Lua倒计时展示：剩余时长的分段格式化

-- 错误：多层 if 手拼，分段算错还不补零
if sec > 3600 then
    text = sec / 3600 .. "时" .. sec % 3600 .. "分"
end

local function fmtLeft(sec)
    if sec < 0 then sec = 0 end
    local h = math.floor(sec / 3600)
    local m = math.floor(sec % 3600 / 60)
    local s = sec % 60
    if h > 0 then
        return string.format("%d:%02d:%02d", h, m, s)
    end
    return string.format("%02d:%02d", m, s)
end
local label = panel:getChildByName("leftTime")
label:setString(fmtLeft(3661))