siftlode/backend/tests/test_playlist_position_lock.py

"""Every request that reads a playlist's item positions and writes new ones locks the
playlist row first.

Without it two adds (two tabs; the rail and the page) both read the same `max(position)` and land
on one position, and a reorder racing an add collides with it — the list's order between the two
rows is then whatever the planner returns. A true two-connection race is not reproducible on
demand, so the test holds the mechanism: the parent row is taken `FOR UPDATE` by each such route.
A Plex reorder that omits a row (added in another tab meanwhile) must not collide with it either.

The lock also comes FIRST — before the request reads or writes a single item row. A remove
that deleted an item and then touched the playlist beside a reorder that went the other way was a
deadlock (a 500 for one of them), and an add that checked "already there?" before the lock let two
adds of one video both insert (a 500 on the unique key).
"""

import re
from datetime import datetime, timezone

import pytest
from sqlalchemy import event

from app.models import (
    Channel,
    Playlist,
    PlaylistItem,
    PlexItem,
    PlexLibrary,
    PlexPlaylist,
    PlexPlaylistItem,
    Video,
)


@pytest.fixture
def locks(db):
    """The tables each request took a row lock on (`SELECT … FROM <t> … FOR UPDATE`)."""
    seen: list[str] = []

    def _record(conn, cursor, statement, *_):
        if "FOR UPDATE" in statement:
            seen.extend(re.findall(r"FROM\s+(\w+)", statement)[:1])

    engine = db.get_bind()
    event.listen(engine, "before_cursor_execute", _record)
    yield seen
    event.remove(engine, "before_cursor_execute", _record)


@pytest.fixture
def statements(db):
    """Every statement a request ran, in order."""
    seen: list[str] = []

    def _record(conn, cursor, statement, *_):
        seen.append(" ".join(statement.split()))

    engine = db.get_bind()
    event.listen(engine, "before_cursor_execute", _record)
    yield seen
    event.remove(engine, "before_cursor_execute", _record)


def _locked_before_items(seen: list[str], parent: str, items: str) -> str | None:
    """The first statement touching `items` must come after a `FOR UPDATE` of `parent`; returns
    that lock statement (None when it came too late or never)."""
    lock = None
    for st in seen:
        if lock is None and "FOR UPDATE" in st and re.search(rf"FROM {parent}\b", st):
            lock = st
        if re.search(rf"\b{items}\b", st):
            return lock
    return lock


def _yt(db, user):
    db.add(Channel(id="UCtest", title="Test"))
    now = datetime.now(timezone.utc)
    for v in ("v1", "v2", "v3"):
        db.add(Video(id=v, channel_id="UCtest", published_at=now))
    pl = Playlist(user_id=user.id, name="L")
    other = Playlist(user_id=user.id, name="M")
    db.add_all([pl, other])
    db.flush()
    db.add(PlaylistItem(playlist_id=pl.id, video_id="v1", position=0))
    db.commit()
    return pl.id, other.id


def _plex(db, user):
    lib = PlexLibrary(plex_key="p1", title="Movies", kind="movie", enabled=True)
    db.add(lib)
    db.flush()
    items = [PlexItem(rating_key=rk, library_id=lib.id, kind="movie", title=rk) for rk in "abcd"]
    db.add_all(items)
    pl = PlexPlaylist(user_id=user.id, title="L")
    db.add(pl)
    db.flush()
    for i, it in enumerate(items[:3]):
        db.add(PlexPlaylistItem(playlist_id=pl.id, item_id=it.id, position=i))
    db.commit()
    return pl.id


YT = Playlist.__table__.name
PLEX = PlexPlaylist.__table__.name


@pytest.mark.parametrize(
    "call",
    [
        lambda c, pid, other: c.post(f"/api/playlists/{pid}/items", json={"video_id": "v2"}),
        lambda c, pid, other: c.post(
            f"/api/playlists/{pid}/items", json={"video_id": "v2", "position": 0}
        ),
        lambda c, pid, other: c.post("/api/playlists/watch-later", json={"video_id": "v2"}),
        lambda c, pid, other: c.post(
            f"/api/playlists/{pid}/items/v1/move", json={"target_playlist_id": other}
        ),
        lambda c, pid, other: c.put(f"/api/playlists/{pid}/order", json={"video_ids": ["v1"]}),
    ],
    ids=["add", "add-at", "watch-later", "move", "reorder"],
)
def test_a_youtube_playlist_write_locks_the_playlist(db, make_user, as_user, locks, call):
    user = make_user()
    pid, other = _yt(db, user)
    r = call(as_user(user), pid, other)
    assert r.status_code == 200, r.text
    assert YT in locks


@pytest.mark.parametrize(
    "call",
    [
        lambda c, pid: c.post(f"/api/plex/playlists/{pid}/items", json={"item_rating_key": "d"}),
        lambda c, pid: c.post(
            f"/api/plex/playlists/{pid}/items/bulk", json={"item_rating_keys": ["d"]}
        ),
        lambda c, pid: c.post(
            f"/api/plex/playlists/{pid}/items/bulk",
            json={"item_rating_keys": ["d"], "positions": [0]},
        ),
        lambda c, pid: c.put(
            f"/api/plex/playlists/{pid}/order", json={"item_rating_keys": ["c", "b", "a"]}
        ),
    ],
    ids=["add", "bulk", "bulk-at", "reorder"],
)
def test_a_plex_playlist_write_locks_the_playlist(db, make_user, as_user, locks, call):
    user = make_user()
    pid = _plex(db, user)
    r = call(as_user(user), pid)
    assert r.status_code == 200, r.text
    assert PLEX in locks


def test_a_plex_reorder_that_omits_a_row_does_not_collide_with_it(db, make_user, as_user):
    """The row "a" was added in another tab after this page loaded its order ["c", "b"]: it keeps
    its place after the given rows instead of sharing position 0 with "c"."""
    user = make_user()
    pid = _plex(db, user)
    r = as_user(user).put(f"/api/plex/playlists/{pid}/order", json={"item_rating_keys": ["c", "b"]})
    assert r.status_code == 200
    db.expire_all()
    rows = db.query(PlexPlaylistItem).filter_by(playlist_id=pid).all()
    by_id = {it.id: it.rating_key for it in db.query(PlexItem).all()}
    got = sorted((r.position, by_id[r.item_id]) for r in rows)
    assert got == [(0, "c"), (1, "b"), (2, "a")]


YT_ITEMS = PlaylistItem.__table__.name
PLEX_ITEMS = PlexPlaylistItem.__table__.name


@pytest.mark.parametrize(
    "call",
    [
        lambda c, pid, other: c.post(f"/api/playlists/{pid}/items", json={"video_id": "v1"}),
        lambda c, pid, other: c.post(
            f"/api/playlists/{pid}/items", json={"video_id": "v2", "position": 0}
        ),
        lambda c, pid, other: c.delete(f"/api/playlists/{pid}/items/v1"),
        lambda c, pid, other: c.post(
            f"/api/playlists/{pid}/items/v1/move", json={"target_playlist_id": other}
        ),
        lambda c, pid, other: c.put(f"/api/playlists/{pid}/order", json={"video_ids": ["v1"]}),
        # the ORM cascade deletes the items before the list row
        lambda c, pid, other: c.delete(f"/api/playlists/{pid}"),
    ],
    ids=["add-present", "add-at", "remove", "move", "reorder", "delete"],
)
def test_a_youtube_item_write_locks_the_playlist_before_any_item(
    db, make_user, as_user, statements, call
):
    user = make_user()
    pid, other = _yt(db, user)
    c = as_user(user)
    statements.clear()
    r = call(c, pid, other)
    assert r.status_code == 200, r.text
    assert _locked_before_items(statements, YT, YT_ITEMS), statements


def test_a_move_locks_both_lists_in_one_ordered_statement(db, make_user, as_user, statements):
    """Two moves A→B and B→A each locking "its" list first would lock crosswise."""
    user = make_user()
    pid, other = _yt(db, user)
    statements.clear()
    r = as_user(user).post(
        f"/api/playlists/{pid}/items/v1/move", json={"target_playlist_id": other}
    )
    assert r.status_code == 200, r.text
    lock = _locked_before_items(statements, YT, YT_ITEMS)
    assert lock and "ORDER BY" in lock, lock
    # BOTH lists in that one statement: one bound id per list in its IN (…) (a single-id lock
    # renders the same IN and ORDER BY)
    listed = re.search(r" IN \((.*?)\) ORDER BY", lock)
    assert listed and len(re.findall(r"%\(\w+\)s", listed.group(1))) == 2, lock


def test_watch_later_add_and_remove_lock_it_before_any_item(db, make_user, as_user, statements):
    user = make_user()
    _yt(db, user)
    c = as_user(user)
    assert c.post("/api/playlists/watch-later", json={"video_id": "v2"}).status_code == 200
    statements.clear()
    assert c.post("/api/playlists/watch-later", json={"video_id": "v2"}).status_code == 200
    assert _locked_before_items(statements, YT, YT_ITEMS), statements
    statements.clear()
    assert c.delete("/api/playlists/watch-later/v2").status_code == 200
    assert _locked_before_items(statements, YT, YT_ITEMS), statements


def test_a_rename_locks_the_playlist(db, make_user, as_user, locks):
    """A rename moves `dirty`, which the scheduled mirror refresh re-reads under this lock."""
    user = make_user()
    pid, _ = _yt(db, user)
    r = as_user(user).patch(f"/api/playlists/{pid}", json={"name": "New"})
    assert r.status_code == 200, r.text
    assert YT in locks


@pytest.mark.parametrize(
    "call",
    [
        lambda c, pid: c.delete(f"/api/plex/playlists/{pid}/items/a"),
        lambda c, pid: c.post(
            f"/api/plex/playlists/{pid}/items/remove-bulk", json={"item_rating_keys": ["a", "b"]}
        ),
        lambda c, pid: c.post(f"/api/plex/playlists/{pid}/items", json={"item_rating_key": "a"}),
    ],
    ids=["remove", "remove-bulk", "add-present"],
)
def test_a_plex_item_write_locks_the_playlist_before_any_item(
    db, make_user, as_user, statements, call
):
    user = make_user()
    pid = _plex(db, user)
    c = as_user(user)
    statements.clear()
    r = call(c, pid)
    assert r.status_code == 200, r.text
    assert _locked_before_items(statements, PLEX, PLEX_ITEMS), statements