"""Add last_seen_at and reason_closed to terminal_sessions

Revision ID: 0015
Revises: 0014
Create Date: 2024-12-18

"""
from typing import Sequence, Union

from alembic import op
import sqlalchemy as sa


# revision identifiers, used by Alembic.
revision: str = '0015'
down_revision: Union[str, None] = '0014'
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    # NOTE: SQLite cannot do `ALTER TABLE ... ADD COLUMN ... DEFAULT CURRENT_TIMESTAMP`.
    # We use batch mode to recreate the table safely.

    with op.batch_alter_table('terminal_sessions', recreate='always') as batch_op:
        batch_op.add_column(sa.Column('last_seen_at', sa.DateTime(timezone=True), nullable=True))
        batch_op.add_column(sa.Column('reason_closed', sa.String(30), nullable=True))

    # Backfill last_seen_at from created_at for existing rows
    op.execute("UPDATE terminal_sessions SET last_seen_at = created_at WHERE last_seen_at IS NULL")

    # Enforce NOT NULL + default for future inserts (recreate table again for SQLite)
    with op.batch_alter_table('terminal_sessions', recreate='always') as batch_op:
        batch_op.alter_column('last_seen_at', nullable=False, server_default=sa.text('CURRENT_TIMESTAMP'))

    # Create indexes for efficient queries
    op.create_index('ix_terminal_sessions_user_status', 'terminal_sessions', ['user_id', 'status'])
    op.create_index('ix_terminal_sessions_last_seen', 'terminal_sessions', ['last_seen_at'])


def downgrade() -> None:
    # Drop indexes
    op.drop_index('ix_terminal_sessions_last_seen', table_name='terminal_sessions')
    op.drop_index('ix_terminal_sessions_user_status', table_name='terminal_sessions')

    # Drop columns (batch mode for SQLite)
    with op.batch_alter_table('terminal_sessions', recreate='always') as batch_op:
        batch_op.drop_column('reason_closed')
        batch_op.drop_column('last_seen_at')