#!/usr/bin/python3
"""
.. moduleauthor:: Eric Torres

Run a backup, creating a snapshot in the process.

Command-Line Arguments
======================

-c, --use-checksums   use rsync's checksum feature to detect file changes
-d, --dry-run         make this backup a dry run
--debug               show debug messages
-n, --name            name to give to the backup snapshot
-p, --port            port that ssh on the destination is listening on
-s, --run-post-sync   run sync syscall after backup
-u, --umask           umask value to use while running backup process
-v, --verbose         show info messages

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

import rbackup.config.config_files as config
import rbackup.rsync
from rbackup.struct.repository import Repository

# ========== Constants ==========
SCRIPT_UMASK = 0000
LOGFORMAT = "==> %(levelname)s %(message)s"
EXTRA_RSYNC_OPTS = {
    "dry_run": "--dry-run",
    "delete": "--delete-after",
    "checksum": "--checksum",
    "update": "--update",
}


# ----- Error Codes -----
E_INVALID_SNAPSHOT_NAME = 2
E_PERMISSION = 13

# ========== 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(**kwargs):
    """Parse command line arguments passed to the script.
        All 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("--debug", action="store_true", help="log debug messages")
    parser.add_argument(
        "-n", "--name", default=None, help="name to give to the snapshot"
    )
    parser.add_argument(
        "-p", "--port", default=22, help="port that ssh on the destination is listening on"
    )
    parser.add_argument(
        "-s",
        "--run-post-sync",
        action="store_true",
        help="run sync operation after backup is complete",
    )
    parser.add_arguemnt(
        "-u", "--umask", type=int, default=None, help="umask value to use while running backup process"
    )
    parser.add_argument(
        "-v", "--verbose", action="store_true", help="log info messages"
    )
    parser.add_argument("repository", help="repository to back up to", metavar="repo")

    return parser.parse_args(**kwargs)


@contextmanager
def change_umask(override=None):
    """Creates a context manager in which the umask is changed.
    This is to ensure that the script's desired umask is not
    visible to the user.

    :param override: non-script-default umask value to use
    :type override: int
    """
    try:
        if override is not None:
            old_umask = os.umask(override)
        else:
            old_umask = os.umask(SCRIPT_UMASK)
        yield
    finally:
        os.umask(old_umask)


# ========== Main Script ==========
if __name__ == "__main__":
    args = parse_cmdline_arguments()
    parsed_config = config.parse_configfile()

    repo = None

    try:
        repo = Repository(args.repository)
    except PermissionError as e:
        syslog.critical(e)
        exit(E_PERMISSION)

    rsync_opts = config.load_list_from_option(
        parsed_config,
        section="main",
        option="RsyncOptions",
        fallback=rbackup.rsync.DEFAULT_RSYNC_OPTS.copy(),
    )

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

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

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

    # We want to iterate through the repository and create the --link-dest
    # options before creating the new snapshot
    link_dests = tuple(f"--link-dest={s.path}" for s in repo)

    curr_snapshot = None

    with change_umask(args.umask), config.merge_include_files() as include_file, config.merge_exclude_files() as exclude_file:
        try:
            curr_snapshot = repo.create_snapshot(args.name)
            rbackup.rsync.rsync(
                *rsync_opts,
                f"--files-from={include_file}",
                f"--exclude-from={exclude_file}",
                *link_dests,
                "/",
                str(curr_snapshot),
            )
        except ValueError as e:
            syslog.critical(e)
            exit(E_INVALID_SNAPSHOT_NAME)
        except CalledProcessError as e:
            syslog.critical("Backup process failed")
            syslog.critical(f"Failing command: {e.cmd}")
            syslog.critical(e.stderr)
            exit(e.returncode)

    if args.run_post_sync:
        syslog.info("Running sync operation")
        os.sync()