chess opening code

I am writing a code that allows you to input your opponent's moves and it will show you your available book moves. I am aware plenty of code like this already exists, I am just writing it for fun. the way that my code works is it checks what has been played with complete lines of openings to see if there is a match. This all boils down to me needing a list of the most common complete lines that occur in the first five moves or so. for example the text below. if anyone knows where I could find a database of this information would be greatly appreciated 

Nice, but I think there is a problem:

Your line is a Ruy Lopez. But if I play 1. Nf3 Nc6 2. e4 e5, etc. could your tool consider this as a RL? There are al lot of transpos like this. In the QG or Kings Indian that start with 1.Nf3 etc.