# 1. Goal
A retail company gives loyalty discounts to its customers. A checkout program needs
three values: the loyalty tier of a customer, the discount percent of a tier, and
the number of points that a customer still needs for the next tier. The program
calls one class for these three values.

# 2. Open questions
None.

# 3. Context
- The interface {{P}}IF_LOYALTY_RULES exists in package $TMP. It is active.
- The interface declares the type of a point value, the type of a tier, the
  constants for all tiers, and three methods. This document does not repeat the
  signature of the interface. Read the interface before you start.
- The three methods are:
  * the method that returns the tier for a point value,
  * the method that returns the discount percent of a tier,
  * the method that returns the number of points that are missing for the next tier.

# 4. Contract
- Create the class {{P}}LOYALTY_EVALUATOR in package $TMP.
- The class is public and final. It has a public constructor without parameters.
- The class implements {{P}}IF_LOYALTY_RULES.
- Do not add other public methods.

# 5. Business rules
Tier of a point value:
1. A point value below zero counts as zero.
2. 0 to 999 points is the basic tier.
3. 1000 to 4999 points is the silver tier.
4. 5000 to 19999 points is the gold tier.
5. 20000 points and more is the platinum tier.

Discount percent of a tier:
6. basic is 0 percent.
7. silver is 3 percent.
8. gold is 7 percent.
9. platinum is 12 percent.
10. Any other tier value is 0 percent.

Points to the next tier:
11. A point value below zero counts as zero.
12. basic needs 1000 points minus the point value.
13. silver needs 5000 points minus the point value.
14. gold needs 20000 points minus the point value.
15. platinum needs 0 points.

# 6. Constraints
- Release target: 8.16.
- Coding standards: Clean ABAP. Methods below 40 statements. No global variables.
  No comment that restates the code.
- Out of scope: do not change {{P}}IF_LOYALTY_RULES.

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