"""phase20 — inspector contract assignments

Adds inspector_assignments table so each inspector can be scoped to one or
more contracts (projects).  Inspectors with no assignments see nothing.

Safe to re-run — uses INFORMATION_SCHEMA existence check.
"""

import sqlalchemy as sa
from alembic import op

revision      = 'phase20_inspector_assignments'
down_revision = 'phase19_issue_mobile_photos'
branch_labels = None
depends_on    = None


def _table_exists(bind, table):
    result = bind.execute(sa.text(
        "SELECT COUNT(*) FROM INFORMATION_SCHEMA.TABLES "
        "WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME = :t"
    ), {"t": table})
    return result.scalar() > 0


def upgrade():
    bind = op.get_bind()
    if not _table_exists(bind, 'inspector_assignments'):
        op.create_table(
            'inspector_assignments',
            sa.Column('id',         sa.Integer(),  nullable=False, autoincrement=True),
            sa.Column('user_id',    sa.Integer(),  nullable=False),
            sa.Column('project_id', sa.Integer(),  nullable=False),
            sa.Column('created_at', sa.DateTime(), nullable=False),
            sa.PrimaryKeyConstraint('id'),
            sa.ForeignKeyConstraint(['user_id'],    ['users.id'],    ondelete='CASCADE'),
            sa.ForeignKeyConstraint(['project_id'], ['projects.id'], ondelete='CASCADE'),
            sa.UniqueConstraint('user_id', 'project_id', name='uq_inspector_project'),
        )
        op.create_index('ix_inspector_assignments_user_id',
                        'inspector_assignments', ['user_id'])


def downgrade():
    bind = op.get_bind()
    if _table_exists(bind, 'inspector_assignments'):
        op.drop_table('inspector_assignments')