"""MBAP codec tests."""

from __future__ import annotations

import pytest

from wago_sim.mbap import (
    MBAP_HEADER_SIZE,
    MbapError,
    MbapFrameReader,
    MbapHeader,
    build_frame,
)


def test_header_roundtrip():
    header = MbapHeader(transaction_id=0x1234, protocol_id=0, length=6, unit_id=1)
    encoded = header.encode()
    assert len(encoded) == 7
    decoded = MbapHeader.decode(encoded + b"\x03\x00\x00\x00\x02")
    assert decoded == header


def test_decode_requires_complete_frame():
    with pytest.raises(MbapError):
        MbapHeader.decode(b"\x00\x01\x00\x00\x00\x06\x01")


def test_protocol_id_rejected():
    with pytest.raises(MbapError):
        MbapHeader.decode(b"\x00\x01\x00\x01\x00\x06\x01\x03\x00\x00\x00\x02")


def test_build_frame():
    frame = build_frame(7, 1, b"\x03\x00\x00\x00\x02")
    assert frame[:2] == (7).to_bytes(2, "big")
    assert frame[4:6] == (6).to_bytes(2, "big")
    assert frame[6] == 1


def test_frame_reader_splits_stream():
    reader = MbapFrameReader()
    f1 = build_frame(1, 1, b"\x03\x00\x00\x00\x02")
    f2 = build_frame(2, 1, b"\x01\x00\x00\x00\x08")
    blob = f1 + f2
    # feed an incomplete header first
    reader.feed(blob[:5])
    assert reader.pop_frame() is None
    # feed through the end of frame 1 (12 bytes): it becomes complete
    reader.feed(blob[5:12])
    h1, p1 = reader.pop_frame()
    assert h1.transaction_id == 1
    assert p1 == b"\x03\x00\x00\x00\x02"
    # frame 2 arrives in pieces
    reader.feed(blob[12:15])
    assert reader.pop_frame() is None
    reader.feed(blob[15:])
    h2, p2 = reader.pop_frame()
    assert h2.transaction_id == 2
    assert p2 == b"\x01\x00\x00\x00\x08"
    assert reader.pop_frame() is None


def test_frame_reader_rejects_bad_protocol():
    reader = MbapFrameReader()
    reader.feed(b"\x00\x01\xDE\xAD\x00\x06\x01\x03\x00\x00\x00\x02")
    import pytest

    with pytest.raises(MbapError):
        reader.pop_frame()