We're migrating customer data from the legacy account-opening system into a new CRM. The legacy system stores the full name in a single field, like 'ZHANG, WEI' or 'O'BRIEN, MARY ANN', and a few records are written as 'WEI ZHANG' with no comma. The new CRM has separate first-name and last-name fields. How would you write the mapping rule?

客户数据要从旧开户系统迁到新 CRM，旧系统把姓名存在一个字段里，比如「ZHANG, WEI」「O'BRIEN, MARY ANN」，还有少数写成「WEI ZHANG」，中间没有逗号；新系统要分成名和姓两个字段。你会怎么写这条映射规则？