"""
Utility helpers for the Eskom app.

Provides:
- safe CSV load
- model metadata loader (from data/model_metadata.json)
- saving predictions
- byte-size formatter
"""

from typing import Optional, Dict, Any
from pathlib import Path
import pandas as pd
import json
import logging

logger = logging.getLogger(__name__)


def safe_read_csv(path: str, nrows: Optional[int] = None) -> Optional[pd.DataFrame]:
    p = Path(path)
    if not p.exists():
        logger.debug("CSV not found: %s", path)
        return None
    try:
        return pd.read_csv(p, nrows=nrows)
    except Exception as e:
        logger.warning("Failed to read CSV %s: %s", path, e)
        return None


def load_model_metadata(path: str = "data/model_metadata.json") -> Dict[str, Any]:
    """
    Loads optional model metadata (training date, metrics, author, notes).
    If the file is absent or malformed, returns a sensible default dict.
    """
    p = Path(path)
    default = {
        "model_type": "unknown",
        "training_date": None,
        "training_rows": None,
        "metrics": {},
        "version": "1.0"
    }
    if not p.exists():
        return default
    try:
        data = json.loads(p.read_text(encoding="utf-8"))
        # merge defaults
        for k, v in default.items():
            if k not in data:
                data[k] = v
        return data
    except Exception as e:
        logger.warning("Failed to parse model metadata: %s", e)
        return default


def save_predictions(df, out_path: str = "data/predictions.csv") -> bool:
    try:
        Path(out_path).parent.mkdir(parents=True, exist_ok=True)
        df.to_csv(out_path, index=False)
        return True
    except Exception as e:
        logger.exception("Failed to save predictions to %s: %s", out_path, e)
        return False


def human_readable_bytes(num: int) -> str:
    """
    Convert bytes to human-readable string.
    """
    for unit in ["B", "KB", "MB", "GB", "TB"]:
        if num < 1024.0:
            return f"{num:.1f}{unit}"
        num /= 1024.0
    return f"{num:.1f}PB"