calculate_priority: resolve non-finite prices to 0 instead of crashing the monitor

tpv-academysports died on 2026-10-08 06:27 UTC and stayed down: six
identical crashes in 8 minutes (each ~2 min after start), then docker's
on-failure:5 gave up. Every one was

    database.py, in calculate_priority
        percentage = int(((original_price - current_price) / original_price) * 100)
    OverflowError: cannot convert float infinity to integer

A monitor builds prices with float() on the retailer's raw field, and
float() accepts "Infinity" / "1e999", so a non-finite price reaches here.
The `not original_price` guard catches None and 0, not inf or nan, and the
exception escapes add_products_to_database -> run_monitor_cycle and kills
the whole process -- one bad product takes the monitor down, and it
crashes again on every restart while that product is listed. Every
monitor that uses this lib has the same exposure.

calculate_priority now returns 0 (the existing "broken prices" bucket)
for a non-finite current/original price, and for a finite pair whose
ratio still overflows (a subnormal original price). Tests cover both;
they fail on the old code (OverflowError, plus ValueError for nan) and
pass now (tests/test_alert_priority.py: 10 passed).

Not changed: the monitor-side float() parsing, which could reject these
prices before they are stored -- worth a look by the monitor owners.

Co-Authored-By: Claude Code Opus 5.5 (ansible-ops, auto-repair) <noreply@anthropic.com>
Signed-off-by: disqualifier <dev@disqualifier.me>

src/monitor_utils/database.py

@@ -7,6 +7,7 @@ alert references for new products and price changes.
 """
 
 import logging
+import math
 from dataclasses import asdict
 from datetime import datetime, timezone
 from functools import cache
@@ -318,10 +319,13 @@ def calculate_priority(document: dict) -> int:
 
     Always recalculated from current and original price so the priority
     reflects the prices at alert time rather than any stale stored
-    percentage. Missing prices, zero original prices, and price increases
-    resolve to priority 0. A product with no MSRP has no percentage to rank
-    on and takes NO_MSRP_PRIORITY instead, since a real 0 would leave it
-    permanently behind every other alert in the claim query's sort. A new
+    percentage. Missing prices, zero original prices, non-finite prices, a
+    discount too large to represent, and price increases resolve to priority
+    0, so one product's bad pricing can never raise out of the whole cycle (a
+    retailer field like "Infinity" survives float() and used to crash the
+    monitor with an OverflowError). A product with no MSRP has no percentage
+    to rank on and takes NO_MSRP_PRIORITY instead, since a real 0 would leave
+    it permanently behind every other alert in the claim query's sort. A new
     listing is floored at NEW_LISTING_PRIORITY for the same reason: it may
     carry any discount at all, and its percentage rank still wins when higher.
 
@@ -337,10 +341,17 @@ def calculate_priority(document: dict) -> int:
     if current_price is None or not original_price:
         return 0
 
+    if not (math.isfinite(current_price) and math.isfinite(original_price)):
+        return 0
+
     if not document.get("hasMsrp", True):
         return NO_MSRP_PRIORITY
 
-    percentage = int(((original_price - current_price) / original_price) * 100)
+    discount = ((original_price - current_price) / original_price) * 100
+    if not math.isfinite(discount):
+        return 0
+
+    percentage = int(discount)
     priority = min(max(percentage // 10, 0), 10)
     if document.get("newListing"):
         return max(priority, NEW_LISTING_PRIORITY)

tests/test_alert_priority.py

@@ -50,6 +50,23 @@ def test_broken_prices_still_outrank_nothing():
     assert calculate_priority(document(None, 100.0, hasMsrp=False)) == 0
 
 
+def test_non_finite_prices_resolve_to_zero_instead_of_raising():
+    """float("Infinity") from a retailer field once crashed the whole monitor."""
+    inf, nan = float("inf"), float("nan")
+    assert calculate_priority(document(50.0, inf)) == 0
+    assert calculate_priority(document(inf, 100.0)) == 0
+    assert calculate_priority(document(-inf, 100.0)) == 0
+    assert calculate_priority(document(nan, 100.0)) == 0
+    assert calculate_priority(document(50.0, nan)) == 0
+    assert calculate_priority(document(50.0, inf, newListing=True)) == 0
+
+
+def test_a_discount_too_large_to_represent_resolves_to_zero():
+    """Finite prices can still overflow the ratio (a subnormal original)."""
+    assert calculate_priority(document(-1e308, 5e-324)) == 0
+    assert calculate_priority(document(1e308, 5e-324)) == 0
+
+
 def test_new_listing_is_floored_not_buried():
     """A low-discount new listing sends regardless, so it must not sort last."""
     assert (