"""Golden tests for WALK_FORWARD_BOOTSTRAP_V1 (governance/todo/v8_9_p3_adoption_plan.yaml P3-B).

Maps to v8.9 proposal golden cases V89_014 (same_regime_sample_low) and
V89_048 (solver_failure -- here, no historical_returns at all).
"""
from __future__ import annotations

import importlib.util
import random
from pathlib import Path

ROOT = Path(__file__).resolve().parents[3]
MODULE_PATH = ROOT / "tools" / "build_walk_forward_bootstrap_v1.py"


def _load_module():
    spec = importlib.util.spec_from_file_location("build_walk_forward_bootstrap_v1", MODULE_PATH)
    module = importlib.util.module_from_spec(spec)
    assert spec.loader is not None
    spec.loader.exec_module(module)
    return module


def _sample_returns(n=30):
    rng = random.Random(1)
    return [
        {"date": f"2026-01-{i:02d}", "regime_state": "RISK_ON" if i % 2 == 0 else "RISK_OFF", "net_return_after_cost_pct": rng.uniform(-2, 2)}
        for i in range(1, n + 1)
    ]


def test_v89_014_regime_filter_with_no_matches_returns_empty_not_substituted() -> None:
    mod = _load_module()
    rng = random.Random(1)
    distribution = mod.regime_matched_resample(_sample_returns(), "NEVER_SEEN_REGIME", 50, rng)
    assert distribution == []


def test_v89_048_no_historical_returns_yields_empty_resample() -> None:
    mod = _load_module()
    rng = random.Random(1)
    distribution = mod.walk_forward_resample([], 50, rng)
    assert distribution == []


def test_walk_forward_uses_only_out_of_sample_70_30_split() -> None:
    mod = _load_module()
    rng = random.Random(1)
    returns = _sample_returns(20)
    distribution = mod.walk_forward_resample(returns, resample_count=20, rng=rng)
    assert len(distribution) == 20


def test_regime_matched_resamples_only_from_filtered_regime() -> None:
    mod = _load_module()
    rng = random.Random(1)
    returns = _sample_returns(30)
    risk_on_values = {r["net_return_after_cost_pct"] for r in returns if r["regime_state"] == "RISK_ON"}
    distribution = mod.regime_matched_resample(returns, "RISK_ON", 50, rng)
    assert all(v in risk_on_values for v in distribution)