"""Persistent memory: SQLite storage + brute-force cosine recall over embeddings.

Each exchange is stored with its OpenAI embedding as a float32 BLOB. Recall
loads all embeddings (optionally scoped to a session) into a matrix and
returns the top-k by cosine similarity. Brute force is fine up to tens of
thousands of rows; swap in a vector index when that stops being true.
"""
from __future__ import annotations

import sqlite3
from dataclasses import dataclass
from datetime import datetime, timezone
from pathlib import Path

import numpy as np

from lyra import llm
from lyra.config import load

SCHEMA = """
CREATE TABLE IF NOT EXISTS exchanges (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    session_id TEXT NOT NULL,
    role TEXT NOT NULL,
    content TEXT NOT NULL,
    embedding BLOB NOT NULL,
    created_at TEXT NOT NULL
);
CREATE INDEX IF NOT EXISTS idx_session_created ON exchanges(session_id, created_at);

CREATE TABLE IF NOT EXISTS sessions (
    id TEXT PRIMARY KEY,
    name TEXT,
    created_at TEXT NOT NULL
);
"""

_conn: sqlite3.Connection | None = None
_conn_path: Path | None = None


def _connection() -> sqlite3.Connection:
    """Lazily open the SQLite connection. Reopens if LYRA_DB_PATH changed (for tests)."""
    global _conn, _conn_path
    cfg = load()
    if _conn is None or _conn_path != cfg.db_path:
        if _conn is not None:
            _conn.close()
        cfg.db_path.parent.mkdir(parents=True, exist_ok=True)
        # check_same_thread=False: the web server runs blocking work in a thread
        # pool, so the singleton connection is touched from threads other than
        # the one that created it. Safe here under single-user, low-concurrency use.
        _conn = sqlite3.connect(cfg.db_path, check_same_thread=False)
        _conn.row_factory = sqlite3.Row
        _conn.executescript(SCHEMA)
        _conn_path = cfg.db_path
    return _conn


@dataclass
class Exchange:
    id: int
    session_id: str
    role: str
    content: str
    created_at: str
    score: float | None = None


def _to_blob(vec: list[float]) -> bytes:
    return np.asarray(vec, dtype=np.float32).tobytes()


def _from_blob(blob: bytes) -> np.ndarray:
    return np.frombuffer(blob, dtype=np.float32)


def remember(session_id: str, role: str, content: str) -> int:
    """Embed and persist a single exchange. Returns the new row id."""
    [embedding] = llm.embed([content])
    now = datetime.now(timezone.utc).isoformat()
    conn = _connection()
    with conn:
        cur = conn.execute(
            "INSERT INTO exchanges (session_id, role, content, embedding, created_at) "
            "VALUES (?, ?, ?, ?, ?)",
            (session_id, role, content, _to_blob(embedding), now),
        )
    return int(cur.lastrowid)


def recent(session_id: str, n: int = 10) -> list[Exchange]:
    """Last `n` exchanges from a session, oldest first."""
    conn = _connection()
    rows = conn.execute(
        "SELECT id, session_id, role, content, created_at FROM exchanges "
        "WHERE session_id = ? ORDER BY id DESC LIMIT ?",
        (session_id, n),
    ).fetchall()
    return [
        Exchange(
            id=r["id"],
            session_id=r["session_id"],
            role=r["role"],
            content=r["content"],
            created_at=r["created_at"],
        )
        for r in reversed(rows)
    ]


def ensure_session(session_id: str, name: str | None = None) -> None:
    """Create the session row if absent; set its name if one is given."""
    now = datetime.now(timezone.utc).isoformat()
    conn = _connection()
    with conn:
        conn.execute(
            "INSERT INTO sessions (id, name, created_at) VALUES (?, ?, ?) "
            "ON CONFLICT(id) DO NOTHING",
            (session_id, name, now),
        )
        if name is not None:
            conn.execute("UPDATE sessions SET name = ? WHERE id = ?", (name, session_id))


def list_sessions() -> list[dict]:
    """All known sessions (named rows + any session that has exchanges), newest first."""
    conn = _connection()
    rows = conn.execute(
        """
        SELECT s.id AS id,
               s.name AS name,
               COALESCE(s.created_at, MIN(e.created_at)) AS created_at
        FROM sessions s
        LEFT JOIN exchanges e ON e.session_id = s.id
        GROUP BY s.id
        UNION
        SELECT e.session_id AS id, NULL AS name, MIN(e.created_at) AS created_at
        FROM exchanges e
        WHERE e.session_id NOT IN (SELECT id FROM sessions)
        GROUP BY e.session_id
        ORDER BY created_at DESC
        """
    ).fetchall()
    return [{"id": r["id"], "name": r["name"]} for r in rows]


def history(session_id: str) -> list[Exchange]:
    """Full conversation for a session, oldest first."""
    conn = _connection()
    rows = conn.execute(
        "SELECT id, session_id, role, content, created_at FROM exchanges "
        "WHERE session_id = ? ORDER BY id ASC",
        (session_id,),
    ).fetchall()
    return [
        Exchange(
            id=r["id"],
            session_id=r["session_id"],
            role=r["role"],
            content=r["content"],
            created_at=r["created_at"],
        )
        for r in rows
    ]


def delete_session(session_id: str) -> None:
    """Remove a session and all its exchanges."""
    conn = _connection()
    with conn:
        conn.execute("DELETE FROM exchanges WHERE session_id = ?", (session_id,))
        conn.execute("DELETE FROM sessions WHERE id = ?", (session_id,))


def recall(query: str, k: int = 5, session_id: str | None = None) -> list[Exchange]:
    """Top-k exchanges semantically similar to `query`, optionally scoped to a session."""
    [q_vec] = llm.embed([query])
    q = np.asarray(q_vec, dtype=np.float32)

    conn = _connection()
    sql = "SELECT id, session_id, role, content, embedding, created_at FROM exchanges"
    params: tuple = ()
    if session_id is not None:
        sql += " WHERE session_id = ?"
        params = (session_id,)
    rows = conn.execute(sql, params).fetchall()
    if not rows:
        return []

    matrix = np.stack([_from_blob(r["embedding"]) for r in rows])
    norms = np.linalg.norm(matrix, axis=1)
    scores = (matrix @ q) / (norms * np.linalg.norm(q) + 1e-9)

    top_idx = np.argsort(scores)[::-1][:k]
    return [
        Exchange(
            id=rows[i]["id"],
            session_id=rows[i]["session_id"],
            role=rows[i]["role"],
            content=rows[i]["content"],
            created_at=rows[i]["created_at"],
            score=float(scores[i]),
        )
        for i in top_idx
    ]