# Data migration: 从 Factory.short_name 的唯一值创建 Brand，并回填 Material.brand

from django.db import migrations


def forwards(apps, schema_editor):
    Factory = apps.get_model('factory', 'Factory')
    Brand = apps.get_model('brand', 'Brand')
    Material = apps.get_model('material', 'Material')

    short_names = (
        Factory.objects
        .exclude(short_name__isnull=True)
        .exclude(short_name='')
        .values_list('short_name', flat=True)
        .distinct()
    )
    for sn in short_names:
        Brand.objects.get_or_create(name=sn)

    for brand in Brand.objects.all():
        Material.objects.filter(factory__short_name=brand.name).update(brand=brand)


def backwards(apps, schema_editor):
    # schema migration 回滚时会删掉 Material.brand 字段，这里无需操作
    pass


class Migration(migrations.Migration):

    dependencies = [
        ('material', '0007_add_brand_fk'),
        ('factory', '0004_rename_brand_to_short_name'),
        ('brand', '0001_initial'),
    ]

    operations = [
        migrations.RunPython(forwards, backwards),
    ]