import sqlalchemy as sa
from alembic import op
from sqlalchemy.dialects import mysql

revision = "0023_stream_window"
down_revision = "0022_run_inputs"
branch_labels = None
depends_on = None


def upgrade():
    # 仅推进续传窗口，原始消息和幂等收据继续保留。
    op.add_column("conversations", sa.Column("stream_cursor", mysql.BIGINT(unsigned=True),
                                            nullable=False, server_default="0"))
    op.alter_column("conversations", "stream_cursor", server_default=None,
                    existing_type=mysql.BIGINT(unsigned=True))


def downgrade():
    op.drop_column("conversations", "stream_cursor")