"""Observed membership intervals.

The table answers "what could the strategy actually have selected on date D?"
Three properties make that answer trustworthy:

1. History starts at the first *observation*. Nothing invents an index effective
   date for a symbol that was already tracked when recording began.
2. Intervals are append-only. Leaving and returning produces two rows, so a
   point-in-time query for the gap correctly answers "not a member".
3. A failed universe fetch records nothing. The seed fallback is ~44 symbols, so
   treating it as an observation would close ~460 memberships on a network blip.
"""

from __future__ import annotations

from collections.abc import AsyncGenerator
from datetime import date

import pytest
from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine

from app.database import Base
from app.models.ticker import Ticker
from app.models.universe_membership import UniverseMembership
from app.services import ticker_service
from app.services import ticker_universe_service as tus

_engine = create_async_engine("sqlite+aiosqlite://", echo=False)
_session_factory = async_sessionmaker(_engine, class_=AsyncSession, expire_on_commit=False)


@pytest.fixture(autouse=True)
async def _setup_tables() -> AsyncGenerator[None, None]:
    async with _engine.begin() as conn:
        await conn.run_sync(Base.metadata.create_all)
    yield
    async with _engine.begin() as conn:
        await conn.run_sync(Base.metadata.drop_all)


@pytest.fixture
async def session() -> AsyncGenerator[AsyncSession, None]:
    async with _session_factory() as s:
        yield s


async def _sync(session, monkeypatch, symbols: list[str], *, source: str = "wikipedia_sp500",
                prune: bool = False) -> dict:
    async def fake_fetch(db, universe):
        return symbols, source

    monkeypatch.setattr(tus, "fetch_universe_symbols", fake_fetch)
    return await tus.bootstrap_universe(session, "sp500", prune_missing=prune)


async def _intervals(session, symbol: str) -> list[tuple]:
    rows = (await session.execute(
        select(UniverseMembership.first_seen_on, UniverseMembership.absent_since)
        .join(Ticker, Ticker.id == UniverseMembership.ticker_id)
        .where(Ticker.symbol == symbol)
        .order_by(UniverseMembership.id)
    )).all()
    return [tuple(r) for r in rows]


async def test_a_live_sync_opens_intervals_without_pruning(session: AsyncSession, monkeypatch):
    """The scheduled job runs prune_missing=False. If membership were only
    recorded on prunes the history would be full of holes."""
    summary = await _sync(session, monkeypatch, ["AAPL", "MSFT"])

    assert summary["membership_observed"] is True
    assert summary["membership_opened"] == 2
    assert summary["membership_closed"] == 0
    assert summary["untracked"] == 0, "recording membership is not pruning"

    intervals = await _intervals(session, "AAPL")
    assert len(intervals) == 1
    first_seen, last_seen = intervals[0]
    assert last_seen is None, "an open interval means still observed"
    assert abs((first_seen - date.today()).days) <= 1


async def test_a_second_sync_does_not_duplicate_an_open_interval(
    session: AsyncSession, monkeypatch
):
    await _sync(session, monkeypatch, ["AAPL"])
    summary = await _sync(session, monkeypatch, ["AAPL"])

    assert summary["membership_opened"] == 0
    assert len(await _intervals(session, "AAPL")) == 1


async def test_leaving_closes_the_interval_and_returning_opens_a_new_one(
    session: AsyncSession, monkeypatch
):
    await _sync(session, monkeypatch, ["AAPL", "LEAVER"])
    closing = await _sync(session, monkeypatch, ["AAPL"])
    assert closing["membership_closed"] == 1

    intervals = await _intervals(session, "LEAVER")
    assert len(intervals) == 1
    assert intervals[0][1] is not None, "departure closes the interval"

    returning = await _sync(session, monkeypatch, ["AAPL", "LEAVER"])
    assert returning["membership_opened"] == 1

    intervals = await _intervals(session, "LEAVER")
    assert len(intervals) == 2, "re-entry appends; it does not reopen"
    assert intervals[0][1] is not None, "the earlier interval keeps its end date"
    assert intervals[1][1] is None


async def test_a_failed_fetch_records_nothing(session: AsyncSession, monkeypatch):
    """A cache or seed result means the live fetch failed. The seed list is a
    fraction of the real universe — closing memberships from it would rewrite
    history on a network blip."""
    await _sync(session, monkeypatch, ["AAPL", "MSFT"])

    for failed_source in ("cache", "seed"):
        summary = await _sync(session, monkeypatch, ["AAPL"], source=failed_source)
        assert summary["membership_observed"] is False
        assert summary["membership_closed"] == 0
        assert summary["membership_opened"] == 0

    # MSFT's membership is untouched: we never looked, so we know nothing new.
    msft = await _intervals(session, "MSFT")
    assert len(msft) == 1
    assert msft[0][1] is None, "still open — a failed fetch is not a departure"


async def test_membership_is_recorded_for_manual_rows_too(session: AsyncSession, monkeypatch):
    """Membership and tracking ownership are independent axes: a manually owned
    symbol that is genuinely in the index still gets intervals."""
    session.add(Ticker(symbol="MINE", tracking_source=ticker_service.SOURCE_MANUAL))
    await session.commit()

    await _sync(session, monkeypatch, ["AAPL", "MINE"])

    mine = (
        await session.execute(select(Ticker).where(Ticker.symbol == "MINE"))
    ).scalar_one()
    assert mine.tracking_source == ticker_service.SOURCE_MANUAL
    assert len(await _intervals(session, "MINE")) == 1


async def test_switching_off_scanning_does_not_close_a_membership(
    session: AsyncSession, monkeypatch
):
    """The index still contains the symbol; we simply stopped looking at it.
    Conflating those would corrupt the point-in-time answer."""
    await _sync(session, monkeypatch, ["AAPL", "MSFT"])
    await ticker_service.set_tracked(session, "MSFT", tracked=False)

    summary = await _sync(session, monkeypatch, ["AAPL", "MSFT"])
    assert summary["membership_closed"] == 0
    assert (await _intervals(session, "MSFT"))[0][1] is None


async def test_pruning_does_not_close_a_membership_by_itself(
    session: AsyncSession, monkeypatch
):
    """Closing happens because the symbol was absent from a live list, not
    because a prune ran — the two just usually coincide."""
    await _sync(session, monkeypatch, ["AAPL", "LEAVER"])
    session.add(Ticker(symbol="MINE", tracking_source=ticker_service.SOURCE_MANUAL))
    await session.commit()

    summary = await _sync(session, monkeypatch, ["AAPL"], prune=True)
    # LEAVER closed because it was absent; MINE never had an interval to close.
    assert summary["membership_closed"] == 1
    assert await _intervals(session, "MINE") == []


async def test_a_failed_fetch_does_not_untrack_anything(session: AsyncSession, monkeypatch):
    """The seed fallback is ~44 symbols against a ~500-symbol universe. Pruning
    from it would untrack the entire index on a single network blip — skipping
    membership recording is only half the safeguard."""
    session.add_all([
        Ticker(symbol=s, tracking_source=ticker_service.SOURCE_INDEX)
        for s in ("AAPL", "MSFT", "NVDA")
    ])
    await session.commit()

    summary = await _sync(session, monkeypatch, ["AAPL"], source="seed", prune=True)

    assert summary["untracked"] == 0, "a failed fetch must not drive pruning"
    live = await session.execute(
        ticker_service.active_only(select(Ticker.symbol).order_by(Ticker.symbol))
    )
    assert list(live.scalars().all()) == ["AAPL", "MSFT", "NVDA"]


async def test_a_failed_fetch_does_not_clear_a_prune_flag(session: AsyncSession, monkeypatch):
    """Re-entry is a claim about the index. A cache fallback is not evidence the
    symbol rejoined it."""
    session.add_all([
        Ticker(symbol=s, tracking_source=ticker_service.SOURCE_INDEX)
        for s in ("AAPL", "LEAVER")
    ])
    await session.commit()
    await _sync(session, monkeypatch, ["AAPL"], prune=True)  # LEAVER untracked

    summary = await _sync(session, monkeypatch, ["AAPL", "LEAVER"], source="cache")
    assert summary["retracked"] == 0, "stale data must not re-admit a symbol"

    leaver = (
        await session.execute(select(Ticker).where(Ticker.symbol == "LEAVER"))
    ).scalar_one()
    assert leaver.untracked_on is not None


# ---------------------------------------------------------------------------
# Interval boundaries, stated as executable rules
# ---------------------------------------------------------------------------


async def _interval(session, symbol: str, universe: str, first: date, absent: date | None):
    """Write one interval directly, so boundary tests don't depend on today."""
    ticker = (
        await session.execute(select(Ticker).where(Ticker.symbol == symbol))
    ).scalar_one_or_none()
    if ticker is None:
        ticker = Ticker(symbol=symbol, tracking_source=ticker_service.SOURCE_INDEX)
        session.add(ticker)
        await session.flush()
    session.add(UniverseMembership(
        ticker_id=ticker.id, universe=universe,
        first_seen_on=first, absent_since=absent,
    ))
    await session.commit()


async def test_membership_bounds_are_lower_inclusive_upper_exclusive(session: AsyncSession):
    """``absent_since`` is the first observation that found the symbol GONE, so
    on that date it is already absent. ``first_seen_on`` is the first that found
    it present, so on that date it is already a member."""
    await _interval(session, "EDGE", "sp500", date(2026, 3, 10), date(2026, 8, 20))

    async def members(d: date) -> list[str]:
        return await tus.members_on(session, "sp500", d)

    assert await members(date(2026, 3, 9)) == [], "the day before first observation"
    assert await members(date(2026, 3, 10)) == ["EDGE"], "lower bound is inclusive"
    assert await members(date(2026, 8, 19)) == ["EDGE"], "still present the day before"
    assert await members(date(2026, 8, 20)) == [], "upper bound is exclusive"


async def test_an_open_interval_has_no_upper_bound(session: AsyncSession):
    await _interval(session, "OPEN", "sp500", date(2026, 3, 10), None)
    assert await tus.members_on(session, "sp500", date(2030, 1, 1)) == ["OPEN"]


async def test_a_gap_between_two_intervals_is_not_membership(session: AsyncSession):
    """The reason re-entry appends instead of reopening."""
    await _interval(session, "GAP", "sp500", date(2026, 1, 5), date(2026, 3, 2))
    await _interval(session, "GAP", "sp500", date(2026, 8, 3), None)

    assert await tus.members_on(session, "sp500", date(2026, 2, 1)) == ["GAP"]
    assert await tus.members_on(session, "sp500", date(2026, 5, 1)) == []
    assert await tus.members_on(session, "sp500", date(2026, 9, 1)) == ["GAP"]


async def test_membership_is_scoped_per_universe(session: AsyncSession):
    await _interval(session, "BOTH", "sp500", date(2026, 1, 5), None)
    await _interval(session, "BOTH", "nasdaq100", date(2026, 6, 1), None)
    await _interval(session, "SPONLY", "sp500", date(2026, 1, 5), None)

    assert await tus.members_on(session, "sp500", date(2026, 7, 1)) == ["BOTH", "SPONLY"]
    assert await tus.members_on(session, "nasdaq100", date(2026, 7, 1)) == ["BOTH"]
    # Before it joined the Nasdaq-100 it was only an S&P name.
    assert await tus.members_on(session, "nasdaq100", date(2026, 5, 1)) == []


async def test_before_recording_began_returns_empty_not_the_current_set(
    session: AsyncSession, monkeypatch
):
    """The honest limit of this table: a date before the first successful live
    sync means "we were not looking", not "the index was empty". Answering with
    today's set would be exactly the survivorship error item 3 exists to end."""
    await _sync(session, monkeypatch, ["AAPL", "MSFT"])

    assert await tus.members_on(session, "sp500", date(2020, 1, 2)) == []
    assert await tus.members_on(session, "sp500", date.today()) == ["AAPL", "MSFT"]