How does the AFL work out who is playing who on what week?

Is it just a matter of drawing out of a barrel or pulling straws out of a hat and then putting the same straw back in again, or is there some method? Next week, Hawthorn will have played Geelong twice in the first 12 rounds and it is not until round 22 that Hawthorn has finally played every team at least one time throughout the year. Hawthorn plays Geelong twice, Port Adelaide twice, Melbourne twice, Fremantle twice all before they have played Carlton one time. Surely common sense says that each team should play each other one time before starting to play each other for the second time. Do they have some reason for this stupid practise of playing the same team twice before you have played every team once?