"""A concurrent index build that failed part-way, then re-run (E31 S5 review), DB-lane.

CREATE INDEX CONCURRENTLY that fails leaves an INVALID index under its name, and alembic_version is not
stamped, so the next start runs the migration again. `IF NOT EXISTS` matched the name and kept the
leftover, which the planner never uses; 0095 then dropped the old channel_id index, leaving `videos`
with no usable one. A re-run now rebuilds the leftover and drops the old index only once the new one is
valid.
"""

from alembic import command
from alembic.config import Config
from sqlalchemy import text

from app.db import engine


def _index(name: str) -> tuple[bool, str] | None:
    with engine.connect() as conn:
        row = conn.execute(
            text(
                "SELECT i.indisvalid, pg_get_indexdef(i.indexrelid) FROM pg_index i "
                "JOIN pg_class c ON c.oid = i.indexrelid WHERE c.relname = :name"
            ),
            {"name": name},
        ).first()
    return None if row is None else (bool(row[0]), row[1])


def _leave_invalid(name: str) -> None:
    """What a build that failed part-way leaves behind: the name taken, the index INVALID."""
    with engine.connect().execution_options(isolation_level="AUTOCOMMIT") as conn:
        conn.execute(text(f"CREATE INDEX {name} ON videos (id)"))
        conn.execute(
            text(f"UPDATE pg_index SET indisvalid = false WHERE indexrelid = '{name}'::regclass")
        )


def test_a_rerun_rebuilds_an_invalid_leftover_before_dropping_the_old_index(db):
    db.rollback()  # CONCURRENTLY waits for every open transaction, this session's too
    cfg = Config("alembic.ini")
    command.downgrade(cfg, "0094_plex_genres_hu_everywhere")
    try:
        _leave_invalid("ix_videos_channel_pub_cover")
        _leave_invalid("ix_videos_views_desc")
    finally:
        command.upgrade(cfg, "head")

    cover = _index("ix_videos_channel_pub_cover")
    assert cover is not None and cover[0], cover
    assert "INCLUDE (duration_seconds" in cover[1]
    assert _index("ix_videos_channel_pub_desc") is None
    views = _index("ix_videos_views_desc")
    assert views is not None and views[0] and "view_count DESC NULLS LAST" in views[1], views