You're likely to get a conviction for driving while impaired. Yes it was certainly a stupid thing to do, and it will likely be hanging over your shoulders for quite some time. You will have to declare the conviction when applying for jobs and when travelling to many countries at least until the clean slate law becomes applicable to you (7 years if you fulfill all the criteria).

I've got no problem with people doing what they want in private so long as it doesn't pose a risk to others, but this is a stupid and easily preventable situation you've put yourself in.

You could possibly apply for discharge without conviction if it outweighs the crime, but unless you're a star rugby player or aspiring lawyer, i don't rate your chances. Diversion is another possibility, but they don't allow it for drink driving convictions, and I'm not sure if drug driving falls under that same umbrella.