logging_setup.py

"""Shared construction of the rotating log file handler.

Centralizes the rotation invariant so both the tray and the CLI log paths
behave identically and the file can never grow without bound (issue #885).

A ``RotatingFileHandler`` only rotates when ``backupCount >= 1``: CPython's
``doRollover`` skips the entire rotation block when ``backupCount == 0``, so
``maxBytes`` is silently ignored and the active file grows forever. We force
at least one backup here regardless of caller input.
"""

from __future__ import annotations

import logging.handlers


_MIN_BYTES = 32 * 1024
_MIN_BACKUPS = 1


def build_log_handler(
    path: str,
    log_max_mb: float = 5,
    backups: int = 1,
) -> logging.handlers.RotatingFileHandler:
    """Create a RotatingFileHandler that actually rotates.

    ``backups`` is clamped to at least 1 so rotation is always active, and
    ``maxBytes`` keeps a small floor so a misconfigured tiny size can't cause
    rotation on every line.
    """
    max_bytes = max(_MIN_BYTES, int(log_max_mb * 1024 * 1024))
    backup_count = max(_MIN_BACKUPS, int(backups))
    return logging.handlers.RotatingFileHandler(
        path,
        maxBytes=max_bytes,
        backupCount=backup_count,
        encoding="utf-8",
    )