"""限流计数后端契约测试（不连 Redis）。

锁定两条必须成立的语义：

1. 正常路径：窗口内计数递增，并把"剩余窗口秒数"作为 `Retry-After` 的来源返回；
   键首次创建（`TTL` 为 -1）时补一次过期，避免出现永不过期的脏计数键。
2. **降级路径**：Redis 构造失败或命令失败一律返回 `None`（=无法判定），由调用方放行。
   限流是保护措施，不能因为 Redis 故障把正常请求全部拒掉——这条如果回归，故障时
   整个平台会 429 全灭。
"""

from typing import Any

from app.infrastructure.rate_limiter import RedisCounterBackend


class FakePipeline:
    def __init__(self, client: "FakeRedis") -> None:
        self._client = client

    async def __aenter__(self) -> "FakePipeline":
        return self

    async def __aexit__(self, *exc: object) -> bool:
        return False

    def incr(self, key: str) -> "FakePipeline":
        self._client.incr_keys.append(key)
        return self

    def ttl(self, key: str) -> "FakePipeline":
        self._client.ttl_keys.append(key)
        return self

    async def execute(self) -> list[Any]:
        if self._client.fail:
            raise ConnectionError("redis unavailable")
        self._client.count += 1
        return [self._client.count, self._client.ttl_value]


class FakeRedis:
    def __init__(self, *, fail: bool = False, ttl_value: int = 42) -> None:
        self.fail = fail
        self.ttl_value = ttl_value
        self.count = 0
        self.incr_keys: list[str] = []
        self.ttl_keys: list[str] = []
        self.expired: list[tuple[str, int]] = []

    def pipeline(self, transaction: bool = False) -> FakePipeline:
        del transaction
        return FakePipeline(self)

    async def expire(self, key: str, seconds: int) -> bool:
        self.expired.append((key, seconds))
        return True


def backend(client: Any) -> RedisCounterBackend:
    return RedisCounterBackend(
        "redis://unused", connect_timeout_seconds=0.1, client_factory=lambda: client
    )


async def test_first_request_counts_one_and_reports_remaining_window() -> None:
    client = FakeRedis(ttl_value=42)

    result = await backend(client).increment("k", 60)

    assert result == (1, 42)
    assert client.incr_keys == ["k"]


async def test_missing_ttl_is_repaired_with_window_expiry() -> None:
    """`TTL` 为 -1 说明键没有过期时间：必须补一次，否则计数永远不归零。"""
    client = FakeRedis(ttl_value=-1)

    result = await backend(client).increment("k", 60)

    assert result == (1, 60)
    assert client.expired == [("k", 60)]


async def test_redis_command_failure_degrades_to_unknown() -> None:
    client = FakeRedis(fail=True)

    assert await backend(client).increment("k", 60) is None


async def test_client_construction_failure_degrades_to_unknown() -> None:
    def exploding_factory() -> Any:
        raise RuntimeError("redis not installed")

    instance = RedisCounterBackend(
        "redis://unused", connect_timeout_seconds=0.1, client_factory=exploding_factory
    )

    assert await instance.increment("k", 60) is None