import itertools

from django.contrib.contenttypes.models import ContentType
from django.db import transaction


def compile_path_node(ct_id, object_id):
    return f'{ct_id}:{object_id}'


def decompile_path_node(repr):
    ct_id, object_id = repr.split(':')
    return int(ct_id), int(object_id)


def object_to_path_node(obj):
    """
    Return a representation of an object suitable for inclusion in a CablePath path. Node representation is in the
    form <ContentType ID>:<Object ID>.
    """
    ct = ContentType.objects.get_for_model(obj)
    return compile_path_node(ct.pk, obj.pk)


def path_node_to_object(repr):
    """
    Given the string representation of a path node, return the corresponding instance. If the object no longer
    exists, return None.
    """
    ct_id, object_id = decompile_path_node(repr)
    ct = ContentType.objects.get_for_id(ct_id)
    return ct.model_class().objects.filter(pk=object_id).first()


def create_cablepath(terminations):
    """
    Create CablePaths for all paths originating from the specified set of nodes.

    :param terminations: Iterable of CableTermination objects
    """
    from dcim.models import CablePath

    cp = CablePath.from_origin(terminations)
    if cp:
        cp.save()


def rebuild_paths(terminations):
    """
    Rebuild all CablePaths which traverse the specified nodes.
    """
    from dcim.models import CablePath

    for obj in terminations:
        cable_paths = CablePath.objects.filter(_nodes__contains=obj)

        with transaction.atomic():
            for cp in cable_paths:
                cp.delete()
                create_cablepath(cp.origins)