"""The EXT attribute implementation."""

import os

from dfvfs.lib import definitions
from dfvfs.lib import errors
from dfvfs.vfs import attribute
from dfvfs.vfs import extent


class EXTExtendedAttribute(attribute.Attribute):
    """EXT extended attribute that uses pyfsext."""

    def __init__(self, fsext_extended_attribute):
        """Initializes an attribute.

        Args:
          fsext_extended_attribute (pyfsext.extended_attribute): EXT extended
              attribute.

        Raises:
          BackEndError: if the pyfsext extended attribute is missing.
        """
        if not fsext_extended_attribute:
            raise errors.BackEndError("Missing pyfsext extended attribute.")

        super().__init__()
        self._fsext_extended_attribute = fsext_extended_attribute

    @property
    def name(self):
        """str: name."""
        return self._fsext_extended_attribute.name

    def GetExtents(self):
        """Retrieves the extents.

        Returns:
          list[Extent]: the extents of the attribute data.
        """
        extents = []
        for extent_index in range(self._fsext_extended_attribute.number_of_extents):
            extent_offset, extent_size, extent_flags = (
                self._fsext_extended_attribute.get_extent(extent_index)
            )

            if extent_flags & 0x1:
                extent_type = definitions.EXTENT_TYPE_SPARSE
            else:
                extent_type = definitions.EXTENT_TYPE_DATA

            data_stream_extent = extent.Extent(
                extent_type=extent_type, offset=extent_offset, size=extent_size
            )
            extents.append(data_stream_extent)

        return extents

    # 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 input/output (IO) object.

        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.
        """
        return self._fsext_extended_attribute.read_buffer(size)

    def seek(self, offset, whence=os.SEEK_SET):
        """Seeks to an offset within the file input/output (IO) object.

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

        Raises:
          OSError: if the seek failed.
        """
        self._fsext_extended_attribute.seek_offset(offset, whence)

    # get_offset() is preferred above tell() by the libbfio layer used in libyal.
    def get_offset(self):
        """Retrieves the current offset into the file input/output (IO) object.

        Returns:
          int: current offset into the file input/output (IO) object.
        """
        return self._fsext_extended_attribute.get_offset()

    # Pythonesque alias for get_offset().
    def tell(self):
        """Retrieves the current offset into the file input/output (IO) object."""
        return self.get_offset()

    def get_size(self):
        """Retrieves the size of the file input/output (IO) object.

        Returns:
          int: size of the file input/output (IO) object.
        """
        return self._fsext_extended_attribute.get_size()

    def seekable(self):
        """Determines if a file input/output (IO) object is seekable.

        Returns:
          bool: True since a file IO object provides a seek method.
        """
        return True
