type introspection

src/ytdl_sub/script/types/function.py

@@ -1,9 +1,14 @@
+import functools
+import inspect
 from abc import ABC
 from abc import abstractmethod
 from dataclasses import dataclass
+from inspect import FullArgSpec
+from typing import Callable
 from typing import Dict
 from typing import List
 from typing import Set
+from typing import Type
 from typing import Union
 from typing import final
 
@@ -47,11 +52,55 @@ class Function(VariableDependency):
 
     def __post_init__(self):
         # TODO: Figure out resolution via introspecting args and outputs of function
+        if len(self.args) != len(self.input_types):
+            raise StringFormattingException(
+                f"Unequal amount of arguments passed to function {self.name}.\n"
+                f"{self._expected_received_error_msg()}"
+            )
+
+        for input_arg, input_arg_type in zip(self.args, self.input_types):
+            if isinstance(input_arg, Function):
+                input_arg = input_arg.output_type
+            elif isinstance(input_arg, Variable):
+                pass  # cannot evaluate the variable yet, so pass
+            if not issubclass(input_arg.__class__, input_arg_type):
+                raise StringFormattingException(
+                    f"Invalid arguments passed to function {self.name}.\n"
+                    f"{self._expected_received_error_msg()}"
+                )
+
+    def _expected_received_error_msg(self) -> str:
+        output_type_names: List[str] = []
+        for arg in self.args:
+            if isinstance(arg, Function):
+                output_type_names.append(f"{arg.name}(...)->{arg.output_type.__name__}")
+            else:
+                output_type_names.append(arg.__class__.__name__)
+
+        return (
+            f"Expected ({', '.join([type_.__name__ for type_ in self.input_types])}).\n"
+            f"Received ({', '.join([output_type_name for output_type_name in output_type_names])})"
+        )
+
+    @property
+    def callable(self) -> Callable[..., Resolvable]:
         try:
-            getattr(Functions, self.name)
+            return getattr(Functions, self.name)
         except AttributeError:
             raise StringFormattingException(f"Function name {self.name} does not exist")
 
+    @functools.cached_property
+    def arg_spec(self) -> FullArgSpec:
+        return inspect.getfullargspec(self.callable)
+
+    @property
+    def input_types(self) -> List[Type[Resolvable]]:
+        return [self.arg_spec.annotations[arg_name] for arg_name in self.arg_spec.args]
+
+    @property
+    def output_type(self) -> Type[Resolvable]:
+        return self.arg_spec.annotations["return"]
+
     @property
     def variables(self) -> Set[Variable]:
         """