__copyright__ = "Copyright © Stichting SciPost (SciPost Foundation)"
__license__ = "AGPL v3"


from django.db.models import Max
from django.utils import timezone

from submissions.models import Submission

from .models import Preprint


def get_new_scipost_identifier(thread_hash=None):
    """
    Return an identifier for a new SciPost preprint (consistent with thread history).

    A SciPost identifier is of the form [YYYY][MM]_[#####]v[vn_nr].

    For an existing thread, different cases must be treated:

    * All preprints in thread are SciPost preprints: the vn_nr is incremented.

    * Previous preprints are all on an external preprint server: a brand new SciPost
      identifier is generated; the vn_nr is put to 1.

    * Previous preprints mix SciPost and external identifiers: the SciPost identifier is
      reused, putting the vn_nr to [nr of previous SciPost subs in thread] + 1.
    """
    now = timezone.now()

    scipost_submissions_in_thread = Submission.objects.filter(
        thread_hash=thread_hash,
        preprint__identifier_w_vn_nr__startswith='scipost')

    # At least one previous submission on SciPost's preprint server
    if len(scipost_submissions_in_thread) > 0:
        identifier = '{}v{}'.format(
            scipost_submissions_in_thread.first().preprint.identifier_w_vn_nr.rpartition('v')[0],
            str(len(scipost_submissions_in_thread) + 1))
        return identifier

    # No previous Submission, or no previous SciPost preprint in thread; new identifier
    current_identifier_prefix = 'scipost_%s%s' % (now.year, str(now.month).rjust(2,'0'))
    try:
        next_identifier_nr = int(Preprint.objects.filter(
            identifier_w_vn_nr__startswith=current_identifier_prefix
        ).first().identifier_w_vn_nr.rpartition('v')[0].rpartition('_')[2]) + 1
    except AttributeError:
        next_identifier_nr = 1

    identifier = 'scipost_{year}{month}_{identifier}v1'.format(
        year=now.year, month=str(now.month).rjust(2, '0'),
        identifier=str(next_identifier_nr).rjust(5, '0')
    )
    return identifier