from __future__ import annotations

from unittest.mock import patch

from yuxi.channel.lifecycle.backoff import BackoffPolicy


class TestBackoffPolicy:
    def test_default_parameters(self):
        policy = BackoffPolicy()
        assert policy.base_ms == 1000
        assert policy.max_ms == 30000
        assert policy.jitter_ms == 1000

    def test_custom_parameters(self):
        policy = BackoffPolicy(base_ms=500, max_ms=10000, jitter_ms=200)
        assert policy.base_ms == 500
        assert policy.max_ms == 10000
        assert policy.jitter_ms == 200

    def test_zero_attempts_uses_base_delay(self):
        policy = BackoffPolicy(base_ms=1000, jitter_ms=0)
        assert policy.compute(0) == 1000

    def test_exponential_growth(self):
        policy = BackoffPolicy(base_ms=1000, jitter_ms=0)
        assert policy.compute(1) == 2000
        assert policy.compute(2) == 4000
        assert policy.compute(3) == 8000

    def test_max_delay_cap(self):
        policy = BackoffPolicy(base_ms=1000, max_ms=5000, jitter_ms=0)
        assert policy.compute(10) == 5000

    def test_negative_attempts_clamped_to_zero(self):
        policy = BackoffPolicy(base_ms=1000, jitter_ms=0)
        assert policy.compute(-1) == 1000
        assert policy.compute(-5) == 1000

    def test_jitter_is_applied(self):
        policy = BackoffPolicy(base_ms=1000, jitter_ms=500)
        with patch.object(policy, "jitter_ms", 500):
            with patch("yuxi.channel.lifecycle.backoff.random.randint", return_value=250):
                assert policy.compute(0) == 1250

    def test_attempts_capped_at_30(self):
        policy = BackoffPolicy(base_ms=1, max_ms=1_000_000_000, jitter_ms=0)
        # 2**30 is large but capped by attempts, not max_ms
        value_30 = policy.compute(30)
        value_31 = policy.compute(31)
        value_100 = policy.compute(100)
        assert value_30 == value_31 == value_100

    def test_jitter_range(self):
        policy = BackoffPolicy(base_ms=1000, jitter_ms=100)
        for _ in range(50):
            delay = policy.compute(0)
            assert 1000 <= delay <= 1100

    def test_jitter_does_not_exceed_max_ms(self):
        policy = BackoffPolicy(base_ms=1000, max_ms=2000, jitter_ms=500)
        with patch("yuxi.channel.lifecycle.backoff.random.randint", return_value=500):
            delay = policy.compute(10)
            assert delay == 2000