"""The data range file-like object."""

import os

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


class DataRange(file_io.FileIO):
    """File input/output (IO) object that maps an in-file data range.

    The data range object allows to expose a single partition within a full disk image
    as a separate file-like object by mapping the data range (offset and size) of the
    volume on top of the full disk image.
    """

    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._current_offset = 0
        self._file_object = None
        self._range_offset = -1
        self._range_size = -1

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

        If the file-like object was passed in the init function the data range file-
        like object does not control the file-like object and should not actually close
        it.
        """
        self._file_object = None
        self._range_offset = -1
        self._range_size = -1

    def _Open(self):
        """Opens the file-like object.

        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 not self._path_spec.HasParent():
            raise errors.PathSpecError("Unsupported path specification without parent.")

        range_offset = getattr(self._path_spec, "range_offset", None)
        range_size = getattr(self._path_spec, "range_size", None)

        if range_offset is None or range_size is None:
            raise errors.PathSpecError(
                "Path specification missing range offset and range size."
            )

        self._SetRange(range_offset, range_size)
        self._file_object = resolver.Resolver.OpenFileObject(
            self._path_spec.parent, resolver_context=self._resolver_context
        )

    def _SetRange(self, range_offset, range_size):
        """Sets the data range (offset and size).

        The data range is used to map a range of data within one file
        (e.g. a single partition within a full disk image) as a file-like object.

        Args:
          range_offset (int): start offset of the data range.
          range_size (int): size of the data range.

        Raises:
          ValueError: if the range offset or range size is invalid.
        """
        if range_offset < 0:
            raise ValueError(
                f"Invalid range offset: {range_offset:d} value out of bounds."
            )

        if range_size < 0:
            raise ValueError(f"Invalid range size: {range_size:d} value out of bounds.")

        self._range_offset = range_offset
        self._range_size = range_size
        self._current_offset = 0

    # 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._range_offset < 0 or self._range_size < 0:
            raise OSError("Invalid data range.")

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

        if self._current_offset >= self._range_size:
            return b""

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

        self._file_object.seek(self._range_offset + self._current_offset, os.SEEK_SET)

        data = self._file_object.read(size)

        self._current_offset += len(data)

        return data

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

        if whence == os.SEEK_CUR:
            offset += self._current_offset
        elif whence == os.SEEK_END:
            offset += self._range_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 in the data range.

        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 data range.

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

        return self._range_size
