"""
SQLite database for user accounts and session metadata.
Uses Python's built-in sqlite3; all DB calls are wrapped with
fastapi.concurrency.run_in_threadpool so they don't block the event loop.
"""
import sqlite3
import shutil
from pathlib import Path
from typing import Optional

from config import DB_PATH, SESSIONS_DIR

SESSION_LIMIT = 999  # effectively unlimited; sessions kept until user deletes manually


def _connect() -> sqlite3.Connection:
    DB_PATH.parent.mkdir(parents=True, exist_ok=True)
    conn = sqlite3.connect(str(DB_PATH), check_same_thread=False)
    conn.row_factory = sqlite3.Row
    return conn


def init_db() -> None:
    """Create tables if they don't exist. Called once at startup."""
    conn = _connect()
    try:
        conn.executescript("""
            CREATE TABLE IF NOT EXISTS users (
                id          TEXT PRIMARY KEY,
                google_id   TEXT UNIQUE NOT NULL,
                email       TEXT NOT NULL,
                name        TEXT,
                picture     TEXT,
                created_at  TEXT NOT NULL DEFAULT (datetime('now'))
            );

            CREATE TABLE IF NOT EXISTS pipeline_sessions (
                session_id  TEXT PRIMARY KEY,
                user_id     TEXT NOT NULL REFERENCES users(id),
                status      TEXT NOT NULL DEFAULT 'idle',
                pdf_name    TEXT,
                last_stage  INTEGER NOT NULL DEFAULT 0,
                created_at  TEXT NOT NULL DEFAULT (datetime('now')),
                updated_at  TEXT NOT NULL DEFAULT (datetime('now'))
            );

            CREATE TABLE IF NOT EXISTS user_events (
                id          INTEGER PRIMARY KEY AUTOINCREMENT,
                user_id     TEXT NOT NULL REFERENCES users(id),
                session_id  TEXT,
                event_type  TEXT NOT NULL,
                meta        TEXT,
                created_at  TEXT NOT NULL DEFAULT (datetime('now'))
            );
        """)
        # Migration: add columns that may not exist in older databases
        for migration in [
            "ALTER TABLE pipeline_sessions ADD COLUMN last_stage INTEGER NOT NULL DEFAULT 0",
            "ALTER TABLE users ADD COLUMN openai_key TEXT",
        ]:
            try:
                conn.execute(migration)
                conn.commit()
            except sqlite3.OperationalError:
                pass  # column already exists
    finally:
        conn.close()


# ---------------------------------------------------------------------------
# Users
# ---------------------------------------------------------------------------

def upsert_user(google_id: str, email: str, name: str, picture: str) -> dict:
    """Insert or update user; return the user row as a dict."""
    import uuid
    conn = _connect()
    try:
        row = conn.execute(
            "SELECT * FROM users WHERE google_id = ?", (google_id,)
        ).fetchone()
        if row:
            conn.execute(
                "UPDATE users SET name=?, picture=? WHERE google_id=?",
                (name, picture, google_id),
            )
            conn.commit()
            row = conn.execute(
                "SELECT * FROM users WHERE google_id = ?", (google_id,)
            ).fetchone()
        else:
            user_id = str(uuid.uuid4())
            conn.execute(
                "INSERT INTO users (id, google_id, email, name, picture) VALUES (?,?,?,?,?)",
                (user_id, google_id, email, name, picture),
            )
            conn.commit()
            row = conn.execute(
                "SELECT * FROM users WHERE id = ?", (user_id,)
            ).fetchone()
        return dict(row)
    finally:
        conn.close()


def get_user_by_id(user_id: str) -> Optional[dict]:
    conn = _connect()
    try:
        row = conn.execute("SELECT * FROM users WHERE id = ?", (user_id,)).fetchone()
        return dict(row) if row else None
    finally:
        conn.close()


def get_user_openai_key(user_id: str) -> Optional[str]:
    conn = _connect()
    try:
        row = conn.execute("SELECT openai_key FROM users WHERE id = ?", (user_id,)).fetchone()
        return row["openai_key"] if row else None
    finally:
        conn.close()


def set_user_openai_key(user_id: str, key: str) -> None:
    conn = _connect()
    try:
        conn.execute("UPDATE users SET openai_key = ? WHERE id = ?", (key, user_id))
        conn.commit()
    finally:
        conn.close()


# ---------------------------------------------------------------------------
# Pipeline sessions
# ---------------------------------------------------------------------------

def save_session_record(session_id: str, user_id: str, pdf_name: str, status: str = "idle") -> None:
    conn = _connect()
    try:
        conn.execute(
            """INSERT OR REPLACE INTO pipeline_sessions (session_id, user_id, status, pdf_name, updated_at)
               VALUES (?, ?, ?, ?, datetime('now'))""",
            (session_id, user_id, status, pdf_name),
        )
        conn.commit()
    finally:
        conn.close()


def update_session_status(session_id: str, status: str, last_stage: int = None) -> None:
    conn = _connect()
    try:
        if last_stage is not None:
            conn.execute(
                "UPDATE pipeline_sessions SET status=?, last_stage=?, updated_at=datetime('now') WHERE session_id=?",
                (status, last_stage, session_id),
            )
        else:
            conn.execute(
                "UPDATE pipeline_sessions SET status=?, updated_at=datetime('now') WHERE session_id=?",
                (status, session_id),
            )
        conn.commit()
    finally:
        conn.close()


def get_sessions_for_user(user_id: str) -> list[dict]:
    conn = _connect()
    try:
        rows = conn.execute(
            """SELECT session_id, status, pdf_name, last_stage, created_at, updated_at
               FROM pipeline_sessions WHERE user_id=? ORDER BY updated_at DESC""",
            (user_id,),
        ).fetchall()
        return [dict(r) for r in rows]
    finally:
        conn.close()


def get_session_record(session_id: str) -> Optional[dict]:
    conn = _connect()
    try:
        row = conn.execute(
            "SELECT * FROM pipeline_sessions WHERE session_id=?", (session_id,)
        ).fetchone()
        return dict(row) if row else None
    finally:
        conn.close()


def delete_session_record(session_id: str) -> None:
    conn = _connect()
    try:
        conn.execute("DELETE FROM pipeline_sessions WHERE session_id=?", (session_id,))
        conn.commit()
    finally:
        conn.close()


def get_sessions_beyond_limit(user_id: str, limit: int = SESSION_LIMIT) -> list[str]:
    """Return session_ids (oldest first) that exceed the per-user limit."""
    conn = _connect()
    try:
        rows = conn.execute(
            """SELECT session_id FROM pipeline_sessions
               WHERE user_id=? ORDER BY updated_at DESC""",
            (user_id,),
        ).fetchall()
        ids = [r["session_id"] for r in rows]
        return ids[limit:]  # everything beyond the limit, oldest last
    finally:
        conn.close()


def enforce_session_limit(user_id: str) -> list[str]:
    """
    Delete sessions beyond SESSION_LIMIT for the user.
    Returns list of deleted session_ids so caller can remove disk data.
    """
    to_delete = get_sessions_beyond_limit(user_id)
    for sid in to_delete:
        delete_session_record(sid)
        # Remove session directory from disk
        session_dir = SESSIONS_DIR / sid
        if session_dir.exists():
            shutil.rmtree(session_dir, ignore_errors=True)
    return to_delete


# ---------------------------------------------------------------------------
# User events
# ---------------------------------------------------------------------------

def log_event(user_id: str, event_type: str, session_id: str = None, meta: dict = None) -> None:
    """Record a user interaction event."""
    import json
    conn = _connect()
    try:
        conn.execute(
            "INSERT INTO user_events (user_id, session_id, event_type, meta) VALUES (?,?,?,?)",
            (user_id, session_id, event_type, json.dumps(meta) if meta else None),
        )
        conn.commit()
    finally:
        conn.close()


def get_events_for_user(user_id: str, limit: int = 500) -> list[dict]:
    """Return recent events for a user, newest first."""
    conn = _connect()
    try:
        rows = conn.execute(
            "SELECT * FROM user_events WHERE user_id=? ORDER BY created_at DESC LIMIT ?",
            (user_id, limit),
        ).fetchall()
        return [dict(r) for r in rows]
    finally:
        conn.close()