英语长难句分析

题目

英语长难句分析
请帮忙分析这句长句.If its message were confined merely to information and that in itself would be difficult if not impossible to achieve,for even a detail such as the choice of the color of a shirt is subtly persuasive-advertising would be so boring that no one wound pay any attention.
中文意思我知道,就想知道这句话的结构怎么分析,谁是谁的从句,修饰的又是谁?
还有.为什么 and that in itself would be difficult 后面又有一个if not impossible to achieve?
if后面不是加句子的吗?这个if和句子开头的if什么关系,如果有两个从句不是应该也有两个主句即两个谓语的吗?
后半句（从for even开始）,哪里是主语?谓语?
问题有些多,谢谢回答的朋友(⊙o⊙)哦!

答案

查找了一些网络资料,发现这个句子有一点问题,现更改如下：If its message were confined merely to information—and that in itself would be difficult if not impossible to achieve, for even a detail such as ...