#!/usr/bin/python3
"""
Run a backup.

Command-Line Arguments
======================
* -c, --use-checksums   use rsync's checksum feature to detect file changes
* -d, --dry-run         make this backup a dry run
* -s, --run-post-sync   run sync syscall after backup
* -v, --verbose         increase script verbosity

On each run of this script, a new snapshot is made and any unchanged
files are hardlinked into this new snapshot.
"""
import argparse
import logging
import os
import sys

from rbackup.hierarchy.repository import Repository
from rbackup.rsync import rsync
from subprocess import CalledProcessError

# ========== Constants ==========
LOGFORMAT = "==> %(levelname)s %(message)s"
RSYNC_DEFAULT_OPTS = [
    "--acls",
    "--archive",
    "--backup",
    "--hard-links",
    "--ignore-missing-args",
    "--prune-empty-dirs",
    "--suffix=.old",
    "--xattrs",
]
EXTRA_RSYNC_OPTS = {
    "dry_run": "--dry-run",
    "delete": "--delete-after",
    "checksum": "--checksum",
    "update": "--update",
}

CONFIG_DIR = "/etc/rbackup"
ETC_INCLUDE_FILE = f"{CONFIG_DIR}/etc-include.conf"
HOME_EXCLUDE_FILE = f"{CONFIG_DIR}/home-exclude.conf"

# ----- Error Codes -----
E_FAILED_PROCESS = 1

# ========== Logging Setup ==========
console_formatter = logging.Formatter(LOGFORMAT)
syslog = logging.getLogger("rbackup")
syslog.setLevel(logging.DEBUG)

stdout_handler = logging.StreamHandler(sys.stdout)
stdout_handler.setLevel(logging.INFO)
stdout_handler.setFormatter(console_formatter)
stdout_handler.addFilter(lambda record: record.levelno <= logging.INFO)

stderr_handler = logging.StreamHandler(sys.stderr)
stderr_handler.setLevel(logging.WARNING)
stderr_handler.setFormatter(console_formatter)

syslog.addHandler(stdout_handler)
syslog.addHandler(stderr_handler)


# ========== Functions ==========
def parse_cmdline_arguments(*args, **kwargs):
    """Parse command line arguments passed to the script.
        All args and kwargs are passed to ArgumentParser.parse_args()

    :rtype: argparse.Namespace object
    """
    parser = argparse.ArgumentParser()
    parser.add_argument(
        "-c",
        "--use-checksums",
        action="store_const",
        dest="extra_rsync_opts",
        const=EXTRA_RSYNC_OPTS["checksum"],
        help="use rsync's checksumming feature to look for changed files",
    )
    parser.add_argument(
        "-d",
        "--dry-run",
        action="append_const",
        dest="extra_rsync_opts",
        const=EXTRA_RSYNC_OPTS["dry_run"],
        help="pass --dry-run to rsync",
    )
    parser.add_argument(
        "-s",
        "--run-post-sync",
        action="store_true",
        help="run sync operation after backup is complete",
    )
    parser.add_argument(
        "-v",
        "--verbose",
        action="store_true",
        help="increase script verbosity",
    )
    parser.add_argument(
        "operation",
        choices=["all", "etc", "home", "pkg", "system"],
        help="the operation to perform",
        metavar="op",
    )
    parser.add_argument(
        "repository", help="repository to back up to", metavar="repo"
    )

    args = parser.parse_args()

    rsync_opts = RSYNC_DEFAULT_OPTS
    if args.extra_rsync_opts is not None:
        rsync_opts.extend(args.extra_rsync_opts)

    args = parser.parse_args()
    repo = Repository(args.repository)

    if args.verbose:
        stdout_handler.setLevel(logging.DEBUG)

    if repo.empty:
        prev_snapshot = None
    else:
        prev_snapshot = repo.curr_snapshot

    repo.create_snapshot()
    curr_snapshot = repo.curr_snapshot

    rsync_opts.append("--backup-dir=backup")

    try:
        DISPATCHER[args.operation](curr_snapshot, prev_snapshot, rsync_opts)
    except CalledProcessError as e:
        syslog.error("Backup process failed")
        syslog.info(f"Failing command: {e.cmd}")
        exit(E_FAILED_PROCESS)

    snapshot_symlink = repo.path / "current"

    try:
        snapshot_symlink.unlink()
    except FileNotFoundError:
        pass

    snapshot_symlink.symlink_to(curr_snapshot.path, target_is_directory=True)

    if args.run_post_sync:
        os.sync()