So I was helping a friend of mine out with his master thesis, as he had no idea about a specific topic in which I had a few years of industrial experience. However, he had no idea about what I was talking about, so I coded a lot of his solutions for him (this is in the field of signal processing, so the programming part is quite important).
Now I find out that he has directly used my code in his thesis and plans publications with this code, all without acknowledging or crediting my contribution in any way. Talking to him yielded no results, as he is convinced that he is right, and since he edited and rewrote my code he doesn't need to acknowledge me. Is this ethical? Is there anything I can/should do?