import math

from bson import ObjectId
from fastapi import HTTPException
from motor.motor_asyncio import AsyncIOMotorDatabase

from app.models.todo import TodoResponse, SearchResponse


class SearchService:
    """MongoDB text index 기반 검색 로직"""

    def __init__(self, db: AsyncIOMotorDatabase):
        self.collection = db["todos"]
        self.categories = db["categories"]

    async def _populate_categories_bulk(self, todo_docs: list[dict]) -> list[TodoResponse]:
        """여러 Todo 문서의 카테고리 정보를 일괄 조회하여 TodoResponse 리스트를 반환한다."""
        # 카테고리 ID 수집
        cat_ids = set()
        for doc in todo_docs:
            cat_id = doc.get("category_id")
            if cat_id:
                try:
                    cat_ids.add(ObjectId(cat_id))
                except Exception:
                    pass

        # 카테고리 일괄 조회
        cat_map: dict[str, dict] = {}
        if cat_ids:
            async for cat in self.categories.find({"_id": {"$in": list(cat_ids)}}):
                cat_map[str(cat["_id"])] = cat

        # TodoResponse 변환
        result = []
        for doc in todo_docs:
            cat_id = str(doc["category_id"]) if doc.get("category_id") else None
            cat = cat_map.get(cat_id) if cat_id else None

            result.append(TodoResponse(
                id=str(doc["_id"]),
                title=doc["title"],
                content=doc.get("content"),
                completed=doc["completed"],
                priority=doc["priority"],
                category_id=cat_id,
                category_name=cat["name"] if cat else None,
                category_color=cat["color"] if cat else None,
                tags=doc.get("tags", []),
                due_date=doc.get("due_date"),
                created_at=doc["created_at"],
                updated_at=doc["updated_at"],
            ))

        return result

    async def search(self, query: str, page: int = 1, limit: int = 20) -> SearchResponse:
        """F-017: 전문 검색
        MongoDB text index를 활용한 전문 검색, text score 기준 정렬, 페이지네이션
        """
        if not query or not query.strip():
            raise HTTPException(status_code=422, detail="검색어를 입력해주세요")

        query = query.strip()

        # MongoDB text search
        search_filter = {"$text": {"$search": query}}

        # 총 개수 조회
        total = await self.collection.count_documents(search_filter)

        # text score 기준 정렬 + 페이지네이션
        skip = (page - 1) * limit
        cursor = self.collection.find(
            search_filter,
            {"score": {"$meta": "textScore"}},
        ).sort(
            [("score", {"$meta": "textScore"})]
        ).skip(skip).limit(limit)

        docs = await cursor.to_list(limit)

        items = await self._populate_categories_bulk(docs)

        return SearchResponse(
            items=items,
            total=total,
            query=query,
            page=page,
            limit=limit,
        )