An elevator with two levels, designed only for one$-$way transport, is to be controlled using a PLC$.$ When the call button on the $1$st floor is pressed, the elevator will descend, and its door will fully open for $3$ seconds. After $3$ seconds, the door will close. If a photocell, capable of detecting people passing through the door, is activated during this time, the timer will reset, and the $3-$second countdown will restart. Once the door has closed, the elevator will move upward when the $"$Up$"$ button inside the elevator is pressed.

After the elevator ascends, its door will open and wait to be called from the lower floor. However, while the elevator is on the upper floor, the door will not close until at least $3$ seconds have passed since the photocell was last activated. Furthermore, the elevator will not move downward until its door has fully closed. Additionally, the elevator will not move unless its door is completely closed.

What is Plc code this problem?