Module:Age

Documentation for this module may be created at Module:Age/doc

--[[ Code for some date functions, including implementations of:
        {{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Calendar functions will be needed in many areas, so this may be superseded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 mw.
]]

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
    end
    if self.year == rhs.year then
        if self.month < rhs.month then
            return true
        end
        if self.month == rhs.month then
            return self.day < rhs.day
        end
    end
    return false
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 .. ',&nbsp;' .. 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 talk:Age|Module error]]:'
    local cat = '[[Category:Age error]]'
    return '<span style="color:black; background-color:pink;">' ..
            prefix .. ' ' .. text .. cat .. '</span>'
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 {{Age in 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 {{Gregorian serial date}}, 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 }