"""Hybrid retriever — metadata filter + FTS + vector retrieval + score fusion."""

from sqlalchemy.ext.asyncio import AsyncSession

from app.features.memory.evidence import retrieve_evidence_bundle_async
from app.features.memory.repo import search_chunks_fts, search_chunks_vector
from app.ports.embedding import EmbeddingProvider


def _rrf_merge(
    fts_items: list[dict], vector_items: list[dict], k: int = 60
) -> list[dict]:
    """Reciprocal Rank Fusion. Merge FTS and vector results by id."""
    scores: dict[str, float] = {}
    for rank, item in enumerate(fts_items):
        cid = item["id"]
        scores[cid] = scores.get(cid, 0) + 1 / (k + rank + 1)
    for rank, item in enumerate(vector_items):
        cid = item["id"]
        scores[cid] = scores.get(cid, 0) + 1 / (k + rank + 1)

    all_items = {x["id"]: x for x in fts_items + vector_items}
    sorted_ids = sorted(scores.keys(), key=lambda i: scores[i], reverse=True)
    return [all_items[i] for i in sorted_ids]


class HybridRetriever:
    """Combine FTS, vector, and metadata filter into evidence bundle."""

    def __init__(
        self,
        db: AsyncSession,
        *,
        embedding_provider: EmbeddingProvider | None = None,
    ):
        self._db = db
        self._embedding = embedding_provider

    async def retrieve(self, user_id: str, query: str, *, top_k: int = 10) -> dict:
        """
        Return evidence bundle:
        {relevant_chunks, relevant_summaries, relevant_facts, timeline_hints, relevant_stories}
        """
        if not query.strip():
            return await retrieve_evidence_bundle_async(
                self._db,
                user_id,
                query,
                top_k=top_k,
                merged_chunk_dicts=[],
            )

        q = query.strip()
        fts_chunks = await search_chunks_fts(
            self._db, user_id=user_id, query=query, limit=top_k * 2
        )

        vector_chunks: list[dict] = []
        if self._embedding and q:
            q_emb = await self._embedding.embed_text(q)
            if q_emb:
                vector_chunks = await search_chunks_vector(
                    self._db, user_id=user_id, query_embedding=q_emb, limit=top_k * 2
                )

        merged = _rrf_merge(fts_chunks, vector_chunks)[:top_k]
        merged_chunk_dicts = [
            {
                "id": c["id"],
                "content": c["content"],
                "chunk_index": c.get("chunk_index", 0),
            }
            for c in merged
        ]

        return await retrieve_evidence_bundle_async(
            self._db,
            user_id,
            query,
            top_k=top_k,
            merged_chunk_dicts=merged_chunk_dicts,
        )