#! /usr/bin/env python3
#
#  db_backup - Backup local MySQL databases.
#  Copyright (C) 2021  HOMEINFO - Digitale Informationssysteme GmbH
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation, either version 3 of the License, or
#  (at your option) any later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <https://www.gnu.org/licenses/>.
"""Backups local databases."""

from argparse import ArgumentParser, Namespace
from datetime import datetime
from io import BytesIO
from logging import INFO, basicConfig, getLogger
from os import linesep
from pathlib import Path
from subprocess import PIPE, CalledProcessError, run
from sys import exit    # pylint: disable=W0622
from tarfile import TarFile, TarInfo, open      # pylint: disable=W0622
from typing import Iterable, Iterator, NamedTuple


LOG_FORMAT = '[%(levelname)s] %(name)s: %(message)s'
LOGGER = getLogger(Path(__file__).stem)
EXCLUDE = {
    'information_schema',
    'mysql',
    'performance_schema'
}


class MySQLDump(NamedTuple):
    """Represents a MySQL table dump."""

    database: str
    table: str
    dump: bytes


def get_args() -> Namespace:
    """Parses the command line arguments."""

    parser = ArgumentParser(description='Backups MariaDB databases.')
    parser.add_argument('-u', '--user', metavar='user', default='backup')
    parser.add_argument('-p', '--passwd', metavar='password')
    parser.add_argument('-e', '--exclude', nargs='*', metavar='database')
    parser.add_argument('-t', '--timestamp', action='store_true')
    parser.add_argument('file')
    return parser.parse_args()


def get_databases(user: str, passwd: str) -> Iterator[str]:
    """Returns a list of database names."""

    command = ['mysql', f'--user={user}', f'--password={passwd}',
               '--skip-column-names', '--execute', 'show databases;']
    result = run(command, check=True, stdout=PIPE, text=True)
    return filter(None, result.stdout.split(linesep))


def get_tables(database: str, *, user: str, passwd: str) -> Iterator[str]:
    """Returns a list of tables in the given database."""

    command = ['mysql', f'--user={user}', f'--password={passwd}',
               '--skip-column-names', '--execute', 'show tables;', database]
    result = run(command, check=True, stdout=PIPE, text=True)
    return filter(None, result.stdout.split(linesep))


def dump_table(database: str, table: str, *,
               user: str, passwd: str) -> MySQLDump:
    """Dumps a table of a database."""

    LOGGER.info('Dumping %s.%s', database, table)
    command = ['mysqldump', f'--user={user}', f'--password={passwd}',
               database, table]
    result = run(command, check=True, stdout=PIPE)
    return MySQLDump(database, table, result.stdout)


def dump_database(database: str, *, user: str, passwd: str) \
        -> Iterator[MySQLDump]:
    """Dumps a database."""

    for table in get_tables(database, user=user, passwd=passwd):
        yield dump_table(database, table, user=user, passwd=passwd)


def dump_databases(databases: Iterable[str], *, user: str, passwd: str) \
        -> Iterator[MySQLDump]:
    """Dumps the given databases."""

    for database in databases:
        yield from dump_database(database, user=user, passwd=passwd)


def dump_databases_to_tarfile(tarfile: TarFile, databases: Iterable[str], *,
                              user: str, passwd: str) -> None:
    """Dumps the given databases to the given tar file."""

    for mysql_dump in dump_databases(databases, user=user, passwd=passwd):
        tarinfo = TarInfo(f'{mysql_dump.database}.{mysql_dump.table}.sql')
        tarinfo.size = len(mysql_dump.dump)
        tarinfo.mode = 0o644
        bytesio = BytesIO(mysql_dump.dump)
        tarfile.addfile(tarinfo, fileobj=bytesio)


def main():
    """Runs the script."""

    args = get_args()
    basicConfig(format=LOG_FORMAT, level=INFO)

    try:
        databases = get_databases(args.user, args.passwd)
    except CalledProcessError as error:
        exit(error.returncode)

    exclude = {*EXCLUDE, *args.exclude}
    databases = filter(lambda db: db not in exclude, databases)

    if args.timestamp:
        timestamp = datetime.now().isoformat()

        try:
            filename = args.file % timestamp
        except TypeError:
            filename = args.file.format(timestamp)
    else:
        filename = args.file

    file = Path(filename)

    if file.exists():
        LOGGER.error('File exists: %s', file)
        exit(1)

    with open(file, mode='w:gz') as tarfile:
        try:
            dump_databases_to_tarfile(
                tarfile, databases, user=args.user, passwd=args.passwd)
        except CalledProcessError as error:
            exit(error.returncode)


if __name__ == '__main__':
    main()