# 1. Goal
Refactor the legacy report {{P}}FLEET_COST_OLD in package $TMP. The report
shows the running cost of each vehicle of a company fleet for a period. The
behavior of the report stays the same. Improve the internal quality of the
source code.

# 2. Open questions
None.

# 3. Context
- The program {{P}}FLEET_COST_OLD exists in package $TMP. It is active and it
  produces a correct result. Its source code is of poor quality.
- The tables {{P}}VEHICLE and {{P}}TRIP exist in package $TMP. They contain
  data. The report reads these two tables.
- The report shows the result in an ALV list.
- The users report no functional defect. Do not change the behavior.
- The report is not in the out-of-scope list. Refactor it in place.

# 4. Contract
- The program keeps the name {{P}}FLEET_COST_OLD and the package $TMP.
- The selection screen keeps these fields, in this order:
  - Parameter P_FROM, type DATS, mandatory.
  - Parameter P_TO, type DATS, mandatory.
  - Select-option S_CAT for the vehicle category.
- The ALV list keeps the same columns with the same names: VEHICLE_ID, PLATE,
  CATEGORY, DISTANCE, FUEL_COST, TOLL_COST, TOTAL_COST, COST_PER_KM.
- The lines of the list and the order of the lines do not change.

# 5. Business rules
The behavior stays the same. The legacy source code of {{P}}FLEET_COST_OLD
contains all the rules. Read the legacy code. Keep every rule. Do not add a
rule and do not remove a rule.

# 6. Constraints
- Release target: 8.16.
- Coding standards: Clean ABAP.
  - Do not read a database table inside a loop.
  - A method has less than 40 statements.
  - The maximum nesting depth is 3.
  - Use meaningful names.
- Out of scope: do not change the tables {{P}}VEHICLE and {{P}}TRIP. Do not
  change the selection screen fields. Do not change the ALV column names.

# 7. Acceptance
- The program {{P}}FLEET_COST_OLD is active and has no syntax error.
- The hidden tests pass.
- Write ABAP Unit tests as local test classes in the program.