"""phase13 — add facility_id to issues, make area_id nullable

Revision ID: phase13_issue_facility
Revises: phase12_performance_indexes
"""

revision      = 'phase13_issue_facility'
down_revision = 'phase_b_mobile_local_id'
branch_labels = None
depends_on    = None

from alembic import op
import sqlalchemy as sa


def upgrade():
    # 1. Add facility_id column (nullable FK to facilities)
    with op.batch_alter_table('issues') as batch_op:
        batch_op.add_column(
            sa.Column('facility_id', sa.Integer(),
                      sa.ForeignKey('facilities.id', ondelete='SET NULL'),
                      nullable=True)
        )

    # 2. Back-fill facility_id for all existing issues that have an area
    op.execute("""
        UPDATE issues
        JOIN areas ON issues.area_id = areas.id
        SET issues.facility_id = areas.facility_id
        WHERE issues.area_id IS NOT NULL
    """)

    # 3. Make area_id nullable (was nullable=False)
    with op.batch_alter_table('issues') as batch_op:
        batch_op.alter_column('area_id',
                              existing_type=sa.Integer(),
                              nullable=True)


def downgrade():
    # Restore area_id to non-nullable (requires no NULL rows)
    with op.batch_alter_table('issues') as batch_op:
        batch_op.alter_column('area_id',
                              existing_type=sa.Integer(),
                              nullable=False)
        batch_op.drop_column('facility_id')