"""Record delisting on tickers instead of deleting them

Revision ID: 032
Revises: 031
Create Date: 2026-08-11 00:00:00.000000

Until now the only way to retire a symbol was ``delete_ticker`` (or
``bootstrap_universe(prune_missing=True)``), both of which cascade through
OHLCV, setups and scores. That destroys exactly the history four research
documents already apologise for: today's tracked universe projected backward
is survivorship-biased, and hard-deleting every delisted name is what causes
it. Keeping the rows preserves the option to fix that later — it does not fix
it by itself, which needs the replay to model a delisting as an exit event.

``delisted_on`` is the effective date (from SEC Form 25/25-NSE/15 where we can
confirm it, else the day it was marked); ``delisted_reason`` is a short code
for how we learned. NULL in both means actively traded — the live signal path
filters on that, while list and admin views keep showing the row so the
delisting is visible rather than silently absent.

Nullable and reversible by design: clearing ``delisted_on`` un-retires a
symbol, which is what makes automatic marking safe where a delete would not be.
"""
from typing import Sequence, Union

from alembic import op
import sqlalchemy as sa


revision: str = "032"
down_revision: Union[str, None] = "031"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    op.add_column("tickers", sa.Column("delisted_on", sa.Date(), nullable=True))
    op.add_column(
        "tickers", sa.Column("delisted_reason", sa.String(length=32), nullable=True)
    )
    # The live path filters "actively traded" on every universe scan; the index
    # keeps that predicate cheap as delisted rows accumulate.
    op.create_index("ix_tickers_delisted_on", "tickers", ["delisted_on"])


def downgrade() -> None:
    op.drop_index("ix_tickers_delisted_on", table_name="tickers")
    op.drop_column("tickers", "delisted_reason")
    op.drop_column("tickers", "delisted_on")