"""Allow walletless Telegram bindings.

Before: every binding had to be tied to a subscribed wallet.
After:  anyone who DMs the bot can subscribe to public alerts; the
        wallet_address column becomes nullable. Uniqueness is on chat_id
        alone — the same Telegram chat can never have two bindings.

A wallet can still have at most one binding (enforced by a partial unique
index on wallet_address WHERE wallet_address IS NOT NULL).

Revision ID: 021
Revises: 020
Create Date: 2026-05-24
"""
from alembic import op
import sqlalchemy as sa

revision = "021"
down_revision = "020"
branch_labels = None
depends_on = None


def upgrade() -> None:
    # SQLite + batch mode → recreates the table preserving rows.
    with op.batch_alter_table("telegram_bindings") as batch:
        batch.alter_column("wallet_address",
                           existing_type=sa.String(64),
                           nullable=True)

    # Drop the old unique constraint on wallet_address (was created via
    # `unique=True`), then add a partial unique index that allows multiple
    # NULL wallets but still prevents two bindings for the same wallet.
    # SQLite quirk: the auto-generated unique index name is
    # `ix_telegram_bindings_wallet_address` (because we also indexed it).
    # We replace it with the partial-unique form.
    with op.batch_alter_table("telegram_bindings") as batch:
        batch.drop_index("ix_telegram_bindings_wallet_address")
    op.create_index(
        "ix_telegram_bindings_wallet_address",
        "telegram_bindings",
        ["wallet_address"],
        unique=True,
        sqlite_where=sa.text("wallet_address IS NOT NULL"),
        postgresql_where=sa.text("wallet_address IS NOT NULL"),
    )


def downgrade() -> None:
    # Note: downgrade FAILS if any walletless rows exist — caller must
    # delete them first. This is intentional (data preservation > graceful
    # downgrade for an opt-in safety net).
    op.drop_index("ix_telegram_bindings_wallet_address", table_name="telegram_bindings")
    with op.batch_alter_table("telegram_bindings") as batch:
        batch.alter_column("wallet_address",
                           existing_type=sa.String(64),
                           nullable=False)
        batch.create_index("ix_telegram_bindings_wallet_address",
                           ["wallet_address"], unique=True)