# 1. Goal

Create the message class and the class-based exception for the training course
booking service. The booking service reports every problem with a message from
the message class. The exception class carries the text of such a message.

# 2. Open questions

None.

# 3. Context

- All objects are in package $TMP.
- The booking service books participants into training courses.
- The old exception class {{P}}CX_LEGACY exists. It takes a hard-coded text and
  does not use a message class. The new exception class replaces it.
- All texts of the booking service come from one message class.

# 4. Contract

- Create the message class {{P}}MSG with the messages of section 5.
- Create the exception class {{P}}CX_BOOKING:
  - It is a class-based exception and inherits from CX_STATIC_CHECK.
  - The constructor has these parameters:
    - iv_msgno TYPE symsgno
    - iv_arg1 TYPE string, default ''
    - iv_arg2 TYPE string, default ''
  - The method GET_TEXT of the interface IF_MESSAGE returns the text of the
    message with the number iv_msgno from {{P}}MSG. The placeholder &1 is
    replaced by iv_arg1 and the placeholder &2 is replaced by iv_arg2.

# 5. Business rules

Message class {{P}}MSG:

1. Message 001, error message, text "Course &1 is fully booked". The booking
   service uses it when a course has no free seat.
2. Message 002, error message, text "Participant &1 is already booked for
   course &2". The booking service uses it for a double booking.
3. Message 003, warning message, text "Course &1 has only &2 free seats left".
   The booking service uses it when a course has few free seats left.
4. Message 004, information message, text "Booking for course &1 is
   confirmed". The booking service uses it for a successful booking.
5. Message 005, warning message, text "Course &1 was cancelled on &2". The
   booking service uses it for a cancelled course.

Exception class {{P}}CX_BOOKING:

6. The constructor stores the message number and the two placeholders.
7. GET_TEXT returns the text of the message with the number iv_msgno from
   {{P}}MSG. The placeholder &1 is replaced by iv_arg1 and the placeholder &2 is
   replaced by iv_arg2.

# 6. Constraints

- Release target: SAP_BASIS 816 (ABAP Platform 2025).
- Coding standards: Clean ABAP. Keep every method below 40 statements. Do not
  produce ATC findings of priority 1 or 2.
- Out of scope: database tables, CDS views, reports, dynpro, and the old
  exception class {{P}}CX_LEGACY.

# 7. Acceptance

- The message class {{P}}MSG is active. It contains the messages 001 to 005 with
  the exact texts of section 5.
- The exception class {{P}}CX_BOOKING is active and has no syntax error.
- The hidden tests pass.
- Write ABAP Unit tests for the messages and the exception class in a global
  test class.