local t = jarvis.context.time

-- Compute day-of-week using Zeller's congruence (0=Saturday).
local y, m, d = t.year, t.month, t.day
if m < 3 then m = m + 12; y = y - 1 end
local K = y % 100
local J = math.floor(y / 100)
local h = (d + math.floor(13 * (m + 1) / 5) + K + math.floor(K / 4) + math.floor(J / 4) - 2 * J) % 7
-- h: 0=Saturday, 1=Sunday, 2=Monday, ... 6=Friday

local days_ru = {
    [0] = "суббота",
    [1] = "воскресенье",
    [2] = "понедельник",
    [3] = "вторник",
    [4] = "среда",
    [5] = "четверг",
    [6] = "пятница",
}

return jarvis.cmd.ok("Сегодня " .. (days_ru[h] or "неизвестный день") .. ".")