QP job offer letter

freinds
I have recently been interviwed for a JOB with qatar petroleum and have been selected for the job.
The interview was held nearly 45 days back
i still did not get the offer letter and when i got to my agent they say they are still waiting for the offer letter
does it take that long to get the job offer letter from qatar petroleum after selection from an interview ?
what about the VIsa how long does it take?
i have been keeping my fingers crossed for the 45 days now?fingers now struck crossed lol!!!
do the company cancel offer after selection in an interview
plz kindly reply