# Source code for psd_tools.psd.header

    """
    File header structure.
    """

    from __future__ import absolute_import, unicode_literals

    import logging

    import attr

    from psd_tools.constants import ColorMode
    from psd_tools.psd.base import BaseElement
    from psd_tools.utils import read_fmt, write_fmt
    from psd_tools.validators import in_, range_

    logger = logging.getLogger(__name__)

    @attr.s(repr=True, slots=True)
    class FileHeader(BaseElement):
        """
        Header section of the PSD file.

        Example::

            from psd_tools.psd.header import FileHeader
            from psd_tools.constants import ColorMode

            header = FileHeader(channels=2, height=359, width=400, depth=8,
                                color_mode=ColorMode.GRAYSCALE)

        .. py:attribute:: signature

            Signature: always equal to ``b'8BPS'``.

        .. py:attribute:: version

            Version number. PSD is 1, and PSB is 2.

        .. py:attribute:: channels

            The number of channels in the image, including any user-defined alpha
            channel.

        .. py:attribute:: height

            The height of the image in pixels.

        .. py:attribute:: width

            The width of the image in pixels.

        .. py:attribute:: depth

            The number of bits per channel.

        .. py:attribute:: color_mode

            The color mode of the file. See
            :py:class:`~psd_tools.constants.ColorMode`
        """

        _FORMAT = "4sH6xHIIHH"

        signature = attr.ib(default=b"8BPS", type=bytes, repr=False)
        version = attr.ib(default=1, type=int, validator=in_((1, 2)))
        channels = attr.ib(default=4, type=int, validator=range_(1, 57))
        height = attr.ib(default=64, type=int, validator=range_(1, 300001))
        width = attr.ib(default=64, type=int, validator=range_(1, 300001))
        depth = attr.ib(default=8, type=int, validator=in_((1, 8, 16, 32)))
        color_mode = attr.ib(
            default=ColorMode.RGB, converter=ColorMode, validator=in_(ColorMode)
        )

        @signature.validator
        def _validate_signature(self, attribute, value):
            if value != b"8BPS":
                raise ValueError("This is not a PSD or PSB file")

        @classmethod
        def read(cls, fp):
            return cls(*read_fmt(cls._FORMAT, fp))

        def write(self, fp):
            return write_fmt(fp, self._FORMAT, *attr.astuple(self))