create ranking system logic

i am building a software project in which exist 5 categories of employees. A, B, C, D, E. Each category will have a rank based on numbers. For example: Category E have 100 employees, then employees will have rank from 1 to 100. The rank may increase or decrease according actions like complete jobs, cancel orders, late time, etc. This means some user may be employee E83 and move positions up or down according different actions. Same rank cannot be applied to more than 1 employee. What i need? 1. create the system logic in order to give instructions to developers to do this job 2. The system should take all factors important like attendance, completion, work amount, rating, etc. 3. i guess the system will add points or substract points and based on that will assign ranking 4. i need people move easilfy from category E to D but each next category should be difficult. I am looking employees if do good job may move from E to A in about 10-12 months. I will provide after award all factors i need to consider 5. the system may downgrade your category. For employees who was downgraded the upgrade should be more easy at least they are continue failing Basically i need a good mathematician for create the logic of this. If i miss out something for make the systeme work i am expecting you recommend me any missing thing.