# This file is released under the GNU GPL, version 3 or a later revision.
# For further details see the COPYING file

import re

import magic


def guess_mimetype(blob):
    """
    uses file magic to determine the mime-type of the given data blob.

    :param blob: file content as read by file.read()
    :type blob: data
    :returns: mime-type, falls back to 'application/octet-stream'
    :rtype: str
    """
    mimetype = 'application/octet-stream'
    # this is a bit of a hack to support different versions of python magic.
    # Hopefully at some point this will no longer be necessary
    #
    # the version with open() is the bindings shipped with the file source from
    # http://darwinsys.com/file/ - this is what is used by the python-magic
    # package on Debian/Ubuntu. However, it is not available on pypi/via pip.
    #
    # the version with from_buffer() is available at
    # https://github.com/ahupp/python-magic and directly installable via pip.
    #
    # for more detail see https://github.com/pazz/alot/pull/588
    if hasattr(magic, 'open'):
        m = magic.open(magic.MAGIC_MIME_TYPE)
        m.load()
        magictype = m.buffer(blob)
    elif hasattr(magic, 'from_buffer'):
        # cf. issue #841
        magictype = magic.from_buffer(blob, mime=True) or magictype
    else:
        raise Exception('Unknown magic API')

    # libmagic does not always return proper mimetype strings, cf. issue #459
    if re.match(r'\w+\/\w+', magictype):
        mimetype = magictype
    return mimetype