import json
import pytest

from perfkit.memtrend import slope_per_cycle, main


def test_slope_linear():
    assert slope_per_cycle([10, 11, 12, 13]) == pytest.approx(1.0)


def test_slope_flat():
    assert slope_per_cycle([5, 5, 5]) == 0.0


def test_slope_noisy_is_least_squares():
    # y = 2x + шум; МНК, а не (last-first)/n
    assert slope_per_cycle([0, 3, 3, 7, 8]) == pytest.approx(2.0)


def test_slope_needs_two_points():
    with pytest.raises(ValueError):
        slope_per_cycle([1.0])
    with pytest.raises(ValueError):
        slope_per_cycle([])


def test_cli_prints_three_slopes(tmp_path, capsys):
    rows = [
        {"scenario": "memory", "repeat": 0, "metrics": {"cycle": c, "heap_used_mb": 100 + 2 * c, "nodes": 1000 + 5 * c, "js_event_listeners": 50}}
        for c in range(4)
    ]
    # записи могут идти не по порядку и вперемешку с чужим сценарием
    lines = [json.dumps(r) for r in reversed(rows)] + [json.dumps({"scenario": "other", "metrics": {"cycle": 0}})]
    (tmp_path / "memory.jsonl").write_text("\n".join(lines) + "\n")
    assert main([str(tmp_path)]) == 0
    out = capsys.readouterr().out
    assert "heap_used_mb" in out and "nodes" in out and "js_event_listeners" in out
    assert "2.000" in out and "5.000" in out and "0.000" in out