handlerchain_class.py

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from abc import ABC, abstractmethod
from threading import Lock
from io import StringIO
 
from .handlerchain_message_class import Message
 
 
class IMessageHandler(ABC):
 
    
    @property
    @abstractmethod
    def ID(self) -> int:
        pass
 
    
    @abstractmethod
    def ProcessMessage(self, message : Message) -> bool:
        pass
 
    
    @abstractmethod
    def ToString(self) -> str:
        pass
 
 
#========================================================================
#========================================================================
#========================================================================
 
 
 
class HandlerChain:
 
    
    def __init__(self) -> None:
        self._messageHandlers = [] # type: list[IMessageHandler]
        self._messageHandlersLock = Lock()
 
    
 
 
    
    def SendMessage(self, message : Message):
        # We make a copy of the handlers so our processing of handlers
        # is not impacted by updates to the master handler list.
        copyof_MessageHandlers = None
        with self._messageHandlersLock:
            copyof_MessageHandlers = self._messageHandlers.copy()
 
        for window in copyof_MessageHandlers:
            if window.ProcessMessage(message):
                break
 
 
    
    def AddHandler(self,  window : IMessageHandler) -> None:
        with self._messageHandlersLock:
            existsInList = False
            for handler in self._messageHandlers:
                if window.ID == handler.ID:
                    existsInList = True
                    break
            if not existsInList:
                self._messageHandlers.append(window)
 
 
    
    def RemoveHandler(self, window : IMessageHandler) -> None:
        with self._messageHandlersLock:
            foundWindow = None
            for handler in self._messageHandlers:
                if window.ID == handler.ID:
                    foundWindow = window
                    break
            if foundWindow:
                self._messageHandlers.remove(foundWindow)
 
 
    
    def ToString(self) -> str:
        output = StringIO()
 
        copyof_MessageHandlers = None
        with self._messageHandlersLock:
            copyof_MessageHandlers = self._messageHandlers.copy()
 
        for window in copyof_MessageHandlers:
            output.write("    {0}\n".format(window.ToString()))
        return output.getvalue()