【进阶实战】攻城战阶段：多阶段切换的状态机封装

local STAGES = {
    { name = "报名", from = 0, lastSec = 259200 },
    { name = "备战", from = 1, lastSec = 3600 },
    { name = "开战", from = 2, lastSec = 7200 },
    { name = "结算", from = 3, lastSec = 1800 },
}
local stageStart = os.time()
local lastStage = 0
local function currentStage()
    local elapsed = os.time() - stageStart
    for i = #STAGES, 1, -1 do
        local offset = 0
        for j = 1, i do
            offset = offset + STAGES[j].lastSec
        end
        if elapsed < offset then
            return i
        end
    end
    return #STAGES
end
local function onStageEnter(stageId)
    sendcentermsg(nil, 249, 255, "攻城进入【" .. STAGES[stageId].name .. "】阶段", 0, 8, "")
    setsysvarex("SiegeStage", stageId, 1)
end
local function tickStage()
    local cur = currentStage()
    if cur ~= lastStage then
        lastStage = cur
        onStageEnter(cur)
    end
end

local function canSignup()
    return currentStage() == 1
end