"""The fake file-like object implementation."""

import os

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


class FakeFile(file_io.FileIO):
    """Fake file input/output (IO) object."""

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

        Args:
          resolver_context (Context): resolver context.
          path_spec (PathSpec): a path specification.
          file_data (bytes): fake file data.
        """
        super().__init__(resolver_context, path_spec)
        self._current_offset = 0
        self._file_data = file_data
        self._size = 0

    def _Close(self):
        """Closes the file-like object."""
        return

    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.
        """
        if self._path_spec.HasParent():
            raise errors.PathSpecError("Unsupported path specification with parent.")

        location = getattr(self._path_spec, "location", None)
        if location is None:
            raise errors.PathSpecError("Path specification missing location.")

        self._current_offset = 0
        self._size = len(self._file_data)

    # 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.")

        if self._current_offset < 0:
            raise OSError(
                f"Invalid current offset: {self._current_offset:d} value less than "
                f"zero."
            )

        if self._file_data is None or self._current_offset >= self._size:
            return b""

        if size is None:
            size = self._size
        if self._current_offset + size > self._size:
            size = self._size - self._current_offset

        start_offset = self._current_offset
        self._current_offset += size
        return self._file_data[start_offset : self._current_offset]

    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.")

        if whence == os.SEEK_CUR:
            offset += self._current_offset
        elif whence == os.SEEK_END:
            offset += self._size
        elif whence != os.SEEK_SET:
            raise OSError("Unsupported whence.")

        if offset < 0:
            raise OSError("Invalid offset value less than zero.")

        self._current_offset = offset

    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._current_offset

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

        Returns:
          int: size of the file data.

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

        return self._size
