"""Give a printer driver a vendor, so one row can serve a whole make.

HP's and Xerox's universal drivers cover 41 of the reference site's 44 printers
between them, but a driver could only be bound to ONE modelnumberid - so covering
them meant 21 near-duplicate rows all pointing at the same package, a table
nobody would keep true. A driver with no model and a vendor now serves every
printer of that make, and a per-model row still wins where one genuinely differs
(a plotter, a card printer, a label printer).

Nullable and guarded: a re-run is a no-op, and existing rows keep working
unchanged because model matching is still tried first.

Revision ID: printers0004drivervendor
Revises: printers0003drivername
"""
from alembic import op
import sqlalchemy as sa


revision = 'printers0004drivervendor'
down_revision = 'printers0003drivername'
branch_labels = None
depends_on = None


def upgrade():
    bind = op.get_bind()
    inspector = sa.inspect(bind)
    columns = {column['name'] for column in inspector.get_columns('printerdrivers')}
    if 'vendorid' not in columns:
        op.add_column('printerdrivers', sa.Column('vendorid', sa.Integer(), nullable=True))
        # No FK constraint: printerdrivers is a plugin table and vendors is core.
        # ADR-008 keeps plugin chains from writing constraints across that line,
        # and the resolver treats a vendor that no longer exists as no match.
        op.create_index('idx_printerdriver_vendor', 'printerdrivers', ['vendorid'])


def downgrade():
    bind = op.get_bind()
    inspector = sa.inspect(bind)
    columns = {column['name'] for column in inspector.get_columns('printerdrivers')}
    if 'vendorid' in columns:
        op.drop_index('idx_printerdriver_vendor', table_name='printerdrivers')
        op.drop_column('printerdrivers', 'vendorid')