【后端接口】邮件系统：附件流转与离线投递

---寄件：附件从寄件人背包转托管
function Mail.sendWithAtt(actor, toName, title, attIdx)
    local toId = Role.idOf(toName)
    if not toId then
        sendmsg(actor, 1, "收件人不存在")
        return false
    end
    -- 附件先从背包摘除进托管态
    local att = Mail.detach(actor, attIdx)
    DB.exec("INSERT INTO mails SET ?", {
        fromId = actor:GetUserId(), toId = toId,
        title = title, att = att, at = os.time(),
        expireAt = os.time() + 7 * 86400,
    })
    sendmsg(actor, 1, "邮件已寄出")
    if Online.isOnline(toId) then
        sendmsg(Role.actorOf(toId), 1, "收到新邮件：" .. title)
    end
    return true
end

---收取：附件入包，邮件标记已领
function Mail.receive(actor, mailId)
    local m = Mail.load(mailId)
    if m.toId ~= actor:GetUserId() then
        return false
    end
    if m.claimed then
        sendmsg(actor, 1, "该邮件已领取")
        return false
    end
    if not giveitem(actor, m.attName, m.attCount) then
        sendmsg(actor, 1, "背包已满，请清理后领取")
        return false
    end
    Mail.markClaimed(mailId)
    return true
end

---过期退回：7 天未领取原路退回
setontimerex(81, 3600)
function Mail.expireScan()
    local rows = DB.query(
        "SELECT id, fromId, title FROM mails " ..
        "WHERE expire_at < ? AND claimed = 0", os.time())
    for _, r in ipairs(rows) do
        Mail.returnToSender(r.id, r.fromId, r.title)
    end
end