"""widen the production event trace for the measurement loop

The loop needs to distinguish two things the trace could not say before: a
measurement task finished while the cycle is still running (task_measured), and the
piece turned over and measured again without closing the cycle (remeasure). Only
the last measurement task of a recipe still produces cycle_completed, because only
that one restarts the interval.

Both values are added in one go. Widening a MySQL enum rewrites the table, so the
values that are already planned go in now rather than one migration at a time -
the same reasoning as the task types in 007.

The events that happen inside a cycle also need to say which task they are about,
so the column comes with them: a task_measured that does not name its task records
nothing usable.

Revision ID: 008_loop_events
Revises: 007_task_type
Create Date: 2026-07-28

"""
from typing import Sequence, Union

from alembic import op
import sqlalchemy as sa

revision: str = '008_loop_events'
down_revision: Union[str, None] = '007_task_type'
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None

OLD_TYPES = ('start', 'cycle_completed', 'line_stop', 'resume', 'close')
NEW_TYPES = (
    'start', 'cycle_completed', 'task_measured', 'remeasure',
    'line_stop', 'resume', 'close',
)


def _alter(values: Sequence[str]) -> None:
    """Restate the column with a new set of allowed values.

    On MySQL this is the ALTER that rewrites the enum. On SQLite, where an enum is
    stored as a plain VARCHAR, batch mode rebuilds the table instead of emitting an
    ALTER the engine does not support - the tests run there.
    """
    with op.batch_alter_table('production_events') as batch:
        batch.alter_column(
            'event_type',
            existing_type=sa.Enum(*OLD_TYPES, name='production_event_type_enum'),
            type_=sa.Enum(*values, name='production_event_type_enum'),
            existing_nullable=False,
        )


def upgrade() -> None:
    _alter(NEW_TYPES)
    with op.batch_alter_table('production_events') as batch:
        batch.add_column(sa.Column('task_id', sa.Integer(), nullable=True))
        batch.create_foreign_key(
            'fk_production_events_task_id', 'recipe_tasks', ['task_id'], ['id'],
        )


def downgrade() -> None:
    with op.batch_alter_table('production_events') as batch:
        batch.drop_constraint('fk_production_events_task_id', type_='foreignkey')
        batch.drop_column('task_id')
    # The new kinds of event have no equivalent in the old vocabulary, and a row
    # left with a value the column no longer accepts would fail the rebuild.
    op.execute(
        "DELETE FROM production_events "
        "WHERE event_type IN ('task_measured', 'remeasure')"
    )
    _alter(OLD_TYPES)