"""case-insensitive usernames (B-57)

Revision ID: c1d4a97b5e10
Revises: be71fdac734e
Create Date: 2026-08-03 18:10:00.000000

"""
from typing import Sequence, Union

from alembic import op
import sqlalchemy as sa


# revision identifiers, used by Alembic.
revision: str = 'c1d4a97b5e10'
down_revision: Union[str, Sequence[str], None] = 'be71fdac734e'
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    """Upgrade schema."""
    # The index cannot be created while two accounts differ only by case, and
    # nothing here may guess which of them is the "real" one: both are custodial
    # accounts that may hold funds, so merging or renaming one automatically would
    # be the migration silently deciding who owns what. Fail loudly instead, naming
    # the collisions, and let the operator rename one account (and tell that user)
    # before retrying. The container runs `alembic upgrade head` at startup, so this
    # surfaces as a refusal to start rather than as a half-applied schema.
    collisions = op.get_bind().exec_driver_sql(
        "SELECT group_concat(username, ', ') FROM users "
        "GROUP BY lower(username) HAVING count(*) > 1"
    ).fetchall()
    if collisions:
        groups = "; ".join(row[0] for row in collisions)
        raise RuntimeError(
            "cannot enforce case-insensitive usernames: these accounts differ only "
            f"by case and must be resolved by hand first — {groups}"
        )

    op.create_index("ix_users_username_lower", "users", [sa.text("lower(username)")], unique=True)


def downgrade() -> None:
    """Downgrade schema."""
    op.drop_index("ix_users_username_lower", table_name="users")