solutions/object_oriented_design/call_center/call_center.ipynb

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   "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)."
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Design a call center"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Constraints and assumptions\n",
    "\n",
    "* What levels of employees are in the call center?\n",
    "    * Operator, supervisor, director\n",
    "* Can we assume operators always get the initial calls?\n",
    "    * Yes\n",
    "* If there is no available operators or the operator can't handle the call, does the call go to the supervisors?\n",
    "    * Yes\n",
    "* If there is no available supervisors or the supervisor can't handle the call, does the call go to the directors?\n",
    "    * Yes\n",
    "* Can we assume the directors can handle all calls?\n",
    "    * Yes\n",
    "* What happens if nobody can answer the call?\n",
    "    * It gets queued\n",
    "* Do we need to handle 'VIP' calls where we put someone to the front of the line?\n",
    "    * No\n",
    "* Can we assume inputs are valid or do we have to validate them?\n",
    "    * Assume they're valid"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Solution"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
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   "outputs": [
    {
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     "output_type": "stream",
     "text": [
      "Overwriting call_center.py\n"
     ]
    }
   ],
   "source": [
    "%%writefile call_center.py\n",
    "from abc import ABCMeta, abstractmethod\n",
    "from collections import deque\n",
    "from enum import Enum\n",
    "\n",
    "\n",
    "class Rank(Enum):\n",
    "\n",
    "    OPERATOR = 0\n",
    "    SUPERVISOR = 1\n",
    "    DIRECTOR = 2\n",
    "\n",
    "\n",
    "class Employee(metaclass=ABCMeta):\n",
    "\n",
    "    def __init__(self, employee_id, name, rank, call_center):\n",
    "        self.employee_id = employee_id\n",
    "        self.name = name\n",
    "        self.rank = rank\n",
    "        self.call = None\n",
    "        self.call_center = call_center\n",
    "\n",
    "    def take_call(self, call):\n",
    "        \"\"\"Assume the employee will always successfully take the call.\"\"\"\n",
    "        self.call = call\n",
    "        self.call.employee = self\n",
    "        self.call.state = CallState.IN_PROGRESS\n",
    "\n",
    "    def complete_call(self):\n",
    "        self.call.state = CallState.COMPLETE\n",
    "        self.call_center.notify_call_completed(self.call)\n",
    "\n",
    "    @abstractmethod\n",
    "    def escalate_call(self):\n",
    "        pass\n",
    "\n",
    "    def _escalate_call(self):\n",
    "        self.call.state = CallState.READY\n",
    "        call = self.call\n",
    "        self.call = None\n",
    "        self.call_center.notify_call_escalated(call)\n",
    "\n",
    "\n",
    "class Operator(Employee):\n",
    "\n",
    "    def __init__(self, employee_id, name):\n",
    "        super(Operator, self).__init__(employee_id, name, Rank.OPERATOR)\n",
    "\n",
    "    def escalate_call(self):\n",
    "        self.call.level = Rank.SUPERVISOR\n",
    "        self._escalate_call()\n",
    "\n",
    "\n",
    "class Supervisor(Employee):\n",
    "\n",
    "    def __init__(self, employee_id, name):\n",
    "        super(Operator, self).__init__(employee_id, name, Rank.SUPERVISOR)\n",
    "\n",
    "    def escalate_call(self):\n",
    "        self.call.level = Rank.DIRECTOR\n",
    "        self._escalate_call()\n",
    "\n",
    "\n",
    "class Director(Employee):\n",
    "\n",
    "    def __init__(self, employee_id, name):\n",
    "        super(Operator, self).__init__(employee_id, name, Rank.DIRECTOR)\n",
    "\n",
    "    def escalate_call(self):\n",
    "        raise NotImplemented('Directors must be able to handle any call')\n",
    "\n",
    "\n",
    "class CallState(Enum):\n",
    "\n",
    "    READY = 0\n",
    "    IN_PROGRESS = 1\n",
    "    COMPLETE = 2\n",
    "\n",
    "\n",
    "class Call(object):\n",
    "\n",
    "    def __init__(self, rank):\n",
    "        self.state = CallState.READY\n",
    "        self.rank = rank\n",
    "        self.employee = None\n",
    "\n",
    "\n",
    "class CallCenter(object):\n",
    "\n",
    "    def __init__(self, operators, supervisors, directors):\n",
    "        self.operators = operators\n",
    "        self.supervisors = supervisors\n",
    "        self.directors = directors\n",
    "        self.queued_calls = deque()\n",
    "\n",
    "    def dispatch_call(self, call):\n",
    "        if call.rank not in (Rank.OPERATOR, Rank.SUPERVISOR, Rank.DIRECTOR):\n",
    "            raise ValueError('Invalid call rank: {}'.format(call.rank))\n",
    "        employee = None\n",
    "        if call.rank == Rank.OPERATOR:\n",
    "            employee = self._dispatch_call(call, self.operators)\n",
    "        if call.rank == Rank.SUPERVISOR or employee is None:\n",
    "            employee = self._dispatch_call(call, self.supervisors)\n",
    "        if call.rank == Rank.DIRECTOR or employee is None:\n",
    "            employee = self._dispatch_call(call, self.directors)\n",
    "        if employee is None:\n",
    "            self.queued_calls.append(call)\n",
    "\n",
    "    def _dispatch_call(self, call, employees):\n",
    "        for employee in employees:\n",
    "            if employee.call is None:\n",
    "                employee.take_call(call)\n",
    "                return employee\n",
    "        return None\n",
    "\n",
    "    def notify_call_escalated(self, call):  # ...\n",
    "    def notify_call_completed(self, call):  # ...\n",
    "    def dispatch_queued_call_to_newly_freed_employee(self, call, employee):  # ..."
   ]
  }
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