-- "Сколько дней до нового года" / "сколько до 15 марта"
local phrase = (jarvis.context.phrase or ""):lower()
local t = jarvis.context.time
local current_year = t.year

local MONTHS = {
    ["январ"]=1, ["феврал"]=2, ["март"]=3, ["апрел"]=4, ["май"]=5, ["мая"]=5, ["июн"]=6,
    ["июл"]=7, ["август"]=8, ["сентябр"]=9, ["октябр"]=10, ["ноябр"]=11, ["декабр"]=12,
}

-- Special phrases
local target_y, target_m, target_d

if phrase:find("нов") and phrase:find("год") then
    target_y, target_m, target_d = current_year + 1, 1, 1
    if t.month == 1 and t.day == 1 then target_y = current_year end
elseif phrase:find("рожд") then
    target_y, target_m, target_d = current_year, 1, 7 -- ru orthodox
elseif phrase:find("8 март") or phrase:find("восьмого март") then
    target_y, target_m, target_d = current_year, 3, 8
elseif phrase:find("9 ма") or phrase:find("девятое ма") then
    target_y, target_m, target_d = current_year, 5, 9
end

-- Generic "до N <месяц>"
if not target_y then
    local d = tonumber(phrase:match("до%s+(%d+)"))
    if d then
        for stem, month in pairs(MONTHS) do
            if phrase:find(stem) then
                target_d, target_m, target_y = d, month, current_year
                break
            end
        end
    end
end

if not target_y then
    return jarvis.cmd.error("Не понял дату.")
end

-- If target this year already passed, jump to next year
local function days_since_epoch(y, m, d)
    -- approximate: works for diffs within ~100 years
    local total = y * 365 + math.floor(y / 4) - math.floor(y / 100) + math.floor(y / 400)
    local cum = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 }
    total = total + cum[m] + (d - 1)
    -- leap-day adjustment
    local leap = (y % 4 == 0 and y % 100 ~= 0) or (y % 400 == 0)
    if leap and m > 2 then total = total + 1 end
    return total
end

local now = days_since_epoch(t.year, t.month, t.day)
local target = days_since_epoch(target_y, target_m, target_d)

if target < now then
    target_y = target_y + 1
    target = days_since_epoch(target_y, target_m, target_d)
end

local diff = target - now
if diff == 0 then
    return jarvis.cmd.ok("Сегодня.")
end

-- Russian grammar: 1 день, 2-4 дня, 5+ дней
local last = diff % 10
local unit = "дней"
if last == 1 and diff % 100 ~= 11 then unit = "день"
elseif last >= 2 and last <= 4 and (diff % 100 < 10 or diff % 100 >= 20) then unit = "дня"
end

return jarvis.cmd.ok(string.format("%d %s.", diff, unit))