"""The SleuthKit (TSK) file-like object implementation."""

import os

import pytsk3

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


class TSKFile(file_io.FileIO):
    """File input/output (IO) object using pytsk3."""

    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_system = None
        self._size = 0
        self._tsk_attribute = None
        self._tsk_file = None

    def _Close(self):
        """Closes the file-like object."""
        self._tsk_attribute = None
        self._tsk_file = 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.
          BackEndError: if pytsk3 returns a non UTF-8 formatted name.
          OSError: if the file-like object could not be opened.
          PathSpecError: if the path specification is incorrect.
        """
        data_stream_name = getattr(self._path_spec, "data_stream", None)

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

        tsk_file = file_entry.GetTSKFile()
        tsk_attribute = None

        # Note that because pytsk3.File does not explicitly defines info
        # we need to check if the attribute exists and has a value other
        # than None.
        if getattr(tsk_file, "info", None) is None:
            raise OSError("Missing attribute info in file (pytsk3.File).")

        # Note that because pytsk3.TSK_FS_FILE does not explicitly defines meta
        # we need to check if the attribute exists and has a value other
        # than None.
        if getattr(tsk_file.info, "meta", None) is None:
            raise OSError("Missing attribute meta in file.info pytsk3.TSK_FS_FILE).")

        # Note that because pytsk3.TSK_FS_META does not explicitly defines size
        # we need to check if the attribute exists.
        if not hasattr(tsk_file.info.meta, "size"):
            raise OSError(
                "Missing attribute size in file.info.meta (pytsk3.TSK_FS_META)."
            )

        # Note that because pytsk3.TSK_FS_META does not explicitly defines type
        # we need to check if the attribute exists.
        if not hasattr(tsk_file.info.meta, "type"):
            raise OSError(
                "Missing attribute type in file.info.meta (pytsk3.TSK_FS_META)."
            )

        if data_stream_name:
            for pytsk_attribute in tsk_file:
                if getattr(pytsk_attribute, "info", None) is None:
                    continue

                attribute_name = getattr(pytsk_attribute.info, "name", None)
                if attribute_name:
                    try:
                        # pytsk3 returns an UTF-8 encoded byte string.
                        attribute_name = attribute_name.decode("utf8")
                    except UnicodeError:
                        raise errors.BackEndError(
                            "pytsk3 returned a non UTF-8 formatted name."
                        )

                attribute_type = getattr(pytsk_attribute.info, "type", None)
                if attribute_type == pytsk3.TSK_FS_ATTR_TYPE_HFS_DATA and (
                    not data_stream_name and not attribute_name
                ):
                    tsk_attribute = pytsk_attribute
                    break

                if attribute_type == pytsk3.TSK_FS_ATTR_TYPE_HFS_RSRC and (
                    data_stream_name == "rsrc"
                ):
                    tsk_attribute = pytsk_attribute
                    break

                if attribute_type == pytsk3.TSK_FS_ATTR_TYPE_NTFS_DATA and (
                    (not data_stream_name and not attribute_name)
                    or (data_stream_name == attribute_name)
                ):
                    tsk_attribute = pytsk_attribute
                    break

                # The data stream is returned as a name-less attribute of type
                # pytsk3.TSK_FS_ATTR_TYPE_DEFAULT.
                if (
                    attribute_type == pytsk3.TSK_FS_ATTR_TYPE_DEFAULT
                    and not data_stream_name
                    and not attribute_name
                ):
                    tsk_attribute = pytsk_attribute
                    break

            if tsk_attribute is None:
                raise OSError(f"Unable to open data stream: {data_stream_name:s}.")

        if not tsk_attribute and tsk_file.info.meta.type != pytsk3.TSK_FS_META_TYPE_REG:
            raise OSError("Not a regular file.")

        self._current_offset = 0
        self._file_system = file_system
        self._tsk_attribute = tsk_attribute
        self._tsk_file = tsk_file

        if self._tsk_attribute:
            self._size = self._tsk_attribute.info.size
        else:
            self._size = self._tsk_file.info.meta.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._current_offset < 0:
            raise OSError("Invalid current offset value less than zero.")

        # The SleuthKit is not POSIX compliant in its read behavior. Therefore
        # pytsk3 will raise an OSError if the read offset is beyond the data size.
        if self._current_offset >= self._size:
            return b""

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

        if self._tsk_attribute:
            data = self._tsk_file.read_random(
                self._current_offset,
                size,
                self._tsk_attribute.info.type,
                self._tsk_attribute.info.id,
            )
        else:
            data = self._tsk_file.read_random(self._current_offset, size)

        # It is possible the that returned data size is not the same as the
        # requested data size. At this layer we don't care and this discrepancy
        # should be dealt with on a higher layer if necessary.
        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 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-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._size
