src/mdis/dispatcher.py

   1 import collections as _collections
   2 import inspect as _inspect
   3 import types as _types
   4
   5 from . import core as _core
   6
   7
   8 class DispatcherMeta(type):
   9     __hooks__ = {}
  10
  11     def __new__(metacls, name, bases, ns):
  12         hooks = {}
  13         ishook = lambda member: isinstance(member, _core.Hook)
  14
  15         for basecls in reversed(bases):
  16             members = _inspect.getmembers(basecls, predicate=ishook)
  17             for (_, hook) in members:
  18                 hooks.update(dict.fromkeys(hook, hook))
  19
  20         conflicts = _collections.defaultdict(list)
  21         for (key, value) in tuple(ns.items()):
  22             if not ishook(value):
  23                 continue
  24             hook = value
  25             for typeid in hook:
  26                 hooks[typeid] = hook
  27                 conflicts[typeid].append(key)
  28             ns[key] = hook
  29
  30         for (typeid, keys) in conflicts.items():
  31             if len(keys) > 1:
  32                 raise ValueError(f"dispatch conflict: {keys!r}")
  33
  34         ns["__hooks__"] = _types.MappingProxyType(hooks)
  35
  36         return super().__new__(metacls, name, bases, ns)
  37
  38     def dispatch(cls, typeid=object):
  39         return cls.__hooks__.get(typeid)
  40
  41
  42 class Dispatcher(metaclass=DispatcherMeta):
  43     def __call__(self, instance):
  44         for typeid in instance.__class__.__mro__:
  45             hook = self.__class__.dispatch(typeid=typeid)
  46             if hook is not None:
  47                 break
  48         if hook is None:
  49             hook = self.__class__.dispatch()
  50         return hook(dispatcher=self, instance=instance)
  51
  52     @_core.hook(object)
  53     def dispatch_object(self, instance):
  54         raise NotImplementedError()