fixed price drops/moved logging outside of init_monitor

src/monitor_utils/database.py

@@ -94,10 +94,12 @@ async def add_products_to_database(
 ):
     """Upsert products, tracking deduplicated price history and emitting alerts.
 
-    Rewrites current fields on each upsert. Prices are recorded in a
-    pastPrices array of price/date entries; a price already present in the
-    array is never recorded again, so each distinct price keeps only its
-    first-seen timestamp. New products and never-before-recorded prices
+    Rewrites current fields on each upsert. priceBeforeDrop is derived here,
+    not by monitors: it is set to the previous stored currentPrice when the new
+    price is lower (a drop) and cleared otherwise, so any price_before_drop on
+    the incoming product is ignored. Prices are recorded in a pastPrices array
+    of price/date entries; a price already present in the array is never
+    recorded again, so each distinct price keeps only its first-seen timestamp. New products and never-before-recorded prices
     upsert an alert referencing the product; a price returning to a value
     already in pastPrices emits nothing, so per-source price oscillation
     (member vs non-member quotes for the same SKU) alerts once per distinct
@@ -133,6 +135,11 @@ async def add_products_to_database(
         document["_id"] = doc_id
         existing_doc = existing.get(doc_id)
         new_price = document.get("currentPrice")
+        previous_price = existing_doc.get("currentPrice") if existing_doc else None
+        document["priceBeforeDrop"] = resolve_price_before_drop(
+            previous_price, new_price
+        )
+
         recorded_prices = extract_recorded_prices(existing_doc)
         never_seen_price = new_price is not None and new_price not in recorded_prices
         set_on_insert = {"discoveredDate": now}
@@ -193,6 +200,29 @@ async def write_alert_ops(
             raise
 
 
+def resolve_price_before_drop(
+    previous_price: float | None, new_price: float | None
+) -> float | None:
+    """Return the pre-drop price when new_price is a drop from previous_price.
+
+    Owns price-drop detection so monitors do not: a drop is a new price strictly
+    below the previously stored one, and its priceBeforeDrop is that prior price.
+    Any other case (no prior price, unchanged, or a rise) is not a drop.
+
+    Args:
+        previous_price: The product's last stored currentPrice, or None when new.
+        new_price: The incoming currentPrice.
+
+    Returns:
+        previous_price on a drop, otherwise None.
+    """
+
+    if previous_price is not None and new_price is not None and new_price < previous_price:
+        return previous_price
+
+    return None
+
+
 def extract_recorded_prices(existing_doc: dict | None) -> set[float]:
     """Return the set of prices already recorded in a document's pastPrices.