Minimum circuits to detect clockwise

The circle can rotate clockwise and back. Use minimum hardware to build a circuit to indicate the direction of rotating.? 

2 sensors are required to find out the direction of rotating. They are placed like at the drawing. One of them is connected to the data input of D flip-flop,and a second one – to the clock input. If the circle rotates the way clock sensor sees the light first while D input (second sensor) is zero – the output of the flip-flop equals zero, and if D input sensor “fires” first – the output of the flip-flop becomes high.