from dataclasses import dataclass

from app.core.config import settings
from app.core.exceptions import AppError


@dataclass(frozen=True)
class VectorSearchHit:
    """向量检索命中：只保存 chunk_uid 和相似度，来源详情从 MySQL 读取。"""

    chunk_uid: str
    score: float


class MilvusVectorStore:
    """Milvus 向量库适配器：按机构 collection 写入和检索知识分片向量。"""

    _mock_store: dict[str, dict[str, list[float]]] = {}

    def __init__(self) -> None:
        self.mock_enabled = settings.milvus_uri.startswith("mock://")
        self._client = None

    def ensure_collection(self, collection_name: str) -> None:
        """集合初始化：不存在时创建 VARCHAR 主键 + FLOAT_VECTOR 的 Milvus collection。"""
        if self.mock_enabled:
            self._mock_store.setdefault(collection_name, {})
            return
        client = self._client_or_raise()
        try:
            if client.has_collection(collection_name=collection_name):
                return
            schema = client.create_schema(auto_id=False, enable_dynamic_field=False)
            from pymilvus import DataType

            schema.add_field(field_name="id", datatype=DataType.VARCHAR, is_primary=True, max_length=128)
            schema.add_field(field_name="vector", datatype=DataType.FLOAT_VECTOR, dim=settings.embedding_dim)
            index_params = client.prepare_index_params()
            index_params.add_index(field_name="vector", index_type="AUTOINDEX", metric_type="COSINE")
            client.create_collection(
                collection_name=collection_name,
                schema=schema,
                index_params=index_params,
                consistency_level="Strong",
            )
        except Exception as exc:  # pragma: no cover - 真实 Milvus 由联调环境验证
            raise AppError("MILVUS_COLLECTION_INIT_FAILED", "milvus collection init failed", 502) from exc

    def upsert_vectors(self, collection_name: str, vectors: list[tuple[str, list[float]]]) -> None:
        """向量写入：使用 chunk_uid 作为 Milvus 主键，保证重复构建可覆盖。"""
        if not vectors:
            return
        self.ensure_collection(collection_name)
        if self.mock_enabled:
            collection = self._mock_store.setdefault(collection_name, {})
            for chunk_uid, vector in vectors:
                collection[chunk_uid] = vector
            return
        client = self._client_or_raise()
        try:
            client.upsert(
                collection_name=collection_name,
                data=[{"id": chunk_uid, "vector": vector} for chunk_uid, vector in vectors],
            )
        except Exception as exc:  # pragma: no cover
            raise AppError("MILVUS_UPSERT_FAILED", "milvus vector upsert failed", 502) from exc

    def search(self, collection_name: str, query_vector: list[float], limit: int) -> list[VectorSearchHit]:
        """向量检索：按余弦相似度返回候选 chunk_uid，后续由业务层过滤阈值。"""
        self.ensure_collection(collection_name)
        if self.mock_enabled:
            return self._mock_search(collection_name, query_vector, limit)
        client = self._client_or_raise()
        try:
            results = client.search(
                collection_name=collection_name,
                data=[query_vector],
                anns_field="vector",
                limit=limit,
                search_params={"metric_type": "COSINE"},
                output_fields=["id"],
            )
        except Exception as exc:  # pragma: no cover
            raise AppError("MILVUS_SEARCH_FAILED", "milvus vector search failed", 502) from exc

        hits: list[VectorSearchHit] = []
        for item in results[0] if results else []:
            entity = item.get("entity") or {}
            chunk_uid = str(entity.get("id") or item.get("id") or "")
            if chunk_uid:
                hits.append(VectorSearchHit(chunk_uid=chunk_uid, score=float(item.get("distance") or item.get("score") or 0)))
        return hits

    def _client_or_raise(self):
        """客户端获取：懒加载 pymilvus，避免未使用知识库时影响现有训练接口。"""
        if self._client is not None:
            return self._client
        try:
            from pymilvus import MilvusClient
        except ImportError as exc:
            raise AppError("MILVUS_CLIENT_NOT_INSTALLED", "pymilvus is required for vector search", 500) from exc
        self._client = MilvusClient(uri=settings.milvus_uri, db_name=settings.milvus_default_db)
        return self._client

    def _mock_search(self, collection_name: str, query_vector: list[float], limit: int) -> list[VectorSearchHit]:
        """Mock检索：用向量点积模拟余弦排序，便于无 Milvus 环境测试。"""
        collection = self._mock_store.get(collection_name, {})
        scored = [
            VectorSearchHit(chunk_uid=chunk_uid, score=(sum(a * b for a, b in zip(query_vector, vector)) + 1.0) / 2.0)
            for chunk_uid, vector in collection.items()
        ]
        return sorted(scored, key=lambda item: item.score, reverse=True)[:limit]