s.47 OAPA carries maximum sentence of 5 years imprisonment. However, if it is the first time you have committed this offence or any other violent offence and you haven't caused any more serious harm than bruising you won't get anywhere near that.
The circumstances as you describe them suggest that you fall into a category 3 s.47 assault - this means that less harm has been caused to the victim and you are less culpable for the harm being caused. However, if it can be shown that the attack was premeditated (you planned it), then you may fall into category 2. If you are category 3, the starting point is a mid level community order but the court can impose anything up to a high level order or band A fine. If you are category 2 then you are facing prison. The starting point is 26 weeks in prison but you may receive anything from a band A fine to 51 weeks in prison. It is worth pointing out that if you were to receive a custodial sentence then it would be automatically halfed as it would be for a period of less than four years.
The fact that the CPS want to have you tried on indictment (at Crown Court) suggests that they may see your offence as more serious than you have represented it to be. This is because Crown Court can impose higher sentences then mags (over 6 months).
My advice is to think very carefully. If you are guilty, as you appear to admit here, get a good solicitor and plead guilty at the EARLIEST opportunity. This will get you 1/3 off your sentence. Also, plead provocation in mitigation and suggest that you would be willing to attend a course to help control your anger. This will undoubtedly give the court a better view of you.
I hope this helps.