"""作业 2 验收测试：LangGraph 后端适配器。

通过标准（对应迁移计划作业 2）：
- ``complete()`` 返回带 ``<state>1002</state>`` 前缀的 ``ChatResult``，
  API 层据此解析阶段码；
- ``stream()`` 先产出含完整 state 前缀的 ``TextDelta``，再产出正文，
  保证 ``stage_code`` 事件先于正文；
- 会话通过 ``thread_id = session_id`` 绑定（图 checkpoint 语义）。

注意：``src/backends/langgraph.py`` 中的 TODO 完成前，
本文件的测试会失败，属于预期状态。
"""

import pytest

from src.backends.chat import ChatInput, TextDelta
from src.backends.langgraph import LangGraphBackend


def make_input() -> ChatInput:
    return ChatInput(
        session_id="session-001",
        text="发生了交通事故",
        client_mode="direct",
    )


@pytest.mark.asyncio
async def test_complete_returns_state_prefixed_result() -> None:
    backend = LangGraphBackend()

    result = await backend.complete(make_input())

    assert result.content.startswith("<state>1002</state>")
    assert "发生了交通事故" in result.content


@pytest.mark.asyncio
async def test_stream_emits_prefix_before_body() -> None:
    backend = LangGraphBackend()

    events = [event async for event in backend.stream(make_input())]

    assert events, "stream 至少应产生一个 TextDelta"
    assert all(isinstance(event, TextDelta) for event in events)
    joined = "".join(event.text for event in events)
    assert joined.startswith("<state>1002</state>")
    assert "发生了交通事故" in joined


@pytest.mark.asyncio
async def test_sessions_are_isolated_by_thread_id() -> None:
    backend = LangGraphBackend()

    first = await backend.complete(make_input())
    second = await backend.complete(make_input())
    other = await backend.complete(
        ChatInput(session_id="session-002", text="你好", client_mode="direct")
    )

    assert first.content != "" and second.content != ""
    assert "你好" in other.content