Leave Rules - Scenarios - Checks to be done during leave application

I have a requriement for my current project. Request you all Gurus to pls help me with the answers. These are the checks to be taken at the time of leave application by user. User will apply for these leaves in ESS Portal

1. PL cannot be combined with CL, If employee is combining and applying for CL which has PL before then at the time of leave application, system to throw error message and should not allow him to apply for it

2. If employee is applying for sick leave in between PL then while applying for SL, should throw error message and should not him to apply for it

3. Holidays / Weekly offs falling betn PL treated as PL

4. To chk for Saturday / sundays / holiday, if these holidays are falling between PL then PL to include / treat these holidays also

Leave taken during notice period, should throw error message and should not allow the user to apply

5. If falling on Friday / Monday or public holiday chk prefix or suffix leave application, either allowed if taking both error

IF leave taken on Friday then shld chk if Monday also employee applying for leave, if yes, then throw error and not allow him to apply, same case with Monday as well

Project wants to go for time evaluation. Wondering how can these checks be done when the user is applying for leave.

Please help