from enum import Enum

class Commands(Enum):
    PLAY = 0
    ADD_TO_PLAYLIST = 1
    CLEAR = 2
    SEARCH_SONG = 3
    SEARCH_ALBUM = 4


class CommandException(Exception):
    """
    The user has introduced an invalid command.
    """
    pass
    

def parse_command(message):
    """
    Parse a mumble message into a possible command.
    If it isn't a command (i.e. a plain message intended for
    another user) we'll return None. If it is a message (starts with !)
    but it is an invalid one, we wil throw an exception.
    """
    current = 0

    if message[current] == '!':
        current += 1

        if message[current:5].tolower() == 'play':
            current += 5 
            return (Commands.PLAY, message[current:])
        elif message[current:4].tolower() == 'add':
            current +=4
            return (Commands.ADD_TO_PLAYLIST, message[current:])
        elif message[current:6].tolower() == 'clear':
            current += 6
            return (Commands.CLEAR, message[current:])
        elif message[current:12].tolower() == 'search_song':
            current += 13
            return (Commands.SEARCH_SONG, message[current:])
        elif message[current:13].tolower() == 'search_album':
            current += 14
            return (Commands.SEARCH_ALBUM, message[current:])
        else:
            raise CommandException('Invalid command.')

    return None