import circuit_breaker as cb_module
from circuit_breaker import CircuitBreaker, CircuitOpenError

import pytest


class _FakeClock:
    """Deterministic stand-in for time.monotonic()."""

    def __init__(self, start: float = 0.0):
        self.now = start

    def __call__(self) -> float:
        return self.now

    def advance(self, seconds: float) -> None:
        self.now += seconds


@pytest.fixture
def clock(monkeypatch):
    fake = _FakeClock()
    monkeypatch.setattr(cb_module.time, "monotonic", fake)
    return fake


def test_before_call_is_a_noop_below_the_failure_threshold(clock):
    breaker = CircuitBreaker(failure_threshold=3, cooldown_seconds=60)
    breaker.record_failure("bing")
    breaker.record_failure("bing")

    breaker.before_call("bing")  # should not raise - only 2 failures so far


def test_before_call_raises_once_threshold_is_reached(clock):
    breaker = CircuitBreaker(failure_threshold=3, cooldown_seconds=60)
    for _ in range(3):
        breaker.record_failure("bing")

    with pytest.raises(CircuitOpenError):
        breaker.before_call("bing")


def test_record_success_closes_the_circuit(clock):
    breaker = CircuitBreaker(failure_threshold=3, cooldown_seconds=60)
    for _ in range(3):
        breaker.record_failure("bing")

    breaker.record_success("bing")

    breaker.before_call("bing")  # back to closed - should not raise


def test_before_call_allows_a_trial_after_the_cooldown_elapses(clock):
    breaker = CircuitBreaker(failure_threshold=3, cooldown_seconds=60)
    for _ in range(3):
        breaker.record_failure("bing")

    clock.advance(61)

    breaker.before_call("bing")  # cooldown elapsed - half-open, should not raise


def test_a_failed_trial_after_cooldown_reopens_for_another_full_cooldown(clock):
    breaker = CircuitBreaker(failure_threshold=3, cooldown_seconds=60)
    for _ in range(3):
        breaker.record_failure("bing")

    clock.advance(61)
    breaker.before_call("bing")  # half-open trial begins
    breaker.record_failure("bing")  # ...and it failed

    clock.advance(30)  # only 30s into the new cooldown
    with pytest.raises(CircuitOpenError):
        breaker.before_call("bing")

    clock.advance(31)  # now past the new 60s cooldown
    breaker.before_call("bing")  # should not raise


def test_keys_are_independent(clock):
    breaker = CircuitBreaker(failure_threshold=2, cooldown_seconds=60)
    for _ in range(2):
        breaker.record_failure("bing")

    breaker.before_call("brave")  # untouched key - should not raise
    with pytest.raises(CircuitOpenError):
        breaker.before_call("bing")


def test_circuit_open_error_carries_the_key_and_remaining_seconds(clock):
    breaker = CircuitBreaker(failure_threshold=1, cooldown_seconds=60)
    breaker.record_failure("bing")

    clock.advance(10)
    with pytest.raises(CircuitOpenError) as exc_info:
        breaker.before_call("bing")

    assert exc_info.value.key == "bing"
    assert exc_info.value.retry_after == pytest.approx(50, abs=0.01)