"""The Volume Shadow Snapshots (VSS) file-like object implementation."""

import os

from dfvfs.file_io import file_io
from dfvfs.lib import errors
from dfvfs.lib import vshadow_helper
from dfvfs.resolver import resolver


class VShadowFile(file_io.FileIO):
    """File input/output (IO) object using pyvshadow."""

    def __init__(self, resolver_context, path_spec):
        """Initializes a file input/output (IO) object.

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

    def _Close(self):
        """Closes the file-like object."""
        self._vshadow_store = None

        self._file_system = None

    def _Open(self):
        """Opens the file-like object defined by path specification.

        Raises:
          AccessError: if the access to open the file was denied.
          OSError: if the file-like object could not be opened.
          PathSpecError: if the path specification is incorrect.
        """
        store_index = vshadow_helper.VShadowPathSpecGetStoreIndex(self._path_spec)
        if store_index is None:
            raise errors.PathSpecError(
                "Unable to retrieve store index from path specification."
            )

        self._file_system = resolver.Resolver.OpenFileSystem(
            self._path_spec, resolver_context=self._resolver_context
        )
        vshadow_volume = self._file_system.GetVShadowVolume()

        if store_index < 0 or store_index >= vshadow_volume.number_of_stores:
            raise errors.PathSpecError(
                f"Unable to retrieve VSS store: {store_index:d} from path "
                f"specification."
            )

        vshadow_store = vshadow_volume.get_store(store_index)
        if not vshadow_store.has_in_volume_data():
            raise OSError(
                f"Unable to open VSS store: {store_index:d} without in-volume "
                f"stored data."
            )

        self._vshadow_store = vshadow_store

    # Note: that the following functions do not follow the style guide
    # because they are part of the file-like object interface.
    # pylint: disable=invalid-name

    def read(self, size=None):
        """Reads a byte string from the file-like object at the current offset.

        The function will read a byte string of the specified size or
        all of the remaining data if no size was specified.

        Args:
          size (Optional[int]): number of bytes to read, where None is all
              remaining data.

        Returns:
          bytes: data read.

        Raises:
          OSError: if the read failed.
        """
        if not self._is_open:
            raise OSError("Not opened.")

        return self._vshadow_store.read(size)

    def seek(self, offset, whence=os.SEEK_SET):
        """Seeks to an offset within the file-like object.

        Args:
          offset (int): offset to seek to.
          whence (Optional(int)): value that indicates whether offset is an absolute
              or relative position within the file.

        Raises:
          OSError: if the seek failed.
        """
        if not self._is_open:
            raise OSError("Not opened.")

        self._vshadow_store.seek(offset, whence)

    def get_offset(self):
        """Retrieves the current offset into the file-like object.

        Returns:
          int: current offset into the file-like object.

        Raises:
          OSError: if the file-like object has not been opened.
        """
        if not self._is_open:
            raise OSError("Not opened.")

        return self._vshadow_store.get_offset()

    def get_size(self):
        """Retrieves the size of the file-like object.

        Returns:
          int: size of the file-like object data.

        Raises:
          OSError: if the file-like object has not been opened.
        """
        if not self._is_open:
            raise OSError("Not opened.")

        return self._vshadow_store.volume_size
