#!/usr/bin/env python3
"""Entry point for the ns8-backup-monitor service.

This module is executed when the package is run as:
    python3 -m ns8_backup_monitor [--config PATH]

Start-up sequence
-----------------
1. Parse the single optional CLI argument (--config).
2. Load and validate the YAML configuration file.
3. Initialise logging (stdout + optional rotating file).
4. Hand control to receiver.run_server(), which blocks forever
   serving the Alertmanager webhook endpoint.

The process is designed to be managed by systemd (see
deploy/ns8-backup-monitor.service); stdout/stderr are captured
by journald when StandardOutput=journal is set in the unit.
"""

import argparse
import sys

from .utils import load_config, setup_logging
from .receiver import run_server


def main():
    """Parse arguments, load config, set up logging, start HTTP server."""

    # ---------------------------------------------------------------------------
    # CLI argument parsing
    # ---------------------------------------------------------------------------
    # Only a single argument is needed: the path to the YAML config file.
    # When omitted, load_config() probes a list of well-known default paths.
    parser = argparse.ArgumentParser(
        description="NS8 Backup Monitor — Alertmanager webhook receiver and correlator"
    )
    parser.add_argument(
        "--config", "-c",
        metavar="PATH",
        help="Path to config.yml (default: auto-detect from known locations)",
        default=None,
    )
    args = parser.parse_args()

    # ---------------------------------------------------------------------------
    # Configuration loading
    # ---------------------------------------------------------------------------
    # Exit immediately with a clear message if the config file is missing.
    # This prevents a confusing traceback on first-run misconfiguration.
    try:
        config = load_config(args.config)
    except FileNotFoundError as e:
        print(f"ERROR: {e}", file=sys.stderr)
        sys.exit(1)

    # ---------------------------------------------------------------------------
    # Logging setup
    # ---------------------------------------------------------------------------
    # Must be done before any module-level loggers are used.
    # When logging.file is empty in config, output goes to stdout only
    # (journald captures it via StandardOutput=journal in the systemd unit).
    setup_logging(config)

    # ---------------------------------------------------------------------------
    # Start HTTP server
    # ---------------------------------------------------------------------------
    # run_server() blocks indefinitely. Systemd handles restart on failure.
    run_server(config)


if __name__ == "__main__":
    main()