# 1. Goal

An energy supplier bills households for electricity. The billing program calls
one function module for each household. The function module calculates the bill
of one month.

# 2. Open questions

None.

# 3. Context

- The function group {{P}}FG_BILL exists in package $TMP. The group is empty.
- The billing program calls the function module once for each household. It
  passes the consumption of the month, the tariff, and the payment method.
- The consumption is a quantity in kilowatt hours (kWh).
- The bill is an amount in euro.

# 4. Contract

- Create the function module {{P}}ENERGY_BILL in function group {{P}}FG_BILL.
- Use this interface:

| Parameter | Kind | Type | Meaning |
| --- | --- | --- | --- |
| iv_consumption | Importing | decfloat34 | Consumption of the month in kWh |
| iv_tariff | Importing | string | Tariff code |
| iv_direct_debit | Importing | abap_bool | abap_true if the customer pays by direct debit |
| ev_bill | Exporting | decfloat34 | Bill in euro |
| invalid_consumption | Exception | | See rule 1 |
| invalid_tariff | Exception | | See rule 2 |

# 5. Business rules

1. If the consumption is less than zero, raise the exception
   INVALID_CONSUMPTION. Do not set the bill.
2. The valid tariff codes are BASIC, GREEN, and NIGHT. Any other tariff code
   raises the exception INVALID_TARIFF. Do not set the bill.
3. Every bill contains a base fee of 12.00 euro.
4. The working price for one kWh is:
   - BASIC: 0.32 euro
   - GREEN: 0.38 euro
   - NIGHT: 0.24 euro
5. For a consumption above 300 kWh, the working price of the part above 300 kWh
   is 80 % of the working price of the tariff.
6. If the customer pays by direct debit, the bill is 2 % lower.
7. Round the bill half up to 2 decimals.

# 6. Constraints

- Release target: ABAP Platform 2025 (SAP_BASIS 816).
- Package: $TMP. Do not use transports.
- Coding standard: Clean ABAP. Keep every method below 40 statements.
- Out of scope: database access, CDS views, reports, ALV, dynpro, and changes
  to other objects.

# 7. Acceptance

- The function module {{P}}ENERGY_BILL is active and has no syntax error.
- The hidden tests pass.
- Write ABAP Unit tests for the function module in a global test class.