Common: Add recursive resolution to DIContainer

monkey/common/di_container.py

@@ -44,21 +44,32 @@ class DIContainer:
         """
         args = []
 
-        # TODO: Need to handle keyword-only arguments, defaults, varars, etc.
+        # TODO: Need to handle keyword-only arguments, defaults, varargs, etc.
         for arg_type in inspect.getfullargspec(type_).annotations.values():
-            new_instance = self._resolve_instance(arg_type)
-            args.append(new_instance)
+            instance = self._resolve_arg_type(arg_type)
+            args.append(instance)
 
         return type_(*args)
 
-    def _resolve_instance(self, arg_type: Type):
+    def _resolve_arg_type(self, arg_type: Type[T]) -> T:
         if arg_type in self._type_registry:
-            return self._type_registry[arg_type]()
+            return self._resolve_type(arg_type)
         elif arg_type in self._instance_registry:
-            return self._instance_registry[arg_type]
+            return self._resolve_instance(arg_type)
 
         raise ValueError(f'Failed to resolve unknown type "{arg_type.__name__}"')
 
+    def _resolve_type(self, arg_type: Type[T]) -> T:
+        try:
+            return self._type_registry[arg_type]()
+        except TypeError:
+            # arg_type has dependencies that must be resolved. Recursively call resolve() to
+            # construct an instance of arg_type with all of the requesite dependencies injected.
+            return self.resolve(self._type_registry[arg_type])
+
+    def _resolve_instance(self, arg_type: Type[T]) -> T:
+        return self._instance_registry[arg_type]
+
     def release(self, interface: Type[T]):
         """
         Deregister's an interface

monkey/tests/unit_tests/common/test_di_container.py

@@ -1,13 +1,15 @@
+import abc
+
 import pytest
 
 from common import DIContainer
 
 
-class IServiceA:
+class IServiceA(metaclass=abc.ABCMeta):
     pass
 
 
-class IServiceB:
+class IServiceB(metaclass=abc.ABCMeta):
     pass
 
 
@@ -157,9 +159,7 @@ def test_instance_overrides_type(container):
     assert id(test_1.service_a) == id(service_a_instance)
 
 
-def test_release_type():
-    container = DIContainer()
-
+def test_release_type(container):
     container.register(IServiceA, ServiceA)
     container.release(IServiceA)
 
@@ -167,12 +167,65 @@ def test_release_type():
         container.resolve(TestClass1)
 
 
-def test_release_instance():
-    container = DIContainer()
+def test_release_instance(container):
     service_a_instance = ServiceA()
-
     container.register_instance(IServiceA, service_a_instance)
+
     container.release(IServiceA)
 
     with pytest.raises(ValueError):
         container.resolve(TestClass1)
+
+
+class IServiceC(metaclass=abc.ABCMeta):
+    pass
+
+
+class ServiceC(IServiceC):
+    def __init__(self, service_a: IServiceA):
+        self.service_a = service_a
+
+
+class TestClass4:
+    def __init__(self, service_c: IServiceC):
+        self.service_c = service_c
+
+
+def test_recursive_resolution__depth_2(container):
+    service_a_instance = ServiceA()
+    container.register_instance(IServiceA, service_a_instance)
+    container.register(IServiceC, ServiceC)
+
+    test4 = container.resolve(TestClass4)
+
+    assert isinstance(test4.service_c, ServiceC)
+    assert id(test4.service_c.service_a) == id(service_a_instance)
+
+
+class IServiceD(metaclass=abc.ABCMeta):
+    pass
+
+
+class ServiceD(IServiceD):
+    def __init__(self, service_c: IServiceC, service_b: IServiceB):
+        self.service_b = service_b
+        self.service_c = service_c
+
+
+class TestClass5:
+    def __init__(self, service_d: IServiceD):
+        self.service_d = service_d
+
+
+def test_recursive_resolution__depth_3(container):
+    container.register(IServiceA, ServiceA)
+    container.register(IServiceB, ServiceB)
+    container.register(IServiceC, ServiceC)
+    container.register(IServiceD, ServiceD)
+
+    test5 = container.resolve(TestClass5)
+
+    assert isinstance(test5.service_d, ServiceD)
+    assert isinstance(test5.service_d.service_b, ServiceB)
+    assert isinstance(test5.service_d.service_c, ServiceC)
+    assert isinstance(test5.service_d.service_c.service_a, ServiceA)