core/logger.py

"""
logger.py — nohup-safe rotating logger for G-MASS evaluation runs.
Owner: D  |  MediSafe-GH · Africa AI Safety Prize 2026
"""

import logging
import os
from logging.handlers import RotatingFileHandler

LOG_DIR  = os.getenv("GMASS_LOG_DIR", "logs")
LOG_FILE = os.path.join(LOG_DIR, "gmass_eval.log")
LOG_FMT  = "%(asctime)s [%(levelname)s] %(name)s — %(message)s"
DATE_FMT = "%Y-%m-%dT%H:%M:%S"


def get_logger(name: str) -> logging.Logger:
    """
    Return a named logger that writes to both console and a rotating log file.
    Safe to call multiple times with the same name — returns the same logger.

    Args:
        name : typically __name__ of the calling module

    Returns:
        Configured logging.Logger instance.

    Example:
        from core.logger import get_logger
        logger = get_logger(__name__)
        logger.info("Evaluation started")
    """
    logger = logging.getLogger(name)

    if logger.handlers:
        return logger  # already configured

    logger.setLevel(logging.DEBUG)

    formatter = logging.Formatter(LOG_FMT, datefmt=DATE_FMT)

    # Console handler — INFO and above
    console = logging.StreamHandler()
    console.setLevel(logging.INFO)
    console.setFormatter(formatter)
    logger.addHandler(console)

    # Rotating file handler — DEBUG and above, 5 MB per file, 3 backups
    try:
        os.makedirs(LOG_DIR, exist_ok=True)
        file_handler = RotatingFileHandler(
            LOG_FILE, maxBytes=5 * 1024 * 1024, backupCount=3, encoding="utf-8"
        )
        file_handler.setLevel(logging.DEBUG)
        file_handler.setFormatter(formatter)
        logger.addHandler(file_handler)
    except OSError:
        logger.warning(f"Could not create log file at {LOG_FILE}. Logging to console only.")

    return logger