"""The budget meter (method-spec §8) — never an unbounded loop, anywhere.

Normative behaviours proved here: token accounting comes from provider-reported
usage only (a missing usage fails CLOSED, never silently stops counting);
crossing a cap raises a STRUCTURED stop event carrying the breached kind, the
limit, and the observed value — never a silent hang.
"""

from __future__ import annotations

import pytest

from portfolio_optimiser_claude.budget import BudgetExceeded, BudgetMeter, UsageAccountingError
from portfolio_optimiser_claude.contracts import TerminationContract


def _meter(max_rounds: int = 5, max_tokens: int = 100) -> BudgetMeter:
    return BudgetMeter(TerminationContract(max_rounds=max_rounds, max_tokens=max_tokens))


class TestTokenAccounting:
    def test_accumulates_provider_reported_usage(self) -> None:
        meter = _meter(max_tokens=100)
        meter.charge_tokens(30)
        meter.charge_tokens(20)
        assert meter.tokens_used == 50

    def test_missing_usage_fails_closed(self) -> None:
        # §8: on counting paths, a response missing usage MUST fail closed —
        # an error, not a silently-uncounted call.
        meter = _meter()
        with pytest.raises(UsageAccountingError):
            meter.charge_tokens(None)
        assert meter.tokens_used == 0

    def test_reaching_the_cap_exactly_does_not_stop(self) -> None:
        meter = _meter(max_tokens=100)
        meter.charge_tokens(100)
        assert meter.tokens_used == 100

    def test_crossing_the_token_cap_raises_structured_stop(self) -> None:
        meter = _meter(max_tokens=100)
        meter.charge_tokens(90)
        with pytest.raises(BudgetExceeded) as exc_info:
            meter.charge_tokens(20)
        stop = exc_info.value
        assert stop.kind == "tokens"
        assert stop.limit == 100
        assert stop.observed == 110


class TestRoundAccounting:
    def test_round_ticks_accumulate(self) -> None:
        meter = _meter(max_rounds=5)
        meter.charge_round()
        meter.charge_round()
        assert meter.rounds_used == 2

    def test_crossing_the_round_cap_raises_structured_stop(self) -> None:
        meter = _meter(max_rounds=2)
        meter.charge_round()
        meter.charge_round()
        with pytest.raises(BudgetExceeded) as exc_info:
            meter.charge_round()
        stop = exc_info.value
        assert stop.kind == "rounds"
        assert stop.limit == 2
        assert stop.observed == 3


def test_caps_come_from_the_startup_contract() -> None:
    # §8/§10: the termination contract already refuses non-positive caps at
    # construction — the meter builds on that, never on loose ints.
    with pytest.raises(Exception):
        TerminationContract(max_rounds=0, max_tokens=100)