交易行行情：近七天成交均价的走势参考

local function recordDeal(itemId, price)
    setsysvarex("sum_" .. itemId,
        (getsysvar("sum_" .. itemId) or 0) + price)
    setsysvarex("cnt_" .. itemId,
        (getsysvar("cnt_" .. itemId) or 0) + 1)
end

local function quote(itemId)
    local sum = getsysvar("sum_" .. itemId) or 0
    local cnt = getsysvar("cnt_" .. itemId) or 0
    if cnt == 0 then
        return "暂无行情"
    end
    local avg = math.floor(sum / cnt)
    return "近 7 天均价 " .. avg .. "，共 " .. cnt .. " 笔"
end