import json
from pathlib import Path

import numpy as np
import pandas as pd

def to_int(x):
    """Convert a hex string or integer to int, returning NaN on failure."""
    if isinstance(x, (int, np.integer)):
        return int(x)
    if isinstance(x, str):
        try:
            return int(x, 16)
        except ValueError:
            return np.nan
    return np.nan

def extract_id(row: pd.Series) -> str:
    """Extracts PGN from metadata or falls back to CAN ID."""
    meta = row.get('j1939_metadata')
    if pd.isna(meta):
        return f"ID: {row['ID']}"
    if isinstance(meta, str):
        try:
            meta = json.loads(meta)
        except json.JSONDecodeError:
            return f"ID: {row['ID']}"
    if isinstance(meta, dict) and 'PGN' in meta:
        return f"PGN: {meta['PGN']}"
    return f"ID: {row['ID']}"

def load_data(file_path: Path) -> pd.DataFrame:
    """Loads Parquet file and adds an Identifier column."""
    df = pd.read_parquet(file_path)
    df['Identifier'] = df.apply(extract_id, axis=1)
    return df