import ctypes
from .constants import Marker, OType, ErrorCode

class Udp1553Header(ctypes.Structure):
    """
    Header structure for the UDP encapsulation of 1553 messages.
    """
    _pack_ = 1
    _fields_ = [
        ("marker_1553", ctypes.c_uint16),
        ("v_major", ctypes.c_uint8),
        ("v_minor", ctypes.c_uint8),
        ("o_type", ctypes.c_uint16),
        ("ta", ctypes.c_uint8),
        ("flags", ctypes.c_uint8),
        ("frame_counter", ctypes.c_uint32),
        ("msg_counter", ctypes.c_uint32),
        ("spare_counter", ctypes.c_uint32),
        ("m_miss", ctypes.c_uint32),
        ("s_miss", ctypes.c_uint32),
        ("ltt", ctypes.c_uint32),
        ("errors", ctypes.c_uint32),
        ("bc_reserved", ctypes.c_uint32 * 2),
        ("rt_reserved", ctypes.c_uint32 * 2),
        ("spare", ctypes.c_uint32 * 3)
    ]

    def __init__(self):
        super().__init__()
        self.marker_1553 = Marker.START_1553
        self.o_type = OType.BC
        self.ltt = 0

class CommandWordStr(ctypes.Structure):
    _pack_ = 1
    _fields_ = [
        ("wc", ctypes.c_ushort, 5),  # Word Count
        ("sa", ctypes.c_ushort, 5),  # Sub Address
        ("tr", ctypes.c_ushort, 1),  # Transmit/Receive
        ("rt", ctypes.c_ushort, 5)   # Remote Terminal Address
    ]

class CommandWord(ctypes.Union):
    """
    MIL-STD-1553 Command Word Union.
    Allows access via raw uint16 or bitfields.
    """
    _pack_ = 1
    _fields_ = [
        ("raw", ctypes.c_uint16),
        ("fields", CommandWordStr)
    ]

    def __init__(self, wc=0, sa=0, tr=0, rt=0):
        super().__init__()
        self.fields.wc = wc if wc != 32 else 0
        self.fields.sa = sa
        self.fields.tr = tr
        self.fields.rt = rt

class StatusWordStr(ctypes.Structure):
    _pack_ = 1
    _fields_ = [
        ("tf", ctypes.c_ushort, 1),    # Terminal Flag
        ("bca", ctypes.c_ushort, 1),   # Broadcast Command Received
        ("sf", ctypes.c_ushort, 1),    # Subsystem Flag
        ("busy", ctypes.c_ushort, 1),  # Busy
        ("brcs", ctypes.c_ushort, 1),  # Broadcast Command Received
        ("reserved", ctypes.c_ushort, 3),
        ("sr", ctypes.c_ushort, 1),    # Service Request
        ("instr", ctypes.c_ushort, 1), # Instrumentation
        ("me", ctypes.c_ushort, 1),    # Message Error
        ("rt", ctypes.c_ushort, 5),    # Remote Terminal Address
    ]

class StatusWord(ctypes.Union):
    """
    MIL-STD-1553 Status Word Union.
    """
    _pack_ = 1
    _fields_ = [
        ("raw", ctypes.c_uint16),
        ("fields", StatusWordStr)
    ]

class Udp1553Message(ctypes.Structure):
    """
    Represents the metadata wrapping the actual payload in the UDP packet.
    Corresponds to udp_1553_msg_t in the previous code.
    """
    _pack_ = 1
    _fields_ = [
        ("marker", ctypes.c_uint16),
        ("cw", CommandWord),
        ("sw", ctypes.c_uint16),  # Status word is often just passed as raw here
        ("error_code", ctypes.c_uint16)
    ]

    def __init__(self, marker=Marker.CTRL_BEGIN, cw=None, sw=0, error_code=ErrorCode.OK):
        super().__init__()
        self.marker = marker
        if cw:
            self.cw = cw
        self.sw = sw
        self.error_code = error_code