# 1. Goal
Calculate delivery dates for sales orders. A delivery date must be a working day.
Weekends and plant holidays are not working days. A planner uses the class before
the system confirms a delivery date.

# 2. Open questions
None.

# 3. Context
- The class {{P}}DELIVERY_SCHEDULE does not exist. Create it in package $TMP.
- The caller gives the plant holidays as a table of dates. The class does not read
  a factory calendar. The class does not read the system date.

# 4. Contract
- Create the class {{P}}DELIVERY_SCHEDULE in package $TMP.
- The class is public, final, and has a public constructor without parameters.
- The class has the public type TY_HOLIDAYS. TY_HOLIDAYS is a standard table of
  dates (TYPE d) with an empty key.
- The class has the public methods below. Do not add other public methods.

```abap
METHODS is_working_day
  IMPORTING iv_date           TYPE d
            it_holidays       TYPE ty_holidays
  RETURNING VALUE(rv_working) TYPE abap_bool.

METHODS next_working_day
  IMPORTING iv_date        TYPE d
            it_holidays    TYPE ty_holidays
  RETURNING VALUE(rv_date) TYPE d.

METHODS add_working_days
  IMPORTING iv_start       TYPE d
            iv_days        TYPE i
            it_holidays    TYPE ty_holidays
  RETURNING VALUE(rv_date) TYPE d.

METHODS count_working_days
  IMPORTING iv_from         TYPE d
            iv_to           TYPE d
            it_holidays     TYPE ty_holidays
  RETURNING VALUE(rv_count) TYPE i.
```

# 5. Business rules
1. The days of the week are Monday, Tuesday, Wednesday, Thursday, Friday, Saturday,
   Sunday.
2. A date is a working day when these two conditions are true:
   - The date is not a Saturday and not a Sunday.
   - The date is not in it_holidays.
3. IS_WORKING_DAY returns abap_true for a working day. It returns abap_false for
   all other days.
4. NEXT_WORKING_DAY returns the first working day that is on iv_date or after
   iv_date.
5. ADD_WORKING_DAYS counts working days.
   - If iv_days is 0, the result is iv_start.
   - If iv_days is greater than 0, the result is the date that is iv_days working
     days after iv_start. Count only working days. Ignore all other days.
   - If iv_days is less than 0, the result is the date that is the absolute value
     of iv_days working days before iv_start. Count only working days. Ignore all
     other days.
   - Example: iv_start is a Friday and iv_days is 1. The result is the next Monday.
   - Example: iv_start is a Monday and iv_days is -1. The result is the Friday
     before.
6. COUNT_WORKING_DAYS counts the working days in the interval from iv_from to
   iv_to. The interval contains iv_from and iv_to.
   - If iv_from is after iv_to, the result is 0.
   - If iv_from is equal to iv_to, the result is 1 for a working day and 0 for all
     other days.
7. it_holidays can be empty. it_holidays can contain dates that are outside the
   interval. it_holidays can contain the same date more than one time. A date that
   occurs more than one time in it_holidays is a holiday.

# 6. Constraints
- Release target: 8.16.
- Coding standards: Clean ABAP. A method has less than 40 statements. No global
  variables. No comment that restates the code.
- Out of scope: do not read a factory calendar. Do not read the system date. Do
  not create other objects.

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