"""`rag/budget.py::RequestBudget` — F-08."""
from __future__ import annotations

import time

import pytest

from rag.budget import RequestBudget, RequestBudgetExhausted
from rag.ports import AnswerGenerationUnavailable


def test_budget_exhausted_is_a_subclass_of_answer_generation_unavailable():
    """Deliberate: every existing `except AnswerGenerationUnavailable:`
    fail-open/fail-closed handler in the codebase must catch this with zero
    changes, since it predates F-08 and already encodes the right behaviour
    for "the provider is unavailable to us right now"."""
    assert issubclass(RequestBudgetExhausted, AnswerGenerationUnavailable)


def test_fresh_budget_has_budget():
    budget = RequestBudget.start(max_wall_clock_ms=20_000, max_calls=5)
    assert budget.has_budget() is True


def test_require_spends_one_call():
    budget = RequestBudget.start(max_wall_clock_ms=20_000, max_calls=2)
    budget.require()
    assert budget.calls_remaining == 1
    budget.require()
    assert budget.calls_remaining == 0
    assert budget.has_budget() is False


def test_require_raises_once_calls_are_exhausted():
    budget = RequestBudget.start(max_wall_clock_ms=20_000, max_calls=1)
    budget.require()
    with pytest.raises(RequestBudgetExhausted):
        budget.require()


def test_require_raises_once_the_deadline_has_passed():
    budget = RequestBudget.start(max_wall_clock_ms=0, max_calls=100)
    time.sleep(0.01)
    assert budget.has_budget() is False
    with pytest.raises(RequestBudgetExhausted):
        budget.require()


def test_a_failed_require_does_not_spend_a_call():
    """`require()` raises before decrementing when there's no budget left —
    `calls_remaining` must not go negative, which would otherwise make a
    budget that's already exhausted look like it has "negative debt" instead
    of cleanly `0`."""
    budget = RequestBudget.start(max_wall_clock_ms=20_000, max_calls=1)
    budget.require()
    for _ in range(3):
        with pytest.raises(RequestBudgetExhausted):
            budget.require()
    assert budget.calls_remaining == 0