local seasons  = {"Chaos", "Discord", "Confusion", "Bureaucracy", "The Aftermath"}
local weekdays = {"Sweetmorn", "Boomtime", "Pungenday", "Prickle-Prickle", "Setting Orange"}
local apostles = {"Mungday", "Mojoday", "Syaday", "Zaraday", "Maladay"}
local holidays = {"Chaoflux", "Discoflux", "Confuflux", "Bureflux", "Afflux"}

local function parse(date)
    local y = tonumber(date:sub(1, 4))
    local m = tonumber(date:sub(6, 7))
    local d = tonumber(date:sub(9, 10))
    return y, m, d
end

local function is_leap_year(y) return (y % 4 == 0 and y % 100 != 0) or y % 400 == 0 end

local function discordian(date)
    local y, m, d = parse(date)
    local yold = $" in the YOLD {y + 1166}."
    local t = os.time({year = y, month = m, day = d})
    local doy = tonumber(os.date("%j", t))
    if is_leap_year(y) then
        if doy == 60 then return "St. Tib's Day" .. yold end
        if doy > 60 then doy -= 1 end
    end
    doy -= 1
    local season_day = doy % 73 + 1
    local season_nr = doy // 73 + 1
    local weekday_nr = doy % 5 + 1
    local holyday = ""
    if season_day == 5  then holyday = $" Celebrate {apostles[season_nr]}!" end
    if season_day == 50 then holyday = $" Celebrate {holidays[season_nr]}!" end
    local season = seasons[season_nr]
    local dow = weekdays[weekday_nr]
    return string.format("%s, day %s of %s%s%s", dow, season_day, season, yold, holyday)
end

local dates = {
   "2010-01-01",
   "2010-01-05",
   "2011-02-19",
   "2012-02-28",
   "2012-02-29",
   "2012-03-01",
   "2013-03-19",
   "2014-05-03",
   "2015-05-31",
   "2016-06-22",
   "2016-07-15",
   "2017-08-12",
   "2018-09-19",
   "2018-09-26",
   "2019-10-24",
   "2020-12-08",
   "2020-12-31"
}

for dates as date do
    local dt = discordian(date)
    print($"{date} = {dt}")
end