Source code for baseband.mark4.file_info

# Licensed under the GPLv3 - see LICENSE
"""The Mark4FileReaderInfo property.

Includes information about what is needed to calcuate times,
number of tracks and offset of first header.
"""

from ..base.file_info import FileReaderInfo, info_item


__all__ = ['Mark4FileReaderInfo']


class Mark4FileReaderInfo(FileReaderInfo):
    """Standardized information on Mark 4 file readers.

    The ``info`` descriptor has a number of standard attributes, which are
    determined from arguments passed in opening the file, from the first header
    (``info.header0``) and from possibly scanning the file to determine the
    duration of frames.  This class has two additional attributes specific to
    Mark 4 files (``ntrack`` and ``offset0``, see below).

    Examples
    --------
    The most common use is simply to print information::

        >>> from baseband.data import SAMPLE_MARK4
        >>> from baseband import mark4
        >>> fh = mark4.open(SAMPLE_MARK4, 'rb')
        >>> fh.info
        Mark4File information:
        format = mark4
        number_of_frames = 2
        frame_rate = 400.0 Hz
        sample_rate = 32.0 MHz
        samples_per_frame = 80000
        sample_shape = (8,)
        bps = 2
        complex_data = False
        readable = True
        ntrack = 64
        offset0 = 2696
        <BLANKLINE>
        missing:  decade, ref_time: needed to infer full times.
        <BLANKLINE>
        checks:  decodable: True
        >>> fh.close()

        >>> fh = mark4.open(SAMPLE_MARK4, 'rb', decade=2010)
        >>> fh.info
        Mark4File information:
        format = mark4
        number_of_frames = 2
        frame_rate = 400.0 Hz
        sample_rate = 32.0 MHz
        samples_per_frame = 80000
        sample_shape = (8,)
        bps = 2
        complex_data = False
        start_time = 2014-06-16T07:38:12.475000000
        readable = True
        ntrack = 64
        offset0 = 2696
        <BLANKLINE>
        checks:  decodable: True
        >>> fh.close()
    """
    attr_names = (FileReaderInfo.attr_names[:-4]
                  + ('ntrack', 'offset0')
                  + FileReaderInfo.attr_names[-4:])
    """Attributes that the container provides."""

    ntrack = info_item(needs='_parent', doc=(
        'Number of "tape tracks" simulated in the disk file.'))
    decade = info_item(needs='_parent', doc=(
        'Decade in which the observations were taken'))
    ref_time = info_item(needs='_parent', doc=(
        'Reference time within 4 years of the observation time'))

    @info_item
    def time_info(self):
        """Additional time info needed to get the start time."""
        time_info = (self.decade, self.ref_time)
        if time_info == (None, None):
            self.missing['decade'] = self.missing['ref_time'] = (
                "needed to infer full times.")
            return None

        return time_info

    @info_item
    def offset0(self):
        """Offset in bytes to the location of the first header."""
        with self._parent.temporary_offset(0) as fh:
            return fh.locate_frames()[0]

    @info_item(needs='offset0')
    def header0(self):
        with self._parent.temporary_offset(self.offset0) as fh:
            return fh.read_header()

    @info_item(needs='header0')
    def frame0(self):
        with self._parent.temporary_offset(self.offset0) as fh:
            return fh.read_frame()

    @info_item(needs='header0')
    def number_of_frames(self):
        """Total number of frames."""
        with self._parent.temporary_offset(
                -self.header0.frame_nbytes, 2) as fh:
            fh.find_header(self.header0, forward=False)
            number_of_frames = ((fh.tell() - self.offset0)
                                / self.header0.frame_nbytes) + 1

        if number_of_frames % 1 == 0:
            return int(number_of_frames)
        else:
            self.warnings['number_of_frames'] = (
                'file contains non-integer number ({}) of frames'
                .format(number_of_frames))
            return None

    # Override just to replace what it "needs".
    @info_item(needs='offset0')
    def format(self):
        return 'mark4'

    @info_item(needs=('header0', 'time_info'))
    def start_time(self):
        """Time of the first sample."""
        return super().start_time