"""The GUID Partition Table (GPT) file-like object implementation."""

import os

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


class GPTFile(file_io.FileIO):
    """File input/output (IO) object using pyvsgpt."""

    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 = None
        self._file_object = None
        self._file_system = None
        self._partition_offset = None
        self._partition_size = None
        self._vsgpt_partition = None

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

        self._vsgpt_partition = None

        self._file_object = 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.
        """
        file_system = resolver.Resolver.OpenFileSystem(
            self._path_spec, resolver_context=self._resolver_context
        )
        entry_index = file_system.GetEntryIndexByPathSpec(self._path_spec)
        if entry_index is None:
            raise errors.PathSpecError(
                "Unable to retrieve entry index from path specification."
            )

        vsgpt_volume = file_system.GetGPTVolume()

        if not vsgpt_volume.has_partition_with_identifier(entry_index):
            raise errors.PathSpecError(
                f"Missing GPT partition with entry index: {entry_index:d}"
            )

        self._file_system = file_system
        self._vsgpt_partition = vsgpt_volume.get_partition_by_identifier(entry_index)

        # Note that using pass-through IO in Python is faster than using
        # the vsgpt_partition read and seek methods.
        self._file_object = resolver.Resolver.OpenFileObject(
            self._path_spec.parent, resolver_context=self._resolver_context
        )
        self._current_offset = 0
        self._partition_offset = self._vsgpt_partition.get_volume_offset()
        self._partition_size = self._vsgpt_partition.get_size()

    # 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._partition_offset < 0 or self._partition_size < 0:
            raise OSError("Invalid partition 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._partition_size:
            return b""

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

        self._file_object.seek(
            self._partition_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._partition_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 partition.

        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 partition.

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

        return self._partition_size
