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


def copiar_rfc_a_m2m(apps, schema_editor):
    """Copia el RFC singular (FK) al lado M2M antes de eliminar el FK."""
    CustomUser = apps.get_model('cuser', 'CustomUser')
    db_alias = schema_editor.connection.alias
    for user in CustomUser.objects.using(db_alias).filter(rfc_old__isnull=False):
        user.rfc.add(user.rfc_old)


def revertir_m2m_a_fk(apps, schema_editor):
    """En reversa: toma el primer RFC del M2M y lo pone de vuelta en el FK temporal."""
    CustomUser = apps.get_model('cuser', 'CustomUser')
    db_alias = schema_editor.connection.alias
    for user in CustomUser.objects.using(db_alias).prefetch_related('rfc'):
        primer_rfc = user.rfc.first()
        if primer_rfc:
            user.rfc_old = primer_rfc
            user.save(update_fields=['rfc_old'])


class Migration(migrations.Migration):

    dependencies = [
        ('cuser', '0004_alter_customuser_rfc'),
        ('customs', '0015_partida_updated_at'),
    ]

    operations = [
        # 1. Renombrar el FK actual a rfc_old para preservar los datos
        migrations.RenameField(
            model_name='customuser',
            old_name='rfc',
            new_name='rfc_old',
        ),
        # 2. Crear el nuevo campo M2M
        migrations.AddField(
            model_name='customuser',
            name='rfc',
            field=models.ManyToManyField(
                blank=True,
                help_text='RFCs de importadores asociados al usuario',
                related_name='users',
                to='customs.importador',
            ),
        ),
        # 3. Copiar datos del FK al M2M
        migrations.RunPython(copiar_rfc_a_m2m, revertir_m2m_a_fk),
        # 4. Eliminar el FK temporal
        migrations.RemoveField(
            model_name='customuser',
            name='rfc_old',
        ),
    ]