# 1. Goal

A furniture shop sells furniture on instalment plans. A checkout program calls one
check before the shop grants an instalment plan to a customer. The program needs
one reason code for each customer.

# 2. Open questions

None.

# 3. Context

- The interface {{P}}IF_CREDIT_CHECK exists in package $TMP. It is active.
- The interface declares the type of the reason, the type of a money amount, the
  constants of the reason codes, and one method.
- The method name, the parameter names and the parameter types are not in this
  document. Read the interface in the system.
- The reason constants have the names OK, AGE, INCOME, OPEN_PLAN and LIMIT.

# 4. Contract

- Create the class {{P}}CREDIT_CHECKER in package $TMP.
- The class is public and final. It has a public constructor without parameters.
- The class implements the interface {{P}}IF_CREDIT_CHECK.
- Do not add other public methods.

# 5. Business rules

The check receives the age of the customer in years, the net monthly income of the
customer, the number of open instalment plans of the customer, and the amount of
the new order. Apply the rules in this sequence. Return the reason of the first
rule that fails.

1. If the age is less than 18, return AGE.
2. If the net monthly income is zero or less, return INCOME.
3. If the number of open instalment plans is 2 or more, return OPEN_PLAN.
4. Calculate the credit limit:
   - Start with three times the net monthly income.
   - Subtract 500 for each open instalment plan.
   - If the age is less than 21, halve the limit and round the result down to
     whole euros. Example: 3750.75 becomes 3750.00.
5. If the amount of the new order is more than the credit limit, return LIMIT.
6. Else return OK.

# 6. Constraints

- Release target: SAP_BASIS 8.16 (ABAP Platform 2025).
- Coding standards: Clean ABAP. Method length below 40 statements. No global
  variables. No comment that restates the code.
- Out of scope: do not change the interface {{P}}IF_CREDIT_CHECK.

# 7. Acceptance

- The class is active and has no syntax error.
- The hidden tests pass.
- Write your own ABAP Unit tests for the class.