"""Cache the interactive tray app version on the endpoint state.

Adds endpointstates.trayversion: the file version of the ShopDB endpoint tray
app, reported by the agent alongside its own agentversion. The tray and the
agent service ship and update independently (they are separate exes and can be
pushed apart), so the tray version is stored as its own field rather than
assumed equal to the agent (AGENT-CONTRACT.md 2).

Nullable so an endpoint with no tray installed, or an older agent that predates
the field, reads as "unknown" rather than an empty string.

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 = 'endpoints0011trayversion'
down_revision = 'endpoints0010renamepolicy'
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', 'trayversion'):
        return
    op.add_column(
        'endpointstates',
        sa.Column('trayversion', sa.String(length=40), nullable=True))


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