# 1. Goal
Refactor the class {{P}}FREIGHT_CALCULATOR. The class calculates the freight cost of a
parcel. The calculation is correct, but the code is hard to read and hard to maintain.
Make the code clean. The behavior and the public API must not change.

# 2. Open questions
None.

# 3. Context
- The class {{P}}FREIGHT_CALCULATOR exists in package $TMP. It is active.
- The class contains legacy code: one long method, nested IF blocks, hard-coded
  numbers, a private attribute that is written but never read, and commented-out code.
- A logistics program calls the class. That program must continue to work without a
  change. Therefore the behavior of the class must stay the same.

# 4. Contract
The public part of the class must stay exactly as it is:
- The class {{P}}FREIGHT_CALCULATOR is public, final, and has a public constructor
  without parameters.
- Public type TY_RESULT with these components: STATUS TYPE c LENGTH 10,
  BASE TYPE p LENGTH 9 DECIMALS 2, SURCHARGE TYPE p LENGTH 9 DECIMALS 2,
  TOTAL TYPE p LENGTH 9 DECIMALS 2.
- Public constant structure C_STATUS with the components OK, WEIGHT and ZONE. Each
  component has the type c LENGTH 10. The values are 'OK', 'WEIGHT' and 'ZONE'.
- Public method CALCULATE:
  IMPORTING iv_weight_kg TYPE p LENGTH 8 DECIMALS 2
            iv_zone      TYPE string
            iv_express   TYPE abap_bool DEFAULT abap_false
  RETURNING VALUE(rs_result) TYPE ty_result.
- Public method IS_ZONE_SUPPORTED:
  IMPORTING iv_zone TYPE string
  RETURNING VALUE(rv_supported) TYPE abap_bool.
- Do not add other public components or public methods.

# 5. Business rules
The rules below describe the behavior of the class. The behavior must not change.
1. Normalize the zone: remove all blanks and convert all letters to upper case. A
   zone is known only if the normalized zone is exactly equal to a zone code. Do not
   shorten the zone and do not extend the zone.
2. Check the weight first. If the weight is not greater than zero, return the status
   WEIGHT with BASE, SURCHARGE and TOTAL equal to zero. This check comes before the
   zone check.
3. If the normalized zone is not known, return the status ZONE with BASE, SURCHARGE
   and TOTAL equal to zero.
4. The rate per kilogram depends on the zone: DE 4.50, AT 5.20, CH 7.80, FR 6.40,
   NL 4.90, PL 5.10, ES 6.90.
5. BASE = rate x weight. Round BASE to 2 decimal places. Round half away from zero.
6. If iv_express is abap_true, SURCHARGE = BASE x 25 / 100, rounded to 2 decimal
   places. Else SURCHARGE is zero.
7. TOTAL = BASE + SURCHARGE.
8. Return the status OK.
9. IS_ZONE_SUPPORTED returns abap_true if the normalized zone is known, else
   abap_false. A blank zone is not known.

# 6. Constraints
- Release target: SAP_BASIS 816 (ABAP Platform 2025).
- Coding standards: Clean ABAP. Every method has less than 40 statements. No global
  variables. No IF block nested deeper than 2 levels. No hard-coded rate in a
  statement: use a constant or a table. Remove the private attribute that is never
  read. Remove the commented-out code. No comment that restates the code.
- Out of scope: do not change the public API, do not change the behavior, do not
  create new global objects, do not change the class name.

# 7. Acceptance
- The class is active and has no syntax error.
- The hidden tests pass.
- Write your own ABAP Unit tests as local test classes in the class.