Unify — Omnichannel AI Sales & Support Assistant

class RAGService:
    """Hybrid retrieval over products: BM25 + semantic + RRF + diversity filter."""

    def retrieve(
        self,
        query: str,
        query_type: str = "descriptive",
        entities: Optional[dict] = None,
        top_k: Optional[int] = None,
    ) -> str:
        self._build_index()
        k = top_k or self.top_k

        # Expand query with NLU entities (color, fabric, sku) and synonyms
        search_query = _expand_query_with_entities(query, entities)
        search_query = _expand_query_synonyms(search_query) or search_query

        # Boost lexical for exact SKU; boost semantic for descriptive queries
        lexical_k = k * 2 if query_type == "exact" else k
        semantic_k = k * 2 if query_type == "descriptive" else k

        lex_idx = self._lexical_search(search_query, lexical_k)
        sem_idx = self._semantic_search(search_query, semantic_k)

        # Reciprocal Rank Fusion: score(d) = Σ 1/(rrf_k + rank_d)
        merged = self._merge_and_dedup(lex_idx, sem_idx, k)

        # Greedy diversity: prefer products with unseen color/fabric combination
        if self.diversity_enabled:
            merged = self._apply_diversity(merged, k)

        lines = [
            _format_product_for_context(self._products[i], self._site_base)
            for i in merged if i < len(self._products)
        ]
        return "CONTEXT FROM PRODUCT CATALOG:\n" + "\n".join(lines)