"""Unit-to-millimetre conversion.

The reference program carries the bench measurement in a comment::

    # 轴0(X)/轴1(Y) 实测: UNITS=10 时 1000用户单位 = 2mm → 每毫米 5000 脉冲
    # 当量5 → 1000单位=1mm，不是100单位=1mm

These are the assertions that keep that comment honest.
"""

from __future__ import annotations

import math

import pytest

from orisys_autocal.motion.units import (
    PULSES_PER_MM,
    mm_to_user_units,
    safe_float,
    user_units_to_mm,
)


@pytest.mark.parametrize(
    ("units", "user_units", "expected_mm"),
    [
        (10.0, 1000.0, 2.0),  # the measured case from the vendor comment
        (5.0, 1000.0, 1.0),  # ...and the second one
        (10.0, 0.0, 0.0),
        (10.0, 5000.0, 10.0),
        (10.0, -1000.0, -2.0),  # negative travel must stay negative
    ],
)
def test_conversion_matches_the_bench_measurement(units, user_units, expected_mm):
    assert user_units_to_mm(user_units, units=units) == pytest.approx(expected_mm)


def test_default_units_is_the_platform_value():
    assert user_units_to_mm(1000.0) == pytest.approx(2.0)
    assert PULSES_PER_MM == 5000.0


def test_conversion_round_trips():
    for units in (1.0, 5.0, 10.0, 37.5):
        millimetres = user_units_to_mm(1234.5, units=units)
        assert mm_to_user_units(millimetres, units=units) == pytest.approx(1234.5)


def test_a_zero_or_negative_scale_is_not_a_number():
    """A bad constant must be visibly unusable, not a plausible number."""
    assert math.isnan(user_units_to_mm(1000.0, pulses_per_mm=0.0))
    assert math.isnan(user_units_to_mm(1000.0, pulses_per_mm=-1.0))
    assert math.isnan(mm_to_user_units(1.0, units=0.0))


@pytest.mark.parametrize(
    "text",
    ["", "   ", "abc", "1,5", None, "nan", "inf", "-inf"],
)
def test_unusable_entries_fall_back(text):
    assert safe_float(text, 42.0) == 42.0


@pytest.mark.parametrize("text", ["0", "0.0", " 0 "])
def test_zero_falls_back_because_it_would_divide(text):
    """A pulse equivalent of zero must never reach the controller."""
    assert safe_float(text, 7.0) == 7.0


@pytest.mark.parametrize(("text", "expected"), [("5", 5.0), (" 2.5 ", 2.5), ("-3", -3.0)])
def test_usable_entries_are_parsed(text, expected):
    assert safe_float(text, 42.0) == expected