"""vision results and reference images cascade with their task

Both `vision_results.task_id` and `vision_reference_images.task_id` were
created (012, 013) with a plain, unnamed foreign key - no ON DELETE clause,
so deleting a task with any camera history or reference image attached fails
on a strict FK check (MySQL) instead of taking the vision rows with it, the
way `production_events.run_id` already does for a closed production run.

The original constraint has no name to drop by (SQLAlchemy leaves inline
`ForeignKey(...)` unnamed unless told otherwise, and MySQL then assigns its
own `<table>_ibfk_N`, which is not portable to reflect on). `sa.inspect`
looks it up at migration time instead of guessing it - the same way on
MySQL and on SQLite (batch mode), where an anonymous FK reflects with
`name=None` and there is nothing to drop before adding the new one.

Reference images on disk are not touched here - deleting a task's row does
not, on its own, know to also delete the file next to it; that gap is
declared open in issue #38 point 6's write-up (`vision_service` has no
single point today that intercepts a task deletion).

Revision ID: 014_vision_fk_ondelete
Revises: 013_reference_images
Create Date: 2026-09-21

"""
from typing import Sequence, Union

from alembic import op
import sqlalchemy as sa

revision: str = '014_vision_fk_ondelete'
down_revision: Union[str, None] = '013_reference_images'
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None

_NEW_FK_NAMES = {
    'vision_results': 'fk_vision_results_task_id',
    'vision_reference_images': 'fk_vision_reference_images_task_id',
}


def _existing_task_id_fk_name(bind, table_name: str) -> Union[str, None]:
    """The name reflection gives the pre-existing `task_id` FK, if any.

    None on SQLite for a constraint that was never named - batch mode then
    has nothing to drop, and just adds the new named one alongside it.
    """
    inspector = sa.inspect(bind)
    for fk in inspector.get_foreign_keys(table_name):
        if fk.get("constrained_columns") == ["task_id"]:
            return fk.get("name")
    return None


def upgrade() -> None:
    bind = op.get_bind()

    for table_name, new_name in _NEW_FK_NAMES.items():
        existing_name = _existing_task_id_fk_name(bind, table_name)
        with op.batch_alter_table(table_name) as batch:
            if existing_name:
                batch.drop_constraint(existing_name, type_='foreignkey')
            batch.create_foreign_key(
                new_name, 'recipe_tasks', ['task_id'], ['id'],
                ondelete='CASCADE',
            )


def downgrade() -> None:
    # Reverse order: reference_images before results, mirroring upgrade().
    for table_name, name in reversed(list(_NEW_FK_NAMES.items())):
        with op.batch_alter_table(table_name) as batch:
            batch.drop_constraint(name, type_='foreignkey')
            batch.create_foreign_key(
                name, 'recipe_tasks', ['task_id'], ['id'],
            )