"""phase26 — vendor/contractor columns on issues

Adds three nullable columns to the issues table:
  vendor_name    VARCHAR(100) — name of the external contractor or vendor
  vendor_contact VARCHAR(200) — phone number or email for the vendor
  vendor_notes   TEXT         — notes about what the vendor is handling

These columns are populated only when a third-party contractor is
assigned to resolve an issue, separate from the internal assigned_to staff user.
"""

import sqlalchemy as sa
from alembic import op

revision      = 'phase26_issue_vendor'
down_revision = 'phase25_inspection_gps'
branch_labels = None
depends_on    = None


def _col_exists(bind, table: str, column: str) -> bool:
    result = bind.execute(sa.text(
        "SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS "
        "WHERE TABLE_SCHEMA = DATABASE() "
        "  AND TABLE_NAME  = :t "
        "  AND COLUMN_NAME = :c"
    ), {'t': table, 'c': column})
    return result.scalar() > 0


def upgrade():
    bind = op.get_bind()

    if not _col_exists(bind, 'issues', 'vendor_name'):
        op.add_column('issues',
            sa.Column('vendor_name', sa.String(100), nullable=True))

    if not _col_exists(bind, 'issues', 'vendor_contact'):
        op.add_column('issues',
            sa.Column('vendor_contact', sa.String(200), nullable=True))

    if not _col_exists(bind, 'issues', 'vendor_notes'):
        op.add_column('issues',
            sa.Column('vendor_notes', sa.Text, nullable=True))


def downgrade():
    op.drop_column('issues', 'vendor_notes')
    op.drop_column('issues', 'vendor_contact')
    op.drop_column('issues', 'vendor_name')