''' Parse OSC packet into dict '''

# set True to enable log messages
DEBUG = True

import struct
import traceback

def _parse_str(body: bytearray) -> (str, int):
    ''' Parse OSC string '''
    try:
        result = ''
        for b in body:
            if b == 0:
                break
            result += chr(b)
        else:
            return None
        l = ((len(result) // 4) + 1) * 4
        if l > len(body):
            return None
        return (result, l)
    except:
        if DEBUG: traceback.print_exc()
        return None

def _parse_int(body: bytearray) -> (int, int):
    ''' Parse OSC int '''
    try:
        return (struct.unpack('>i', body[0:4])[0], 4)
    except:
        if DEBUG: traceback.print_exc()
        return None

def _parse_float(body: bytearray) -> (float, int):
    ''' Parse OSC float '''
    try:
        return (struct.unpack('>f', body[0:4])[0], 4)
    except:
        if DEBUG: traceback.print_exc()
        return None

def parse(body: bytearray) -> dict | None:
    ''' Parse OSC datagram into dict. '''
    # too short
    if len(body) < 8:
        if DEBUG: print('[OSC PARSER] Body is shorter than 8 bytes')
        return None
    # does not start with slash
    if body[0] != ord('/'):
        if DEBUG: print('[OSC PARSER] First byte of packet is not forward slash')
        return None
    # get the address
    addr = _parse_str(body)
    if not addr:
        if DEBUG: print('[OSC PARSER] Failed to parse address (OSC-string)')
        return None
    # edit body
    body = body[addr[1]:]
    # get the type tag
    type_tag = _parse_str(body)
    if not type_tag:
        if DEBUG: print('[OSC PARSER] Failed to parse type tag (OSC-string)')
        return None
    # edit body
    body = body[type_tag[1]:]
    # type is invalid
    if type_tag[0][0] != ',':
        if DEBUG: print('[OSC PARSER] The first symbol of type tag must be comma')
        return None
    # arguments
    args = []
    # type parsers
    type_parsers = {
        'i': _parse_int,
        'f': _parse_float,
        's': _parse_str
    }
    # parse the arguments
    for arg_type in type_tag[0][1:]:
        # parse body if parser exists
        if arg_type not in type_parsers:
            if DEBUG: print('[OSC PARSER] Argument of type \'%s\' can\'t be parsed by this library' % arg_type)
            return None
        parse_result = type_parsers[arg_type](body)
        # failed to parse
        if parse_result is None:
            if DEBUG: print('[OSC PARSER] Failed to parse an argument of type \'%s\'' % arg_type)
            return None
        # success
        args.append(parse_result[0])
        body = body[parse_result[1]:]
    # result
    return {
        'addr': addr[0],
        'type_tag': type_tag[0],
        'args': args
    }