"""限流闸门契约测试（文档 §3.5 的 429、§3.6 的 `RATE_LIMITED`，标注为可重试）。

覆盖用户要求的三条：正常放行、超限拒绝且码与 `Retry-After` 正确、Redis 不可用时
降级放行；另加三条边界：

- 闸门关闭（`RATE_LIMIT_ENABLED=false`）时不访问后端；
- 认证先于限流（未带令牌仍是 401，不会被限流改写成 429）；
- 计数维度按"用户 + 路由模板"，而不是原始 URL——否则 `/{run_id}` 这类路径每个资源
  都会各自计数，限流形同虚设。

全部进程内调用，不连 Redis（后端是替身），也不连数据库（放行路径用替身 Service）。
"""

from collections.abc import AsyncIterator
from typing import Any

import pytest
from fastapi import Request
from fastapi.testclient import TestClient

from app.api.dependencies.auth import build_request_context
from app.api.dependencies.database import get_session
from app.core.config import get_settings
from app.core.contracts import RequestContext
from app.main import create_app

MESSAGES = "/api/v1/conversations/session-1/messages"
RUN_DETAIL = "/api/v1/agent-runs/run-1"


class FakeBackend:
    """替身计数后端：固定返回给定的 `(计数, 剩余秒数)`，或 `None`（后端不可用）。"""

    def __init__(self, result: tuple[int, int] | None) -> None:
        self.result = result
        self.calls: list[tuple[str, int]] = []

    async def increment(self, key: str, window_seconds: int) -> tuple[int, int] | None:
        self.calls.append((key, window_seconds))
        return self.result


class RecordingService:
    def __init__(self, session: Any) -> None:
        del session

    async def messages(
        self, session_id: str, context: RequestContext, limit: int, before: int | None = None
    ) -> dict[str, object]:
        return {"data": []}


async def override_session() -> AsyncIterator[Any]:
    yield object()


def build_client(
    monkeypatch: pytest.MonkeyPatch,
    *,
    backend: FakeBackend | None,
    user_id: str = "9001",
    max_requests: int = 2,
    enabled: bool = True,
) -> TestClient:
    monkeypatch.setattr(
        "app.api.dependencies.rate_limit.get_settings",
        lambda: get_settings().model_copy(update={
            "rate_limit_enabled": enabled,
            "rate_limit_window_seconds": 60,
            "rate_limit_max_requests": max_requests,
            "rate_limit_key_prefix": "test:rate_limit",
        }),
    )
    if backend is not None:
        monkeypatch.setattr(
            "app.api.dependencies.rate_limit.get_counter_backend", lambda: backend
        )
    monkeypatch.setattr("app.api.controllers.conversations.ConversationService", RecordingService)

    application = create_app()

    async def context(request: Request) -> RequestContext:
        built = RequestContext(user_id=user_id, trace_id="trace-rate",
                              permissions=("conversation:read", "agent:run"))
        request.state.request_context = built
        return built

    application.dependency_overrides[build_request_context] = context
    application.dependency_overrides[get_session] = override_session
    return TestClient(application)


def test_request_within_limit_is_allowed(monkeypatch: pytest.MonkeyPatch) -> None:
    backend = FakeBackend((2, 30))  # 恰好等于阈值：文档语义是"超过"才拒绝
    expected_key = "test:rate_limit:9001:GET:/api/v1/conversations/{session_id}/messages"

    with build_client(monkeypatch, backend=backend, max_requests=2) as client:
        response = client.get(MESSAGES)

    assert response.status_code == 200
    assert backend.calls == [(expected_key, 60)]


def test_request_over_limit_returns_429_with_code_and_retry_after(
    monkeypatch: pytest.MonkeyPatch
) -> None:
    backend = FakeBackend((3, 17))

    with build_client(monkeypatch, backend=backend, max_requests=2) as client:
        response = client.get(MESSAGES)

    assert response.status_code == 429
    assert response.headers["Retry-After"] == "17"
    body = response.json()
    assert set(body) == {"error", "meta"}
    assert body["error"]["code"] == "RATE_LIMITED"
    assert body["error"]["retryable"] is True  # 文档 §3.6：该码可重试
    assert body["error"]["field_errors"] == []
    assert body["meta"]["trace_id"] == "trace-rate"


def test_redis_unavailable_degrades_to_allow(monkeypatch: pytest.MonkeyPatch) -> None:
    """Redis 不可用时必须放行：保护措施不能变成全量拒绝。"""
    backend = FakeBackend(None)

    with build_client(monkeypatch, backend=backend) as client:
        response = client.get(MESSAGES)

    assert response.status_code == 200
    assert len(backend.calls) == 1  # 确实尝试过判定，只是判定不出来


def test_disabled_limit_does_not_touch_backend(monkeypatch: pytest.MonkeyPatch) -> None:
    backend = FakeBackend((99, 5))

    with build_client(monkeypatch, backend=backend, enabled=False) as client:
        response = client.get(MESSAGES)

    assert response.status_code == 200
    assert backend.calls == []


def test_authentication_precedes_rate_limiting(monkeypatch: pytest.MonkeyPatch) -> None:
    """未带令牌 + 已超限：必须仍是 401（限流不得掩盖鉴权失败）。"""
    application = create_app()
    monkeypatch.setattr(
        "app.api.dependencies.rate_limit.get_settings",
        lambda: get_settings().model_copy(update={"rate_limit_max_requests": 1}),
    )
    monkeypatch.setattr(
        "app.api.dependencies.rate_limit.get_counter_backend", lambda: FakeBackend((99, 5))
    )

    with TestClient(application) as client:
        response = client.get(MESSAGES)

    assert response.status_code == 401
    assert response.json()["error"]["code"] == "AUTHENTICATION_REQUIRED"


def test_counter_key_uses_route_template_and_user(monkeypatch: pytest.MonkeyPatch) -> None:
    """计数维度：同一路由模板下不同 `run_id` 共用一个计数器，不同用户互相隔离。"""
    first = FakeBackend((1, 60))
    second = FakeBackend((1, 60))

    with build_client(monkeypatch, backend=first, user_id="9001") as client:
        client.get("/api/v1/agent-runs/run-1")
        client.get("/api/v1/agent-runs/run-2")
    with build_client(monkeypatch, backend=second, user_id="9002") as client:
        client.get(RUN_DETAIL)

    assert first.calls == [
        ("test:rate_limit:9001:GET:/api/v1/agent-runs/{run_id}", 60),
        ("test:rate_limit:9001:GET:/api/v1/agent-runs/{run_id}", 60),
    ]
    assert second.calls == [("test:rate_limit:9002:GET:/api/v1/agent-runs/{run_id}", 60)]