from __future__ import annotations

import pytest

from genesis.state_machine import StateTransitionError, SessionStateMachine


# ---------- 正常流转 ----------

def test_initial_state_is_uploading():
    sm = SessionStateMachine()
    assert sm.state == "uploading"


def test_unknown_initial_state_rejected():
    with pytest.raises(StateTransitionError):
        SessionStateMachine(initial="bogus")


def test_unknown_target_state_rejected():
    sm = SessionStateMachine()
    with pytest.raises(StateTransitionError):
        sm.transition("bogus")


def test_happy_path_full_flow():
    sm = SessionStateMachine()
    sm.transition("parsing")
    sm.transition("awaiting_parse_confirm")
    sm.transition("impact_running")
    sm.transition("awaiting_impact_confirm")
    sm.transition("writing")
    sm.transition("qa")
    sm.transition("done")
    assert sm.state == "done"


# ---------- 非法转移拒绝 ----------

def test_illegal_transition_rejected():
    sm = SessionStateMachine()
    with pytest.raises(StateTransitionError):
        sm.transition("writing")  # uploading → writing 非法


def test_done_is_terminal_no_transition_out():
    sm = SessionStateMachine()
    sm.transition("parsing")
    sm.transition("awaiting_parse_confirm")
    sm.transition("impact_running")
    sm.transition("awaiting_impact_confirm")
    sm.transition("writing")
    sm.transition("qa")
    sm.transition("done")
    with pytest.raises(StateTransitionError):
        sm.transition("writing")


# ---------- T3: cancelled + resume ----------

def test_cancel_from_running_state():
    sm = SessionStateMachine()
    sm.transition("parsing")
    sm.transition("awaiting_parse_confirm")
    sm.transition("impact_running")
    sm.transition("awaiting_impact_confirm")
    sm.transition("writing")
    sm.cancel()
    assert sm.state == "cancelled"
    assert sm.cancelled_from == "writing"


def test_cancel_from_done_is_illegal():
    sm = SessionStateMachine()
    sm.transition("parsing")
    sm.transition("awaiting_parse_confirm")
    sm.transition("impact_running")
    sm.transition("awaiting_impact_confirm")
    sm.transition("writing")
    sm.transition("qa")
    sm.transition("done")
    with pytest.raises(StateTransitionError):
        sm.cancel()


def test_resume_returns_to_interrupted_state():
    sm = SessionStateMachine()
    sm.transition("parsing")
    sm.transition("awaiting_parse_confirm")
    sm.transition("impact_running")
    sm.transition("awaiting_impact_confirm")
    sm.transition("writing")
    sm.cancel()
    sm.resume()
    assert sm.state == "writing"


def test_resume_without_cancel_is_illegal():
    sm = SessionStateMachine()
    sm.transition("parsing")
    with pytest.raises(StateTransitionError):
        sm.resume()  # 非 cancelled 状态不能 resume


def test_cancelled_cannot_jump_to_arbitrary_state():
    sm = SessionStateMachine()
    sm.transition("parsing")
    sm.cancel()
    with pytest.raises(StateTransitionError):
        sm.transition("done")  # cancelled 只能 resume 回中断前状态


def test_resume_after_resume_allows_forward_progress():
    # 取消 → resume → 再次取消 → resume 循环稳定（cancelled_from 保持最后一次中断点）
    sm = SessionStateMachine()
    sm.transition("parsing")
    sm.transition("awaiting_parse_confirm")
    sm.transition("impact_running")
    sm.cancel()
    sm.resume()
    assert sm.state == "impact_running"
    sm.transition("awaiting_impact_confirm")
    sm.transition("writing")
    sm.cancel()
    assert sm.cancelled_from == "writing"
    sm.resume()
    assert sm.state == "writing"