"""Latest-AU H.264 mmap: overwrite unread payloads; seq is monotonic."""
from nal_shm import AU_MAX, NalReader, NalWriter


def test_writer_seq_starts_at_one_and_increments(tmp_path):
    path = str(tmp_path / "cam-01.h264")
    w = NalWriter(path, max_payload=64)
    assert w.write(b"\x00\x00\x00\x01\x65" + b"x" * 10) == 1
    assert w.write(b"\x00\x00\x00\x01\x41" + b"y" * 10) == 2
    w.close()


def test_reader_returns_latest_payload(tmp_path):
    path = str(tmp_path / "cam-01.h264")
    w = NalWriter(path, max_payload=64)
    w.write(b"first-access-unit-xxxx")
    w.write(b"second-access-unit-yyy")
    r = NalReader(path)
    seq, payload = r.read()
    assert seq == 2
    assert payload.startswith(b"second-access-unit")
    w.close()
    r.close()


def test_reader_none_when_no_new_au(tmp_path):
    path = str(tmp_path / "cam-01.h264")
    w = NalWriter(path, max_payload=64)
    w.write(b"only-once")
    r = NalReader(path)
    assert r.read()[0] == 1
    assert r.read() is None
    w.close()
    r.close()


def test_write_drops_oversize_payload(tmp_path):
    path = str(tmp_path / "cam-01.h264")
    w = NalWriter(path, max_payload=8)
    assert w.write(b"123456789") == 0
    w.close()


def test_au_max_is_bounded():
    assert AU_MAX >= 64 * 1024
    assert AU_MAX <= 2 * 1024 * 1024