tests/test_leverage.py

"""Phase 5 (leverage + ruin): loans, margin calls, short P&L, bankruptcy/exile.

GPU-free and deterministic. Mechanics tests drive the engine with a no-op policy
(so trading never perturbs prices) and control prices / positions / pebbles
directly, mirroring tests/test_information_war.py. Loan settlement is timed off
LOAN_TERM_TURNS; margin calls are driven by writing last_price against an open
short held by the no-op policy.

Run:  python -m pytest tests/ -q
"""

import sys
from pathlib import Path

sys.path.insert(0, str(Path(__file__).resolve().parents[1]))

from ttw.dummy import make_random_policy
from ttw.game import Game
from ttw.moves import MOVE_COSTS
from ttw.world import (
    EXILE_CHAPTER_TURNS,
    LOAN_INTEREST_RATE,
    MARGIN_MAINTENANCE,
    MARGIN_POST,
    ShortPosition,
    short_unrealized_pnl,
)


def _noop_policy(world, name):
    return [], []


def _game(policy=None, seed=1):
    return Game(policy or _noop_policy, deck_seed=seed)


def _step_to_turn(g, turn: int) -> None:
    """Step the no-op world forward until world.turn reaches `turn`."""
    while g.world.turn < turn:
        g.step()


# --- (1) a loan that is paid in full repays and warms the borrower -------------
def test_loan_repaid_debits_borrower_credits_patron_and_warms():
    g = _game()
    borrower = g.world.creatures["Mossback"]
    borrower.pebbles = 1000  # plenty to repay principal + interest
    g.queue_player_move("lend", target="Mossback", amount=100)
    g.step()  # turn 1: loan issued
    loan = g.world.patron.loans[-1]
    interest = 100 * LOAN_INTEREST_RATE // 100
    assert loan.outstanding == 100 + interest
    borrower_after_loan = borrower.pebbles  # includes the +100 principal credit
    purse_before_settle = g.world.patron.purse
    _step_to_turn(g, loan.due_turn)  # step to the due turn -> settlement runs
    assert loan.repaid
    assert borrower.pebbles == borrower_after_loan - (100 + interest)
    assert g.world.patron.purse == purse_before_settle + (100 + interest)
    assert any(e["type"] == "loan_repaid" and e["borrower"] == "Mossback" for e in g.world.log)
    rel = g.world.creatures["Mossback"].relationships.get("Patron")
    assert rel is not None and rel.sentiment > 0  # gratitude landed


# --- (2) a borrower drained below the balance defaults, souring it -------------
def test_loan_default_drains_borrower_and_sours():
    g = _game()
    g.queue_player_move("lend", target="Bramble", amount=100)
    g.step()  # turn 1: loan issued
    loan = g.world.patron.loans[-1]
    sentiment_before = (
        g.world.creatures["Bramble"].relationships.get("Patron").sentiment
    )
    g.world.creatures["Bramble"].pebbles = 5  # too poor to clear the balance
    _step_to_turn(g, loan.due_turn)
    assert loan.defaulted
    assert g.world.creatures["Bramble"].pebbles == 0  # paid all it had
    assert loan.outstanding > 0
    assert any(e["type"] == "loan_defaulted" and e["borrower"] == "Bramble" for e in g.world.log)
    rel = g.world.creatures["Bramble"].relationships.get("Patron")
    assert rel.sentiment < sentiment_before  # resentment landed


# --- (3) a breached short with an empty purse is force-covered -----------------
def test_margin_call_forced_cover_realizes_loss_and_closes():
    g = _game()
    short = ShortPosition(good="honey", qty=5, entry_price=9.0, margin=MARGIN_POST)
    g.world.patron.shorts.append(short)
    g.world.patron.purse = 0  # cannot top up
    g.world.last_price["honey"] = 20.0  # price rose against the short -> loss
    g.step()
    pnl = int((9.0 - 20.0) * 5)  # -55
    assert not short.open
    assert g.world.patron.realized_pnl == pnl
    cover = [e for e in g.world.log if e["type"] == "margin_call"]
    assert cover and cover[-1]["resolution"] == "forced_cover"
    assert any(e["type"] == "short_covered" and e["good"] == "honey" for e in g.world.log)


# --- (4) the same breach with a funded purse tops up instead -------------------
def test_margin_call_top_up_keeps_short_open_and_debits_purse():
    g = _game()
    short = ShortPosition(good="honey", qty=5, entry_price=9.0, margin=MARGIN_POST)
    g.world.patron.shorts.append(short)
    g.world.patron.purse = 500  # can fund the shortfall
    g.world.last_price["honey"] = 20.0  # same breach as the forced-cover case
    pnl = short_unrealized_pnl(short, g.world.last_price)
    equity = MARGIN_POST + pnl
    need = int(MARGIN_MAINTENANCE * MARGIN_POST) - equity
    purse_before = g.world.patron.purse
    g.step()
    assert short.open  # the position survives
    assert short.margin == MARGIN_POST + need
    assert g.world.patron.purse == purse_before - need
    call = [e for e in g.world.log if e["type"] == "margin_call"]
    assert call and call[-1]["resolution"] == "topped_up"


# --- (5) unrealized P&L formula and a no-double-count realization ---------------
def test_unrealized_pnl_formula_and_clean_realization():
    g = _game()
    short = ShortPosition(good="honey", qty=4, entry_price=9.0, margin=MARGIN_POST)
    g.world.patron.shorts.append(short)
    g.world.last_price["honey"] = 15.0
    expected = int((9.0 - 15.0) * 4)  # -24
    assert short_unrealized_pnl(short, g.world.last_price) == expected
    g.world.patron.purse = 0  # force the cover so the unrealized P&L is realized
    realized_before = g.world.patron.realized_pnl
    g.step()
    assert not short.open
    assert g.world.patron.realized_pnl == realized_before + expected  # moved exactly once
    realized_after_first = g.world.patron.realized_pnl
    g.step()  # a closed short must not be re-settled
    assert g.world.patron.realized_pnl == realized_after_first


# --- (6) creature bankruptcy routes through reversible exile, conserves --------
def test_bankruptcy_routes_through_exile_and_conserves_the_system():
    g = Game(make_random_policy(seed=7), deck_seed=1)
    # System invariant for pure loan flows: creature pebbles + purse + open margin.
    def system_total():
        return (
            sum(c.pebbles for c in g.world.creatures.values())
            + g.world.patron.purse
            + sum(s.margin for s in g.world.patron.shorts if s.open)
        )

    g.queue_player_move("lend", target="Pip", amount=80)
    g.step()  # turn 1: loan issued (a pure transfer + Patron purse debit)
    loan = g.world.patron.loans[-1]
    _step_to_turn(g, loan.due_turn - 1)  # up to the turn before settlement
    # Leave Pip with a few pebbles, below the loan balance: the default pays what
    # it has (a transfer) and writes off the rest (a ledger number, not pebbles),
    # so the pebble/margin system stays conserved. Capture the baseline AFTER this
    # edit so the manual top-down does not itself look like a leak, then assert the
    # invariant holds from here across the default, exile, and re-entry.
    g.world.creatures["Pip"].pebbles = 5
    total0 = system_total()
    g.step()  # the due turn: default -> bankruptcy candidate -> exile
    assert loan.defaulted
    assert "Pip" in g.world.exiled
    assert "Pip" not in {c.name for c in g.world.alive()}
    assert any(e["type"] == "bankruptcy" and e["who"] == "Pip" for e in g.world.log)
    assert system_total() == total0  # the default + exile turn conserved the ledger
    # Clearing keeps working and pebbles/margin stay conserved across the window
    # and the re-entry, because loan settlement only transfers pebbles.
    for _ in range(EXILE_CHAPTER_TURNS + 2):
        g.step()
        for c in g.world.creatures.values():
            assert c.pebbles >= 0
            assert all(q >= 0 for q in c.inventory.values())
        assert system_total() == total0
    assert "Pip" in {c.name for c in g.world.alive()}  # re-entered intact


# --- (7) constant honesty: a short's margin equals its purse cost --------------
def test_margin_post_equals_short_purse_cost():
    assert MARGIN_POST == -MOVE_COSTS["short"]["purse"]


# --- (8) the Patron's own ruin is reachable and does not halt the step ---------
def test_patron_ruin_sets_flag_and_does_not_raise():
    g = _game()
    g.world.patron.purse = 0
    g.world.patron.realized_pnl = -10  # net worth <= 0 with no shorts or loans
    assert g.world.patron.net_worth(g.world.last_price) <= 0
    g.step()  # must not raise
    assert g.world.patron.ruined
    assert any(e["type"] == "bankruptcy" and e["who"] == "Patron" for e in g.world.log)


# --- (9) lend still pays the target and injects context (Phase 1 intact) -------
def test_lend_still_pays_target_and_injects_context():
    g = _game()
    target = g.world.creatures["Mossback"]
    before = target.pebbles
    g.world.pending_moves.append({"kind": "lend", "target": "Mossback", "amount": 50})
    # Inspect the credit + context inside the turn, before patron_context is cleared.
    from ttw import moves

    ev = moves.apply_move(g.world, {"kind": "lend", "target": "Mossback", "amount": 50})
    assert ev["applied"]
    assert target.pebbles == before + 50
    assert any("lent you 50 pebbles" in line for line in target.patron_context)
    assert g.world.patron.loans  # the additive Loan ledger entry exists