Add Online Chat solution

solutions/object_oriented_design/online_chat/online_chat.ipynb

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+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "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)."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Design an online chat"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Constraints and assumptions\n",
+    "\n",
+    "* Assume we'll focus on the following workflows:\n",
+    "    * Text conversations only\n",
+    "    * Users\n",
+    "        * Add a user\n",
+    "        * Remove a user\n",
+    "        * Update a user\n",
+    "        * Add to a user's friends list\n",
+    "            * Add friend request\n",
+    "                * Approve friend request\n",
+    "                * Reject friend request\n",
+    "        * Remove from a user's friends list\n",
+    "    * Create a group chat\n",
+    "        * Invite friends to a group chat\n",
+    "        * Post a message to a group chat\n",
+    "    * Private 1-1 chat\n",
+    "        * Invite a friend to a private chat\n",
+    "        * Post a meesage to a private chat\n",
+    "* No need to worry about scaling initially"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Solution"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Overwriting online_chat.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile online_chat.py\n",
+    "from abc import ABCMeta\n",
+    "\n",
+    "\n",
+    "class UserService(object):\n",
+    "\n",
+    "    __metaclass__ = Singleton\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",
+    "\n",
+    "class 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",
+    "\n",
+    "class Chat(metaclass=ABCMeta):\n",
+    "\n",
+    "    def __init__(self, chat_id):\n",
+    "        self.chat_id = chat_id\n",
+    "        self.users = []\n",
+    "        self.messages = []\n",
+    "\n",
+    "\n",
+    "class 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",
+    "\n",
+    "class GroupChat(Chat):\n",
+    "\n",
+    "    def add_user(self, user):  # ...\n",
+    "    def remove_user(self, user):  # ... \n",
+    "\n",
+    "\n",
+    "class 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",
+    "\n",
+    "class 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",
+    "\n",
+    "class RequestStatus(Enum):\n",
+    "\n",
+    "    UNREAD = 0\n",
+    "    READ = 1\n",
+    "    ACCEPTED = 2\n",
+    "    REJECTED = 3\n",
+    "\n",
+    "\n",
+    "class Singleton(type):\n",
+    "\n",
+    "    _instances = {}\n",
+    "    def __call__(cls, *args, **kwargs):\n",
+    "        if cls not in cls._instances:\n",
+    "            cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)\n",
+    "        return cls._instances[cls]"
+   ]
+  }
+ ],
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+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
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+}

solutions/object_oriented_design/online_chat/online_chat.py

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