"""Merge legacy heads, add cashiers, prevent duplicate entries and prize places."""
from alembic import op
import sqlalchemy as sa

revision = "20260913_staff_concurrency"
down_revision = ("20260701_perf_indexes", "41aae82e631b")
branch_labels = None
depends_on = None


def upgrade():
    connection = op.get_bind()
    # Stop safely on ambiguous historical results; never silently delete prizes.
    checks = (
        ("participations", "lottery_id, account_number", "account_number IS NOT NULL"),
        ("participations", "lottery_id, user_id", "account_number IS NULL AND user_id IS NOT NULL"),
        ("winners", "lottery_id, place", "1=1"),
    )
    for table, columns, predicate in checks:
        duplicate = connection.execute(sa.text(
            f"SELECT 1 FROM {table} WHERE {predicate} GROUP BY {columns} HAVING COUNT(*) > 1 LIMIT 1"
        )).first()
        if duplicate:
            raise RuntimeError(f"Duplicate {table} ({columns}); review duplicates before migrating. No data removed.")
    op.add_column("users", sa.Column("is_cashier", sa.Boolean(), server_default=sa.false(), nullable=False))
    with op.batch_alter_table("participations") as batch:
        batch.create_unique_constraint("uq_participation_account", ["lottery_id", "account_number"])
    op.create_index("uq_participation_user", "participations", ["lottery_id", "user_id"], unique=True,
                    postgresql_where=sa.text("account_number IS NULL"), sqlite_where=sa.text("account_number IS NULL"))
    with op.batch_alter_table("winners") as batch:
        batch.create_unique_constraint("uq_winner_place", ["lottery_id", "place"])


def downgrade():
    with op.batch_alter_table("winners") as batch:
        batch.drop_constraint("uq_winner_place", type_="unique")
    op.drop_index("uq_participation_user", table_name="participations")
    with op.batch_alter_table("participations") as batch:
        batch.drop_constraint("uq_participation_account", type_="unique")
    op.drop_column("users", "is_cashier")