1 files changed, 77 insertions, 0 deletions
diff --git a/rag/retriever/rerank.py b/rag/retriever/rerank.py
new file mode 100644
index 0000000..08a9a27
--- /dev/null
+++ b/rag/retriever/rerank.py
@@ -0,0 +1,77 @@
+import os
+from abc import abstractmethod
+from typing import Type
+
+import cohere
+from loguru import logger as log
+from sentence_transformers import CrossEncoder
+
+from rag.generator.prompt import Prompt
+
+
+class AbstractReranker(type):
+    _instances = {}
+
+    def __call__(cls, *args, **kwargs):
+        if cls not in cls._instances:
+            instance = super().__call__(*args, **kwargs)
+            cls._instances[cls] = instance
+        return cls._instances[cls]
+
+    @abstractmethod
+    def rank(self, prompt: Prompt) -> Prompt:
+        return prompt
+
+
+class Reranker(metaclass=AbstractReranker):
+    def __init__(self) -> None:
+        self.model = CrossEncoder(os.environ["RERANK_MODEL"])
+        self.top_k = int(os.environ["RERANK_TOP_K"])
+
+    def rank(self, prompt: Prompt) -> Prompt:
+        if prompt.documents:
+            results = self.model.rank(
+                query=prompt.query,
+                documents=[d.text for d in prompt.documents],
+                return_documents=False,
+                top_k=self.top_k,
+            )
+            ranking = list(filter(lambda x: x.get("score", 0.0) > 0.5, results))
+            log.debug(
+                f"Reranking gave {len(ranking)} relevant documents of {len(prompt.documents)}"
+            )
+            prompt.documents = [
+                prompt.documents[r.get("corpus_id", 0)] for r in ranking
+            ]
+        return prompt
+
+
+class CohereReranker(metaclass=AbstractReranker):
+    def __init__(self) -> None:
+        self.client = cohere.Client(os.environ["COHERE_API_KEY"])
+        self.top_k = int(os.environ["RERANK_TOP_K"])
+
+    def rank(self, prompt: Prompt) -> Prompt:
+        if prompt.documents:
+            response = self.client.rerank(
+                model="rerank-english-v3.0",
+                query=prompt.query,
+                documents=[d.text for d in prompt.documents],
+                top_n=self.top_k,
+            )
+            ranking = list(filter(lambda x: x.relevance_score > 0.5, response.results))
+            log.debug(
+                f"Reranking gave {len(ranking)} relevant documents of {len(prompt.documents)}"
+            )
+            prompt.documents = [prompt.documents[r.index] for r in ranking]
+        return prompt
+
+
+def get_reranker(model: str) -> Type[AbstractReranker]:
+    match model:
+        case "local":
+            return Reranker()
+        case "cohere":
+            return CohereReranker()
+        case _:
+            exit(1)