"""搜索建议服务:纯 keyword 续接词(高频词)。

- search_keywords(prefix_keys @> ARRAY['美'], ORDER BY weight DESC)
- fallback: 表空时回退实时 ts_stat(冷启动 / worker 没刷新过)
"""
from __future__ import annotations

import logging

from sqlalchemy import desc, select
from sqlalchemy.ext.asyncio import AsyncSession

from app.models.search_keyword import SearchKeyword

logger = logging.getLogger("news.search")


class SearchService:
    """搜索建议 service — 仅返回 keyword 续接词。

    设计:输入 prefix,返回 { query, keywords[] }。
    - keywords 是 ts_stat 聚合后的高频词(从 articles.title_zh + body_zh_text + commentary 算)
    - 用 GIN 数组索引 prefix_keys @> ARRAY['前缀'],亚毫秒
    - 表空时回退到实时 ts_stat 聚合(慢但能用)
    """

    def __init__(self, session: AsyncSession):
        self.session = session

    async def suggestions(
        self,
        q: str,
        limit: int = 10,
    ) -> dict[str, list[dict]]:
        """返回搜索建议(仅 keywords)。

        Args:
            q: 前缀(1-20 字符)
            limit: 最多返回多少(默认 10,最大 20)

        Returns:
            {"query": q, "keywords": [{"word", "weight", "source"}, ...]}
        """
        q = q.strip()
        if not q:
            return {"query": q, "keywords": []}

        # 1) 查 search_keywords(GIN 数组包含,亚毫秒)
        kw_rows = await self.session.execute(
            select(SearchKeyword.keyword, SearchKeyword.weight, SearchKeyword.source)
            .where(SearchKeyword.prefix_keys.contains([q]))
            .order_by(desc(SearchKeyword.weight))
            .limit(limit)
        )
        keywords = [
            {"word": row.keyword, "weight": row.weight, "source": row.source}
            for row in kw_rows.all()
        ]

        # 2) 冷启动 fallback:表空时回退到实时 ts_stat 聚合
        if not keywords:
            keywords = await self._fallback_keywords(q, limit)

        return {"query": q, "keywords": keywords}

    async def _fallback_keywords(self, q: str, limit: int) -> list[dict]:
        """回退:ts_stat 实时聚合(慢但能用)。

        - 从 articles.title_zh + body_zh_text 实时 to_tsvector(chinese_zh)
        - 适用:search_keywords 表空 + worker 没刷新过
        - ts_stat(text) 单参 — 第二参 weights mask 不能传 'a'(zhparser 不标 A 权重会 0 行)
        """
        from sqlalchemy import text

        sql = text(
            """
            SELECT word, nentry::int AS weight
            FROM ts_stat(
                $$SELECT to_tsvector('chinese_zh',
                    coalesce(title_zh, '') || ' ' || coalesce(body_zh_text, '')
                )
                FROM articles
                WHERE title_zh IS NOT NULL OR body_zh_text IS NOT NULL
                LIMIT 500$$
            ) AS s
            WHERE word LIKE :prefix
            ORDER BY nentry DESC
            LIMIT :lim
            """
        )
        rows = (
            await self.session.execute(sql, {"prefix": f"{q}%", "lim": limit})
        ).all()
        return [{"word": r.word, "weight": r.weight, "source": "ts_stat_live"} for r in rows]