Module:Age

-- Code for some date functions, including implementations of:       8973 days                 age_days        24 years, 7 months     age_ym               gsd_ymd Calendar functions will be needed in many areas, so this may be superseded by some other system, perhaps using PHP functions accessed via mediawiki.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 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) -- this uses an interesting trick of Lua: -- * and reurns 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 -- * or returns the first argument if it is not false, and the second argument if the first is false -- * so, if number is 1, and evaluates (true and singular) returning (singular); or evaluates (singular or plural), finds singular non-false, and returns singular -- * 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

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

local function is_leap_year(year) -- Return true if year is a leap year, assuming Gregorian calendar. return year % 4 == 0 and (year % 100 ~= 0 or year % 400 == 0) end

local function days_in_month(year, month) -- 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) then return 29 end return month_days[month] end

-- A table to get 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            return rawget(self, key)        end    })

local function date_component(named, positional, component) -- Return the first of the two arguments that is not nil and is not empty. -- If both are nil, return the current date component, if specified. -- The returned value is nil or is a number. -- This translates empty arguments passed to the template to nil, and -- optionally replaces a nil argument with a value from the current date. named = strip_to_nil(named) if named then 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

local function gsd(year, month, day) -- Return the Gregorian serial day (an integer >= 1) for the given date, -- or return nil if the date is invalid (only check that year >= 1). -- This is the number of days from the start of 1 AD (there is no year 0). -- This code implements the logic in Template:Gregorian serial date. if year < 1 then return nil end local floor = math.floor local days_this_year = (month - 1) * 30.5 + day if month > 2 then if is_leap_year(year) then days_this_year = days_this_year - 1 else days_this_year = days_this_year - 2 end if month > 8 then days_this_year = days_this_year + 0.9 end end days_this_year = floor(days_this_year + 0.5) year = year - 1 local days_from_past_years = year * 365 + floor(year / 4) - floor(year / 100) + floor(year / 400) return days_from_past_years + days_this_year end

local Date = { -- A naive date that assumes the Gregorian calendar always applied. year = 0,  -- 1 to 9999 (0 if never set) month = 1, -- 1 to 12 day = 1,   -- 1 to 31 isvalid = false, new = function (self, o)       o = o or {} setmetatable(o, self) self.__index = self return o   end }

function Date:__lt(rhs) -- Return true if self < rhs. if self.year < rhs.year then return true elseif self.year == rhs.year then if self.month < rhs.month then return true elseif self.month == rhs.month then return self.day < rhs.day end end return false -- 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)))) -- would be just as efficient, as lua does not evaluate second argument of (true or second_argument) -- 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 end

function Date:set_current -- Set date from current time (UTC) and return self. self.year = current.year self.month = current.month self.day = current.day self.isvalid = true return self end

function Date:set_ymd(y, m, d)   -- Set date from year, month, day (strings or numbers) and return self. -- LATER: If m is a name like "March" or "mar", translate it to a month. y = tonumber(y) m = tonumber(m) d = tonumber(d) if type(y) == 'number' and type(m) == 'number' and type(d) == 'number' then self.year = y       self.month = m        self.day = d        self.isvalid = (1 <= y and y <= 9999 and 1 <= m and m <= 12 and                        1 <= d and d <= days_in_month(y, m)) end return self end

local DateDiff = { -- Simple difference between two dates, assuming Gregorian calendar. isnegative = false, -- true if second date is before first years = 0, months = 0, days = 0, new = function (self, o)       o = o or {} setmetatable(o, self) self.__index = self return o   end }

function DateDiff:set(date1, date2) -- Set difference between the two dates, and return self. -- Difference is negative if the second date is older than the first. local isnegative if date2 < date1 then isnegative = true date1, date2 = date2, date1 else isnegative = false end -- It is known that date1 <= date2. local y1, m1, d1 = date1.year, date1.month, date1.day local y2, m2, d2 = date2.year, date2.month, date2.day local years, months, days = y2 - y1, m2 - m1, d2 - d1   if days < 0 then days = days + days_in_month(y1, m1) months = months - 1 end if months < 0 then months = months + 12 years = years - 1 end self.years, self.months, self.days, self.isnegative = years, months, days, isnegative return self end

function DateDiff:age_ym -- 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

local function error_wikitext(text) -- Return message for display when template parameters are invalid. local prefix = 'Module error:' local cat = '' return ' ' .. prefix .. ' ' .. text .. cat .. ' ' end

local function age_days(frame) -- Return age in days between two given dates, or   -- between given date and current date. -- This code implements the logic in Template:Age in days. -- Like 8973 days, a missing argument is replaced from the current -- date, so can get a bizarre mixture of specified/current y/m/d. local args = frame:getParent.args local year1 = date_component(args.year1, args[1], 'year' ) local month1 = date_component(args.month1, args[2], 'month') local day1  = date_component(args.day1 , args[3], 'day'  ) local year2 = date_component(args.year2, args[4], 'year' ) 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

local function age_ym(frame) -- Return age in years and months between two given dates, or   -- between given date and current date. local args = frame:getParent.args local fields = {} for i = 1, 6 do       fields[i] = strip_to_nil(args[i]) end local date1, date2 if fields[1] and fields[2] and fields[3] then date1 = Date:new:set_ymd(fields[1], fields[2], fields[3]) 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

local function gsd_ymd(frame) -- Return Gregorian serial day of the given date, or the current date. -- Like, a missing argument is replaced from the -- current date, so can get a bizarre mixture of specified/current y/m/d. -- This accepts positional arguments, although the original template does not. local args = frame:getParent.args local year = date_component(args.year, args[1], 'year' ) local month = date_component(args.month, args[2], 'month') local day  = date_component(args.day , args[3], 'day'  ) local result = gsd(year, month, day) if result then return tostring(result) end return error_wikitext('Cannot handle dates before the year 1 AD') end

return { age_days = age_days, age_ym = age_ym, gsd = gsd_ymd }