"""Compat module to handle files security on Windows and Linux"""
from __future__ import absolute_import

from contextlib import contextmanager
import errno
import os  # pylint: disable=os-module-forbidden
import stat
from typing import Any
from typing import Dict
from typing import Generator
from typing import Optional

try:
    import ntsecuritycon
    import pywintypes
    import win32api
    import win32con
    import win32file
    import win32security
    import winerror
except ImportError:
    POSIX_MODE = True
else:
    POSIX_MODE = False


# Windows umask implementation, since Windows does not have a concept of umask by default.
# We choose 022 as initial value since it is the default one on most Linux distributions, and
# it is a decent choice to not have write permissions for group owner and everybody by default.
# We use a class here to avoid needing to define a global variable, and the potential mistakes
# that could happen with this kind of pattern.
class _WindowsUmask:
    """Store the current umask to apply on Windows"""
    def __init__(self) -> None:
        self.mask = 0o022


_WINDOWS_UMASK = _WindowsUmask()


def chmod(file_path: str, mode: int) -> None:
    """
    Apply a POSIX mode on given file_path:

      - for Linux, the POSIX mode will be directly applied using chmod,
      - for Windows, the POSIX mode will be translated into a Windows DACL that make sense for
        Certbot context, and applied to the file using kernel calls.

    The definition of the Windows DACL that correspond to a POSIX mode, in the context of Certbot,
    is explained at https://github.com/certbot/certbot/issues/6356 and is implemented by the
    method `_generate_windows_flags()`.

    :param str file_path: Path of the file
    :param int mode: POSIX mode to apply
    """
    if POSIX_MODE:
        os.chmod(file_path, mode)
    else:
        _apply_win_mode(file_path, mode)


def umask(mask: int) -> int:
    """
    Set the current numeric umask and return the previous umask. On Linux, the built-in umask
    method is used. On Windows, our Certbot-side implementation is used.

    :param int mask: The user file-creation mode mask to apply.
    :rtype: int
    :return: The previous umask value.
    """
    if POSIX_MODE:
        return os.umask(mask)

    previous_umask = _WINDOWS_UMASK.mask
    _WINDOWS_UMASK.mask = mask
    return previous_umask


@contextmanager
def temp_umask(mask: int) -> Generator[None, None, None]:
    """
    Apply a umask temporarily, meant to be used in a `with` block. Uses the Certbot
    implementation of umask.

    :param int mask: The user file-creation mode mask to apply temporarily
    """
    old_umask: Optional[int] = None
    try:
        old_umask = umask(mask)
        yield None
    finally:
        if old_umask is not None:
            umask(old_umask)


# One could ask why there is no copy_ownership() function, or even a reimplementation
# of os.chown() that would modify the ownership of file without touching the mode itself.
# This is because on Windows, it would require recalculating the existing DACL against
# the new owner, since the DACL is composed of ACEs that targets a specific user, not dynamically
# the current owner of a file. This action would be necessary to keep consistency between
# the POSIX mode applied to the file and the current owner of this file.
# Since copying and editing arbitrary DACL is very difficult, and since we actually know
# the mode to apply at the time the owner of a file should change, it is easier to just
# change the owner, then reapply the known mode, as copy_ownership_and_apply_mode() does.
def copy_ownership_and_apply_mode(src: str, dst: str, mode: int,
                                  copy_user: bool, copy_group: bool) -> None:
    """
    Copy ownership (user and optionally group on Linux) from the source to the
    destination, then apply given mode in compatible way for Linux and Windows.
    This replaces the os.chown command.

    :param str src: Path of the source file
    :param str dst: Path of the destination file
    :param int mode: Permission mode to apply on the destination file
    :param bool copy_user: Copy user if `True`
    :param bool copy_group: Copy group if `True` on Linux (has no effect on Windows)
    """
    if POSIX_MODE:
        stats = os.stat(src)
        user_id = stats.st_uid if copy_user else -1
        group_id = stats.st_gid if copy_group else -1
        # On Windows, os.chown does not exist. This is checked through POSIX_MODE value,
        # but MyPy/PyLint does not know it and raises an error here on Windows.
        # We disable specifically the check to fix the issue.
        os.chown(dst, user_id, group_id)
    elif copy_user:
        # There is no group handling in Windows
        _copy_win_ownership(src, dst)

    chmod(dst, mode)


# Quite similar to copy_ownership_and_apply_mode, but this time the DACL is copied from
# the source file on Windows. The DACL stays consistent with the dynamic rights of the
# equivalent POSIX mode, because ownership and mode are copied altogether on the destination
# file, so no recomputing of the DACL against the new owner is needed, as it would be
# for a copy_ownership alone method.
def copy_ownership_and_mode(src: str, dst: str,
                            copy_user: bool = True, copy_group: bool = True) -> None:
    """
    Copy ownership (user and optionally group on Linux) and mode/DACL
    from the source to the destination.

    :param str src: Path of the source file
    :param str dst: Path of the destination file
    :param bool copy_user: Copy user if `True`
    :param bool copy_group: Copy group if `True` on Linux (has no effect on Windows)
    """
    if POSIX_MODE:
        # On Linux, we just delegate to chown and chmod.
        stats = os.stat(src)
        user_id = stats.st_uid if copy_user else -1
        group_id = stats.st_gid if copy_group else -1
        os.chown(dst, user_id, group_id)
        chmod(dst, stats.st_mode)
    else:
        if copy_user:
            # There is no group handling in Windows
            _copy_win_ownership(src, dst)
        _copy_win_mode(src, dst)


def check_mode(file_path: str, mode: int) -> bool:
    """
    Check if the given mode matches the permissions of the given file.
    On Linux, will make a direct comparison, on Windows, mode will be compared against
    the security model.

    :param str file_path: Path of the file
    :param int mode: POSIX mode to test
    :rtype: bool
    :return: True if the POSIX mode matches the file permissions
    """
    if POSIX_MODE:
        return stat.S_IMODE(os.stat(file_path).st_mode) == mode

    return _check_win_mode(file_path, mode)


def check_owner(file_path: str) -> bool:
    """
    Check if given file is owned by current user.

    :param str file_path: File path to check
    :rtype: bool
    :return: True if given file is owned by current user, False otherwise.
    """
    if POSIX_MODE:
        return os.stat(file_path).st_uid == os.getuid()

    # Get owner sid of the file
    security = win32security.GetFileSecurity(file_path, win32security.OWNER_SECURITY_INFORMATION)
    user = security.GetSecurityDescriptorOwner()

    # Compare sids
    return _get_current_user() == user


def check_permissions(file_path: str, mode: int) -> bool:
    """
    Check if given file has the given mode and is owned by current user.

    :param str file_path: File path to check
    :param int mode: POSIX mode to check
    :rtype: bool
    :return: True if file has correct mode and owner, False otherwise.
    """
    return check_owner(file_path) and check_mode(file_path, mode)


def open(file_path: str, flags: int, mode: int = 0o777) -> int:  # pylint: disable=redefined-builtin
    """
    Wrapper of original os.open function, that will ensure on Windows that given mode
    is correctly applied.

    :param str file_path: The file path to open
    :param int flags: Flags to apply on file while opened
    :param int mode: POSIX mode to apply on file when opened,
        Python defaults will be applied if ``None``
    :returns: the file descriptor to the opened file
    :rtype: int
    :raise: OSError(errno.EEXIST) if the file already exists and os.O_CREAT & os.O_EXCL are set,
            OSError(errno.EACCES) on Windows if the file already exists and is a directory, and
            os.O_CREAT is set.
    """
    if POSIX_MODE:
        # On Linux, invoke os.open directly.
        return os.open(file_path, flags, mode)

    # Windows: handle creation of the file atomically with proper permissions.
    if flags & os.O_CREAT:
        # If os.O_EXCL is set, we will use the "CREATE_NEW", that will raise an exception if
        # file exists, matching the API contract of this bit flag. Otherwise, we use
        # "CREATE_ALWAYS" that will always create the file whether it exists or not.
        disposition = win32con.CREATE_NEW if flags & os.O_EXCL else win32con.CREATE_ALWAYS

        attributes = win32security.SECURITY_ATTRIBUTES()
        security = attributes.SECURITY_DESCRIPTOR
        user = _get_current_user()
        dacl = _generate_dacl(user, mode, _WINDOWS_UMASK.mask)
        # We set second parameter to 0 (`False`) to say that this security descriptor is
        # NOT constructed from a default mechanism, but is explicitly set by the user.
        # See https://docs.microsoft.com/en-us/windows/desktop/api/securitybaseapi/nf-securitybaseapi-setsecuritydescriptorowner  # pylint: disable=line-too-long
        security.SetSecurityDescriptorOwner(user, 0)
        # We set first parameter to 1 (`True`) to say that this security descriptor contains
        # a DACL. Otherwise second and third parameters are ignored.
        # We set third parameter to 0 (`False`) to say that this security descriptor is
        # NOT constructed from a default mechanism, but is explicitly set by the user.
        # See https://docs.microsoft.com/en-us/windows/desktop/api/securitybaseapi/nf-securitybaseapi-setsecuritydescriptordacl  # pylint: disable=line-too-long
        security.SetSecurityDescriptorDacl(1, dacl, 0)

        handle = None
        try:
            handle = win32file.CreateFile(file_path, win32file.GENERIC_READ,
                                          win32file.FILE_SHARE_READ & win32file.FILE_SHARE_WRITE,
                                          attributes, disposition, 0, None)
        except pywintypes.error as err:
            # Handle native windows errors into python errors to be consistent with the API
            # of os.open in the situation of a file already existing or locked.
            if err.winerror == winerror.ERROR_FILE_EXISTS:
                raise OSError(errno.EEXIST, err.strerror)
            if err.winerror == winerror.ERROR_SHARING_VIOLATION:
                raise OSError(errno.EACCES, err.strerror)
            raise err
        finally:
            if handle:
                handle.Close()

        # At this point, the file that did not exist has been created with proper permissions,
        # so os.O_CREAT and os.O_EXCL are not needed anymore. We remove them from the flags to
        # avoid a FileExists exception before calling os.open.
        return os.open(file_path, flags ^ os.O_CREAT ^ os.O_EXCL)

    # Windows: general case, we call os.open, let exceptions be thrown, then chmod if all is fine.
    fd = os.open(file_path, flags)
    chmod(file_path, mode)
    return fd


def makedirs(file_path: str, mode: int = 0o777) -> None:
    """
    Rewrite of original os.makedirs function, that will ensure on Windows that given mode
    is correctly applied.

    :param str file_path: The file path to open
    :param int mode: POSIX mode to apply on leaf directory when created, Python defaults
                     will be applied if ``None``
    """
    current_umask = umask(0)
    try:
        # Since Python 3.7, os.makedirs does not set the given mode to the intermediate
        # directories that could be created in the process. To keep things safe and consistent
        # on all Python versions, we set the umask accordingly to have all directories
        # (intermediate and leaf) created with the given mode.
        umask(current_umask | 0o777 ^ mode)

        if POSIX_MODE:
            return os.makedirs(file_path, mode)

        orig_mkdir_fn = os.mkdir
        try:
            # As we know that os.mkdir is called internally by os.makedirs, we will swap the
            # function in os module for the time of makedirs execution on Windows.
            os.mkdir = mkdir  # type: ignore
            return os.makedirs(file_path, mode)
        finally:
            os.mkdir = orig_mkdir_fn
    finally:
        umask(current_umask)


def mkdir(file_path: str, mode: int = 0o777) -> None:
    """
    Rewrite of original os.mkdir function, that will ensure on Windows that given mode
    is correctly applied.

    :param str file_path: The file path to open
    :param int mode: POSIX mode to apply on directory when created, Python defaults
                     will be applied if ``None``
    """
    if POSIX_MODE:
        return os.mkdir(file_path, mode)

    attributes = win32security.SECURITY_ATTRIBUTES()
    security = attributes.SECURITY_DESCRIPTOR
    user = _get_current_user()
    dacl = _generate_dacl(user, mode, _WINDOWS_UMASK.mask)
    security.SetSecurityDescriptorOwner(user, False)
    security.SetSecurityDescriptorDacl(1, dacl, 0)

    try:
        win32file.CreateDirectory(file_path, attributes)
    except pywintypes.error as err:
        # Handle native windows error into python error to be consistent with the API
        # of os.mkdir in the situation of a directory already existing.
        if err.winerror == winerror.ERROR_ALREADY_EXISTS:
            raise OSError(errno.EEXIST, err.strerror, file_path, err.winerror)
        raise err

    return None


def replace(src: str, dst: str) -> None:
    """
    Rename a file to a destination path and handles situations where the destination exists.

    :param str src: The current file path.
    :param str dst: The new file path.
    """
    if hasattr(os, 'replace'):
        # Use replace if possible. Since we don't support Python 2 on Windows
        # and os.replace() was added in Python 3.3, we can assume that
        # os.replace() is always available on Windows.
        getattr(os, 'replace')(src, dst)
    else:
        # Otherwise, use os.rename() that behaves like os.replace() on Linux.
        os.rename(src, dst)


def realpath(file_path: str) -> str:
    """
    Find the real path for the given path. This method resolves symlinks, including
    recursive symlinks, and is protected against symlinks that creates an infinite loop.

    :param str file_path: The path to resolve
    :returns: The real path for the given path
    :rtype: str
    """
    original_path = file_path

    # os.path.realpath also resolves symlinks
    path = os.path.realpath(file_path)
    if os.path.islink(path):
        # If path returned by realpath is still a link, it means that it failed to
        # resolve the symlink because of a loop.
        # See realpath code: https://github.com/python/cpython/blob/master/Lib/posixpath.py
        raise RuntimeError('Error, link {0} is a loop!'.format(original_path))
    return path


def readlink(link_path: str) -> str:
    """
    Return a string representing the path to which the symbolic link points.

    :param str link_path: The symlink path to resolve
    :return: The path the symlink points to
    :returns: str
    :raise: ValueError if a long path (260> characters) is encountered on Windows
    """
    path = os.readlink(link_path)

    if POSIX_MODE:
        return path

    # At this point, we know we are on Windows and that the path returned uses
    # the extended form which begins with the prefix \\?\

    # Max length of a normal path is 260 characters on Windows, including the non printable
    # termination character "<NUL>". The termination character is not included in Python
    # strings, giving a max length of 259 characters, + 4 characters for the extended form
    # prefix, to an effective max length 263 characters on a string representing a normal path.
    if len(path) < 264:
        return path[4:]

    raise ValueError("Long paths are not supported by Certbot on Windows.")


# On Windows is_executable run from an unprivileged shell may claim that a path is
# executable when it is executable only if run from a privileged shell. This result
# is due to the fact that GetEffectiveRightsFromAcl calculate effective rights
# without taking into consideration if the target user has currently required the
# elevated privileges or not. However this is not a problem since certbot always
# requires to be run under a privileged shell, so the user will always benefit
# from the highest (privileged one) set of permissions on a given file.
def is_executable(path: str) -> bool:
    """
    Is path an executable file?

    :param str path: path to test
    :return: True if path is an executable file
    :rtype: bool
    """
    if POSIX_MODE:
        return os.path.isfile(path) and os.access(path, os.X_OK)

    return _win_is_executable(path)


def has_world_permissions(path: str) -> bool:
    """
    Check if everybody/world has any right (read/write/execute) on a file given its path.

    :param str path: path to test
    :return: True if everybody/world has any right to the file
    :rtype: bool
    """
    if POSIX_MODE:
        return bool(stat.S_IMODE(os.stat(path).st_mode) & stat.S_IRWXO)

    security = win32security.GetFileSecurity(path, win32security.DACL_SECURITY_INFORMATION)
    dacl = security.GetSecurityDescriptorDacl()

    return bool(dacl.GetEffectiveRightsFromAcl({
        'TrusteeForm': win32security.TRUSTEE_IS_SID,
        'TrusteeType': win32security.TRUSTEE_IS_USER,
        'Identifier': win32security.ConvertStringSidToSid('S-1-1-0'),
    }))


def compute_private_key_mode(old_key: str, base_mode: int) -> int:
    """
    Calculate the POSIX mode to apply to a private key given the previous private key.

    :param str old_key: path to the previous private key
    :param int base_mode: the minimum modes to apply to a private key
    :return: the POSIX mode to apply
    :rtype: int
    """
    if POSIX_MODE:
        # On Linux, we keep read/write/execute permissions
        # for group and read permissions for everybody.
        old_mode = (stat.S_IMODE(os.stat(old_key).st_mode) &
                    (stat.S_IRGRP | stat.S_IWGRP | stat.S_IXGRP | stat.S_IROTH))
        return base_mode | old_mode

    # On Windows, the mode returned by os.stat is not reliable,
    # so we do not keep any permission from the previous private key.
    return base_mode


def has_same_ownership(path1: str, path2: str) -> bool:
    """
    Return True if the ownership of two files given their respective path is the same.
    On Windows, ownership is checked against owner only, since files do not have a group owner.

    :param str path1: path to the first file
    :param str path2: path to the second file
    :return: True if both files have the same ownership, False otherwise
    :rtype: bool

    """
    if POSIX_MODE:
        stats1 = os.stat(path1)
        stats2 = os.stat(path2)
        return (stats1.st_uid, stats1.st_gid) == (stats2.st_uid, stats2.st_gid)

    security1 = win32security.GetFileSecurity(path1, win32security.OWNER_SECURITY_INFORMATION)
    user1 = security1.GetSecurityDescriptorOwner()

    security2 = win32security.GetFileSecurity(path2, win32security.OWNER_SECURITY_INFORMATION)
    user2 = security2.GetSecurityDescriptorOwner()

    return user1 == user2


def has_min_permissions(path: str, min_mode: int) -> bool:
    """
    Check if a file given its path has at least the permissions defined by the given minimal mode.
    On Windows, group permissions are ignored since files do not have a group owner.

    :param str path: path to the file to check
    :param int min_mode: the minimal permissions expected
    :return: True if the file matches the minimal permissions expectations, False otherwise
    :rtype: bool
    """
    if POSIX_MODE:
        st_mode = os.stat(path).st_mode
        return st_mode == st_mode | min_mode

    # Resolve symlinks, to get a consistent result with os.stat on Linux,
    # that follows symlinks by default.
    path = realpath(path)

    # Get owner sid of the file
    security = win32security.GetFileSecurity(
        path, win32security.OWNER_SECURITY_INFORMATION | win32security.DACL_SECURITY_INFORMATION)
    user = security.GetSecurityDescriptorOwner()
    dacl = security.GetSecurityDescriptorDacl()
    min_dacl = _generate_dacl(user, min_mode)

    for index in range(min_dacl.GetAceCount()):
        min_ace = min_dacl.GetAce(index)

        # On a given ACE, index 0 is the ACE type, 1 is the permission mask, and 2 is the SID.
        # See: http://timgolden.me.uk/pywin32-docs/PyACL__GetAce_meth.html
        mask = min_ace[1]
        user = min_ace[2]

        effective_mask = dacl.GetEffectiveRightsFromAcl({
            'TrusteeForm': win32security.TRUSTEE_IS_SID,
            'TrusteeType': win32security.TRUSTEE_IS_USER,
            'Identifier': user,
        })

        if effective_mask != effective_mask | mask:
            return False

    return True


def _win_is_executable(path: str) -> bool:
    if not os.path.isfile(path):
        return False

    security = win32security.GetFileSecurity(path, win32security.DACL_SECURITY_INFORMATION)
    dacl = security.GetSecurityDescriptorDacl()

    mode = dacl.GetEffectiveRightsFromAcl({
        'TrusteeForm': win32security.TRUSTEE_IS_SID,
        'TrusteeType': win32security.TRUSTEE_IS_USER,
        'Identifier': _get_current_user(),
    })

    return mode & ntsecuritycon.FILE_GENERIC_EXECUTE == ntsecuritycon.FILE_GENERIC_EXECUTE


def _apply_win_mode(file_path: str, mode: int) -> None:
    """
    This function converts the given POSIX mode into a Windows ACL list, and applies it to the
    file given its path. If the given path is a symbolic link, it will resolved to apply the
    mode on the targeted file.
    """
    file_path = realpath(file_path)
    # Get owner sid of the file
    security = win32security.GetFileSecurity(file_path, win32security.OWNER_SECURITY_INFORMATION)
    user = security.GetSecurityDescriptorOwner()

    # New DACL, that will overwrite existing one (including inherited permissions)
    dacl = _generate_dacl(user, mode)

    # Apply the new DACL
    security.SetSecurityDescriptorDacl(1, dacl, 0)
    win32security.SetFileSecurity(file_path, win32security.DACL_SECURITY_INFORMATION, security)


def _generate_dacl(user_sid: Any, mode: int, mask: Optional[int] = None) -> Any:
    if mask:
        mode = mode & (0o777 - mask)
    analysis = _analyze_mode(mode)

    # Get standard accounts from "well-known" sid
    # See the list here:
    # https://support.microsoft.com/en-us/help/243330/well-known-security-identifiers-in-windows-operating-systems
    system = win32security.ConvertStringSidToSid('S-1-5-18')
    admins = win32security.ConvertStringSidToSid('S-1-5-32-544')
    everyone = win32security.ConvertStringSidToSid('S-1-1-0')

    # New dacl, without inherited permissions
    dacl = win32security.ACL()

    # If user is already system or admins, any ACE defined here would be superseded by
    # the full control ACE that will be added after.
    if user_sid not in [system, admins]:
        # Handle user rights
        user_flags = _generate_windows_flags(analysis['user'])
        if user_flags:
            dacl.AddAccessAllowedAce(win32security.ACL_REVISION, user_flags, user_sid)

    # Handle everybody rights
    everybody_flags = _generate_windows_flags(analysis['all'])
    if everybody_flags:
        dacl.AddAccessAllowedAce(win32security.ACL_REVISION, everybody_flags, everyone)

    # Handle administrator rights
    full_permissions = _generate_windows_flags({'read': True, 'write': True, 'execute': True})
    dacl.AddAccessAllowedAce(win32security.ACL_REVISION, full_permissions, system)
    dacl.AddAccessAllowedAce(win32security.ACL_REVISION, full_permissions, admins)

    return dacl


def _analyze_mode(mode: int) -> Dict[str, Dict[str, int]]:
    return {
        'user': {
            'read': mode & stat.S_IRUSR,
            'write': mode & stat.S_IWUSR,
            'execute': mode & stat.S_IXUSR,
        },
        'all': {
            'read': mode & stat.S_IROTH,
            'write': mode & stat.S_IWOTH,
            'execute': mode & stat.S_IXOTH,
        },
    }


def _copy_win_ownership(src: str, dst: str) -> None:
    # Resolve symbolic links
    src = realpath(src)

    security_src = win32security.GetFileSecurity(src, win32security.OWNER_SECURITY_INFORMATION)
    user_src = security_src.GetSecurityDescriptorOwner()

    security_dst = win32security.GetFileSecurity(dst, win32security.OWNER_SECURITY_INFORMATION)
    # Second parameter indicates, if `False`, that the owner of the file is not provided by some
    # default mechanism, but is explicitly set instead. This is obviously what we are doing here.
    security_dst.SetSecurityDescriptorOwner(user_src, False)

    win32security.SetFileSecurity(dst, win32security.OWNER_SECURITY_INFORMATION, security_dst)


def _copy_win_mode(src: str, dst: str) -> None:
    # Resolve symbolic links
    src = realpath(src)

    # Copy the DACL from src to dst.
    security_src = win32security.GetFileSecurity(src, win32security.DACL_SECURITY_INFORMATION)
    dacl = security_src.GetSecurityDescriptorDacl()

    security_dst = win32security.GetFileSecurity(dst, win32security.DACL_SECURITY_INFORMATION)
    security_dst.SetSecurityDescriptorDacl(1, dacl, 0)
    win32security.SetFileSecurity(dst, win32security.DACL_SECURITY_INFORMATION, security_dst)


def _generate_windows_flags(rights_desc: Dict[str, int]) -> int:
    # Some notes about how each POSIX right is interpreted.
    #
    # For the rights read and execute, we have a pretty bijective relation between
    # POSIX flags and their generic counterparts on Windows, so we use them directly
    # (respectively ntsecuritycon.FILE_GENERIC_READ and ntsecuritycon.FILE_GENERIC_EXECUTE).
    #
    # But ntsecuritycon.FILE_GENERIC_WRITE does not correspond to what one could expect from a
    # write access on Linux: for Windows, FILE_GENERIC_WRITE does not include delete, move or
    # rename. This is something that requires ntsecuritycon.FILE_ALL_ACCESS.
    # So to reproduce the write right as POSIX, we will apply ntsecuritycon.FILE_ALL_ACCESS
    # subtracted of the rights corresponding to POSIX read and POSIX execute.
    #
    # Finally, having read + write + execute gives a ntsecuritycon.FILE_ALL_ACCESS,
    # so a "Full Control" on the file.
    #
    # A complete list of the rights defined on NTFS can be found here:
    # https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2003/cc783530(v=ws.10)#permissions-for-files-and-folders
    flag = 0
    if rights_desc['read']:
        flag = flag | ntsecuritycon.FILE_GENERIC_READ
    if rights_desc['write']:
        flag = flag | (ntsecuritycon.FILE_ALL_ACCESS
                       ^ ntsecuritycon.FILE_GENERIC_READ
                       ^ ntsecuritycon.FILE_GENERIC_EXECUTE)
    if rights_desc['execute']:
        flag = flag | ntsecuritycon.FILE_GENERIC_EXECUTE

    return flag


def _check_win_mode(file_path: str, mode: int) -> bool:
    # Resolve symbolic links
    file_path = realpath(file_path)
    # Get current dacl file
    security = win32security.GetFileSecurity(file_path, win32security.OWNER_SECURITY_INFORMATION
                                             | win32security.DACL_SECURITY_INFORMATION)
    dacl = security.GetSecurityDescriptorDacl()

    # Get current file owner sid
    user = security.GetSecurityDescriptorOwner()

    if not dacl:
        # No DACL means full control to everyone
        # This is not a deterministic permissions set.
        return False

    # Calculate the target dacl
    ref_dacl = _generate_dacl(user, mode)

    return _compare_dacls(dacl, ref_dacl)


def _compare_dacls(dacl1: Any, dacl2: Any) -> bool:
    """
    This method compare the two given DACLs to check if they are identical.
    Identical means here that they contains the same set of ACEs in the same order.
    """
    return ([dacl1.GetAce(index) for index in range(dacl1.GetAceCount())] ==
            [dacl2.GetAce(index) for index in range(dacl2.GetAceCount())])


def _get_current_user() -> Any:
    """
    Return the pySID corresponding to the current user.
    """
    # We craft the account_name ourselves instead of calling for instance win32api.GetUserNameEx,
    # because this function returns nonsense values when Certbot is run under NT AUTHORITY\SYSTEM.
    # To run Certbot under NT AUTHORITY\SYSTEM, you can open a shell using the instructions here:
    # https://blogs.technet.microsoft.com/ben_parker/2010/10/27/how-do-i-run-powershell-execommand-prompt-as-the-localsystem-account-on-windows-7/
    account_name = r"{0}\{1}".format(win32api.GetDomainName(), win32api.GetUserName())
    # LookupAccountName() expects the system name as first parameter. By passing None to it,
    # we instruct Windows to first search the matching account in the machine local accounts,
    # then into the primary domain accounts, if the machine has joined a domain, then finally
    # into the trusted domains accounts. This is the preferred lookup mechanism to use in Windows
    # if there is no reason to use a specific lookup mechanism.
    # See https://docs.microsoft.com/en-us/windows/desktop/api/winbase/nf-winbase-lookupaccountnamea
    return win32security.LookupAccountName(None, account_name)[0]
