A 47-year-old man was allegedly attacked by his 35-year-old male roommate sometime Wednesday night.  Port Huron Police were called to St. Joseph Mercy Port Huron at 6:30 a.m. Thursday to investigate reports of unlawful imprisonment of an adult.  The victim who is mentally challenged, suffered minor injuries.  He reported that he had been assaulted in the past by the roommate and had previously been padlocked and held prisoner in a room in the residence in the 2200 block of 10^th Street in Port Huron.  The suspect was taken into custody at about noon yesterday following a search of the residence by a special response team.  Victim alleged that there was a marijuana growing operation as well as firearms in the residence. Arraignment is expected to take place today.