FUNCTION {{p}}energy_bill
  IMPORTING
    iv_consumption  TYPE decfloat34
    iv_tariff       TYPE string
    iv_direct_debit TYPE abap_bool
  EXPORTING
    ev_bill TYPE decfloat34
  EXCEPTIONS
    invalid_consumption
    invalid_tariff.

  CONSTANTS lc_base_fee TYPE decfloat34 VALUE '12.00'.
  CONSTANTS lc_tier_limit TYPE decfloat34 VALUE '300'.
  CONSTANTS lc_tier_factor TYPE decfloat34 VALUE '0.8'.
  CONSTANTS lc_debit_factor TYPE decfloat34 VALUE '0.98'.

  IF iv_consumption < 0.
    RAISE invalid_consumption.
  ENDIF.

  DATA lv_rate TYPE decfloat34.
  CASE iv_tariff.
    WHEN 'BASIC'.
      lv_rate = '0.32'.
    WHEN 'GREEN'.
      lv_rate = '0.38'.
    WHEN 'NIGHT'.
      lv_rate = '0.24'.
    WHEN OTHERS.
      RAISE invalid_tariff.
  ENDCASE.

  DATA lv_standard_qty TYPE decfloat34.
  DATA lv_reduced_qty TYPE decfloat34.
  IF iv_consumption > lc_tier_limit.
    lv_standard_qty = lc_tier_limit.
    lv_reduced_qty = iv_consumption - lc_tier_limit.
  ELSE.
    lv_standard_qty = iv_consumption.
    lv_reduced_qty = 0.
  ENDIF.

  DATA lv_bill TYPE decfloat34.
  lv_bill = lc_base_fee + lv_standard_qty * lv_rate
            + lv_reduced_qty * lv_rate * lc_tier_factor.
  IF iv_direct_debit = abap_true.
    lv_bill = lv_bill * lc_debit_factor.
  ENDIF.

  ev_bill = round( val = lv_bill dec = 3 mode = cl_abap_math=>round_half_up ).
ENDFUNCTION.