Module:Age: Difference between revisions

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         return tostring(number) .. sep .. ((number == 1) and singular or plural)
         return tostring(number) .. sep .. ((number == 1) and singular or plural)
         -- this uses an interesting trick of Lua:
         -- 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
         --  * 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
         --  * or returns the first argument if it is not false, and the second argument if the first is false
         --  * 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
         --  * so, if number is 1, and evaluates (true and singular) returning (singular); or evaluates (singular or plural), finds singular non-false, and returns singular

    Revision as of 13:39, 28 May 2016

    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    Calendar functions will be needed in many areas, so this may be superseded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 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 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
        --  * 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 .. ',&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 }