"""The Volume Shadow Snapshots (VSS) file system implementation."""

import pyvshadow

from dfvfs.lib import definitions
from dfvfs.lib import errors
from dfvfs.lib import vshadow_helper
from dfvfs.path import vshadow_path_spec
from dfvfs.resolver import resolver
from dfvfs.vfs import file_system
from dfvfs.vfs import vshadow_file_entry


class VShadowFileSystem(file_system.FileSystem):
    """File system that uses pyvshadow."""

    TYPE_INDICATOR = definitions.TYPE_INDICATOR_VSHADOW

    def __init__(self, resolver_context, path_spec):
        """Initializes a file system.

        Args:
          resolver_context (Context): resolver context.
          path_spec (PathSpec): a path specification.
        """
        super().__init__(resolver_context, path_spec)
        self._file_object = None
        self._vshadow_volume = None

    def _Close(self):
        """Closes the file system.

        Raises:
          OSError: if the close failed.
        """
        self._vshadow_volume.close()
        self._vshadow_volume = None
        self._file_object = None

    def _Open(self, mode="rb"):
        """Opens the file system object defined by path specification.

        Args:
          mode (Optional[str]): file access mode. The default is 'rb' which
              represents read-only binary.

        Raises:
          AccessError: if the access to open the file was denied.
          OSError: if the file system object could not be opened.
          PathSpecError: if the path specification is incorrect.
          ValueError: if the path specification is invalid.
        """
        if not self._path_spec.HasParent():
            raise errors.PathSpecError("Unsupported path specification without parent.")

        file_object = resolver.Resolver.OpenFileObject(
            self._path_spec.parent, resolver_context=self._resolver_context
        )

        vshadow_volume = pyvshadow.volume()
        vshadow_volume.open_file_object(file_object)

        self._file_object = file_object
        self._vshadow_volume = vshadow_volume

    def FileEntryExistsByPathSpec(self, path_spec):
        """Determines if a file entry for a path specification exists.

        Args:
          path_spec (PathSpec): path specification.

        Returns:
          bool: True if the file entry exists.
        """
        store_index = vshadow_helper.VShadowPathSpecGetStoreIndex(path_spec)

        # The virtual root file has no corresponding store index but
        # should have a location.
        if store_index is None:
            location = getattr(path_spec, "location", None)
            return location is not None and location == self.LOCATION_ROOT

        return 0 <= store_index < self._vshadow_volume.number_of_stores

    def GetFileEntryByPathSpec(self, path_spec):
        """Retrieves a file entry for a path specification.

        Args:
          path_spec (PathSpec): path specification.

        Returns:
          VShadowFileEntry: file entry or None if not available.
        """
        store_index = vshadow_helper.VShadowPathSpecGetStoreIndex(path_spec)

        # The virtual root file has no corresponding store index but
        # should have a location.
        if store_index is None:
            location = getattr(path_spec, "location", None)
            if location is None or location != self.LOCATION_ROOT:
                return None

            return vshadow_file_entry.VShadowFileEntry(
                self._resolver_context, self, path_spec, is_root=True, is_virtual=True
            )

        if store_index < 0 or store_index >= self._vshadow_volume.number_of_stores:
            return None

        return vshadow_file_entry.VShadowFileEntry(
            self._resolver_context, self, path_spec
        )

    def GetRootFileEntry(self):
        """Retrieves the root file entry.

        Returns:
          VShadowFileEntry: file entry or None if not available.
        """
        path_spec = vshadow_path_spec.VShadowPathSpec(
            location=self.LOCATION_ROOT, parent=self._path_spec.parent
        )
        return self.GetFileEntryByPathSpec(path_spec)

    def GetVShadowStoreByPathSpec(self, path_spec):
        """Retrieves a VSS store for a path specification.

        Args:
          path_spec (PathSpec): path specification.

        Returns:
          pyvshadow.store: a VSS store or None if not available.
        """
        store_index = vshadow_helper.VShadowPathSpecGetStoreIndex(path_spec)
        if store_index is None:
            return None

        return self._vshadow_volume.get_store(store_index)

    def GetVShadowVolume(self):
        """Retrieves a VSS volume.

        Returns:
          pyvshadow.volume: a VSS volume.
        """
        return self._vshadow_volume
