"If I where you I ^would do^ the same" Vs. "If I where you I ^would have done^ the same"

Question

I called my friend and he answered the call and then ask me: "Is it emergency? because if not now I'm in a very important meeting. If it is not emergency, I'll call you immediately later." Later he called me and he was sorry about that. I told him "If I were you I would do the same".

Now, someone noted me to say "If I were you I would have done the same". My question if is it correct and if it is not what is the difference between

"If I were you, I would do the same.

"If I were you, I would have done the same"

and why it is correct to use one form and no the other form.

Answer 1

In the situation you have described "If I were you, I would have done the same" is correct. It is called the mixed conditional sentence. If I were you refers to the present and it is unreal. I would have done the same is unreal too but it refers to the past. Your friend told you that he would call you back in the past, that's why you need to use the pattern would + have + past participle. Here are more examples like this:

1. If I were you, I wouldn't have made such a mistake. (the mistake was made in the past and in the second part of the sentence I refer to the past)
2. If I were you, I would have quit such a lousy job a long time ago. (in other words, you had to do it a long time ago; again, we refer to the past)

If I were you, I would do the same is a conditional sentence of the second type. It means both parts of the sentence refer to the present. That is, if I were you now, I would act in the same way now.

Answer 2

Let me put the structure of the Second Conditional for you. " Sub+ be verb (mostly were+..., + Sub+ would/should/could/might+ v1(a present form of the verb)+ Ext..... As you see this structure follows the present form of the situation. If you put "Have" in a sentence it goes straight to past. This is also not wrong but the scenario you wrote should be in present form.