import pytest

from gausse.physics.force import (
    force_on_slug_newtons,
    saturation_scale,
    solenoid_field_estimate_tesla,
)


def test_field_estimate_scales_with_current_and_turns():
    b_low = solenoid_field_estimate_tesla(mu_eff=100, total_turns=100, coil_length_m=0.05, current_a=10)
    b_high = solenoid_field_estimate_tesla(mu_eff=100, total_turns=100, coil_length_m=0.05, current_a=100)
    assert b_high > b_low


def test_saturation_scale_is_one_below_bsat():
    assert saturation_scale(b_estimate_tesla=0.5, b_sat_tesla=1.8) == pytest.approx(1.0)


def test_saturation_scale_clamps_above_bsat():
    scale = saturation_scale(b_estimate_tesla=3.6, b_sat_tesla=1.8)
    assert scale == pytest.approx(0.5)


def test_force_scales_as_current_squared():
    # F = 0.5*I^2*dL/dx: без клэмпа (см. модуль-докстринг force.py про энергобаланс)
    # сила должна расти строго как I^2, иначе нарушится точный энергобаланс контура.
    f_low = force_on_slug_newtons(current_a=5, dl_dx=1e-3)
    f_high = force_on_slug_newtons(current_a=50, dl_dx=1e-3)
    assert f_high / f_low == pytest.approx(100.0)


def test_force_zero_at_zero_current():
    assert force_on_slug_newtons(current_a=0, dl_dx=1e-3) == pytest.approx(0.0)