feat: add minimum charge helper for final demo

[Galzi1]

Adds a small pricing helper so we can validate the full github-pr-kb flow on the final extractor behavior with new review comments and new comment IDs.

[qodo-code-review]

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Review Summary by Qodo

Add minimum charge pricing helper function

✨ Enhancement

Walkthroughs

Description

• Adds minimum charge helper function for pricing validation
• Ensures subtotal never falls below specified floor amount
• Supports discount application with minimum charge constraint

Diagram

flowchart LR
  A["Subtotal + Discount"] --> B["Apply Discount"]
  B --> C["Enforce Minimum Charge Floor"]
  C --> D["Calculate Total with Tax"]

Loading

File Changes

1. demo_app.py ✨ Enhancement +12/-0

Add minimum charge pricing helper function

• Adds new calculate_total_with_minimum_charge() function
• Applies discount to subtotal with minimum charge floor constraint
• Returns final total including sales tax on adjusted subtotal
• Complements existing discount calculation functions

demo_app.py

---

[qodo-code-review]

Code Review by Qodo

🐞 Bugs (2)   📘 Rule violations (0)   📎 Requirement gaps (0)   🎨 UX Issues (0)

🐞\ ≡ Correctness (2)

1. Missing input validation 🐞 ≡

Description

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.

Code

demo_app.py[R57-66]

+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."""
+
+    adjusted_subtotal = max(subtotal - discount_amount, minimum_charge)
+    return calculate_total(adjusted_subtotal, sales_tax_rate=sales_tax_rate)

Evidence

The existing absolute-discount helper explicitly guards against negative discounts, but the new
helper performs subtraction directly with no validation, so a negative discount increases the
subtotal and gets taxed. Similarly, a negative minimum_charge can let adjusted_subtotal go negative
and then calculate_total will return a negative taxed total.

demo_app.py[23-31]
demo_app.py[57-66]
demo_app.py[8-21]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

### 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.

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---

2. Minimum charge may surcharge 🐞 ≡

Description

If minimum_charge is greater than subtotal, adjusted_subtotal becomes minimum_charge even when
discount_amount is 0, which increases the charge despite the helper describing a discount flow. This
ambiguity can cause accidental overcharging unless the behavior is clarified or constrained.

Code

demo_app.py[R63-65]

+    """Apply a discount before tax, but never reduce the subtotal below a floor."""
+
+    adjusted_subtotal = max(subtotal - discount_amount, minimum_charge)

Evidence

The implementation uses max(subtotal - discount_amount, minimum_charge), which mathematically can
exceed the original subtotal when minimum_charge > subtotal. The docstring frames the helper as
applying a discount with a floor, which commonly implies it should not raise the pre-discount
subtotal.

demo_app.py[57-66]

Agent prompt

The issue below was found during a code review. Follow the provided context and guidance below and implement a solution

### Issue description
`minimum_charge` currently acts as a hard floor on the post-discount subtotal, which can *increase* the subtotal if `minimum_charge > subtotal`.

### Issue Context
The function docstring describes applying a discount with a floor, but doesn’t explicitly state whether it is allowed to raise the charge above the original subtotal (i.e., a true “minimum order charge”).

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

### Options to fix
Pick one and make it explicit:
1) If surcharging is NOT intended: clamp/validate so it cannot exceed the original subtotal (e.g., raise if `minimum_charge > subtotal`, or compute `max(subtotal - discount_amount, min(minimum_charge, subtotal))`).
2) If surcharging IS intended: update the docstring/name to clearly state it enforces a minimum final pre-tax charge and may increase small subtotals.

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---

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[Galzi1]

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.

[Galzi1]

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.

[Galzi1]

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.

[qodo-code-review]

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