{"id":"ood-call-center","title":"Design a call center","sections":[{"id":"constraints-and-assumptions","title":"Constraints and assumptions","html":"Constraints and assumptions
\n\n- What levels of employees are in the call center?\n
\n- Operator, supervisor, director
\n
\n \n- Can we assume operators always get the initial calls?\n\n
\n- If there is no available operators or the operator can't handle the call, does the call go to the supervisors?\n\n
\n- If there is no available supervisors or the supervisor can't handle the call, does the call go to the directors?\n\n
\n- Can we assume the directors can handle all calls?\n\n
\n- What happens if nobody can answer the call?\n\n
\n- Do we need to handle 'VIP' calls where we put someone to the front of the line?\n\n
\n- Can we assume inputs are valid or do we have to validate them?\n\n
\n
","headings":[]},{"id":"solution","title":"Solution","html":"Solution
\nfrom abc import ABCMeta, abstractmethod\nfrom collections import deque\nfrom enum import Enum\n\n\nclass Rank(Enum):\n\n OPERATOR = 0\n SUPERVISOR = 1\n DIRECTOR = 2\n\n\nclass 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\nclass 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\nclass 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\nclass 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\nclass CallState(Enum):\n\n READY = 0\n IN_PROGRESS = 1\n COMPLETE = 2\n\n\nclass Call(object):\n\n def __init__(self, rank):\n self.state = CallState.READY\n self.rank = rank\n self.employee = None\n\n\nclass 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): # ...
","headings":[]}],"sourceFiles":[{"name":"call_center.py","url":"https://github.com/donnemartin/system-design-primer/blob/master/solutions/object_oriented_design/call_center/call_center.py","html":"from abc import ABCMeta, abstractmethod\nfrom collections import deque\nfrom enum import Enum\n\n\nclass Rank(Enum):\n\n OPERATOR = 0\n SUPERVISOR = 1\n DIRECTOR = 2\n\n\nclass 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\nclass 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\nclass 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\nclass 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 NotImplementedError('Directors must be able to handle any call')\n\n\nclass CallState(Enum):\n\n READY = 0\n IN_PROGRESS = 1\n COMPLETE = 2\n\n\nclass Call(object):\n\n def __init__(self, rank):\n self.state = CallState.READY\n self.rank = rank\n self.employee = None\n\n\nclass 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 pass\n\n def notify_call_completed(self, call):\n pass\n\n def dispatch_queued_call_to_newly_freed_employee(self, call, employee):\n pass
"}]}