Module:Age

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

-- Code to implement {{age in years and months}}.
-- This could be extended to handle the many other {{age}} templates.
-- However, calendar functions will be needed in many areas, so this may be
-- superseded by some other system, perhaps using functions from the PHP host.

local MINUS = '−'  -- Unicode U+2212 MINUS SIGN (UTF-8: e2 88 92)

local function number_name(number, singular, plural, sep)
    plural = plural or (singular .. 's')
    sep = sep or ' '
    return tostring(number) .. sep .. ((number == 1) and singular or plural)
end

local function strip(text)
    -- If text is a string, return its content with no leading/trailing
    -- whitespace. Otherwise return nil (a nil argument gives a nil result).
    if type(text) == 'string' then
        return text:match("^%s*(.-)%s*$")
    end
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

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:set_current()
    -- Set date from current time (UTC) and return self.
    local d = os.date('!*t')
    self.year = d.year
    self.month = d.month
    self.day = d.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

function Date:less_than(rhs)
    -- Set 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

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:less_than(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.
    -- TODO Get opinions on whether the prefix and category are suitable.
    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 get_parms(pframe)
    -- Return date1, date2 from parameters to template.
    -- If date1 is missing or invalid, the returned date1 is nil.
    -- If date2 is missing, the returned date2 is the current date.
    -- If date2 is invalid, the returned date2 is nil.
    local args = {}  -- arguments passed to template
    for i = 1, 6 do
        args[i] = strip(pframe.args[i])
    end
    local date1, date2
    if args[1] and args[2] and args[3] then
        date1 = Date:new():set_ymd(args[1], args[2], args[3])
        if not date1.isvalid then
            date1 = nil
        end
    end
    if args[4] and args[5] and args[6] then
        date2 = Date:new():set_ymd(args[4], args[5], args[6])
        if not date2.isvalid then
            date2 = nil
        end
    else
        date2 = Date:new():set_current()
    end
    return date1, date2
end

local function age_ym(frame)
    local date1, date2 = get_parms(frame:getParent())
    if date1 then
        if not date2 then
            return error_wikitext('Second date should be year, month, day')
        end
        local diff = DateDiff:new():set(date1, date2)
        return diff:age_ym()
    end
    return error_wikitext('Need date: year, month, day')
end

return { age_ym = age_ym }