src/mdis/dispatcher.py

   1 import collections as _collections
   2 import inspect as _inspect
   3 import operator as _operator
   4
   5 from . import core as _core
   6
   7
   8 class DispatcherMeta(type):
   9     def __new__(metacls, name, bases, ns):
  10         conflicts = _collections.defaultdict(list)
  11         for (key, value) in tuple(ns.items()):
  12             if not isinstance(value, _core.CallHook):
  13                 continue
  14             hook = value
  15             for typeid in hook:
  16                 conflicts[typeid].append(key)
  17             ns[key] = hook
  18
  19         for (typeid, keys) in conflicts.items():
  20             if len(keys) > 1:
  21                 raise ValueError(f"dispatch conflict: {keys!r}")
  22
  23         return super().__new__(metacls, name, bases, ns)
  24
  25     def __init__(cls, name, bases, ns):
  26         hooks = {}
  27         for hook in map(_operator.itemgetter(1), _inspect.getmembers(cls,
  28                 predicate=lambda member: isinstance(member, _core.CallHook))):
  29             for typeid in hook:
  30                 hooks[typeid] = hook
  31         cls.__hooks = hooks
  32         return super().__init__(name, bases, ns)
  33
  34     def dispatch(cls, typeid=object):
  35         return cls.__hooks.get(typeid)
  36
  37
  38 class Dispatcher(metaclass=DispatcherMeta):
  39     def __call__(self, instance):
  40         for typeid in instance.__class__.__mro__:
  41             hook = self.__class__.dispatch(typeid=typeid)
  42             if hook is not None:
  43                 break
  44         if hook is None:
  45             hook = self.__class__.dispatch()
  46         return hook(dispatcher=self, instance=instance)
  47
  48     @_core.hook(object)
  49     def dispatch_object(self, instance):
  50         raise NotImplementedError()