# 1. Goal
Calculate the emptying fee for one septic tank. The depot program calls one
function module for each emptying job. The function module must have the same
interface as the sample function module, because the depot program calls all fee
modules in the same way.

# 2. Open questions
None.

# 3. Context
- Function group {{P}}FG_SEWER exists in package $TMP.
- Function module {{P}}SEWER_SAMPLE exists in this group. It is the sample fee
  module. Its interface is the interface that all fee modules must use.
- A drainage company empties septic tanks. The depot program sends the size of
  the tank, the distance from the depot, and the connection type of the
  property.

# 4. Contract
- Create the function module {{P}}SEWER_FEE in function group {{P}}FG_SEWER.
- Use exactly the interface of {{P}}SEWER_SAMPLE:
  - importing iv_tank_litres type i
  - importing iv_distance_km type i
  - importing iv_mains_sewer type abap_bool
  - exporting ev_skip type abap_bool
  - changing cv_fee type decfloat34
  - exception invalid_litres

# 5. Business rules
1. If iv_tank_litres is less than 1, raise the exception INVALID_LITRES.
2. Set the skip flag to false. Rule 4 is the only exception.
3. The base fee is 75.00. The base fee covers the first 1000 litres of the
   tank.
4. If the property is connected to the mains sewer, no emptying is necessary.
   Set the skip flag to true and do not change the fee. Do not apply rules 5
   to 7.
5. Each started 500 litres above 1000 litres adds 20.00 to the fee. Example:
   1000 litres add 0.00, 1001 litres add 20.00, 1500 litres add 20.00, and
   1501 litres add 40.00.
6. The travel fee is 1.50 for each kilometre of iv_distance_km. The travel fee
   is not more than 60.00.
7. The fee is the base fee of rule 3 plus the volume fee of rule 5 plus the
   travel fee of rule 6. The fee is not more than 900.00.

# 6. Constraints
- Release target: 7.40 SP05. Use only syntax that exists in 7.40 SP05. Do not
  use syntax that is newer than 7.40 SP05.
- Out of scope: do not change {{P}}SEWER_SAMPLE.
- Coding standards: Clean ABAP. A method has less than 40 statements.
- Out of scope: no database access, no ALV, no dynpro.

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