#!/usr/bin/python
# -*- coding: utf-8 -*-

from __future__ import annotations

import os
import re
import subprocess
from functools import cache
from pathlib import Path
from subprocess import PIPE, Popen, check_output
from sys import exit
from uuid import UUID

import config

DISK_BY_UUID = Path("/dev/disk/by-uuid")
MAPPER_PATH = Path("/dev/mapper")

"""
Erstes Backup muss für alle notwendigen Datasets durchgeführt werden mit
# zfs send -Rv rpool/ROOT@zfs-auto-snap_daily-2018-06-14-1648 | zfs receive -dvF backup1
"""


def main():
    verify_running_as_root()
    local_pool = Pool(config.local_pool_to_backup)
    external_pool = ExternalPool.find_from_dict(config.backup_pools)
    external_pool.import_()
    try:
        local_pool.backup_to(external_pool)
        clean_old_snapshots(external_pool)
    finally:
        external_pool.export()


class ZFS:
    @staticmethod
    def get_datasets(name: str) -> list[Dataset]:
        datasets_str = get_output_of_command(
            [
                config.ZFS,
                "list",
                "-H",
                "-d",
                "1",
                "-o",
                "name",
                "-t",
                "filesystem",
                name,
            ]
        )
        # we omit the first return value, which is the pool, not the dataset
        datasets_list = datasets_str.split("\n")[1:]
        return [Dataset(d) for d in datasets_list]

    @staticmethod
    def import_pool_from_directory(name, directory) -> None:
        # -N: no mount
        # -d: directory to search the pool in
        run_command([config.ZPOOL, "import", "-N", "-d", directory, name])

    @staticmethod
    def export_pool(name) -> None:
        run_command([config.ZPOOL, "export", name])

    @staticmethod
    def get_snapshots(name) -> list[Snapshot]:
        return [
            Snapshot(name)
            for name in get_output_of_command(
                [
                    config.ZFS,
                    "list",
                    "-r",
                    "-t",
                    "snapshot",
                    "-o",
                    "name",
                    "-H",
                    "-d",
                    "1",
                    name,
                ]
            ).split()
        ]

    @staticmethod
    def destroy(full_name, *, recursive=False):
        if config.local_pool_to_backup in full_name:
            msg = "ALERT! Tried to delete in local pool!"
            raise Exception(msg)
        cmdline = [config.ZFS, "destroy"]
        if recursive:
            cmdline.append("-r")
        cmdline.append(full_name)
        run_command(cmdline)

    @staticmethod
    def send(old_snap: Snapshot, new_snap: Snapshot) -> Popen[str]:
        sender = Popen(
            [config.ZFS, "send", "-R", "-I", old_snap, new_snap], stdout=PIPE
        )
        return sender

    @staticmethod
    def receive(sender: Popen[str], pool_name):
        # -d  Discard the first element of the sent snapshot's file system name
        # -F  Force a rollback of the file system to the most recent snapshot before performing the receive operation.
        # -u  File system that is associated with the received stream is not mounted.
        check_output(
            [config.ZFS, "receive", "-d", "-F", "-u", pool_name],
            stdin=sender.stdout,
        )


class Disk:
    def __init__(self, uuid: UUID, name: str):
        self.uuid = uuid
        self._decrypted = False
        self._name = name

    def decrypt(self) -> None:
        self._verify_mapper_entry_not_in_use()
        self._decrypt_with_cryptsetup()
        self._decrypted = True

    def _decrypt_with_cryptsetup(self):
        run_command([config.CRYPTSETUP, "open", self._path, self._mapper_entry])

    def _verify_mapper_entry_not_in_use(self):
        for item in MAPPER_PATH.iterdir():
            if self._mapper_entry == item.name:
                raise IOError(f"mapper entry {self._mapper_entry} already exists")

    @property
    def _path(self) -> Path:
        return DISK_BY_UUID / str(self.uuid)

    @property
    def _mapper_entry(self) -> str:
        return f"crypt-{self._name}"

    def encrypt(self):
        get_output_of_command([config.CRYPTSETUP, "close", self._name])
        self._decrypted = False


def get_last_common_snapshot(ds1: Dataset, ds2: Dataset) -> Snapshot:
    common_snapshots = [
        local_snap
        for local_snap in ds1.snapshots_matching_backup_tags
        for remote_snap in ds2.snapshots_matching_backup_tags
        if local_snap.snapname == remote_snap.snapname
    ]
    common_snapshots.sort()
    return common_snapshots[-1]


class Pool:
    def __init__(self, name):
        self.name = name

    @property
    @cache
    def datasets(self) -> list[Dataset]:
        return ZFS.get_datasets(self.name)

    @property
    @cache
    def datasets_to_backup(self) -> list[Dataset]:
        return [
            d for d in self.datasets if d.qualified_name not in config.do_not_backup
        ]

    def backup_to(self, external_pool: ExternalPool):
        for local_dataset in self.datasets_to_backup:
            remote_dataset = external_pool.search_dataset(
                local_dataset.name_without_pool
            )
            last_common_snapshot = get_last_common_snapshot(
                remote_dataset, local_dataset
            )
            last_local_snapshot: Snapshot = (
                local_dataset.snapshots_matching_backup_tags[-1]
            )
            sender = ZFS.send(last_common_snapshot, last_local_snapshot)
            ZFS.receive(sender, external_pool.name)


class ExternalPool(Pool):
    def __init__(self, name: str, disk: Disk):
        super().__init__(name)
        self._imported: bool = False
        self._disk = disk

    def import_(self) -> None:
        self._disk.decrypt()
        self._import_from_directory(MAPPER_PATH)

    def export(self) -> None:
        self._export_pool()
        self._disk.encrypt()

    def _import_from_directory(self, directory: Path) -> None:
        ZFS.import_pool_from_directory(self.name, directory)

    def _export_pool(self) -> None:
        ZFS.export_pool(self.name)

    @classmethod
    def find_from_dict(cls, backup_pools: dict[str, UUID]) -> ExternalPool:
        present_uuids = [item.name for item in DISK_BY_UUID.iterdir()]
        for pool_name, disk_uuid in backup_pools.items():
            if str(disk_uuid) in present_uuids:
                disk = Disk(disk_uuid, pool_name)
                return cls(pool_name, disk)
        else:
            print("Could not find a backup drive")
            exit(1)

    def search_dataset(self, name_without_pool: str) -> Dataset:
        qualified_name = self.name + "/" + name_without_pool
        for dataset in self.datasets_to_backup:
            if qualified_name == dataset.qualified_name:
                return dataset


class Dataset:
    def __init__(self, qualified_name: str):
        self.qualified_name = qualified_name

    def __repr__(self):
        return self.qualified_name

    @property
    def name_without_pool(self) -> str:
        return self.qualified_name.split("/", maxsplit=1)[1]

    @property
    @cache
    def snapshots(self) -> list[Snapshot]:
        """get qualified snapshot names that are direct children of the dataset"""
        return ZFS.get_snapshots(self.qualified_name)

    @property
    @cache
    def snapshots_matching_backup_tags(self) -> list[Snapshot]:
        snapshots = [
            snapshot for snapshot in self.snapshots if snapshot.matches_backup_tags
        ]
        snapshots.sort()
        return snapshots

    @property
    def last_snapshot(self) -> Snapshot:
        for snapshot in self.snapshots[::-1]:
            if snapshot.matches_backup_tags:
                return snapshot


class Snapshot:
    def __init__(self, qualified_name: str):
        self.qualified_name = qualified_name

    def __lt__(self, other: Snapshot) -> bool:
        return self.snapname < other.snapname

    @property
    def snapname(self) -> str:
        return self.qualified_name.split("@")[1]

    @property
    def matches_backup_tags(self) -> bool:
        return bool(
            re.search("@" + ".*".join(config.snapshot_tag), self.qualified_name)
        )

    @property
    def name_without_pool(self) -> str:
        return self.qualified_name.split("/", maxsplit=1)[1]


# def clean_old_snapshots(dataset, pool):
#    snapshots = get_snapshots(pool)  # full name like 'pool/dataset@snapshot'
#    # get just the dataset name without the pool
#    actual_dataset = dataset.split("/")[-1]
#    # print('actual_dataset', actual_dataset)
#    for interval in config.keep.keys():
#        # print('interval', interval)
#        # e.g. 'data@zfs-auto-snap_daily', 'ubuntu@zfs-auto-snap_hourly', ...
#        pattern = actual_dataset + "@" + config.snapshot_tag[0] + ".*" + interval
#        snapshots_in_interval = []
#        for snapshot in snapshots:
#            result = re.search(pattern, snapshot)
#            if result is not None:
#                snapshots_in_interval.append(snapshot)
#        snapshots_in_interval.sort()
#        for i in range(len(snapshots_in_interval) - config.keep[interval]):
#            to_delete = snapshots_in_interval[i]
#            print("  Lösche veralteten Snapshot {}".format(to_delete))
#            zfs_destroy(to_delete, recursive=True)
#


def run_command(cmdline: list[str]):
    subprocess.call(cmdline)


def get_output_of_command(cmdline: str | list[str]) -> str:
    if isinstance(cmdline, str):
        cmdline = [cmdline]
    return subprocess.check_output(cmdline).strip().decode()


def verify_running_as_root():
    if os.getuid() > 0:
        print("Run as root.")
        exit(1)


def clean_old_snapshots(external_pool: ExternalPool) -> None:  # TODO
    ...


if __name__ == "__main__":
    main()