"""add account_id to AI branching tables

Revision ID: 478c159e5654
Revises: cc214c63aa30
Create Date: 2026-04-09 00:00:00.000000
"""
from typing import Sequence, Union
from alembic import op
import sqlalchemy as sa

revision: str = '478c159e5654'
down_revision: Union[str, None] = 'cc214c63aa30'
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    ai_tables = ('session_branches', 'session_handoffs', 'fork_points', 'ai_session_steps')

    # Step 1: ADD COLUMN (nullable)
    for table in ai_tables:
        op.add_column(table, sa.Column('account_id', sa.UUID(), nullable=True))
        op.create_foreign_key(
            f'fk_{table}_account_id', table, 'accounts',
            ['account_id'], ['id'], ondelete='CASCADE',
        )

    op.add_column('ai_suggestions', sa.Column('account_id', sa.UUID(), nullable=True))
    op.create_foreign_key(
        'fk_ai_suggestions_account_id', 'ai_suggestions', 'accounts',
        ['account_id'], ['id'], ondelete='CASCADE',
    )

    # Step 2: BACKFILL
    for table in ai_tables:
        op.execute(f"""
            UPDATE {table} t
            SET account_id = ai.account_id
            FROM ai_sessions ai
            WHERE t.session_id = ai.id
              AND t.account_id IS NULL
        """)

    op.execute("""
        UPDATE ai_suggestions s
        SET account_id = u.account_id
        FROM users u
        WHERE s.user_id = u.id
          AND s.account_id IS NULL
    """)

    # Step 3: VERIFY zero NULLs
    for table in ai_tables + ('ai_suggestions',):
        result = op.get_bind().execute(
            sa.text(f"SELECT COUNT(*) FROM {table} WHERE account_id IS NULL")
        )
        count = result.scalar()
        if count > 0:
            raise RuntimeError(
                f"ROLLBACK: {count} NULL account_id rows in {table}."
            )

    # Step 4: SET NOT NULL
    for table in ai_tables + ('ai_suggestions',):
        op.alter_column(table, 'account_id', nullable=False)

    # Step 5: CREATE INDEX
    for table in ai_tables + ('ai_suggestions',):
        op.create_index(f'ix_{table}_account_id', table, ['account_id'])


def downgrade() -> None:
    for table in ('session_branches', 'session_handoffs', 'fork_points',
                  'ai_session_steps', 'ai_suggestions'):
        op.drop_index(f'ix_{table}_account_id', table_name=table)
        op.drop_constraint(f'fk_{table}_account_id', table, type_='foreignkey')
        op.drop_column(table, 'account_id')