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Add Online Chat solution
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‎solutions/object_oriented_design/online_chat/__init__.py‎

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‎solutions/object_oriented_design/online_chat/online_chat.ipynb‎

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/system-design-primer-primer)."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Design an online chat"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Constraints and assumptions\n",
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"\n",
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"* Assume we'll focus on the following workflows:\n",
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" * Text conversations only\n",
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" * Users\n",
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" * Add a user\n",
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" * Remove a user\n",
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" * Update a user\n",
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" * Add to a user's friends list\n",
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" * Add friend request\n",
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" * Approve friend request\n",
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" * Reject friend request\n",
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" * Remove from a user's friends list\n",
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" * Create a group chat\n",
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" * Invite friends to a group chat\n",
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" * Post a message to a group chat\n",
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" * Private 1-1 chat\n",
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" * Invite a friend to a private chat\n",
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" * Post a meesage to a private chat\n",
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"* No need to worry about scaling initially"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Solution"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Overwriting online_chat.py\n"
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]
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}
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],
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"source": [
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"%%writefile online_chat.py\n",
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"from abc import ABCMeta\n",
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"\n",
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"\n",
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"class UserService(object):\n",
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"\n",
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" __metaclass__ = Singleton\n",
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"\n",
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" def __init__(self):\n",
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" self.users_by_id = {} # key: user id, value: User\n",
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"\n",
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" def add_user(self, user_id, name, pass_hash): # ...\n",
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" def remove_user(self, user_id): # ...\n",
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" def add_friend_request(self, from_user_id, to_user_id): # ...\n",
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" def approve_friend_request(self, from_user_id, to_user_id): # ...\n",
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" def reject_friend_request(self, from_user_id, to_user_id): # ...\n",
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"\n",
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"\n",
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"class User(object):\n",
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"\n",
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" def __init__(self, user_id, name, pass_hash):\n",
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" self.user_id = user_id\n",
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" self.name = name\n",
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" self.pass_hash = pass_hash\n",
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" self.friends_by_id = {} # key: friend id, value: User\n",
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" self.friend_ids_to_private_chats = {} # key: friend id, value: private chats\n",
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" self.group_chats_by_id = {} # key: chat id, value: GroupChat\n",
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" self.received_friend_requests_by_friend_id = {} # key: friend id, value: AddRequest\n",
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" self.sent_friend_requests_by_friend_id = {} # key: friend id, value: AddRequest\n",
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"\n",
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" def message_user(self, friend_id, message): # ...\n",
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" def message_group(self, group_id, message): # ...\n",
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" def send_friend_request(self, friend_id): # ...\n",
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" def receive_friend_request(self, friend_id): # ...\n",
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" def approve_friend_request(self, friend_id): # ...\n",
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" def reject_friend_request(self, friend_id): # ...\n",
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"\n",
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"\n",
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"class Chat(metaclass=ABCMeta):\n",
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"\n",
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" def __init__(self, chat_id):\n",
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" self.chat_id = chat_id\n",
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" self.users = []\n",
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" self.messages = []\n",
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"\n",
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"\n",
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"class PrivateChat(Chat):\n",
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"\n",
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" def __init__(self, first_user, second_user):\n",
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" super(PrivateChat, self).__init__()\n",
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" self.users.append(first_user)\n",
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" self.users.append(second_user)\n",
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"\n",
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"\n",
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"class GroupChat(Chat):\n",
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"\n",
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" def add_user(self, user): # ...\n",
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" def remove_user(self, user): # ... \n",
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"\n",
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"\n",
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"class Message(object):\n",
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"\n",
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" def __init__(self, message_id, message, timestamp):\n",
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" self.message_id = message_id\n",
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" self.message = message\n",
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" self.timestamp = timestamp\n",
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"\n",
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"\n",
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"class AddRequest(object):\n",
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"\n",
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" def __init__(self, from_user_id, to_user_id, request_status, timestamp):\n",
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" self.from_user_id = from_user_id\n",
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" self.to_user_id = to_user_id\n",
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" self.request_status = request_status\n",
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" self.timestamp = timestamp\n",
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"\n",
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"\n",
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"class RequestStatus(Enum):\n",
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"\n",
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" UNREAD = 0\n",
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" READ = 1\n",
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" ACCEPTED = 2\n",
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" REJECTED = 3\n",
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"\n",
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"\n",
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"class Singleton(type):\n",
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"\n",
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" _instances = {}\n",
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" def __call__(cls, *args, **kwargs):\n",
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" if cls not in cls._instances:\n",
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" cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)\n",
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" return cls._instances[cls]"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.4.3"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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}

‎solutions/object_oriented_design/online_chat/online_chat.py‎

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from abc import ABCMeta
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class UserService(object):
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__metaclass__ = Singleton
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def __init__(self):
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self.users_by_id = {} # key: user id, value: User
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def add_user(self, user_id, name, pass_hash): # ...
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def remove_user(self, user_id): # ...
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def add_friend_request(self, from_user_id, to_user_id): # ...
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def approve_friend_request(self, from_user_id, to_user_id): # ...
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def reject_friend_request(self, from_user_id, to_user_id): # ...
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class User(object):
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def __init__(self, user_id, name, pass_hash):
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self.user_id = user_id
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self.name = name
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self.pass_hash = pass_hash
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self.friends_by_id = {} # key: friend id, value: User
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self.friend_ids_to_private_chats = {} # key: friend id, value: private chats
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self.group_chats_by_id = {} # key: chat id, value: GroupChat
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self.received_friend_requests_by_friend_id = {} # key: friend id, value: AddRequest
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self.sent_friend_requests_by_friend_id = {} # key: friend id, value: AddRequest
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def message_user(self, friend_id, message): # ...
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def message_group(self, group_id, message): # ...
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def send_friend_request(self, friend_id): # ...
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def receive_friend_request(self, friend_id): # ...
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def approve_friend_request(self, friend_id): # ...
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def reject_friend_request(self, friend_id): # ...
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class Chat(metaclass=ABCMeta):
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def __init__(self, chat_id):
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self.users = []
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self.chat_id = chat_id
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self.messages = []
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class PrivateChat(Chat):
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def __init__(self, first_user, second_user):
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super(PrivateChat, self).__init__()
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self.users.append(first_user)
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self.users.append(second_user)
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class GroupChat(Chat):
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def add_user(self, user): # ...
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def remove_user(self, user): # ...
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class Message(object):
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def __init__(self, message_id, message, timestamp):
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self.message_id = message_id
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self.message = message
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self.timestamp = timestamp
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class AddRequest(object):
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def __init__(self, from_user_id, to_user_id, request_status, timestamp):
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self.from_user_id = from_user_id
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self.to_user_id = to_user_id
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self.request_status = request_status
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self.timestamp = timestamp
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class RequestStatus(Enum):
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UNREAD = 0
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READ = 1
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ACCEPTED = 2
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REJECTED = 3
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class Singleton(type):
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_instances = {}
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def __call__(cls, *args, **kwargs):
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if cls not in cls._instances:
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cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
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return cls._instances[cls]

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