cal.lua

#!/usr/bin/env lua

conky_color = "${color2}%2d${color}"

t = os.date("*t", os.time())
year, month, currentday = t.year, t.month, t.day

daystart = os.date("*t", os.time{year=year,month=month,day=01}).wday

--require 'pl.pretty'.dump(daystart)

month_name = os.date("%B")

days_in_month = {
    31, 28, 31, 30, 31, 30,
    31, 31, 30, 31, 30, 31
}

-- check for leap year
-- Any year that is evenly divisible by 4 is a leap year
-- Any year that is evenly divisible by 100 is a leap year if
-- it is also evenly divisible by 400.
LeapYear = function (year)
    return year % 4 == 0 and (year % 100 ~= 0 or year % 400 == 0)
end

if LeapYear(year) then
    days_in_month[2] = 29
end

title_start = (20 - (string.len(month_name) + 5)) / 2

title = string.rep(" ", math.floor(title_start + 0.5)) .. -- add padding to center the title
        (" %s %s\n Mo Tu We Th Fr Sa Su\n"):format(month_name, year)

io.write("${color4}" .. title .. "${color}")

function seq(a, b)
    if a > b then
        return
    else
        return a, seq(a + 1, b)
    end
end

days = days_in_month[month]

io.write("${color}")
io.write(
    string.format(
        string.rep("   ", daystart-2) ..
        string.rep(" %2d", days), seq(1, days)
    ):gsub(string.rep(".", 21), "%0\n")
     :gsub(("%2d"):format(currentday),
           (conky_color):format(currentday),
           1
     ) .. "\n"
)
io.write("${color}")