# 1. Goal
A pharmacy dispenses prescription items. Before the pharmacy dispenses a
prescription, it validates the prescription. The validation raises a class-based
exception with one reason and one message for each problem. The pharmacy program
needs the validation class and the exception class.

# 2. Open questions
None.

# 3. Context
- The class {{P}}DRUG_MASTER is in package $TMP. It is active. It is the drug
  master data of the pharmacy. Do not change it.
  - Public type TY_DRUG_ID: character, length 10.
  - Public structure TY_DRUG with the components DRUG_ID (TY_DRUG_ID) and
    MAX_DAILY_DOSE (integer, milligram).
  - Public method GET_DRUG with the importing parameter IV_DRUG_ID (TY_DRUG_ID)
    and the returning parameter RS_DRUG (TY_DRUG). If the drug is not in the
    master data, RS_DRUG is initial.
- The drug master data contains these drugs and maximum daily doses:
  PARA500 4000, IBU400 1200, AMOX500 1500, META50 200, SALB100 800.
- A prescription has an issue date, a number of valid days and items. Each item
  has a drug, a quantity and a daily dose.

# 4. Contract
## 4.1 Exception class {{P}}CX_PRESC_ERROR
- Create the class in package $TMP.
- The class inherits from CX_ROOT.
- Public type TY_REASON: character, length 12.
- Public constant structure C_REASON with the components EMPTY, EXPIRED,
  QUANTITY, UNKNOWN, DOSE and DUPLICATE. Each component has the type TY_REASON
  and the value of its own name.
- Public constructor with the importing parameter IV_REASON (TY_REASON).
- Public method GET_REASON with the returning parameter RV_REASON (TY_REASON).
- Public method GET_MESSAGE_TEXT with the returning parameter RV_TEXT (string).
  GET_MESSAGE_TEXT returns the message of the reason:
  - EMPTY: The prescription has no items
  - EXPIRED: The prescription is expired
  - QUANTITY: The quantity is not positive
  - UNKNOWN: The drug is not in the drug master
  - DOSE: The daily dose is not allowed
  - DUPLICATE: The drug appears more than once

## 4.2 Check class {{P}}PRESCRIPTION_CHECK
- Create the class in package $TMP.
- The class is public and final. It has a public constructor without parameters.
- Public type TY_DRUG_ID: character, length 10.
- Public structure TY_ITEM with the components DRUG_ID (TY_DRUG_ID), QUANTITY
  (integer) and DAILY_DOSE (integer).
- Public table type TT_ITEM: standard table of TY_ITEM with empty key.
- Public method VALIDATE with these importing parameters:
  - IV_ISSUE_DATE (type d)
  - IV_VALID_DAYS (integer)
  - IV_AS_OF_DATE (type d)
  - IT_ITEM (TT_ITEM)
  and the addition RAISING {{P}}CX_PRESC_ERROR.
- Do not add other public methods.

# 5. Business rules
VALIDATE applies the rules in this sequence. It raises {{P}}CX_PRESC_ERROR with
the reason of the first rule that fails.
1. If IT_ITEM is empty, the reason is EMPTY.
2. If IV_AS_OF_DATE is later than IV_ISSUE_DATE plus IV_VALID_DAYS days, the
   reason is EXPIRED.
3. Process the items in the sequence of the table. For each item:
   3.1 If QUANTITY is less than 1, the reason is QUANTITY.
   3.2 If DRUG_ID is not in the drug master data, the reason is UNKNOWN.
   3.3 If DAILY_DOSE is less than 1, or if DAILY_DOSE is greater than the
       maximum daily dose of the drug, the reason is DOSE.
4. If one DRUG_ID occurs in more than one item, the reason is DUPLICATE.
5. Else VALIDATE returns without an exception.
The dates are always valid dates.

# 6. Constraints
- Release target: SAP_BASIS 816 (ABAP Platform 2025).
- Package: $TMP. Do not use a transport request.
- Coding standards: Clean ABAP. Methods below 40 statements. No global
  variables. Pass large parameters by reference. No comment that restates the
  code.
- Out of scope: do not change {{P}}DRUG_MASTER.

# 7. Acceptance
- Both classes are active and have no syntax error.
- The hidden tests pass.
- Write your own ABAP Unit tests for {{P}}PRESCRIPTION_CHECK.