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fix: don't show consumption for partial fills (#194) #196

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Merged
dannymcc merged 1 commit into from
May 21, 2026
Merged

fix: don't show consumption for partial fills (#194) #196

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63 changes: 27 additions & 36 deletions app/models.py
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Original file line number Diff line number Diff line change
Expand Up @@ -600,45 +600,36 @@ class FuelLog(db.Model):
def get_consumption(self, consumption_unit=None, volume_unit='L'):
"""Calculate consumption for this fill-up.

For full-tank fill-ups, sum every litre poured between the previous
full tank and this one (inclusive) and divide by the distance covered
— the "fill-to-fill" method. Partial fills between two full tanks are
therefore counted (issue #169). If any of the intervening logs is
flagged ``is_missed``, the figure is unknowable and we return None.

For partial fills, compare against the immediately preceding log of
any type to give an instantaneous "fuel added per km" estimate; this
is a rough indicator, not a true consumption figure.
Only meaningful for full-tank fills: sum every litre poured between
the previous full tank and this one (inclusive) and divide by the
distance covered — the "fill-to-fill" method. Partial fills between
two full tanks are therefore counted in the next full tank's figure
(issue #169). If any of the intervening logs is flagged ``is_missed``,
the figure is unknowable and we return None.

Partial fills return None: the litres added in a top-up tell you
nothing about consumption over the preceding distance, and surfacing
a number there is misleading (issue #194).
"""
if not self.volume:
if not self.volume or not self.is_full_tank:
return None

if self.is_full_tank:
prev_full = FuelLog.query.filter(
FuelLog.vehicle_id == self.vehicle_id,
FuelLog.odometer < self.odometer,
FuelLog.is_full_tank == True,
).order_by(FuelLog.odometer.desc()).first()
if not prev_full:
return None
distance = self.odometer - prev_full.odometer
between = FuelLog.query.filter(
FuelLog.vehicle_id == self.vehicle_id,
FuelLog.odometer > prev_full.odometer,
FuelLog.odometer <= self.odometer,
).all()
if any(log.is_missed for log in between):
return None
volume_native = sum(log.volume for log in between if log.volume)
else:
prev_log = FuelLog.query.filter(
FuelLog.vehicle_id == self.vehicle_id,
FuelLog.odometer < self.odometer,
).order_by(FuelLog.odometer.desc()).first()
if not prev_log:
return None
distance = self.odometer - prev_log.odometer
volume_native = self.volume
prev_full = FuelLog.query.filter(
FuelLog.vehicle_id == self.vehicle_id,
FuelLog.odometer < self.odometer,
FuelLog.is_full_tank == True,
).order_by(FuelLog.odometer.desc()).first()
if not prev_full:
return None
distance = self.odometer - prev_full.odometer
between = FuelLog.query.filter(
FuelLog.vehicle_id == self.vehicle_id,
FuelLog.odometer > prev_full.odometer,
FuelLog.odometer <= self.odometer,
).all()
if any(log.is_missed for log in between):
return None
volume_native = sum(log.volume for log in between if log.volume)

if distance > 0 and volume_native > 0:
odometer_unit = self.vehicle.get_effective_odometer_unit()
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42 changes: 23 additions & 19 deletions tests/test_fuel.py
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Original file line number Diff line number Diff line change
Expand Up @@ -96,7 +96,8 @@ def test_delete_fuel_log(self, auth_client, sample_fuel_log):


class TestPartialFillConsumption:
"""#122 — consumption should be calculated for partial fills."""
"""#194 — partial fills return no consumption; the next full fill
captures the partial volume over the whole interval (#169)."""

def test_full_tank_consumption_unchanged(self, app, test_user, sample_vehicle):
log1 = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
Expand All @@ -108,17 +109,14 @@ def test_full_tank_consumption_unchanged(self, app, test_user, sample_vehicle):
# 42L / 500km * 100 = 8.4 L/100km
assert abs(log2.get_consumption() - 8.4) < 0.01

def test_partial_fill_returns_consumption(self, app, test_user, sample_vehicle):
def test_partial_fill_returns_none(self, app, test_user, sample_vehicle):
log1 = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
date=date(2024, 1, 1), odometer=10000, volume=40, is_full_tank=True)
log2 = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
date=date(2024, 1, 10), odometer=10200, volume=20, is_full_tank=False)
db.session.add_all([log1, log2])
db.session.commit()
# 20L / 200km * 100 = 10.0 L/100km
consumption = log2.get_consumption()
assert consumption is not None
assert abs(consumption - 10.0) < 0.01
assert log2.get_consumption() is None

def test_partial_fill_no_previous_log_returns_none(self, app, test_user, sample_vehicle):
log = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
Expand All @@ -134,21 +132,27 @@ def test_no_volume_returns_none(self, app, test_user, sample_vehicle):
db.session.commit()
assert log.get_consumption() is None

def test_partial_fill_uses_any_previous_log(self, app, test_user, sample_vehicle):
"""Partial fill looks back to the nearest log regardless of fill type."""
log1 = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
date=date(2024, 1, 1), odometer=10000, volume=40, is_full_tank=True)
log2 = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
date=date(2024, 1, 8), odometer=10300, volume=15, is_full_tank=False)
log3 = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
date=date(2024, 1, 15), odometer=10500, volume=20, is_full_tank=False)
db.session.add_all([log1, log2, log3])
def test_issue_194_partial_then_full(self, app, test_user, sample_vehicle):
"""#194 — Steve's reported scenario:
full (62.8L) → partial 3.8L (no consumption) → full 62.1L (real figure
spans the whole interval and includes the 3.8L top-up).
"""
full_a = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
date=date(2026, 5, 11), odometer=10000, volume=62.8,
is_full_tank=True)
partial = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
date=date(2026, 5, 20), odometer=10557, volume=3.8,
is_full_tank=False)
full_b = FuelLog(vehicle_id=sample_vehicle.id, user_id=test_user.id,
date=date(2026, 5, 21), odometer=10600, volume=62.1,
is_full_tank=True)
db.session.add_all([full_a, partial, full_b])
db.session.commit()
# log3 looks back to log2 (nearest), not log1
# 20L / 200km * 100 = 10.0 L/100km
consumption = log3.get_consumption()
assert partial.get_consumption() is None
# (3.8 + 62.1) / 600 * 100 = 10.983 L/100km
consumption = full_b.get_consumption()
assert consumption is not None
assert abs(consumption - 10.0) < 0.01
assert abs(consumption - 10.983) < 0.01

def test_full_tank_sums_intervening_partials(self, app, test_user, sample_vehicle):
"""#169 — full tank consumption must sum partial fills since the previous full."""
Expand Down