"""Tests des festen Zeitschritts (Akkumulator)."""

import pytest

from sandbox.physics import FixedTimestep

STEP = 1 / 120


def test_a_60_fps_frame_runs_two_physics_steps() -> None:
    timestep = FixedTimestep(STEP, max_steps_per_frame=8)
    assert timestep.advance(1 / 60) == 2
    assert timestep.alpha == pytest.approx(0, abs=1e-6)


def test_short_frames_accumulate() -> None:
    timestep = FixedTimestep(STEP, max_steps_per_frame=8)
    assert timestep.advance(1 / 240) == 0
    assert timestep.alpha == pytest.approx(0.5)
    assert timestep.advance(1 / 240) == 1


def test_no_steps_are_lost_through_rounding() -> None:
    timestep = FixedTimestep(STEP, max_steps_per_frame=8)
    total = sum(timestep.advance(1 / 60) for _ in range(1000))
    assert total == 2000


def test_alpha_stays_in_the_unit_interval() -> None:
    timestep = FixedTimestep(STEP, max_steps_per_frame=8)
    for frame in (0.003, 0.011, 0.017, 0.0001, 0.02):
        timestep.advance(frame)
        assert 0 <= timestep.alpha < 1


def test_huge_frames_are_capped_to_avoid_the_spiral_of_death() -> None:
    timestep = FixedTimestep(STEP, max_steps_per_frame=5)
    assert timestep.advance(2.0) == 5
    assert timestep.alpha == 0  # der Rückstand wurde verworfen
    assert timestep.advance(1 / 60) == 2


def test_reset_discards_accumulated_time() -> None:
    timestep = FixedTimestep(STEP, max_steps_per_frame=8)
    timestep.advance(STEP * 0.9)
    timestep.reset()
    assert timestep.alpha == 0
    assert timestep.advance(STEP * 0.5) == 0


def test_invalid_arguments_are_rejected() -> None:
    with pytest.raises(ValueError, match="positiv"):
        FixedTimestep(0, 8)
    with pytest.raises(ValueError, match="mindestens"):
        FixedTimestep(STEP, 0)
    with pytest.raises(ValueError, match="negativ"):
        FixedTimestep(STEP, 8).advance(-0.1)