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_is_reduced_once_saturated():
    common = dict(dl_dx_unsaturated=1e-3, mu_eff=200, total_turns=300, coil_length_m=0.05, b_sat_tesla=1.8)
    force_unsaturated = force_on_slug_newtons(current_a=5, **common)
    force_saturated = force_on_slug_newtons(current_a=500, **common)
    # без клэмпа сила росла бы как I^2 (в 10000 раз); с насыщением рост должен быть намного меньше
    assert force_saturated / force_unsaturated < 5000


def test_force_zero_at_zero_current():
    common = dict(dl_dx_unsaturated=1e-3, mu_eff=200, total_turns=300, coil_length_m=0.05, b_sat_tesla=1.8)
    assert force_on_slug_newtons(current_a=0, **common) == pytest.approx(0.0)