"""Cache the warn-only reconciler drift on the endpoint state.

Adds endpointstates.driftjson: a per-asset JSON snapshot of the monitors a site
policy (or the shipped bundle) expects to be running on an endpoint but which the
latest agent report does not show as running. It is computed server-side on every
agent check-in and overwritten in place, the same ledger pattern the other state
snapshots (servicesjson, portsjson) already use - one current row per asset, no
history. Warn-only: nothing here is auto-remediated, it exists so an operator can
see the drift and intervene manually.

Nullable so an endpoint that has never checked in since the column landed reads
as "never computed" rather than "no drift".

Idempotent: the column-add checks the live schema first, so a db.create_all()
site (which built the column from the model already) and a re-run both stay clean
on strict MySQL 8.
"""
from alembic import op

import sqlalchemy as sa


# revision identifiers, used by Alembic.
revision = 'endpoints0008drift'
down_revision = 'endpoints0007shippedpolicy'
branch_labels = None
depends_on = None


def _has_column(table_name, column_name):
    from sqlalchemy import inspect

    inspector = inspect(op.get_bind())
    if not inspector.has_table(table_name):
        return False
    return any(col['name'] == column_name
               for col in inspector.get_columns(table_name))


def upgrade():
    if _has_column('endpointstates', 'driftjson'):
        return
    op.add_column(
        'endpointstates',
        sa.Column('driftjson', sa.Text(length=16777215), nullable=True))


def downgrade():
    if not _has_column('endpointstates', 'driftjson'):
        return
    op.drop_column('endpointstates', 'driftjson')