If I had had enough time,Iwould have done the work better.这句话为什么有两个had连用?

虚拟语气的问题楼上都说很好了,唯一补充的是这个句子是现在完成时的虚拟语气.“有时间”是have time,现在完成时是have had time,这个能理解吧?那么代入虚拟语气,主句 have done 变身为 would have done,这个也能理解吧?从句的have had time中的第一个have也随之要变成过去时,因此结果就是 had had 了.