"""The FAT file system implementation."""

import pyfsfat

from dfvfs.lib import definitions
from dfvfs.lib import errors
from dfvfs.path import fat_path_spec
from dfvfs.resolver import resolver
from dfvfs.vfs import fat_file_entry
from dfvfs.vfs import file_system


class FATFileSystem(file_system.FileSystem):
    """File system that uses pyfsfat."""

    TYPE_INDICATOR = definitions.TYPE_INDICATOR_FAT

    LOCATION_ROOT = "\\"
    PATH_SEPARATOR = "\\"

    def __init__(self, resolver_context, path_spec):
        """Initializes an FAT 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._fsfat_volume = None
        self._root_directory_identifier = None

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

        Raises:
          OSError: if the close failed.
        """
        self._fsfat_volume = None
        self._file_object = None

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

        Args:
          mode (Optional[str]): file access mode.

        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
        )

        fsfat_volume = pyfsfat.volume()
        fsfat_volume.open_file_object(file_object)
        fsfat_root_directory = fsfat_volume.get_root_directory()

        self._file_object = file_object
        self._fsfat_volume = fsfat_volume
        self._root_directory_identifier = fsfat_root_directory.identifier

    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.

        Raises:
          BackEndError: if the file entry cannot be opened.
        """
        # Opening a file by identifier is faster than opening a file by location,
        # but does not preserve the VFAT long file name.
        fsfat_file_entry = None
        location = getattr(path_spec, "location", None)
        identifier = getattr(path_spec, "identifier", None)

        try:
            if location is not None:
                fsfat_file_entry = self._fsfat_volume.get_file_entry_by_path(location)
            elif identifier is not None:
                fsfat_file_entry = self._fsfat_volume.get_file_entry_by_identifier(
                    identifier
                )

        except OSError as exception:
            raise errors.BackEndError(exception)

        return fsfat_file_entry is not None

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

        Args:
          path_spec (PathSpec): path specification.

        Returns:
          FATFileEntry: file entry or None if not available.

        Raises:
          BackEndError: if the file entry cannot be opened.
        """
        # Opening a file by identifier is faster than opening a file by location,
        # but does not preserve the VFAT long file name.
        fsfat_file_entry = None
        location = getattr(path_spec, "location", None)
        identifier = getattr(path_spec, "identifier", None)

        if (
            location == self.LOCATION_ROOT
            or identifier == self._root_directory_identifier
        ):
            fsfat_file_entry = self._fsfat_volume.get_root_directory()
            return fat_file_entry.FATFileEntry(
                self._resolver_context,
                self,
                path_spec,
                fsfat_file_entry=fsfat_file_entry,
                is_root=True,
            )

        try:
            if location is not None:
                fsfat_file_entry = self._fsfat_volume.get_file_entry_by_path(location)
            elif identifier is not None:
                fsfat_file_entry = self._fsfat_volume.get_file_entry_by_identifier(
                    identifier
                )

        except OSError as exception:
            raise errors.BackEndError(exception)

        if fsfat_file_entry is None:
            return None

        return fat_file_entry.FATFileEntry(
            self._resolver_context, self, path_spec, fsfat_file_entry=fsfat_file_entry
        )

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

        Args:
          path_spec (PathSpec): a path specification.

        Returns:
          pyfsfat.file_entry: file entry.

        Raises:
          PathSpecError: if the path specification is missing location and
              identifier.
        """
        # Opening a file by identifier is faster than opening a file by location,
        # but does not preserve the VFAT long file name.
        location = getattr(path_spec, "location", None)
        identifier = getattr(path_spec, "identifier", None)

        if location is not None:
            fsfat_file_entry = self._fsfat_volume.get_file_entry_by_path(location)
        elif identifier is not None:
            fsfat_file_entry = self._fsfat_volume.get_file_entry_by_identifier(
                identifier
            )
        else:
            raise errors.PathSpecError(
                "Path specification missing location and identifier."
            )

        return fsfat_file_entry

    def GetFATVolume(self):
        """Retrieves the FAT volume.

        Returns:
          pyfsfat.volume: a FAT volume.
        """
        return self._fsfat_volume

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

        Returns:
          FATFileEntry: file entry.
        """
        path_spec = fat_path_spec.FATPathSpec(
            location=self.LOCATION_ROOT,
            identifier=self._root_directory_identifier,
            parent=self._path_spec.parent,
        )
        return self.GetFileEntryByPathSpec(path_spec)
