import ctypes
import socket

from pybusmonitor1553.core.dispatcher import MessageDispatcher
from pybusmonitor1553.lib1553.headers import UDP1553Header, UDP1553MessageHeader, CommandWordUnion
from pybusmonitor1553.lib1553.constants import Subaddress


def _make_packet_with_cw(sub_addr, transmit=False, data_len=64, udp_marker=None):
    cw = CommandWordUnion(rt_addr=0, sub_addr=sub_addr, word_count=0, transmit=transmit)
    msg_hdr = UDP1553MessageHeader(command_word_union=cw)
    udp_hdr = UDP1553Header()
    if udp_marker is not None:
        udp_hdr.marker1553 = udp_marker

    header_bytes = ctypes.string_at(ctypes.addressof(udp_hdr), ctypes.sizeof(udp_hdr))
    msg_hdr_bytes = ctypes.string_at(ctypes.addressof(msg_hdr), ctypes.sizeof(msg_hdr))
    data_bytes = b"\x00" * data_len
    return header_bytes + msg_hdr_bytes + data_bytes


def test_invalid_magic_number_returns_none():
    disp = MessageDispatcher()
    # Provide wrong marker
    raw = _make_packet_with_cw(int(Subaddress.RX_SETTINGS), transmit=False, udp_marker=0xFFFF)
    h, msg = disp.parse_packet(raw)
    assert h is None and msg is None


def test_unknown_subaddress_returns_header_and_none():
    disp = MessageDispatcher()
    # Use a subaddress not registered (0 is not in registry)
    raw = _make_packet_with_cw(0, transmit=False)
    h, msg = disp.parse_packet(raw)
    assert h is not None and msg is None


def test_message_class_instantiation_exception_is_handled(monkeypatch):
    disp = MessageDispatcher()

    # Create a faulty class that raises on construction
    class Faulty:
        SUBADDRESS = int(Subaddress.RX_SETTINGS)
        IS_TRANSMIT = False
        def __init__(self, data):
            raise RuntimeError("boom")

    key = (int(Subaddress.RX_SETTINGS), False)
    # Replace registry entry with faulty
    disp._registry[key] = Faulty

    raw = _make_packet_with_cw(int(Subaddress.RX_SETTINGS), transmit=False)
    h, msg = disp.parse_packet(raw)
    assert h is not None and msg is None


def test_udp_start_handles_socket_error(monkeypatch):
    # Monkeypatch socket.socket to raise on bind
    import socket as _socket

    class FakeSock:
        def __init__(self, *a, **k):
            pass
        def setsockopt(self, *a, **k):
            pass
        def bind(self, addr):
            raise OSError("bind failed")

    monkeypatch.setattr(_socket, 'socket', lambda *a, **k: FakeSock())

    from pybusmonitor1553.core.network import UdpHandler
    h = UdpHandler(rx_ip='127.0.0.1', rx_port=0)
    # Should not raise
    h.start()
    assert not h._running


def test_udp_send_handles_send_error():
    from pybusmonitor1553.core.network import UdpHandler

    h = UdpHandler(rx_ip='127.0.0.1', rx_port=0)

    class BadSock:
        def sendto(self, data, addr):
            raise RuntimeError("send error")

    h._sock = BadSock()
    # Should not raise
    h.send(b'data')


def test_receive_loop_handles_exceptions_and_exits():
    from pybusmonitor1553.core.network import UdpHandler

    h = UdpHandler(rx_ip='127.0.0.1', rx_port=0)

    class ExplodingSock:
        def recvfrom(self, n):
            # set running False as side-effect then raise
            h._running = False
            raise RuntimeError("recv boom")

    h._sock = ExplodingSock()
    h._running = True
    # Run the loop; it should catch the exception and then exit
    h._receive_loop()
    assert not h._running