'day'  )
    local gsd1 = gsd(year1, month1, day1)
    local gsd2 = gsd(year2, month2, day2)
    if gsd1 and gsd2 then
        local sign = ''
        local result = gsd2 - gsd1
        if result < 0 then
            sign = MINUS
            result = -result
        end
        return sign .. tostring(result)
    end
    return error_wikitext('Cannot handle dates before the year 1 AD')
end
end


local function age_ym(frame)
local function date_to_jd(frame)
    -- Return age in years and months between two given dates, or
-- Return Julian date (a number) from a date which may include a time,
    -- between given date and current date.
-- or the current date ('currentdate') or current date and time ('currentdatetime').
    local args = frame:getParent().args
-- The word 'Julian' is accepted for the Julian calendar.
    local fields = {}
local Date = get_exports(frame)
    for i = 1, 6 do
local args = frame:getParent().args
        fields[i] = strip_to_nil(args[i])
local date = Date(args[1], args[2], args[3], args[4], args[5], args[6], args[7])
    end
if date then
    local date1, date2
return tostring(date.jd)
    if fields[1] and fields[2] and fields[3] then
end
        date1 = Date:new():set_ymd(fields[1], fields[2], fields[3])
return message('Need valid year/month/day or "currentdate"')
    end
    if not (date1 and date1.isvalid) then
        return error_wikitext('Need date: year, month, day')
    end
    if fields[4] and fields[5] and fields[6] then
        date2 = Date:new():set_ymd(fields[4], fields[5], fields[6])
        if not date2.isvalid then
            return error_wikitext('Second date should be year, month, day')
        end
    else
        date2 = Date:new():set_current()
    end
    return DateDiff:new():set(date1, date2):age_ym()
end
end


local function gsd_ymd(frame)
local function time_interval(frame)
    -- Return Gregorian serial day of the given date, or the current date.
-- This implements {{time interval}}.
    -- Like {{Gregorian serial date}}, a missing argument is replaced from the
-- There are two positional arguments: date1, date2.
    -- current date, so can get a bizarre mixture of specified/current y/m/d.
-- The default for each is the current date and time.
    -- This accepts positional arguments, although the original template does not.
-- Result is date2 - date1 formatted.
    local args = frame:getParent().args
local Date = get_exports(frame)
    local year  = date_component(args.year , args[1], 'year' )
local args = frame:getParent().args
    local month = date_component(args.month, args[2], 'month')
local parms = {
    local day  = date_component(args.day  , args[3], 'day' )
want_duration = yes(args.duration),
    local result = gsd(year, month, day)
range = yes(args.range) or (args.range == 'dash' and 'dash' or nil),
    if result then
want_sc = yes(args.sc),
        return tostring(result)
}
    end
local fix = yes(args.fix) and 'fix' or ''
    return error_wikitext('Cannot handle dates before the year 1 AD')
local date1 = Date(fix, 'partial', strip_to_nil(args[1]) or 'currentdatetime')
if not date1 then
return message('Invalid start date in first parameter')
end
local date2 = Date(fix, 'partial', strip_to_nil(args[2]) or 'currentdatetime')
if not date2 then
return message('Invalid end date in second parameter')
end
parms.diff = date2 - date1
for argname, translate in pairs(translate_parameters) do
local parm = strip_to_nil(args[argname])
if parm then
parm = translate[parm]
if parm == nil then  -- test for nil because false is a valid setting
return message('Parameter ' .. argname .. '=' .. args[argname] .. ' is invalid')
end
parms[argname] = parm
end
end
if parms.round then
local round = parms.round
local show = parms.show
if round ~= 'on' then
if show then
if show.id ~= round then
return message('Parameter show=' .. args.show .. ' conflicts with round=' .. args.round)
end
else
parms.show = translate_parameters.show[round]
end
end
parms.round = true
end
return date_difference(parms)
end
end


return { age_days = age_days, age_ym = age_ym, gsd = gsd_ymd }
return {
age_generic = age_generic,         -- can emulate several age templates
gsd = date_to_gsd,                 -- Template:Gregorian_serial_date
extract = date_extract,            -- Template:Extract
jd_to_date = jd_to_date,          -- Template:?
JULIANDAY = date_to_jd,            -- Template:JULIANDAY
time_interval = time_interval,    -- Template:Time_interval
}
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