Create reranker.py

reranker.py

@@ -0,0 +1,11 @@
+from sentence_transformers import CrossEncoder
+
+class CrossEncoderRanker:
+    def __init__(self, model_name="BAAI/bge-reranker-large"):
+        self.model = CrossEncoder(model_name)
+
+    def rank(self, question: str, chunks: list, top_k: int = 5):
+        pairs = [(question, chunk) for chunk in chunks]
+        scores = self.model.predict(pairs)
+        ranked = sorted(zip(chunks, scores), key=lambda x: x[1], reverse=True)
+        return ranked[:top_k]  # [(chunk, score), ...]