Robobass:
I have read a few tutorials on the ACS712, but none have gone into using it as a current sensing A/B switch.
Put another way. You would never (very very unlikely to) find a tutorial on how to do this project. Many folks confuse applications with projects. Unless you are reading a walk-through of a project (such as you might find in a magazine), the tutorials are based on how to use (apply) an item in the field. Such as how to use an ACS712 to measure current or how to wire a DPDT relay to control the direction of a DC motor. Now you take the two applications and make a project. Use the ACS712 to read current and then to control the direction of a motor.