#!/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

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

ETC_INCLUDE_FILE = "/etc/rbackup/etc-include.conf"

# ========== 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 backup_all(s, rsync_opts):
    raise NotImplementedError


def backup_etc(s, rsync_opts):
    """Create a backup of /etc

    :param s: snapshot to back up to
    :type s: Snapshot object
    :param opts: options to pass to rsync
    :type opts: list
    """
    local_opts = rsync_opts
    local_opts.append(f"--files-from={ETC_INCLUDE_FILE}")

    syslog.debug("Creating directory {s.etc_path}")
    s.etc_dir.mkdir(parents=True, exist_ok=False)
    rsync(*local_opts, "/etc/", str(s.etc_path))


def backup_home():
    raise NotImplementedError


def backup_pkgmanager():
    raise NotImplementedError


def backup_system():
    raise NotImplementedError


DISPATCHER = {
    "all": backup_all,
    "etc": backup_etc,
    "home": backup_home,
    "system": backup_system,
}


# ========== Main Script ==========
if __name__ == "__main__":
    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 = []
    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(f"--link-dest={prev_snapshot}")
    rsync_opts.append("--backup-dir=backup")

    DISPATCHER[args.operation](curr_snapshot, rsync_opts)

    snapshot_symlink = repo.path / "current"

    try:
        snapshot_symlink.unlink()
    except FileNotFoundError:
        pass

    snapshot_symlink.symlink_to(curr_snapshot, target_is_directory=True)

    if args.run_post_sync:
        os.sync()