"""Record who handed a drive back, not just when.

usbcheckouts held the checkout identity (sso, checkoutname) and, for the
return, only checkintime. Returning a drive for a colleague is a supported
kiosk flow - usb_kiosk_allow_return_for_others gates it and the kiosk asks for
confirmation - but the row it wrote attributed the check-in to the HOLDER. The
person who actually walked the drive back was recorded nowhere, so the custody
history and the audit report both named somebody who was not there.

Two columns rather than one: the badge is what the scanner emits and what joins
to a directory, and the name is what a report has to print when the directory
no longer resolves that badge.

Nullable, and not backfilled. A row closed before this column existed is one
where the returner was not recorded; copying the holder's badge into it would
manufacture evidence that the holder returned it, which is the exact claim this
migration exists to stop making.

Idempotent, so a re-run on an already-migrated database is a no-op.

Revision ID: usb0004checkinidentity
Revises: usb0003scanfields
"""
from alembic import op
import sqlalchemy as sa


revision = 'usb0004checkinidentity'
down_revision = 'usb0003scanfields'
branch_labels = None
depends_on = None

NEW_COLUMNS = (
    ('checkinsso', sa.String(length=20)),
    ('checkinname', sa.String(length=100)),
)


def upgrade():
    bind = op.get_bind()
    insp = sa.inspect(bind)
    if 'usbcheckouts' not in insp.get_table_names():
        return
    cols = {c['name'] for c in insp.get_columns('usbcheckouts')}
    for name, coltype in NEW_COLUMNS:
        if name not in cols:
            op.add_column('usbcheckouts',
                          sa.Column(name, coltype, nullable=True))


def downgrade():
    bind = op.get_bind()
    insp = sa.inspect(bind)
    if 'usbcheckouts' not in insp.get_table_names():
        return
    cols = {c['name'] for c in insp.get_columns('usbcheckouts')}
    for name, _ in NEW_COLUMNS:
        if name in cols:
            op.drop_column('usbcheckouts', name)