# 1. Goal
A rail infrastructure manager charges a track access fee to train operating
companies. A billing program calls one function module for each operating day.
The function module calculates the fee of each train path and groups the result
by train category.

# 2. Open questions
None.

# 3. Context
- Function group {{P}}FG_TRACK exists in package $TMP.
- Function module {{P}}TRACK_SAMPLE exists in this group. It shows the interface
  that the billing program uses. Do not change it.
- The global class {{P}}TRACK_TYPES exists in package $TMP. It only holds the row
  types of the input and of the result. Do not change it. Its public types are:
  - TY_PATH: PATH_ID (type N, length 8), TRAIN_CAT (type C, length 2),
    DISTANCE_KM (packed, length 13, 2 decimals), NIGHT_FLAG (type C, length 1).
  - TT_PATH: standard table of TY_PATH.
  - TY_FEE: TRAIN_CAT (type C, length 2), PATH_COUNT (type I), TOTAL_KM (packed,
    length 13, 2 decimals), TOTAL_FEE (packed, length 13, 2 decimals).
  - TT_FEE: standard table of TY_FEE.
- The billing program builds a standard table with the components of TY_PATH and
  reads a standard table with the components of TY_FEE. The component names are
  the interface between the billing program and the function module.

# 4. Contract
Create the function module {{P}}TRACK_FEE in function group {{P}}FG_TRACK with
this interface:
- Importing parameter IT_PATHS, type STANDARD TABLE.
- Exporting parameter ET_FEES, type STANDARD TABLE.
- Exceptions INVALID_DISTANCE and INVALID_CATEGORY.
The two table parameters are generic standard tables. Their row components are
fixed by TY_PATH and TY_FEE of {{P}}TRACK_TYPES.

# 5. Business rules
1. A train path with DISTANCE_KM less than or equal to zero is not valid. Raise
   the exception INVALID_DISTANCE.
2. The rate of a train category is:
   - IC: 1.20 per kilometre
   - RG: 0.90 per kilometre
   - FR: 0.60 per kilometre
   - SP: 1.50 per kilometre
3. A train category that is not in rule 2 is not valid. Raise the exception
   INVALID_CATEGORY.
4. The fee of one path is DISTANCE_KM multiplied by the rate of its train
   category.
5. If NIGHT_FLAG is 'X', multiply the fee of the path by 1.20.
6. Round the fee of the path half up to two decimals.
7. The minimum fee of one path is 5.00. If the fee of the path is less than
   5.00, use 5.00.
8. The result table has one row for each train category that occurs in the
   input table.
9. PATH_COUNT is the number of paths of the category.
10. TOTAL_KM is the sum of DISTANCE_KM of the paths of the category.
11. TOTAL_FEE is the sum of the fees of the paths of the category.
12. Sort the result table in ascending order of TRAIN_CAT.
13. If the input table is empty, the result table is empty. Do not raise an
    exception.

# 6. Constraints
- Release target: 8.16.
- Coding standard: Clean ABAP. Keep methods below 40 statements. Pass large
  parameters by reference.
- Out of scope: do not change {{P}}TRACK_SAMPLE or {{P}}TRACK_TYPES.

# 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.