# Generated migration for eventify_id field

import secrets

from django.db import migrations, models

EVENTIFY_ID_CHARS = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789'


def generate_unique_eventify_id(existing_ids):
    for _ in range(100):
        candidate = 'EVT-' + ''.join(secrets.choice(EVENTIFY_ID_CHARS) for _ in range(8))
        if candidate not in existing_ids:
            return candidate
    raise RuntimeError("Could not generate a unique Eventify ID after 100 attempts")


def backfill_eventify_ids(apps, schema_editor):
    User = apps.get_model('accounts', 'User')
    existing_ids = set(User.objects.exclude(eventify_id__isnull=True).values_list('eventify_id', flat=True))
    users_to_update = []
    for user in User.objects.filter(eventify_id__isnull=True):
        new_id = generate_unique_eventify_id(existing_ids)
        existing_ids.add(new_id)
        user.eventify_id = new_id
        users_to_update.append(user)
    User.objects.bulk_update(users_to_update, ['eventify_id'])


def reverse_backfill(apps, schema_editor):
    pass  # No-op: reversing just leaves IDs set, which is fine


class Migration(migrations.Migration):

    dependencies = [
        ('accounts', '0011_user_allowed_modules_alter_user_id'),
    ]

    operations = [
        # Step 1: Add the column as nullable
        migrations.AddField(
            model_name='user',
            name='eventify_id',
            field=models.CharField(blank=True, db_index=True, editable=False, max_length=12, null=True, unique=True),
        ),
        # Step 2: Backfill all existing users
        migrations.RunPython(backfill_eventify_ids, reverse_backfill),
        # Step 3: Make the field non-nullable
        migrations.AlterField(
            model_name='user',
            name='eventify_id',
            field=models.CharField(blank=False, db_index=True, editable=False, max_length=12, null=False, unique=True),
        ),
    ]