import numpy as np

try:
    import faiss
    from sentence_transformers import SentenceTransformer
except ImportError:
    faiss = None
    SentenceTransformer = None

_model = None

def semantic_available():
    return faiss is not None and SentenceTransformer is not None

def _get_model():
    global _model
    if _model is None:
        _model = SentenceTransformer("all-MiniLM-L6-v2")
    return _model

def semantic_refine(query, results, k=5):
    """
    In-memory, ephemeral semantic refinement.
    No persistence, no external calls.
    """
    if not semantic_available() or not results:
        return results

    texts = [r.get("snippet", "") for r in results]
    model = _get_model()

    embeddings = model.encode(texts, normalize_embeddings=True)
    index = faiss.IndexFlatIP(embeddings.shape[1])
    index.add(np.array(embeddings))

    q_emb = model.encode([query], normalize_embeddings=True)
    _, idx = index.search(np.array(q_emb), min(k, len(results)))

    return [results[i] for i in idx[0]]