"""hybrid retrieval: generated FTS column on chunks + query_log.fts_hits

Revision ID: 0002
Revises: 0001
Create Date: 2026-08-21

A7/A8 (revised 2026-08-21, owner permission): retrieval becomes hybrid
(cosine top-N + Postgres full-text top-N, RRF-fused). This adds:

* ``chunks.tsv`` — generated ``TSVECTOR`` (``to_tsvector('english',
  content) STORED``) + GIN index for the lexical candidate list.
* ``query_log.fts_hits`` — INT, nullable (pre-existing rows stay NULL:
  the column only carries meaning from hybrid retrieval onward).
"""
from __future__ import annotations

import sqlalchemy as sa

from alembic import op

revision = "0002"
down_revision = "0001"
branch_labels = None
depends_on = None


def upgrade() -> None:
    op.execute(
        "ALTER TABLE chunks "
        "ADD COLUMN tsv tsvector "
        "GENERATED ALWAYS AS (to_tsvector('english', content)) STORED"
    )
    op.execute("CREATE INDEX ix_chunks_tsv ON chunks USING gin (tsv)")
    op.add_column("query_log", sa.Column("fts_hits", sa.Integer(), nullable=True))


def downgrade() -> None:
    op.drop_column("query_log", "fts_hits")
    op.execute("DROP INDEX IF EXISTS ix_chunks_tsv")
    op.execute("ALTER TABLE chunks DROP COLUMN IF EXISTS tsv")