"""MEATER decode tests.

These pin the community-derived decode so a refactor cannot silently change
it. They do NOT prove the decode is correct -- only bench comparison against
the MEATER app can do that. See docs/PROTOCOL_NOTES.md.
"""

from __future__ import annotations

import pytest

from smokescreen.sources.meater import decode_battery, decode_temperature


def payload(tip: int, ambient_raw: int, ambient_offset: int) -> bytes:
    return (
        tip.to_bytes(2, "little")
        + ambient_raw.to_bytes(2, "little")
        + ambient_offset.to_bytes(2, "little")
        + b"\x00\x00"
    )


def test_tip_decodes_to_sixteenths_of_a_degree():
    # 400 counts -> (400 + 8) / 16 = 25.5 C
    tip_c, _ = decode_temperature(payload(400, 0, 0))
    assert tip_c == pytest.approx(25.5)


def test_zero_counts_is_just_above_freezing():
    tip_c, _ = decode_temperature(payload(0, 0, 0))
    assert tip_c == pytest.approx(0.5)


def test_ambient_never_reads_below_tip():
    """The max(0, ...) term means ambient floors at the tip temperature."""
    tip_c, ambient_c = decode_temperature(payload(1000, 0, 200))
    assert ambient_c == pytest.approx(tip_c)


def test_ambient_rises_above_tip_when_raw_exceeds_offset():
    tip_c, ambient_c = decode_temperature(payload(1000, 500, 48))
    assert ambient_c > tip_c


def test_short_payload_is_rejected_not_guessed():
    with pytest.raises(ValueError):
        decode_temperature(b"\x01\x02")


def test_battery_scales_by_ten():
    assert decode_battery((7).to_bytes(2, "little")) == 70


def test_battery_clamps_to_100():
    assert decode_battery((25).to_bytes(2, "little")) == 100


def test_short_battery_payload_is_rejected():
    with pytest.raises(ValueError):
        decode_battery(b"\x01")