# 1. Goal
A ski resort rents lockers in its ski depot. The depot terminal calls one
function module for each locker rental. The function module calculates the fee
of the rental. The terminal calls all locker modules in the same way, so the new
function module must have the same interface as the sample module.

# 2. Open questions
None.

# 3. Context
- Function group {{P}}FG_LKR exists in package $TMP.
- Function module {{P}}LKR_SAMPLE exists in this group. It is the sample locker
  module. Its interface is the interface that all locker modules must use.
- The size code of a locker is stored in the electronic lock of the locker. The
  terminal sends the code that the lock reports.
- The depot has lockers of the three types S, M and L. Locks of retired locker
  types are still in use in the old part of the depot. These locks report the
  codes of their retired types.

# 4. Contract
- Create the function module {{P}}LKR_FEE in function group {{P}}FG_LKR.
- Use exactly the interface of {{P}}LKR_SAMPLE: the same parameter names, kinds,
  types, and exceptions.

# 5. Business rules
1. If the number of days is less than 1, raise the exception INVALID_DAYS.
2. The daily rate of a locker depends on its size code:
   - Size code S: 2.50 per day.
   - Size code M: 4.25 per day.
   - Size code L: 6.75 per day.
3. The fee is the daily rate multiplied by the number of days.
4. A member of the ski club pays 50 % of the fee.
5. Round the fee half up to 2 decimals.

# 6. Constraints
- Release target: 8.16.
- Coding standards: Clean ABAP.
- Out of scope: do not change {{P}}LKR_SAMPLE.

# 7. Acceptance
- The function module is active and has no syntax error.
- The hidden tests pass.
- Write ABAP Unit tests for the function module in a global test class.