{"id":"ood-online-chat","title":"Design an online chat","sections":[{"id":"constraints-and-assumptions","title":"Constraints and assumptions","html":"

Constraints and assumptions

\n","headings":[]},{"id":"solution","title":"Solution","html":"

Solution

\n
from abc import ABCMeta\n\n\nclass UserService(object):\n\n    def __init__(self):\n        self.users_by_id = {}  # key: user id, value: User\n\n    def add_user(self, user_id, name, pass_hash):  # ...\n    def remove_user(self, user_id):  # ...\n    def add_friend_request(self, from_user_id, to_user_id):  # ...\n    def approve_friend_request(self, from_user_id, to_user_id):  # ...\n    def reject_friend_request(self, from_user_id, to_user_id):  # ...\n\n\nclass User(object):\n\n    def __init__(self, user_id, name, pass_hash):\n        self.user_id = user_id\n        self.name = name\n        self.pass_hash = pass_hash\n        self.friends_by_id = {}  # key: friend id, value: User\n        self.friend_ids_to_private_chats = {}  # key: friend id, value: private chats\n        self.group_chats_by_id = {}  # key: chat id, value: GroupChat\n        self.received_friend_requests_by_friend_id = {}  # key: friend id, value: AddRequest\n        self.sent_friend_requests_by_friend_id = {}  # key: friend id, value: AddRequest\n\n    def message_user(self, friend_id, message):  # ...\n    def message_group(self, group_id, message):  # ...\n    def send_friend_request(self, friend_id):  # ...\n    def receive_friend_request(self, friend_id):  # ...\n    def approve_friend_request(self, friend_id):  # ...\n    def reject_friend_request(self, friend_id):  # ...\n\n\nclass Chat(metaclass=ABCMeta):\n\n    def __init__(self, chat_id):\n        self.chat_id = chat_id\n        self.users = []\n        self.messages = []\n\n\nclass PrivateChat(Chat):\n\n    def __init__(self, first_user, second_user):\n        super(PrivateChat, self).__init__()\n        self.users.append(first_user)\n        self.users.append(second_user)\n\n\nclass GroupChat(Chat):\n\n    def add_user(self, user):  # ...\n    def remove_user(self, user):  # ... \n\n\nclass Message(object):\n\n    def __init__(self, message_id, message, timestamp):\n        self.message_id = message_id\n        self.message = message\n        self.timestamp = timestamp\n\n\nclass AddRequest(object):\n\n    def __init__(self, from_user_id, to_user_id, request_status, timestamp):\n        self.from_user_id = from_user_id\n        self.to_user_id = to_user_id\n        self.request_status = request_status\n        self.timestamp = timestamp\n\n\nclass RequestStatus(Enum):\n\n    UNREAD = 0\n    READ = 1\n    ACCEPTED = 2\n    REJECTED = 3
","headings":[]}],"sourceFiles":[{"name":"online_chat.py","url":"https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/online_chat/online_chat.py","html":"
from abc import ABCMeta\nfrom enum import Enum\n\n\nclass UserService(object):\n\n    def __init__(self):\n        self.users_by_id = {}  # key: user id, value: User\n\n    def add_user(self, user_id, name, pass_hash):\n        pass\n\n    def remove_user(self, user_id):\n        pass\n\n    def add_friend_request(self, from_user_id, to_user_id):\n        pass\n\n    def approve_friend_request(self, from_user_id, to_user_id):\n        pass\n\n    def reject_friend_request(self, from_user_id, to_user_id):\n        pass\n\n\nclass User(object):\n\n    def __init__(self, user_id, name, pass_hash):\n        self.user_id = user_id\n        self.name = name\n        self.pass_hash = pass_hash\n        self.friends_by_id = {}  # key: friend id, value: User\n        self.friend_ids_to_private_chats = {}  # key: friend id, value: private chats\n        self.group_chats_by_id = {}  # key: chat id, value: GroupChat\n        self.received_friend_requests_by_friend_id = {}  # key: friend id, value: AddRequest\n        self.sent_friend_requests_by_friend_id = {}  # key: friend id, value: AddRequest\n\n    def message_user(self, friend_id, message):\n        pass\n\n    def message_group(self, group_id, message):\n        pass\n\n    def send_friend_request(self, friend_id):\n        pass\n\n    def receive_friend_request(self, friend_id):\n        pass\n\n    def approve_friend_request(self, friend_id):\n        pass\n\n    def reject_friend_request(self, friend_id):\n        pass\n\n\nclass Chat(metaclass=ABCMeta):\n\n    def __init__(self, chat_id):\n        self.chat_id = chat_id\n        self.users = []\n        self.messages = []\n\n\nclass PrivateChat(Chat):\n\n    def __init__(self, first_user, second_user):\n        super(PrivateChat, self).__init__()\n        self.users.append(first_user)\n        self.users.append(second_user)\n\n\nclass GroupChat(Chat):\n\n    def add_user(self, user):\n        pass\n\n    def remove_user(self, user):\n        pass\n\n\nclass Message(object):\n\n    def __init__(self, message_id, message, timestamp):\n        self.message_id = message_id\n        self.message = message\n        self.timestamp = timestamp\n\n\nclass AddRequest(object):\n\n    def __init__(self, from_user_id, to_user_id, request_status, timestamp):\n        self.from_user_id = from_user_id\n        self.to_user_id = to_user_id\n        self.request_status = request_status\n        self.timestamp = timestamp\n\n\nclass RequestStatus(Enum):\n\n    UNREAD = 0\n    READ = 1\n    ACCEPTED = 2\n    REJECTED = 3
"}]}