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feat: add minimum charge helper for final demo #10

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Merged
Galzi1 merged 1 commit into from
Apr 11, 2026
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feat: add minimum charge helper for final demo #10

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12 changes: 12 additions & 0 deletions demo_app.py
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Original file line number Diff line number Diff line change
Expand Up @@ -52,3 +52,15 @@ def calculate_total_with_capped_percentage_discount(
discount_amount = min(subtotal * discount_rate, max_discount_amount)
discounted_subtotal = subtotal - discount_amount
return calculate_total(discounted_subtotal, sales_tax_rate=sales_tax_rate)


def calculate_total_with_minimum_charge(
subtotal: float,
sales_tax_rate: float,
discount_amount: float,
minimum_charge: float = 0.0,
) -> float:
"""Apply a discount before tax, but never reduce the subtotal below a floor."""

@Galzi1 Galzi1 Apr 11, 2026

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Please document whether minimum_charge is a pre-tax subtotal floor or a final customer-facing total floor. That distinction affects pricing policy, invoicing, and refunds, so it should be explicit in the docstring.


adjusted_subtotal = max(subtotal - discount_amount, minimum_charge)

@Galzi1 Galzi1 Apr 11, 2026

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We should validate minimum_charge here. If it is negative or greater than the subtotal, this helper can either produce negative pre-tax amounts or increase the charge instead of only enforcing a floor.

return calculate_total(adjusted_subtotal, sales_tax_rate=sales_tax_rate)

@Galzi1 Galzi1 Apr 11, 2026

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I would normalize the floored subtotal here and then delegate to the existing discount helper so one path stays responsible for discount clamping rules instead of spreading pricing math across multiple helpers.

Comment on lines +57 to +66

@qodo-code-review qodo-code-review Bot Apr 11, 2026

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Action required

1. Missing input validation 🐞 Bug ≡ Correctness

calculate_total_with_minimum_charge accepts negative discount_amount and/or minimum_charge, which
can silently increase the subtotal (negative discount) or allow negative totals (negative
minimum_charge). This is inconsistent with calculate_total_with_discount, which rejects negative
discounts, and can lead to incorrect financial charges.
Agent Prompt 
### Issue description
`calculate_total_with_minimum_charge()` currently allows invalid negative inputs.
- `discount_amount < 0` makes the function *increase* the subtotal (`subtotal - (-x)`), leading to overcharging.
- `minimum_charge < 0` can produce negative subtotals/totals.

### Issue Context
`calculate_total_with_discount()` already treats negative discounts as an error, so the new helper should match that contract to avoid surprising callers.

### Fix Focus Areas
- demo_app.py[57-66]
- demo_app.py[23-31]

### Suggested change
Add guards similar to:
- `if discount_amount < 0: raise ValueError(...)`
- `if minimum_charge < 0: raise ValueError(...)`
Optionally consider validating `subtotal >= 0` if this module assumes non-negative subtotals elsewhere.

ⓘ Copy this prompt and use it to remediate the issue with your preferred AI generation tools

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