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Add costs to each row in yearly usage API

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This will replace the manual calculations in Admin [^1][^2] for SMS
and also in API [^3] for annual letter costs.

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 without making
assumptions about when we change our rates.

Since the calculation now depends on annual billing, we need to
change all the tests to make sure a suitable row exists. I've also
adjusted the test data to match the assumption that there can only
be one SMS rate per bst_date.

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 [^4] 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]: 474d7dfda8/app/templates/views/usage.html (L98)
[^4]: 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 fc378fed96
commit cd84928a1e
4 changed files with 119 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
app/billing/billing_schemas.py
View File

@@ -23,6 +23,7 @@ def serialize_ft_billing_remove_emails(rows):
"notifications_sent": row.notifications_sent,
"rate": float(row.rate),
"postage": row.postage,
"cost": float(row.cost),
}
for row in rows
if row.notification_type != 'email'
@@ -38,7 +39,9 @@ def serialize_ft_billing_yearly_totals(rows):
"chargeable_units": row.chargeable_units,
"notifications_sent": row.notifications_sent,
"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
]

63
app/dao/fact_billing_dao.py
View File

@@ -223,6 +223,7 @@ def fetch_billing_totals_for_year(service_id, year):
# TEMPORARY: while we migrate away from "billing_units"
func.sum(query.c.billable_units).label("billable_units"),
func.sum(query.c.chargeable_units).label("chargeable_units"),
func.sum(query.c.cost).label("cost"),
).group_by(
query.c.rate,
query.c.notification_type
@@ -280,6 +281,7 @@ def fetch_monthly_billing_for_year(service_id, year):
# TEMPORARY: while we migrate away from "billing_units"
func.sum(query.c.billable_units).label("billable_units"),
func.sum(query.c.chargeable_units).label("chargeable_units"),
func.sum(query.c.cost).label("cost"),
).group_by(
query.c.rate,
query.c.notification_type,
@@ -311,6 +313,7 @@ def query_service_email_usage_for_year(service_id, year):
FactBilling.billable_units.label("chargeable_units"),
FactBilling.rate,
FactBilling.notification_type,
literal(0).label("cost"),
).filter(
FactBilling.service_id == service_id,
FactBilling.bst_date >= year_start,
@@ -334,6 +337,7 @@ 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,
@@ -343,9 +347,61 @@ def query_service_letter_usage_for_year(service_id, year):
def query_service_sms_usage_for_year(service_id, year):
"""
Returns rows from the ft_billing table with some calculated values like cost,
incorporating the SMS free allowance e.g.
(
bst_date=2022-04-27,
notifications_sent=12,
chargeable_units=12,
rate=0.0165,
[cost=0 <== covered by the free allowance],
[cost=0.198 <== if free allowance exhausted],
[cost=0.099 <== only some free allowance left],
...
)
In order to calculate how much free allowance is left, we need to work out
how much was used for previous bst_dates - cumulative_chargeable_units -
which we then subtract from the free allowance for the year.
cumulative_chargeable_units is calculated using a "window" clause, which has
access to all the rows identified by the query filter. Note that it's not
affected by any GROUP BY clauses that happen in outer queries.
https://www.postgresql.org/docs/current/tutorial-window.html
ASSUMPTION: rates always change at midnight i.e. there can only be one rate
on a given bst_date. This means we don't need to worry about how to assign
free allowance if it happens to run out when a rate changes.
"""
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 is "ASC" by default
order_by=[FactBilling.bst_date],
# first row to previous row
rows=(None, -1)
),
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
)
# Subquery for the number of chargeable_units that we will actually charge
# for, after taking any remaining free allowance into account.
charged_units = func.greatest(chargeable_units - cumulative_free_remainder, 0)
return db.session.query(
FactBilling.bst_date,
FactBilling.postage, # should always be "none"
@@ -355,11 +411,16 @@ def query_service_sms_usage_for_year(service_id, year):
chargeable_units.label("chargeable_units"),
FactBilling.rate,
FactBilling.notification_type,
(charged_units * FactBilling.rate).label("cost")
).join(
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,
)

11
tests/app/billing/test_rest.py
View File

@@ -147,6 +147,8 @@ def set_up_monthly_data():
billable_unit=1,
rate=0.33,
postage='second')
create_annual_billing(service_id=service.id, free_sms_fragment_limit=4, financial_year_start=2016)
return service
@@ -174,6 +176,7 @@ def test_get_yearly_usage_by_monthly_from_ft_billing(admin_request, notify_db_se
assert letter_row["notifications_sent"] == 30
assert letter_row["rate"] == 0.33
assert letter_row["postage"] == "second"
assert letter_row["cost"] == 9.9
assert sms_row["month"] == "April"
assert sms_row["notification_type"] == "sms"
@@ -182,6 +185,8 @@ def test_get_yearly_usage_by_monthly_from_ft_billing(admin_request, notify_db_se
assert sms_row["notifications_sent"] == 30
assert sms_row["rate"] == 0.162
assert sms_row["postage"] == "none"
# free allowance is 4, so (30 - 4) * 0.162
assert sms_row["cost"] == 4.212
def set_up_yearly_data():
@@ -189,6 +194,7 @@ 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):
@@ -209,6 +215,8 @@ 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
@@ -251,6 +259,7 @@ def test_get_yearly_billing_usage_summary_from_ft_billing(admin_request, notify_
assert json_response[0]['notifications_sent'] == 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
@@ -258,6 +267,7 @@ def test_get_yearly_billing_usage_summary_from_ft_billing(admin_request, notify_
assert json_response[1]['notifications_sent'] == 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
@@ -265,3 +275,4 @@ def test_get_yearly_billing_usage_summary_from_ft_billing(admin_request, notify_
assert json_response[2]['notifications_sent'] == 550
assert json_response[2]['rate'] == 0.0162
assert json_response[2]['letter_total'] == 0
assert json_response[2]['cost'] == 13.3002

45
tests/app/dao/test_ft_billing_dao.py
View File

@@ -73,8 +73,8 @@ def set_up_yearly_data_variable_rates():
letter_template = create_template(service=service, template_type="letter")
create_ft_billing(bst_date='2018-05-16', template=sms_template, rate=0.162)
create_ft_billing(bst_date='2018-05-17', template=sms_template, rate_multiplier=2, rate=0.162, billable_unit=2)
create_ft_billing(bst_date='2018-05-16', template=sms_template, rate_multiplier=2, rate=0.0150, billable_unit=2)
create_ft_billing(bst_date='2018-05-17', template=sms_template, rate_multiplier=2, rate=0.0150, billable_unit=2)
create_ft_billing(bst_date='2018-05-16', template=sms_template, rate_multiplier=2, rate=0.162, billable_unit=2)
create_ft_billing(bst_date='2018-05-16', template=letter_template, rate=0.33, postage='second')
create_ft_billing(
@@ -426,6 +426,7 @@ def test_get_rate_for_letters_when_page_count_is_zero(notify_db_session):
def test_fetch_monthly_billing_for_year(notify_db_session):
service = set_up_yearly_data()
create_annual_billing(service_id=service.id, free_sms_fragment_limit=10, financial_year_start=2016)
results = fetch_monthly_billing_for_year(service.id, 2016)
assert len(results) == 48
@@ -436,6 +437,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
assert results[0].billable_units == 30
assert results[0].chargeable_units == 0
assert results[0].rate == Decimal('0')
assert results[0].cost == Decimal('0')
assert str(results[1].month) == "2016-04-01"
assert results[1].notification_type == 'letter'
@@ -443,6 +445,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
assert results[1].billable_units == 30
assert results[1].chargeable_units == 30
assert results[1].rate == Decimal('0.30')
assert results[1].cost == Decimal('9')
assert str(results[1].month) == "2016-04-01"
assert results[2].notification_type == 'letter'
@@ -450,6 +453,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
assert results[2].billable_units == 30
assert results[2].chargeable_units == 30
assert results[2].rate == Decimal('0.33')
assert results[2].cost == Decimal('9.9')
assert str(results[3].month) == "2016-04-01"
assert results[3].notification_type == 'sms'
@@ -457,6 +461,8 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
assert results[3].billable_units == 30
assert results[3].chargeable_units == 30
assert results[3].rate == Decimal('0.162')
# free allowance is 10, so (30 - 10) * 0.162
assert results[3].cost == Decimal('3.24')
assert str(results[4].month) == "2016-05-01"
assert str(results[47].month) == "2017-03-01"
@@ -464,6 +470,7 @@ def test_fetch_monthly_billing_for_year(notify_db_session):
def test_fetch_monthly_billing_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_monthly_billing_for_year(service.id, 2018)
# Test data is only for the month of May
@@ -475,6 +482,7 @@ def test_fetch_monthly_billing_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 str(results[1].month) == "2018-05-01"
assert results[1].notification_type == 'letter'
@@ -482,6 +490,7 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
assert results[1].billable_units == 2
assert results[1].chargeable_units == 2
assert results[1].rate == Decimal('0.36')
assert results[1].cost == Decimal('0.72')
assert str(results[2].month) == "2018-05-01"
assert results[2].notification_type == 'sms'
@@ -489,6 +498,8 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
assert results[2].billable_units == 4
assert results[2].chargeable_units == 4
assert results[2].rate == Decimal('0.015')
# 1 free units on the 17th
assert results[2].cost == Decimal('0.045')
assert str(results[3].month) == "2018-05-01"
assert results[3].notification_type == 'sms'
@@ -496,6 +507,8 @@ def test_fetch_monthly_billing_for_year_variable_rates(notify_db_session):
assert results[3].billable_units == 5
assert results[3].chargeable_units == 5
assert results[3].rate == Decimal('0.162')
# 5 free units on the 16th
assert results[3].cost == Decimal('0')
@freeze_time('2018-08-01 13:30:00')
@@ -504,6 +517,7 @@ def test_fetch_monthly_billing_for_year_adds_data_for_today(notify_db_session):
template = create_template(service=service, template_type="sms")
create_rate(start_date=datetime.utcnow() - timedelta(days=1), value=0.158, notification_type='sms')
create_annual_billing(service_id=service.id, free_sms_fragment_limit=1000, financial_year_start=2018)
for i in range(1, 32):
create_ft_billing(bst_date='2018-07-{}'.format(i), template=template)
@@ -519,6 +533,7 @@ 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
@@ -527,28 +542,48 @@ def test_fetch_billing_totals_for_year(notify_db_session):
assert results[0].billable_units == 365
assert results[0].chargeable_units == 0
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
@@ -557,24 +592,30 @@ 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 == 2
assert results[1].billable_units == 2
assert results[1].chargeable_units == 2
assert results[1].rate == Decimal('0.36')
assert results[1].cost == Decimal('0.72')
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')
# 1 free unit on the 17th
assert results[2].cost == Decimal('0.045')
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')
# 5 free units on the 16th
assert results[3].cost == Decimal('0')
def test_delete_billing_data(notify_db_session):