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backend/app/rules/dedup_rules.py

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+"""Transaction deduplication rules.
+
+Determines whether two transaction records likely represent the same
+underlying financial event captured from different screenshots / pages.
+"""
+from datetime import timedelta
+
+from app.models.transaction import TransactionRecord
+
+TIME_WINDOW = timedelta(minutes=5)
+
+
+def is_duplicate_pair(a: TransactionRecord, b: TransactionRecord) -> bool:
+    # Rule 1: exact order_no match
+    if a.order_no and b.order_no and a.order_no == b.order_no:
+        return True
+
+    # Rule 2: same amount + close time + same account tail
+    if (
+        float(a.amount) == float(b.amount)
+        and a.trade_time
+        and b.trade_time
+        and abs(a.trade_time - b.trade_time) <= TIME_WINDOW
+    ):
+        if a.self_account_tail_no and b.self_account_tail_no:
+            if a.self_account_tail_no == b.self_account_tail_no:
+                return True
+        # same counterparty and close time is also strong signal
+        if a.counterparty_name and a.counterparty_name == b.counterparty_name:
+            return True
+
+    return False