Import/calculations improvements

inventory-server/db/functions.sql

@@ -76,7 +76,9 @@ $function$;
 
 -- =============================================================================
 -- get_weighted_avg_cost: Weighted average cost from receivings up to a given date.
--- Uses all non-canceled receivings (no row limit) weighted by quantity.
+-- Prefers receivings from the 365 days before p_date so decade-old costs don't
+-- weigh equally with recent ones; falls back to the lifetime average when the
+-- product had no receivings in that window.
 -- =============================================================================
 CREATE OR REPLACE FUNCTION public.get_weighted_avg_cost(
     p_pid bigint,
@@ -97,8 +99,21 @@ BEGIN
     FROM receivings
     WHERE pid = p_pid
         AND received_date <= p_date
+        AND received_date > p_date - INTERVAL '365 days'
         AND status != 'canceled';
 
+    IF weighted_cost IS NULL THEN
+        SELECT
+            CASE
+                WHEN SUM(qty_each) > 0 THEN SUM(cost_each * qty_each) / SUM(qty_each)
+                ELSE NULL
+            END INTO weighted_cost
+        FROM receivings
+        WHERE pid = p_pid
+            AND received_date <= p_date
+            AND status != 'canceled';
+    END IF;
+
     RETURN weighted_cost;
 END;
 $function$;