import django.db.models.deletion
from django.db import migrations, models


def populate_denormalized_fields(apps, schema_editor):
    """
    Copy site ForeignKey values to the scope GFK.
    """
    Prefix = apps.get_model('ipam', 'Prefix')
    db_alias = schema_editor.connection.alias

    prefixes = Prefix.objects.using(db_alias).filter(site__isnull=False).prefetch_related('site')
    for prefix in prefixes:
        prefix._region_id = prefix.site.region_id
        prefix._site_group_id = prefix.site.group_id
        prefix._site_id = prefix.site_id
        # Note: Location cannot be set prior to migration

    Prefix.objects.using(db_alias).bulk_update(prefixes, ['_region', '_site_group', '_site'], batch_size=100)


class Migration(migrations.Migration):
    dependencies = [
        ('dcim', '0193_poweroutlet_color'),
        ('ipam', '0071_prefix_scope'),
    ]

    operations = [
        migrations.AddField(
            model_name='prefix',
            name='_location',
            field=models.ForeignKey(
                blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='dcim.location'
            ),
        ),
        migrations.AddField(
            model_name='prefix',
            name='_region',
            field=models.ForeignKey(
                blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='dcim.region'
            ),
        ),
        migrations.AddField(
            model_name='prefix',
            name='_site',
            field=models.ForeignKey(blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='dcim.site'),
        ),
        migrations.AddField(
            model_name='prefix',
            name='_site_group',
            field=models.ForeignKey(
                blank=True, null=True, on_delete=django.db.models.deletion.CASCADE, to='dcim.sitegroup'
            ),
        ),
        # Populate denormalized FK values
        migrations.RunPython(code=populate_denormalized_fields, reverse_code=migrations.RunPython.noop),
        # Delete the site ForeignKey
        migrations.RemoveField(
            model_name='prefix',
            name='site',
        ),
    ]


def oc_prefix_remove_fields(objectchange, reverting):
    for data in (objectchange.prechange_data, objectchange.postchange_data):
        if data is not None:
            data.pop('site', None)


objectchange_migrators = {
    'ipam.prefix': oc_prefix_remove_fields,
}