"""phase38 — facility QR tokens

Adds facilities.qr_token VARCHAR(64) NULL + unique index. The token backs the
public, login-less facility QR scan page (GET /f/<token>) which shows recent
inspection scores, open-issue counts, and a 30-day score trend for that
facility — counts + scores only, no free text, no names, no photos.

NULL for all existing rows; Facility.ensure_qr_token() generates lazily when
staff first open the QR card / bulk sheet.

Idempotent: INFORMATION_SCHEMA column + index existence checks — safe to
re-run across every tenant DB (CLAUDE.md rule 14). Revision id kept ≤ 32
chars (alembic_version.version_num is VARCHAR(32)).
"""

import sqlalchemy as sa
from alembic import op

revision      = 'phase38_facility_qr'
down_revision = 'phase37_contract_recipients'
branch_labels = None
depends_on    = None


def _column_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 _index_exists(bind, table: str, index: str) -> bool:
    result = bind.execute(sa.text(
        "SELECT COUNT(*) FROM information_schema.statistics "
        "WHERE table_schema = DATABASE() AND table_name = :t AND index_name = :i"
    ), {'t': table, 'i': index})
    return result.scalar() > 0


def upgrade():
    bind = op.get_bind()
    if not _column_exists(bind, 'facilities', 'qr_token'):
        op.execute(sa.text(
            "ALTER TABLE facilities ADD COLUMN qr_token VARCHAR(64) NULL"
        ))
    if not _index_exists(bind, 'facilities', 'uq_facilities_qr_token'):
        op.execute(sa.text(
            "CREATE UNIQUE INDEX uq_facilities_qr_token ON facilities (qr_token)"
        ))


def downgrade():
    bind = op.get_bind()
    if _index_exists(bind, 'facilities', 'uq_facilities_qr_token'):
        op.execute(sa.text('DROP INDEX uq_facilities_qr_token ON facilities'))
    if _column_exists(bind, 'facilities', 'qr_token'):
        op.execute(sa.text('ALTER TABLE facilities DROP COLUMN qr_token'))