"""Hybrid-Retrieval: BM25 (FTS5) + Dense (bge-m3) -> RRF-Fusion,
milde Stand-Aktualitätsgewichtung und kontrollierte cross_ref-Erweiterung.
"""
from __future__ import annotations

import json
import sqlite3
from dataclasses import dataclass, field
from pathlib import Path

import numpy as np

from .config import Config
from .normalize import fts_query
from .ollama_client import OllamaClient


@dataclass
class ChunkResult:
    chunk_id: int
    entry_id: str
    section: str
    text: str
    title: str
    stand: str
    work: str
    chapter: str
    topic: str
    tags: list = field(default_factory=list)
    legal_bases: list = field(default_factory=list)
    cross_refs: list = field(default_factory=list)
    batch: int = 0
    score: float = 0.0
    source: str = "fused"  # bm25 | dense | fused | cross_ref


def _section_priority(section: str) -> int:
    """Kontext-Sektionen priorisieren: Inhalt vor Navigation.

    „Verweise“-Sektionen sind Navigationslisten (KB-IDs) — sie tragen
    Retrieval-Signal (Stichworte), sind aber als Kontextblock wertlos und
    provozieren Fehlverweigerungen. BM25-Längennormalisierung rangiert sie
    bevorzugt, daher wird pro Eintrag bewusst die beste Inhaltssektion
    gewählt (Fix 2026-09-14, q-008).
    """
    s = (section or "").casefold()
    if s.startswith("zusammenfassung"):
        return 0
    if s.startswith("kernwerte"):
        return 1
    if s.startswith("rechtsgrundlagen"):
        return 2
    if s.startswith("payroll"):
        return 3
    if s.startswith("verweise"):
        return 5
    return 4


class Retriever:
    def __init__(self, cfg: Config, db_path: str | None = None, client=None):
        self.cfg = cfg
        self.db_path = str(db_path or cfg.db_path)
        if not Path(self.db_path).is_file():
            raise RuntimeError(
                f"index fehlt ({self.db_path}) — zuerst 'python -m agent.cli ingest' ausführen"
            )
        self._con = sqlite3.connect(self.db_path)
        self._con.row_factory = sqlite3.Row
        self._client = client
        self._owns_client = client is None
        self._mat: np.ndarray | None = None
        self._mat_chunk_ids: list[int] | None = None
        row = self._con.execute("SELECT MIN(stand), MAX(stand) FROM chunks").fetchone()
        self._stand_min = int((row[0] or "2026-01").replace("-", ""))
        self._stand_max = int((row[1] or "2026-01").replace("-", ""))

    def close(self) -> None:
        self._con.close()
        if self._owns_client and self._client is not None:
            self._client.close()

    # -- Index-Kennzahlen ---------------------------------------------------

    def stats(self) -> dict:
        n_chunks = self._con.execute("SELECT COUNT(*) FROM chunks").fetchone()[0]
        n_entries = self._con.execute(
            "SELECT COUNT(DISTINCT entry_id) FROM chunks"
        ).fetchone()[0]
        n_vec = self._con.execute(
            "SELECT COUNT(*) FROM vectors WHERE model = ?",
            (self.cfg.embed_model,),
        ).fetchone()[0]
        meta = dict(self._con.execute("SELECT key, value FROM meta").fetchall())
        return {
            "n_entries": n_entries,
            "n_chunks": n_chunks,
            "n_vectors": n_vec,
            "dense_available": n_vec > 0 and not self.cfg.embed_off,
            "stand_min": str(self._stand_min),
            "stand_max": str(self._stand_max),
            "built_at": meta.get("built_at"),
        }

    # -- Einzelverfahren ----------------------------------------------------

    def _bm25(self, question: str, limit: int) -> dict[int, float]:
        q = fts_query(question)
        if not q:
            return {}
        rows = self._con.execute(
            "SELECT rowid, bm25(chunks_fts) AS rank FROM chunks_fts "
            "WHERE chunks_fts MATCH ? ORDER BY rank LIMIT ?",
            (q, limit),
        ).fetchall()
        # bm25(): kleinere Werte = besser -> negieren für "größer = besser"
        return {r["rowid"]: -float(r["rank"]) for r in rows}

    def _dense(self, question: str, limit: int) -> dict[int, float]:
        if self.cfg.embed_off:
            return {}
        self._ensure_matrix()
        if self._mat is None or len(self._mat) == 0:
            return {}
        if self._client is None:
            self._client = OllamaClient(
                self.cfg.ollama_url,
                embed_timeout_s=self.cfg.embed_timeout_s,
                chat_timeout_s=self.cfg.chat_timeout_s,
            )
        try:
            qvec = np.asarray(
                self._client.embed(self.cfg.embed_model, [question])[0],
                dtype=np.float32,
            )
        except Exception:
            return {}  # Ollama nicht erreichbar -> BM25-only weiter
        qn = np.linalg.norm(qvec)
        if qn == 0:
            return {}
        sims = self._mat_norm @ (qvec / qn)
        order = np.argsort(-sims)[:limit]
        return {self._mat_chunk_ids[i]: float(sims[i]) for i in order}

    def _ensure_matrix(self) -> None:
        if self._mat is not None:
            return
        rows = self._con.execute(
            "SELECT c.chunk_id, v.vec, v.dim FROM chunks c "
            "JOIN vectors v ON v.content_hash = c.content_hash AND v.model = ?",
            (self.cfg.embed_model,),
        ).fetchall()
        if not rows:
            self._mat = np.zeros((0, 1), dtype=np.float32)
            self._mat_chunk_ids = []
            return
        ids = [r[0] for r in rows]
        mat = np.vstack(
            [np.frombuffer(r[1], dtype=np.float32) for r in rows]
        )
        norms = np.linalg.norm(mat, axis=1, keepdims=True)
        self._mat = mat
        self._mat_norm = mat / np.where(norms == 0, 1.0, norms)
        self._mat_chunk_ids = ids

    # -- Metadaten & Fusion -------------------------------------------------

    def _stand_factor(self, stand: str) -> float:
        if self._stand_max <= self._stand_min:
            return 0.0
        try:
            s = int(stand.replace("-", ""))
        except (ValueError, AttributeError):
            return 0.0
        f = (s - self._stand_min) / (self._stand_max - self._stand_min)
        return min(1.0, max(0.0, f))

    def _fetch_chunks(self, chunk_ids: list[int]) -> dict[int, sqlite3.Row]:
        out: dict[int, sqlite3.Row] = {}
        for i in range(0, len(chunk_ids), 500):
            part = chunk_ids[i:i + 500]
            qm = ",".join("?" * len(part))
            for r in self._con.execute(
                f"SELECT * FROM chunks WHERE chunk_id IN ({qm})", part
            ).fetchall():
                out[r["chunk_id"]] = r
        return out

    def _row_to_result(self, row: sqlite3.Row, score: float, source: str) -> ChunkResult:
        return ChunkResult(
            chunk_id=row["chunk_id"],
            entry_id=row["entry_id"],
            section=row["section"],
            text=row["text"],
            title=row["title"],
            stand=row["stand"],
            work=row["work"],
            chapter=row["chapter"],
            topic=row["topic"],
            tags=json.loads(row["tags"]),
            legal_bases=json.loads(row["legal_bases"]),
            cross_refs=json.loads(row["cross_refs"]),
            batch=row["batch"],
            score=score,
            source=source,
        )

    def _representative_chunk(
        self, entry_id: str, ranked: list[ChunkResult]
    ) -> ChunkResult:
        """Beste Inhaltssektion des Eintrags als Kontextblock.

        Bevorzugt die rangierte (gefundene) Sektion mit bester Priorität;
        traf der Eintrag nur über „Verweise“, wird seine beste Inhalts-
        sektion aus dem Index nachgeladen (source="section-swap").
        """
        content = [c for c in ranked if _section_priority(c.section) < 5]
        if content:
            return min(content, key=lambda c: (_section_priority(c.section), -c.score))
        rows = self._con.execute(
            "SELECT * FROM chunks WHERE entry_id = ? AND section NOT LIKE 'Verweise%' "
            "ORDER BY CASE WHEN section LIKE 'Zusammenfassung%' THEN 0 "
            "WHEN section LIKE 'Kernwerte%' THEN 1 ELSE 2 END, chunk_id LIMIT 1",
            (entry_id,),
        ).fetchall()
        if rows:
            return self._row_to_result(rows[0], 0.0, "section-swap")
        return ranked[0]  # Eintrag hat nur Verweise-Sektionen

    def _best_chunk_of_entry(self, entry_id: str) -> ChunkResult | None:
        rows = self._con.execute(
            "SELECT * FROM chunks WHERE entry_id = ? "
            "ORDER BY CASE WHEN section LIKE 'Zusammenfassung%' THEN 0 ELSE 1 END, "
            "chunk_id LIMIT 1",
            (entry_id,),
        ).fetchall()
        if not rows:
            return None
        return self._row_to_result(rows[0], 0.0, "cross_ref")

    # -- öffentliche Suche --------------------------------------------------

    def search(self, question: str, n_entries: int | None = None) -> list[ChunkResult]:
        """Liefert die Top-Kontextblöcke (Hauptretrieval + cross_ref-Erweiterung)."""
        n = n_entries or self.cfg.context_blocks
        pool = self.cfg.candidate_pool
        bm = self._bm25(question, pool)
        try:
            dn = self._dense(question, pool)
        except Exception:
            dn = {}
        fused: dict[int, float] = {}
        for ranking, weight in ((bm, 1.0), (dn, self.cfg.dense_weight)):
            ordered = sorted(ranking.items(), key=lambda kv: -kv[1])
            for rank, (cid, _) in enumerate(ordered):
                fused[cid] = fused.get(cid, 0.0) + weight / (self.cfg.rrf_k + rank)
        if not fused:
            return []

        rows = self._fetch_chunks(list(fused))
        results: list[ChunkResult] = []
        for cid, score in fused.items():
            if cid not in rows:
                continue
            source = "fused" if (cid in bm and cid in dn) else (
                "bm25" if cid in bm else "dense"
            )
            score += self.cfg.recency_boost * self._stand_factor(rows[cid]["stand"])
            results.append(self._row_to_result(rows[cid], score, source))
        results.sort(key=lambda r: -r.score)

        # Bester Chunk je Eintrag -> Kontext (Entry-Level-Dedup).
        # Der Vertreter-Chunk ist die beste Inhaltssektion des Eintrags,
        # nicht die Rangfolge-Beste (vgl. _section_priority).
        main: list[ChunkResult] = []
        seen: set[str] = set()
        by_entry: dict[str, list[ChunkResult]] = {}
        for r in results:
            by_entry.setdefault(r.entry_id, []).append(r)
        for entry_id, chunks in by_entry.items():
            if len(main) >= n:
                break
            seen.add(entry_id)
            main.append(self._representative_chunk(entry_id, chunks))

        # cross_ref-Erweiterung (kontrolliert, markiert, begrenzt)
        extra: list[ChunkResult] = []
        budget = self.cfg.cross_ref_max_extra
        for r in main[: self.cfg.cross_ref_expand]:
            for ref in r.cross_refs:
                if budget <= 0:
                    break
                if ref in seen:
                    continue
                er = self._best_chunk_of_entry(ref)
                if er is not None:
                    extra.append(er)
                    seen.add(ref)
                    budget -= 1
        return main + extra