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Add costs to each row in yearly usage API

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This will replace the manual calculation in Admin [^1] for SMS and
also in API [^2] for letters.

Doing the calculation here also means we correctly attribute free
allowance to the earliest rows in the billing table - Admin doesn't
know when a given rate was applied so can't do this with the data
currently returned from the API.

Since the calculation now depends on annual billing, we need to
change all the tests to make sure a suitable row exists.

Note about "OVER" clause
========================

Using "rows=" ("ROWS BETWEEN") makes more sense than "range=" as
we want the remainder to be incremental within each group in a
"GROUP BY" clause, as well as between groups i.e

  # ROWS BETWEEN (arbitrary numbers to illustrate)
  date=2021-04-03, units=3, cost=3.29
  date=2021-04-03, units=2, cost=4.17
  date=2021-04-04, units=2, cost=5.10

  vs.

  # RANGE BETWEEN
  date=2021-04-03, units=3, cost=4.17
  date=2021-04-03, units=2, cost=4.17
  date=2021-04-04, units=2, cost=5.10

See [^3] for more details and examples.

[^1]: https://github.com/alphagov/notifications-admin/blob/master/app/templates/views/usage.html#L60
[^2]: 072c3b2079/app/billing/billing_schemas.py (L37)
[^3]: https://learnsql.com/blog/difference-between-rows-range-window-functions/
This commit is contained in:
Ben Thorner
2022-04-20 17:14:17 +01:00
parent 0af791e417
commit 106da583ea
4 changed files with 67 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
app/billing/billing_schemas.py
View File

@@ -34,7 +34,9 @@ def serialize_ft_billing_yearly_totals(rows):
"billing_units": row.billable_units,
"chargeable_units": row.chargeable_units,
"rate": float(row.rate),
# TEMPORARY: while we migrate to "cost" in the Admin app
"letter_total": float(row.billable_units * row.rate) if row.notification_type == 'letter' else 0,
"cost": float(row.cost),
}
for row in rows
]

33
app/dao/fact_billing_dao.py
View File

@@ -206,6 +206,7 @@ def fetch_billing_totals_for_year(service_id, year):
func.sum(query.c.chargeable_units).label("chargeable_units"),
query.c.rate.label("rate"),
query.c.notification_type.label("notification_type"),
func.sum(query.c.cost).label("cost"),
).group_by(
query.c.rate,
query.c.notification_type
@@ -287,6 +288,7 @@ def query_service_email_usage_for_year(service_id, year):
FactBilling.notifications_sent.label("chargeable_units"),
FactBilling.rate,
FactBilling.notification_type,
literal(0).label("cost"),
).filter(
FactBilling.service_id == service_id,
FactBilling.bst_date >= year_start,
@@ -303,6 +305,7 @@ def query_service_letter_usage_for_year(service_id, year):
FactBilling.notifications_sent.label("chargeable_units"),
FactBilling.rate,
FactBilling.notification_type,
(FactBilling.notifications_sent * FactBilling.rate).label("cost"),
).filter(
FactBilling.service_id == service_id,
FactBilling.bst_date >= year_start,
@@ -315,16 +318,44 @@ def query_service_sms_usage_for_year(service_id, year):
year_start, year_end = get_financial_year_dates(year)
chargeable_units = FactBilling.billable_units * FactBilling.rate_multiplier
# Subquery for the number of chargeable units in all rows preceding this one,
# which might be none if this is the first row (hence the "coalesce").
cumulative_chargeable_units = func.coalesce(
func.sum(chargeable_units).over(
order_by=[
FactBilling.bst_date, # order is "ASC" by default
FactBilling.rate # ensures test stability for rows on the same day
],
rows=(None, -1) # ROWS BETWEEN UNBOUNDED PRECEDING AND 1 ROW PRECEDING
),
literal(0)
)
# Subquery for how much free allowance we have left before the current row,
# so we can work out the cost for this row after taking it into account.
cumulative_free_remainder = func.greatest(
AnnualBilling.free_sms_fragment_limit - cumulative_chargeable_units,
0
)
return db.session.query(
FactBilling.notifications_sent,
chargeable_units.label("chargeable_units"),
FactBilling.rate,
FactBilling.notification_type,
(
func.greatest(chargeable_units - cumulative_free_remainder, literal(0)) *
FactBilling.rate
).label("cost")
).outerjoin(
AnnualBilling,
AnnualBilling.service_id == service_id
).filter(
FactBilling.service_id == service_id,
FactBilling.bst_date >= year_start,
FactBilling.bst_date <= year_end,
FactBilling.notification_type == SMS_TYPE
FactBilling.notification_type == SMS_TYPE,
AnnualBilling.financial_year_start == year,
)

6
tests/app/billing/test_rest.py
View File

@@ -185,6 +185,7 @@ def set_up_yearly_data():
sms_template = create_template(service=service, template_type="sms")
email_template = create_template(service=service, template_type="email")
letter_template = create_template(service=service, template_type="letter")
for month in range(1, 13):
mon = str(month).zfill(2)
for day in range(1, monthrange(2016, month)[1] + 1):
@@ -205,6 +206,8 @@ def set_up_yearly_data():
rate=0.33,
postage='second')
start_date, end_date = get_month_start_and_end_date_in_utc(datetime(2016, int(mon), 1))
create_annual_billing(service_id=service.id, free_sms_fragment_limit=4, financial_year_start=2016)
return service
@@ -246,15 +249,18 @@ def test_get_yearly_billing_usage_summary_from_ft_billing(admin_request, notify_
assert json_response[0]['chargeable_units'] == 275
assert json_response[0]['rate'] == 0
assert json_response[0]['letter_total'] == 0
assert json_response[0]['cost'] == 0
assert json_response[1]['notification_type'] == 'letter'
assert json_response[1]['billing_units'] == 275
assert json_response[1]['chargeable_units'] == 275
assert json_response[1]['rate'] == 0.33
assert json_response[1]['letter_total'] == 90.75
assert json_response[1]['cost'] == 90.75
assert json_response[2]['notification_type'] == 'sms'
assert json_response[2]['billing_units'] == 825
assert json_response[2]['chargeable_units'] == 825
assert json_response[2]['rate'] == 0.0162
assert json_response[2]['letter_total'] == 0
assert json_response[2]['cost'] == 13.3002

27
tests/app/dao/test_ft_billing_dao.py
View File

@@ -502,6 +502,7 @@ def test_fetch_monthly_billing_for_year_adds_data_for_today(notify_db_session):
def test_fetch_billing_totals_for_year(notify_db_session):
service = set_up_yearly_data()
create_annual_billing(service_id=service.id, free_sms_fragment_limit=1000, financial_year_start=2016)
results = fetch_billing_totals_for_year(service_id=service.id, year=2016)
assert len(results) == 4
@@ -510,28 +511,48 @@ def test_fetch_billing_totals_for_year(notify_db_session):
assert results[0].billable_units == 365
assert results[0].chargeable_units == 365
assert results[0].rate == Decimal('0')
assert results[0].cost == Decimal('0')
assert results[1].notification_type == 'letter'
assert results[1].notifications_sent == 365
assert results[1].billable_units == 365
assert results[1].chargeable_units == 365
assert results[1].rate == Decimal('0.3')
assert results[1].cost == Decimal('109.5')
assert results[2].notification_type == 'letter'
assert results[2].notifications_sent == 365
assert results[2].billable_units == 365
assert results[2].chargeable_units == 365
assert results[2].rate == Decimal('0.33')
assert results[2].cost == Decimal('120.45')
assert results[3].notification_type == 'sms'
assert results[3].notifications_sent == 365
assert results[3].billable_units == 365
assert results[3].chargeable_units == 365
assert results[3].rate == Decimal('0.162')
assert results[3].cost == Decimal('0')
def test_fetch_billing_totals_for_year_uses_current_annual_billing(notify_db_session):
service = set_up_yearly_data()
create_annual_billing(service_id=service.id, free_sms_fragment_limit=400, financial_year_start=2015)
create_annual_billing(service_id=service.id, free_sms_fragment_limit=0, financial_year_start=2016)
result = next(
result for result in
fetch_billing_totals_for_year(service_id=service.id, year=2016)
if result.notification_type == 'sms'
)
assert result.chargeable_units == 365
assert result.cost > 0
def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
service = set_up_yearly_data_variable_rates()
create_annual_billing(service_id=service.id, free_sms_fragment_limit=6, financial_year_start=2018)
results = fetch_billing_totals_for_year(service_id=service.id, year=2018)
assert len(results) == 4
@@ -540,24 +561,30 @@ def test_fetch_billing_totals_for_year_variable_rates(notify_db_session):
assert results[0].billable_units == 1
assert results[0].chargeable_units == 1
assert results[0].rate == Decimal('0.33')
assert results[0].cost == Decimal('0.33')
assert results[1].notification_type == 'letter'
assert results[1].notifications_sent == 1
assert results[1].billable_units == 1
assert results[1].chargeable_units == 1
assert results[1].rate == Decimal('0.36')
assert results[1].cost == Decimal('0.36')
assert results[2].notification_type == 'sms'
assert results[2].notifications_sent == 1
assert results[2].billable_units == 4
assert results[2].chargeable_units == 4
assert results[2].rate == Decimal('0.015')
# 4 units sent on the 16th, 0 on the 17th
assert results[2].cost == Decimal('0')
assert results[3].notification_type == 'sms'
assert results[3].notifications_sent == 2
assert results[3].billable_units == 5
assert results[3].chargeable_units == 5
assert results[3].rate == Decimal('0.162')
# 1 free unit on the 16th, 1 on the 17th (+ 3 paid)
assert results[3].cost == Decimal('0.486') # (5 - 2) * 0.162
def test_delete_billing_data(notify_db_session):