YOU SAID:

you've done this before havent you

INTO JAPANESE

あなたはあなたがいない前にこれをしました

BACK INTO ENGLISH

You did this before you weren't

INTO JAPANESE

あなたはそうでない前にこれをしました

BACK INTO ENGLISH

You did this before you didn't

INTO JAPANESE

あなたがしなかった前にあなたはこれをしました

BACK INTO ENGLISH

You did this before you didn't