Applying a flux boundary condition with concentration as a limiting condition

Hello,

I am using 'Transport of Diluted Species' with a constant flux J0 boundary condition. I need to reverse this flux to -J0 when a maximum concentration is reached at the boundary. And then the flux must reverese back to +J0 when the concentration drops to 0 at the boundary. I need to perform this charge - discharge cycle multiple number of times.

Note - I cannot use a function of time to define this boundary condition as the time at which maximum and minimum concentration is reached is unknown.