"""
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/>.

Copyright © 2019 Cloud Linux Software Inc.

This software is also available under ImunifyAV commercial license,
see <https://www.imunify360.com/legal/eula>
"""
import asyncio
import base64
import logging
import os
import re
import shutil
from pathlib import Path
from typing import Callable, Iterable, List, Set, Tuple

from defence360agent.contracts.config import ANTIVIRUS_MODE, Malware
from defence360agent.subsys.panels.hosting_panel import HostingPanel
from defence360agent.utils import check_run
from imav.malwarelib.model import MalwareIgnorePath
from imav.malwarelib.scan.crontab import crontab_path

logger = logging.getLogger(__name__)

# location of admin provided watched and ignored paths
_ADMIN_PATH = Path("/etc/sysconfig/imunify360/malware-filters-admin-conf")
# location of internal configs, shipped with imunify360-firewall
_INTERNAL_PATH = Path("/var/imunify360/files/realtime-av-conf/v1")
# location of processed configs
_PROCESSED_PATH = _ADMIN_PATH / "processed"

_PD_NAME = "pd-combined.txt"
_INTERNAL_NAME = "av-internal.txt"
_ADMIN_NAME = "av-admin.txt"
_ADMIN_PATHS_NAME = "av-admin-paths.txt"
_IGNORED_SUB_DIR = "ignored"
_MAX_PATTERN_LENGTH = 64000

_SERVICE = "imunify-realtime-av"
_PD_PREPARE = "/usr/bin/i360-exclcomp"


class PatternLengthError(Exception):
    """Raised when pattern's length is too big."""

    pass


def _save_basedirs(dir: Path, basedirs: Set[str]) -> None:
    """Save list of basedirs in a file inside dir."""
    with (dir / "basedirs-list.txt").open("w") as f:
        for basedir in sorted(basedirs):
            f.write(os.path.realpath(basedir) + "\n")


def _split_paths(paths: List[str]) -> Tuple[List[str], List[str]]:
    """Split paths into two lists: absolute and relative.

    Relative paths start with +. This + sign is removed from resulting path."""
    absolute, relative = [], []
    for path in paths:
        if path.startswith("+"):
            relative.append(path[1:])
        else:
            absolute.append(path)
    return absolute, relative


def _read_list(path: Path) -> List[str]:
    """Read file at path and return its lines as a list.

    Empty lines or lines starting with '#' symbol are skipped. Lines are
    stripped of leading and trailing whitespace. If the file does not exist,
    empty list is returned."""
    try:
        with path.open() as f:
            lines = [line.strip() for line in f]
            return [x for x in lines if len(x) > 0 and not x.startswith("#")]
    except FileNotFoundError:
        return []


class _Watched(list):
    """Holds a list of watched glob patterns ready to be saved."""

    def __init__(self, w: List[str], basedirs: Set[str]) -> None:
        super().__init__()
        absolute, relative = _split_paths(w)
        self.extend(
            os.path.realpath(p)
            for p in absolute + self._extend_relative(relative, basedirs)
            if self._is_valid(p)
        )

    @staticmethod
    def _is_valid(pattern: str) -> bool:
        """Return True if watched pattern is valid."""
        if not pattern.startswith("/"):
            logger.warning(
                "skipping watched path %s: not starts with /", pattern
            )
            return False
        return True

    @staticmethod
    def _extend_relative(paths: List[str], basedirs: Set[str]) -> List[str]:
        """Join basedirs with all paths and return resulting list."""
        extended = []
        for path in paths:
            for basedir in basedirs:
                extended.append(os.path.join(basedir, path))
        return extended

    def save(self, path: Path) -> None:
        """Save watched list at specified path."""
        with path.open("w") as f:
            f.write("\n".join(self))


class _Ignored(str):
    """Holds a list of ignored regexp patterns ready to be saved."""

    @staticmethod
    def _is_valid_relative(pattern: str) -> bool:
        """Return True if relative ignored pattern is valid."""
        if pattern.startswith("^"):
            logger.warning(
                "skipping relative ignored path %s: starts with ^", pattern
            )
            return False
        return True

    @staticmethod
    def _remove_leading_slash(pattern: str) -> str:
        """Remove leading slash from pattern, if present."""
        if pattern.startswith("/"):
            return pattern[1:]
        return pattern

    @staticmethod
    def _compiles(pattern: str) -> bool:
        """Return True if pattern successfully compiles as regexp."""
        try:
            re.compile(pattern)
            return True
        except Exception:
            logger.warning(
                "skipping ignored pattern %s: invalid regex", pattern
            )
            return False

    @classmethod
    def from_patterns(
        cls, patterns: List[str], basedirs: Set[str]
    ) -> "_Ignored":
        """Build single ignored regexp from given patterns and basedirs."""
        absolute, relative = _split_paths(patterns)
        absolute = [p for p in absolute if cls._compiles(p)]
        relative = [
            cls._remove_leading_slash(p)
            for p in relative
            if cls._is_valid_relative(p) and cls._compiles(p)
        ]
        if len(basedirs) > 0 and len(relative) > 0:
            relative_pattern = "^(?:{})/(?:{})".format(
                "|".join(basedirs), "|".join(relative)
            )
            absolute.append(relative_pattern)
        pat = "|".join(absolute)
        if pat == "":
            pat = "^$"
        return _Ignored(pat)

    def save(self, path: Path):
        """Save ignored list at specified path."""
        if len(self) > _MAX_PATTERN_LENGTH:
            raise PatternLengthError(
                "{} pattern is too long ({})".format(path, len(self))
            )
        with path.open("w") as f:
            f.write(self)


def _read_configs(panel: str, name: str) -> Tuple[List[str], List[str]]:
    """Read internal and admin lists from files with given name."""
    common_dir = _INTERNAL_PATH / "common"
    internal = _read_list(common_dir / name)

    panel_path = _INTERNAL_PATH / panel.lower()
    if panel_path.exists():
        internal.extend(_read_list(panel_path / name))

    return internal, _read_list(_ADMIN_PATH / name)


class _WatchedCtx:
    def __init__(self, internal: _Watched, admin: _Watched) -> None:
        self.internal = internal
        self.admin = admin

    def save(self, dir: Path) -> None:
        w = dir / "watched"
        w.mkdir(exist_ok=True)
        self.internal.save(w / _INTERNAL_NAME)
        self.admin.save(w / _ADMIN_NAME)


def _watched_context(
    panel_name: str, basedirs: Set[str], *, extra: Iterable[str]
) -> _WatchedCtx:
    internal_watched, admin_watched = _read_configs(panel_name, "watched.txt")
    internal_watched.extend(extra)
    return _WatchedCtx(
        _Watched(internal_watched, basedirs), _Watched(admin_watched, basedirs)
    )


class _IgnoredCtx:
    def __init__(
        self, internal: _Ignored, admin: _Ignored, pd: _Ignored
    ) -> None:
        self.internal = internal
        self.admin = admin
        self.pd = pd

    def save(self, dir: Path) -> None:
        w = dir / _IGNORED_SUB_DIR
        w.mkdir(exist_ok=True)
        self.internal.save(w / _INTERNAL_NAME)
        self.admin.save(w / _ADMIN_NAME)
        self.pd.save(w / _PD_NAME)


def _ignored_context(panel_name: str, basedirs: Set[str]) -> _IgnoredCtx:
    internal_ignored, admin_ignored = _read_configs(panel_name, "ignored.txt")

    return _IgnoredCtx(
        _Ignored.from_patterns(internal_ignored, basedirs),
        _Ignored.from_patterns(admin_ignored, basedirs),
        _Ignored.from_patterns(internal_ignored + admin_ignored, basedirs),
    )


def _admin_ignored_paths(dir: Path) -> None:
    ignored_paths = MalwareIgnorePath.path_list()
    ignored_paths_base64 = b"".join(
        base64.b64encode(os.fsencode(path)) + b"\n" for path in ignored_paths
    )
    target = dir / _IGNORED_SUB_DIR / _ADMIN_PATHS_NAME
    target.write_bytes(ignored_paths_base64)


def _contain_changes(dir1: Path, dir2: Path) -> bool:
    """Compare content of two folders if files in this directory are the
    same return False."""
    for file in dir1.iterdir():
        if file.is_dir():
            if _contain_changes(file, dir2 / file.name):
                return True
        if not file.is_file():
            continue
        other = dir2 / file.name
        if not other.exists():
            return True
        if file.read_bytes() != other.read_bytes():
            return True
    return False


def _save_configs(dir: Path, savers: List[Callable[[Path], None]]) -> bool:
    """Save configs in directory dir using saves callable.

    Each function in savers will be called with single dir argument."""
    temp = dir.with_suffix(".tmp")
    if temp.exists():
        shutil.rmtree(str(temp))
    temp.mkdir()

    for save in savers:
        save(temp)

    if dir.exists():
        backup = dir.with_name(".backup")
        if backup.exists():
            shutil.rmtree(str(backup))
        dir.rename(backup)
        try:
            temp.rename(dir)
        except Exception:
            backup.rename(dir)
            raise
        return _contain_changes(dir, backup)
    else:
        temp.rename(dir)
        return True


def _update_pd_symlink() -> None:
    target = _PROCESSED_PATH / _IGNORED_SUB_DIR / _PD_NAME
    source = _ADMIN_PATH / _PD_NAME
    try:
        # source.exists() returns False for broken symlink.
        # so call lstat() and if it throws exception, source does not exist.
        _ = source.lstat()
    except FileNotFoundError:
        source.symlink_to(target)
    else:
        if not (
            source.is_symlink() and os.readlink(str(source)) == str(target)
        ):
            source.unlink()
            source.symlink_to(target)


def generate_configs() -> bool:
    """Generate new malware paths filters config."""
    panel = HostingPanel()
    basedirs = panel.basedirs()

    extra_watched = set()
    if Malware.CRONTABS_SCAN_ENABLED:
        extra_watched.add(str(crontab_path()))

    changed = _save_configs(
        _PROCESSED_PATH,
        [
            lambda dir: _save_basedirs(dir, {*basedirs, *extra_watched}),
            _watched_context(panel.NAME, basedirs, extra=extra_watched).save,
            _ignored_context(panel.NAME, basedirs).save,
            _admin_ignored_paths,
        ],
    )
    _update_pd_symlink()
    return changed


async def reload_services() -> None:  # pragma: no cover
    tasks = [
        check_run(["service", _SERVICE, "restart"]),
        check_run([_PD_PREPARE]),
    ]
    for t in tasks:
        try:
            await t
        except asyncio.CancelledError:
            raise
        except Exception as e:
            logger.warning("realtime_av.reload_services exception: %s", e)


def should_be_running() -> bool:
    return not ANTIVIRUS_MODE and Malware.INOTIFY_ENABLED