"""The Extended File System (EXT) file-like object implementation."""

import os

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


class EXTFile(file_io.FileIO):
    """File input/output (IO) object using pyfsext.file_entry."""

    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._fsext_file_entry = None

    def _Close(self):
        """Closes the file-like object."""
        self._fsext_file_entry = 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.
          NotSupported: if a data stream, like the resource or named fork, is
              requested to be opened.
          OSError: if the file-like object could not be opened.
          PathSpecError: if the path specification is incorrect.
        """
        data_stream = getattr(self._path_spec, "data_stream", None)
        if data_stream:
            raise errors.NotSupported(
                f"Open data stream: {data_stream:s} not supported."
            )

        self._file_system = resolver.Resolver.OpenFileSystem(
            self._path_spec, resolver_context=self._resolver_context
        )
        file_entry = self._file_system.GetFileEntryByPathSpec(self._path_spec)
        if not file_entry:
            raise OSError("Unable to open file entry.")

        fsext_file_entry = file_entry.GetEXTFileEntry()
        if not fsext_file_entry:
            raise OSError("Unable to open EXT file entry.")

        self._fsext_file_entry = fsext_file_entry

    # 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._fsext_file_entry.read(size=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._fsext_file_entry.seek(offset, whence)

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

        Return:
          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._fsext_file_entry.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._fsext_file_entry.get_size()
