import secrets
import uuid

from django.db import migrations, models
from django.db.backends.base.schema import BaseDatabaseSchemaEditor
from django.db.migrations.state import StateApps


def generate_api_key() -> str:
    """
    This is a copy of zerver.lib.utils.generate_api_key. Importing code that's prone
    to change in a migration is something we generally avoid, to ensure predictable,
    consistent behavior of the migration across time.
    """

    api_key = ""
    while len(api_key) < 32:
        api_key += secrets.token_urlsafe(3 * 9).replace("_", "").replace("-", "")
    return api_key[:32]


def generate_realm_uuid_owner_secret() -> str:
    token = generate_api_key()

    return f"zuliprealm_{token}"


def backfill_realm_uuid_and_secret(
    apps: StateApps, schema_editor: BaseDatabaseSchemaEditor
) -> None:
    Realm = apps.get_model("zerver", "Realm")

    max_id = Realm.objects.aggregate(models.Max("id"))["id__max"]
    if max_id is None:
        # Nothing to do if there are no realms yet.
        return

    BATCH_SIZE = 100
    lower_bound = 0

    while lower_bound < max_id:
        realms_to_update = []
        for realm in Realm.objects.filter(
            id__gt=lower_bound,
            id__lte=lower_bound + BATCH_SIZE,
            # We're setting uuid and uuid_owner_secret together, so it's enough
            # to query for one of them being None.
            uuid=None,
        ).only("id", "uuid", "uuid_owner_secret"):
            realm.uuid = uuid.uuid4()
            realm.uuid_owner_secret = generate_realm_uuid_owner_secret()
            realms_to_update.append(realm)
        lower_bound += BATCH_SIZE

        Realm.objects.bulk_update(realms_to_update, ["uuid", "uuid_owner_secret"])


class Migration(migrations.Migration):
    atomic = False

    dependencies = [
        ("zerver", "0479_realm_uuid_realm_uuid_owner_secret"),
    ]

    operations = [
        migrations.RunPython(
            backfill_realm_uuid_and_secret,
            reverse_code=migrations.RunPython.noop,
            elidable=True,
        ),
    ]