from abc import ABCMeta, abstractmethod

class IObserver(metaclass = ABCMeta):
    @abstractmethod
    def update(self, value):
        pass
    
    def __enter__(self):
        return self
    
    @abstractmethod
    def __exit__(self, exc_type, exc_value, traceback):
        pass

class IPublisher(metaclass = ABCMeta):
    _observers = set()
    
    def attach(self, observer):
        if not isinstance(observer, IObserver):
            raise TypeError('Observer not derived from IObserver')
        self._observers |= {observer}
        
    def detach(self, observer):
        self._observers -= {observer}
        
    def notify(self, msg=None):
        for observer in self._observers:
            if msg is None:
                observer.update()
            else:
                observer.update(msg)
                
    def __enter__(self):
        return self
    
    def __exit__(self, exc_type, exc_value, traceback):
        self._observers.clear()

class KPIs(IPublisher):
    _open_tickets = -1
    _closed_tickets = -1
    _new_tickets = -1
    
    @property
    def open_tickets(self):
        return self._open_tickets
    
    @property
    def closed_tickets(self):
        return self._closed_tickets
    
    @property
    def new_tickets(self):
        return self._new_tickets
    
    def set_kpis(self, open_tickets, closed_tickets, new_tickets, msg=None):
        self._open_tickets = open_tickets
        self._closed_tickets = closed_tickets
        self._new_tickets = new_tickets
        
        self.notify(msg)    

class CurrentKPIs(IObserver):
    open_tickets = -1
    closed_tickets = -1
    new_tickets = -1
    
    def __init__(self, kpis):
        self._kpis = kpis
        kpis.attach(self)
        
    def update(self, msg=None):
        self.open_tickets = self._kpis.open_tickets
        self.closed_tickets = self._kpis.closed_tickets
        self.new_tickets = self._kpis.new_tickets
        self.display(msg)
        
    def display(self, msg=None):
        print(f'Current KPIs ({msg}):\nOpen: {self.open_tickets}'
              f'\nClosed: {self.closed_tickets}\nNew: {self.new_tickets}\n')
        
    def __exit__(self, exc_type, exc_value, traceback):
        self._kpis.detach(self)

class ForecastKPIs(IObserver):
    open_tickets = -1
    closed_tickets = -1
    new_tickets = -1
    
    def __init__(self, kpis):
        self._kpis = kpis
        kpis.attach(self)
        
    def update(self, msg=None):
        self.open_tickets = self._kpis.open_tickets
        self.closed_tickets = self._kpis.closed_tickets
        self.new_tickets = self._kpis.new_tickets
        self.display(msg)
        
    def display(self, msg):
        print(f'Forecast KPIs ({msg}):\nOpen: {self.open_tickets}'
              f'\nClosed: {self.closed_tickets}\nNew: {self.new_tickets}\n')
        
    def __exit__(self, exc_type, exc_value, traceback):
        self._kpis.detach(self)

kpis.set_kpis(100, 120, 160)    # No more notifications fired

class IObservable(metaclass = ABCMeta):
    _observers = set()
    
    def subscribe(self, observer):
        self._observers |= {observer}
        
    def unsubscribe(self, observer):
        self._observers -= {observer}
        
    def emit(self, val):
        for observer in self._observers:
            observer(val)
                
    def __enter__(self):
        return self
    
    def __exit__(self, exc_type, exc_value, traceback):
        self._observers.clear()

class NewKPIs(IObservable):
    _open_tickets = -1
    _closed_tickets = -1
    _new_tickets = -1
    
    def set_kpis(self, open_tickets, closed_tickets, new_tickets):
        self._open_tickets = open_tickets
        self._closed_tickets = closed_tickets
        self._new_tickets = new_tickets
        
        self.emit((self._open_tickets, self._closed_tickets, self._new_tickets))    

def currKPI(val):
    x, y, z = val
    print(f'Current KPIs:\nOpen: {x}\nClosed: {y}\nNew: {z}\n')
    
def foreKPI(val):
    x, y, z = val
    print(f'Forecast KPIs:\nOpen: {x}\nClosed: {y}\nNew: {z}\n')