"""可解释路由评分层单元测试（T-R1，采纳 ai-model-router 设计）。"""
import pytest

from router_system.explain import CandidateProfile, explain_routing
from router_system.router import build_router


def _cand(domain, capability, cost=1.0, latency=100.0, reliability=0.9, fail=None):
    return CandidateProfile(domain=domain, model=f"m-{domain}", capability=capability,
                            cost_per_mtok=cost, nominal_latency_ms=latency,
                            reliability=reliability, difficulty_score=0.5,
                            hard_fail_reason=fail)


def test_hard_filter_rejects_with_reason():
    """硬过滤淘汰带人话理由，被拒者不进排名。"""
    exp = explain_routing([
        _cand("code", 1.0),
        _cand("math", 0.0, fail="无规则命中（capability=0）"),
    ])
    assert exp.winner == "code"
    assert any(r["domain"] == "math" and "无规则命中" in r["reason"] for r in exp.rejected)
    assert all(s["domain"] != "math" for s in exp.ranked)


def test_all_rejected_falls_back():
    """全部候选被硬过滤：决策者是大模型回退，置信度取基准 0.8。"""
    exp = explain_routing([_cand("code", 0.0, fail="x"), _cand("math", 0.0, fail="y")])
    assert exp.winner == "fallback"
    assert exp.confidence == 0.80
    assert len(exp.rejected) == 2


def test_zero_cost_local_beats_costly():
    """成本效率维平滑映射：零成本恒 1.0，贵模型显著吃亏。"""
    cheap = explain_routing([_cand("code", 1.0, cost=0.0, latency=1.0)]).ranked[0]
    pricey = explain_routing([_cand("math", 1.0, cost=2.5, latency=800.0)]).ranked[0]
    assert cheap["dims"]["cost_efficiency"] == 1.0
    assert pricey["dims"]["cost_efficiency"] < 0.5
    assert cheap["total"] > pricey["total"]


def test_confidence_gap_derivation():
    """置信度 = 0.8 + 分差：独苗封顶 0.99，双候选同分回落 0.8。"""
    single = explain_routing([_cand("code", 1.0)])
    tied = explain_routing([_cand("code", 1.0), _cand("math", 1.0)])
    assert single.confidence == 0.99
    assert tied.confidence == 0.80


def test_tie_break_is_deterministic():
    """同分决胜按领域名字典序（与仓库既有确定性约定一致）。"""
    exp = explain_routing([_cand("zeta", 1.0), _cand("alpha", 1.0)])
    assert exp.winner == "alpha"


def test_weights_snapshot_and_rank_order():
    """排名按 total 降序，权重快照随解释输出。"""
    exp = explain_routing([
        _cand("code", 1.0, cost=0.0, latency=1.0),
        _cand("math", 0.5, cost=2.0, latency=900.0),
    ])
    totals = [s["total"] for s in exp.ranked]
    assert totals == sorted(totals, reverse=True)
    assert exp.weights["capability"] == 0.35


@pytest.mark.asyncio
async def test_route_attaches_explanation():
    """主链路返回结构化 route_explanation；缓存命中路径为 None。"""
    router = build_router()
    r1 = await router.route("用 Python 写一个快速排序函数")
    assert r1.route_explanation is not None
    assert r1.route_explanation["winner"] == "code"
    assert any("explain:" in step for step in r1.route)
    assert any("无规则命中" in r["reason"]
               for r in r1.route_explanation["rejected"])
    r2 = await router.route("用 Python 写一个快速排序函数")
    assert r2.cache_hit is True
    assert r2.route_explanation is None


@pytest.mark.asyncio
async def test_low_confidence_explains_fallback():
    """低置信度直连回退：解释层给出 fallback 胜者与拒绝名单。"""
    router = build_router()
    r = await router.route("今天天气怎么样")
    assert r.upgraded is True
    assert r.route_explanation is not None
    assert r.route_explanation["winner"] == "fallback"