feat: manually mirror opencoze's code from bytedance

Change-Id: I09a73aadda978ad9511264a756b2ce51f5761adf

backend/infra/impl/document/rerank/rrf/rrf.go

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2025 coze-dev Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package rrf
+
+import (
+	"context"
+	"fmt"
+	"sort"
+
+	"github.com/coze-dev/coze-studio/backend/infra/contract/document/rerank"
+	"github.com/coze-dev/coze-studio/backend/pkg/lang/ptr"
+)
+
+func NewRRFReranker(k int64) rerank.Reranker {
+	if k == 0 {
+		k = 60
+	}
+	return &rrfReranker{k}
+}
+
+type rrfReranker struct {
+	k int64
+}
+
+func (r *rrfReranker) Rerank(ctx context.Context, req *rerank.Request) (*rerank.Response, error) {
+	if req == nil || req.Data == nil || len(req.Data) == 0 {
+		return nil, fmt.Errorf("invalid request: no data provided")
+	}
+	id2Score := make(map[string]float64)
+	id2Data := make(map[string]*rerank.Data)
+	for _, resultList := range req.Data {
+		for rank := range resultList {
+			result := resultList[rank]
+			if result != nil && result.Document != nil {
+				score := 1.0 / (float64(rank) + float64(r.k))
+				if score > id2Score[result.Document.ID] {
+					id2Score[result.Document.ID] = score
+					id2Data[result.Document.ID] = result
+				}
+			}
+		}
+	}
+	var sorted []*rerank.Data
+	for _, data := range id2Data {
+		sorted = append(sorted, data)
+	}
+	sort.Slice(sorted, func(i, j int) bool {
+		return id2Score[sorted[i].Document.ID] > id2Score[sorted[j].Document.ID]
+	})
+	topN := int64(len(sorted))
+	if req.TopN != nil && ptr.From(req.TopN) != 0 && ptr.From(req.TopN) < topN {
+		topN = ptr.From(req.TopN)
+	}
+
+	return &rerank.Response{SortedData: sorted[:topN]}, nil
+}