"""搜索服务 — FTS5 关键词搜索 + ChromaDB 语义搜索，命中片段高亮，分页。"""

from __future__ import annotations

import logging
import math
import re

from sqlalchemy import text
from sqlalchemy.orm import Session, joinedload

from app.config import settings
from app.models import Paper

logger = logging.getLogger(__name__)

# ── 输入清洗 ──────────────────────────────────────────────────────────

# FTS5 查询语法中的特殊字符，用户输入时需要移除
_FTS5_SPECIAL = re.compile(r'["{}()^+:]')


def _sanitize_query(raw: str) -> str:
    """清洗用户输入，生成安全的 FTS5 MATCH 表达式。

    - 移除 FTS5 特殊字符
    - 按空白拆分为 token，用 AND 连接
    - 空字符串返回 None
    """
    cleaned = _FTS5_SPECIAL.sub("", raw.strip())
    tokens = cleaned.split()
    if not tokens:
        return None
    return " AND ".join(tokens)


# ── 核心搜索 ──────────────────────────────────────────────────────────


def search_papers(
    db: Session,
    *,
    query: str | None = None,
    tag: str | None = None,
    sort: str = "relevance",
    page: int = 1,
    page_size: int = 20,
    mode: str = "keyword",
) -> dict:
    """搜索论文，支持 keyword (FTS5) 和 semantic (ChromaDB) 两种模式。

    返回::
        {
            "results": list[Paper],
            "snippets": dict[int, dict],   # paper_id → {title_zh, abstract}
            "total": int,
            "page": int,
            "total_pages": int,
            "distances": dict[str, float],  # arxiv_id → distance (仅 semantic)
        }
    """
    # ── semantic 模式 ──
    if mode == "semantic" and settings.CHROMA_ENABLED and query:
        return _search_semantic(db, query, tag, sort, page, page_size)

    # ── keyword 模式（默认）──
    match_expr = _sanitize_query(query) if query else None

    # ── 无关键词 + 无标签 → 空结果 ──
    if not match_expr and not tag:
        return {
            "results": [],
            "snippets": {},
            "total": 0,
            "page": page,
            "total_pages": 0,
            "distances": {},
        }

    # ── 构建条件性 JOIN 和 WHERE 片段 ──
    tag_join = ""
    tag_where = ""
    tag_params: dict = {}
    if tag:
        tag_join = "JOIN paper_tags pt ON pt.paper_id = p.id"
        tag_where = "AND pt.tag = :tag"
        tag_params["tag"] = tag

    offset = (page - 1) * page_size

    if match_expr:
        return _search_with_fts(
            db, match_expr, tag_join, tag_where, tag_params,
            sort, page, page_size, offset,
        )
    else:
        return _search_tag_only(
            db, tag, sort, page, page_size, offset,
        )


def _search_with_fts(
    db: Session,
    match_expr: str,
    tag_join: str,
    tag_where: str,
    tag_params: dict,
    sort: str,
    page: int,
    page_size: int,
    offset: int,
) -> dict:
    """有关键词时的 FTS5 MATCH 搜索。"""
    params = {"query": match_expr, "limit": page_size, "offset": offset}
    params.update(tag_params)

    order = "bm25(papers_fts)" if sort == "relevance" else "p.paper_date DESC, p.upvotes DESC"

    # ── 主查询：取 ID + rank + snippet ──
    rows_sql = text(f"""
        SELECT
            p.id,
            papers_fts.rank,
            snippet(papers_fts, 1, '<mark>', '</mark>', '...', 32) AS snippet_title_zh,
            snippet(papers_fts, 2, '<mark>', '</mark>', '...', 32) AS snippet_abstract
        FROM papers_fts
        JOIN papers p ON p.id = papers_fts.rowid
        {tag_join}
        WHERE papers_fts MATCH :query
        {tag_where}
        ORDER BY {order}
        LIMIT :limit OFFSET :offset
    """)
    fts_rows = db.execute(rows_sql, params).fetchall()

    # ── 计数查询 ──
    count_sql = text(f"""
        SELECT COUNT(DISTINCT papers_fts.rowid)
        FROM papers_fts
        JOIN papers p ON p.id = papers_fts.rowid
        {tag_join}
        WHERE papers_fts MATCH :query
        {tag_where}
    """)
    total = db.execute(count_sql, params).scalar() or 0

    paper_ids = [row[0] for row in fts_rows]
    snippets = {
        row[0]: {"title_zh": row[2], "abstract": row[3]}
        for row in fts_rows
    }

    papers = _load_papers_by_ids(db, paper_ids, sort, {row[0]: row[1] for row in fts_rows})

    return {
        "results": papers,
        "snippets": snippets,
        "total": total,
        "page": page,
        "total_pages": math.ceil(total / page_size) if total else 0,
        "distances": {},
    }


def _search_semantic(
    db: Session,
    query: str,
    tag: str | None,
    sort: str,
    page: int,
    page_size: int,
) -> dict:
    """ChromaDB 语义搜索，失败时回退到 FTS5。"""
    try:
        from app.services.embedder import search_similar

        top_k = page_size * 3  # 多取一些用于 tag 过滤
        candidates = search_similar(query, top_k=top_k)
    except Exception:
        logger.exception("Semantic search failed, falling back to keyword")
        candidates = []

    if not candidates:
        # 回退到 FTS5
        return _search_with_fts(
            db,
            _sanitize_query(query) or query,
            "JOIN paper_tags pt ON pt.paper_id = p.id" if tag else "",
            "AND pt.tag = :tag" if tag else "",
            {"tag": tag} if tag else {},
            sort, page, page_size, (page - 1) * page_size,
        )

    # 按 arxiv_id 从 DB 加载完整数据
    arxiv_ids = [c["arxiv_id"] for c in candidates]
    distance_map = {c["arxiv_id"]: c["distance"] for c in candidates}

    papers_query = (
        db.query(Paper)
        .filter(Paper.arxiv_id.in_(arxiv_ids))
        .options(
            joinedload(Paper.authors),
            joinedload(Paper.tags),
            joinedload(Paper.summary_status),
            joinedload(Paper.bookmark),
            joinedload(Paper.reading_status),
        )
    )
    if tag:
        papers_query = papers_query.filter(Paper.tags.any(tag=tag))

    papers = papers_query.all()

    # 按语义距离排序
    id_order = {aid: idx for idx, aid in enumerate(arxiv_ids)}
    papers.sort(key=lambda p: id_order.get(p.arxiv_id, 999))

    # 分页
    total = len(papers)
    start = (page - 1) * page_size
    page_papers = papers[start:start + page_size]

    return {
        "results": page_papers,
        "snippets": {},
        "total": total,
        "page": page,
        "total_pages": math.ceil(total / page_size) if total else 0,
        "distances": distance_map,
    }


def _search_tag_only(
    db: Session,
    tag: str,
    sort: str,
    page: int,
    page_size: int,
    offset: int,
) -> dict:
    """只有标签筛选，无关键词。"""
    order = "p.paper_date DESC, p.upvotes DESC" if sort == "date" else "p.paper_date DESC, p.upvotes DESC"

    rows_sql = text(f"""
        SELECT p.id
        FROM papers p
        JOIN paper_tags pt ON pt.paper_id = p.id
        WHERE pt.tag = :tag
        ORDER BY {order}
        LIMIT :limit OFFSET :offset
    """)
    rows = db.execute(rows_sql, {"tag": tag, "limit": page_size, "offset": offset}).fetchall()

    count_sql = text("""
        SELECT COUNT(DISTINCT p.id)
        FROM papers p
        JOIN paper_tags pt ON pt.paper_id = p.id
        WHERE pt.tag = :tag
    """)
    total = db.execute(count_sql, {"tag": tag}).scalar() or 0

    paper_ids = [row[0] for row in rows]
    papers = _load_papers_by_ids(db, paper_ids)

    return {
        "results": papers,
        "snippets": {},
        "total": total,
        "page": page,
        "total_pages": math.ceil(total / page_size) if total else 0,
        "distances": {},
    }


def _load_papers_by_ids(
    db: Session,
    paper_ids: list[int],
    sort: str | None = None,
    rank_map: dict[int, float] | None = None,
) -> list[Paper]:
    """根据 ID 列表加载完整 ORM 对象，保持原始排序。"""
    if not paper_ids:
        return []

    papers = (
        db.query(Paper)
        .filter(Paper.id.in_(paper_ids))
        .options(
            joinedload(Paper.authors),
            joinedload(Paper.tags),
            joinedload(Paper.summary_status),
            joinedload(Paper.bookmark),
            joinedload(Paper.reading_status),
        )
        .all()
    )

    # 按 FTS rank / tag-only 原始顺序排列
    id_order = {pid: idx for idx, pid in enumerate(paper_ids)}
    papers.sort(key=lambda p: id_order.get(p.id, 0))
    return papers


# ── 辅助查询 ──────────────────────────────────────────────────────────


def get_all_tags(db: Session) -> list[str]:
    """返回所有不重复的标签，按字母排序。"""
    rows = db.execute(
        text("SELECT DISTINCT tag FROM paper_tags ORDER BY tag")
    ).fetchall()
    return [row[0] for row in rows]