【后端接口】当铺系统：典当与赎回的定价

---典当：估价的七折放款
function Pawn.pledge(actor, makeIndex)
    local player = class(actor)
    if not player then return false end
    local item = Pawn.locate(actor, makeIndex)
    if not item then return false end
    local value = Pawn.evaluate(item)
    local loan = math.floor(value * 0.7)
    -- 赎回价：本金加 20% 的利钱
    local redeemPrice = math.floor(loan * 1.2)
    delitembymakeindex(actor, makeIndex)
    giveitem(actor, "金币", loan)
    Pawn.book(actor, item, loan, redeemPrice, os.time() + 7 * 86400)
    sendmsg(actor, 1, "典当放款 " .. loan ..
        " 金币，7 天内 " .. redeemPrice .. " 金币赎回")
    return true
end

---赎回：到期前的本利结清
function Pawn.redeem(actor, ticketId)
    local player = class(actor)
    if not player then return false end
    local t = Pawn.ticketOf(actor, ticketId)
    if not t then return false end
    if os.time() > t.expireAt then
        sendmsg(actor, 1, "当票已过期，进入死当处理")
        return false
    end
    if not checkitemw(actor, "金币", t.redeemPrice) then
        sendmsg(actor, 1, "金币不足，赎回需 " .. t.redeemPrice)
        return false
    end
    takeitem(actor, "金币", t.redeemPrice, 0, "赎回")
    giveitem(actor, t.itemName, 1)
    Pawn.clearTicket(ticketId)
    sendmsg(actor, 1, "赎回成功：" .. t.itemName)
    return true
end