CLASS {{P}}COURSE_BOOKING DEFINITION PUBLIC FINAL CREATE PUBLIC.
  PUBLIC SECTION.
    TYPES ty_course_id TYPE c LENGTH 10.
    TYPES ty_category  TYPE c LENGTH 10.
    TYPES:
      BEGIN OF ty_course_info,
        course_id  TYPE ty_course_id,
        title      TYPE c LENGTH 40,
        free_seats TYPE i,
      END OF ty_course_info.
    TYPES tt_course_info TYPE STANDARD TABLE OF ty_course_info WITH EMPTY KEY.

    METHODS get_free_seats
      IMPORTING iv_course_id         TYPE ty_course_id
      RETURNING VALUE(rv_free_seats) TYPE i.

    METHODS is_bookable
      IMPORTING iv_course_id       TYPE ty_course_id
                iv_seats           TYPE i
      RETURNING VALUE(rv_bookable) TYPE abap_bool.

    METHODS list_bookable_courses
      IMPORTING iv_category       TYPE ty_category
                iv_seats          TYPE i
      RETURNING VALUE(rt_courses) TYPE tt_course_info.

  PRIVATE SECTION.
    TYPES:
      BEGIN OF ty_course,
        course_id TYPE ty_course_id,
        title     TYPE c LENGTH 40,
        capacity  TYPE i,
        booked    TYPE i,
      END OF ty_course.

    METHODS read_course
      IMPORTING iv_course_id     TYPE ty_course_id
      RETURNING VALUE(rs_course) TYPE ty_course.

    METHODS calculate_free_seats
      IMPORTING is_course      TYPE ty_course
      RETURNING VALUE(rv_free) TYPE i.
ENDCLASS.


CLASS {{P}}COURSE_BOOKING IMPLEMENTATION.
  METHOD get_free_seats.
    rv_free_seats = calculate_free_seats( read_course( iv_course_id ) ).
  ENDMETHOD.

  METHOD is_bookable.
    IF iv_seats < 1.
      rv_bookable = abap_false.
      RETURN.
    ENDIF.
    rv_bookable = xsdbool( iv_seats <= calculate_free_seats( read_course( iv_course_id ) ) ).
  ENDMETHOD.

  METHOD list_bookable_courses.
    DATA lt_course TYPE STANDARD TABLE OF ty_course WITH EMPTY KEY.

    SELECT course_id, title, capacity, booked
      FROM {{P}}COURSE
      WHERE category = @iv_category
      INTO TABLE @lt_course.

    LOOP AT lt_course INTO DATA(ls_course).
      DATA(lv_free) = calculate_free_seats( ls_course ).
      IF lv_free < iv_seats.
        CONTINUE.
      ENDIF.
      rt_courses = VALUE #( BASE rt_courses
                            ( course_id  = ls_course-course_id
                              title      = ls_course-title
                              free_seats = lv_free ) ).
    ENDLOOP.

    SORT rt_courses BY course_id.
  ENDMETHOD.

  METHOD read_course.
    SELECT SINGLE course_id, title, capacity, booked
      FROM {{P}}COURSE
      WHERE course_id = @iv_course_id
      INTO @rs_course.
  ENDMETHOD.

  METHOD calculate_free_seats.
    rv_free = is_course-capacity + is_course-booked.
    IF rv_free < 0.
      rv_free = 0.
    ENDIF.
  ENDMETHOD.
ENDCLASS.