#!/usr/bin/python3
#
# This file is part of Plinth.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero 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 Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#

"""
Configuration helper for filesystem snapshots.
"""

import augeas
import argparse
import json
import os
import subprocess

FSTAB = '/etc/fstab'
AUG_FSTAB = '/files/etc/fstab'


def parse_arguments():
    """Return parsed command line arguments as dictionary."""
    parser = argparse.ArgumentParser()
    subparsers = parser.add_subparsers(dest='subcommand', help='Sub command')

    subparsers.add_parser('setup', help='Configure snapper')
    subparsers.add_parser('list', help='List snapshots')
    subparsers.add_parser('create', help='Create snapshot')

    subparser = subparsers.add_parser('delete', help='Delete snapshot')
    subparser.add_argument('number', help='Number of snapshot to delete')

    subparser = subparsers.add_parser('rollback', help='Rollback to snapshot')
    subparser.add_argument('number', help='Number of snapshot to rollback to')

    return parser.parse_args()


def subcommand_setup(_):
    """Configure snapper."""
    # Check if root config exists.
    command = ['snapper', 'list-configs']
    process = subprocess.run(command, stdout=subprocess.PIPE, check=True)
    output = process.stdout.decode()

    # Create root config if needed.
    if 'root' not in output:
        command = ['snapper', 'create-config', '/']
        subprocess.run(command, check=True)

    _add_fstab_entry('/')


def _add_fstab_entry(mount_point):
    """Add mountpoint for subvolumes."""
    snapshots_mount_point = os.path.join(mount_point, '.snapshots')

    aug = augeas.Augeas(flags=augeas.Augeas.NO_LOAD +
                        augeas.Augeas.NO_MODL_AUTOLOAD)
    aug.set('/augeas/load/Fstab/lens', 'Fstab.lns')
    aug.set('/augeas/load/Fstab/incl[last() + 1]', FSTAB)
    aug.load()

    spec = None
    for entry in aug.match(AUG_FSTAB + '/*'):
        entry_mount_point = aug.get(entry + '/file')
        if entry_mount_point == snapshots_mount_point:
            return

        if entry_mount_point == mount_point and \
           aug.get(entry + '/vfstype') == 'btrfs':
            spec = aug.get(entry + '/spec')

    if spec:
        aug.set(AUG_FSTAB + '/01/spec', spec)
        aug.set(AUG_FSTAB + '/01/file', snapshots_mount_point)
        aug.set(AUG_FSTAB + '/01/vfstype', 'btrfs')
        aug.set(AUG_FSTAB + '/01/opt', 'subvol')
        aug.set(AUG_FSTAB + '/01/opt/value', '.snapshots')
        aug.set(AUG_FSTAB + '/01/dump', '0')
        aug.set(AUG_FSTAB + '/01/passno', '1')
        aug.save()


def subcommand_list(_):
    """List snapshots."""
    command = ['snapper', 'list']
    process = subprocess.run(command, stdout=subprocess.PIPE, check=True)
    lines = process.stdout.decode().splitlines()
    keys = ('type', 'number', 'pre_number', 'date', 'user', 'cleanup',
            'description')
    snapshots = []
    for line in lines[2:]:
        parts = [part.strip() for part in line.split('|')]
        snapshots.append(dict(zip(keys, parts)))

    default = _get_default_snapshot()
    for snapshot in snapshots:
        snapshot['is_default'] = (snapshot['number'] == default)

    print(json.dumps(snapshots))


def _get_default_snapshot():
    """Return the default snapshot by looking at default subvolume."""
    command = ['btrfs', 'subvolume', 'get-default', '/']
    process = subprocess.run(command, stdout=subprocess.PIPE, check=True)
    output = process.stdout.decode()

    output_parts = output.split()
    if len(output_parts) >= 9:
        path = output.split()[8]
        path_parts = path.split('/')
        if len(path_parts) == 3 and path_parts[0] == '.snapshots':
            return path_parts[1]

    return None


def subcommand_create(_):
    """Create snapshot."""
    command = ['snapper', 'create', '--description', 'manually created']
    subprocess.run(command, check=True)


def subcommand_delete(arguments):
    """Delete snapshot."""
    command = ['snapper', 'delete', arguments.number]
    subprocess.run(command, check=True)


def subcommand_rollback(arguments):
    """Rollback to snapshot."""
    command = ['snapper', 'rollback', '--description', 'created by rollback',
               arguments.number]
    subprocess.run(command, check=True)


def main():
    """Parse arguments and perform all duties."""
    arguments = parse_arguments()

    subcommand = arguments.subcommand.replace('-', '_')
    subcommand_method = globals()['subcommand_' + subcommand]
    subcommand_method(arguments)


if __name__ == '__main__':
    main()