When attempting to apply brakes, the pedal sunk to the floor with no result. On subsequent attempts, the left front brake activated and locked up while there was no apparent effect on the other 3 wheels. The car veered to the left as a result of the one brake being applied, and began to travel down the road at an angle of about 45 degrees. Correction was required to steer out, the brake remained locked up and not responding to the pedal. Automatic emergency braking and forward collision warning systems did not activate and my vehicle collided with the one ahead. AWD seemed to activate just prior to the collision, which assisted in correcting the brake lockup. Inspection of the vehicle seems to indicate electrical issues caused a brake booster fault, and likely caused failure of the emergency braking systems to activate. These issues first appeared the day of the accident, no error messages or trouble codes were present. It appears the braking system is faulty, due to electronic controls, seemingly. The car is available for inspection. The left front rotor is scored deeply and the artifacts on the asphalt indicate that the left front tire was dragging/skidding up to the point of impact.