import json

class Message:
    MESSAGE_TYPES = {}

    @classmethod
    def decode(cls, raw):
        hash = json.loads(raw)
        tag = hash['tag']
        return cls.MESSAGE_TYPES[tag].from_hash(hash)

    def json(self):
        hash = self.to_hash()
        return json.dumps(self.to_hash())

def message(name):
    def decorate(class_decl):
        Message.MESSAGE_TYPES[name] = class_decl
        return class_decl
    return decorate

@message('config')
class InitialConfig(Message):
    def __init__(self, user, game):
        self.user = user
        self.game = game

    @classmethod
    def from_hash(cls, d):
        return cls(user=d['user'], game=d['game'])

    def to_hash(self):
        return {'user': self.user, 'game': self.game}

@message('post')
class Post(Message):
    def __init__(self, author, content):
        self.author = author
        self.content = content

    @classmethod
    def from_hash(cls, d):
        return cls(author=d['author'], content=d['content'])

    def to_hash(self):
        return {
            'tag': 'post',
            'author': self.author,
            'content': self.content,
        }