import hashlib
import subprocess
import sys
from pathlib import Path

SCRIPT = Path(__file__).with_name("nl_mkimage.py")


def build(tmp_path, payload=b"\x01\x02\x03" * 100, device="evk", version="1.2.3"):
    src = tmp_path / "fw_gz.img"
    src.write_bytes(payload)
    out = tmp_path / "fw_ota.img"
    subprocess.run(
        [sys.executable, str(SCRIPT), "--image", str(src), "--device", device,
         "--version", version, "--out", str(out)],
        check=True,
    )
    return src, out


def test_appends_512_byte_trailer(tmp_path):
    src, out = build(tmp_path)
    data = out.read_bytes()
    assert len(data) == len(src.read_bytes()) + 512
    assert data[: len(src.read_bytes())] == src.read_bytes()
    trailer = data[-512:]
    assert trailer[0:4] == b"NINL"
    assert trailer[4] == 1
    assert trailer[5:21].rstrip(b"\x00") == b"evk"
    assert trailer[21:37].rstrip(b"\x00") == b"1.2.3"
    assert trailer[37:69] == hashlib.sha256(src.read_bytes()).digest()
    assert set(trailer[69:]) == {0xFF}


def test_rejects_long_fields(tmp_path):
    src = tmp_path / "fw_gz.img"
    src.write_bytes(b"x")
    r = subprocess.run(
        [sys.executable, str(SCRIPT), "--image", str(src), "--device", "0123456789abcdef",
         "--version", "1", "--out", str(tmp_path / "o.img")],
        capture_output=True, text=True,
    )
    assert r.returncode != 0
    assert "device" in r.stderr


def test_refuses_image_that_already_has_a_trailer(tmp_path):
    _, out = build(tmp_path)
    r = subprocess.run(
        [sys.executable, str(SCRIPT), "--image", str(out), "--device", "evk",
         "--version", "1.2.3", "--out", str(tmp_path / "again.img")],
        capture_output=True, text=True,
    )
    assert r.returncode != 0
    assert "trailer" in r.stderr