【高级技巧】降采样：高频指标的定窗采样封装

local STEP = 10
local cur = {}
local history = {}
local function sample(key, value)
    local slot = math.floor(os.time() / STEP)
    local b = cur[key]
    if not b or b.slot ~= slot then
        if b then
            b.avg = math.floor(b.sum / b.n)
            local h = history[key]
            h[#h + 1] = b.slot .. "|" .. b.avg
            if #h > 360 then
                table.remove(h, 1)
            end
        else
            history[key] = {}
        end
        cur[key] = { slot = slot, sum = value, n = 1,
            min = value, max = value }
    else
        b.sum = b.sum + value
        b.n = b.n + 1
        if value < b.min then
            b.min = value
        end
        if value > b.max then
            b.max = value
        end
    end
end

local function recentAvg(key, windows)
    local h = history[key] or {}
    local total, n = 0, 0
    for i = math.max(1, #h - windows + 1), #h do
        local avg = tonumber(string.match(h[i], "|(%d+)$"))
        if avg then
            total = total + avg
            n = n + 1
        end
    end
    if n == 0 then
        return 0
    end
    return math.floor(total / n)
end