plan: document the calculate_rates function

plan.py

@@ -4,42 +4,11 @@ import math
 import collections
 
 from fractions import Fraction
-from typing import Dict, Iterable
+from typing import Dict, List
 
 import satisfactory
 
 
-def calculate_rates(recipes: Iterable[str], remain: Dict[str,Fraction]):
-    required_items = collections.defaultdict(Fraction)
-
-    while remain:
-        for dst_name, dst_rate in remain.pop().items():
-            required_items[dst_name] += dst_rate
-
-            dst = recipes[dst_name]
-            if not recipes.is_component(dst_name):
-                continue
-
-            dst_recipe = recipes[dst_name]['recipes'][0]
-            src_recipe = recipes[dst_name]['recipes'][0]
-
-            normal_rate = Fraction(
-                dst_recipe['output'][dst_name],
-                dst_recipe['crafting_time']
-            )
-
-            scale = dst_rate / normal_rate
-
-            for src_name, src_count in src_recipe['input'].items():
-                src_rate = Fraction(
-                    src_count,
-                    dst_recipe['crafting_time']
-                ) * scale
-                remain.append({src_name: src_rate})
-
-    return required_items
-
-
 def basic_rate(recipe: Dict) -> Fraction:
     """
     Calculate the rate at which the item is crafted with the default recipe.
@@ -52,6 +21,49 @@ def basic_rate(recipe: Dict) -> Fraction:
         )
 
 
+def calculate_rates(
+        recipes: satisfactory.Cookbook,
+        remain: List[Dict[str, Fraction]]
+) -> Dict[str, Fraction]:
+    """
+    Calculate the total production rates needed to produce items at the rates
+    listed in 'remain' using the provided recipes.
+    :param recipes: The source Cookbook
+    :param remain: A mapping from requested items to their desired rate.
+    :return: A mapping from all required items to their required output rates.
+    """
+
+    # Iteratively accumulate a mapping from items to required rates
+    required_items = collections.defaultdict(Fraction)
+
+    while remain:
+        for dst_name, dst_rate in remain.pop().items():
+            # Append the requested item
+            required_items[dst_name] += dst_rate
+
+            # We can't craft resources, so just ignore them.
+            if not recipes.is_component(dst_name):
+                assert recipes.is_resource(dst_name)
+                continue
+
+            # Assume we're using the default recipe
+            dst_recipe = recipes[dst_name]['recipes'][0]
+
+            # Calculate the fraction of the base rate we need to satisfy, and
+            # append our (scaled) inputs to the request queue.
+            normal_rate = basic_rate(dst_recipe)
+            scale = dst_rate / normal_rate
+
+            for src_name, src_count in dst_recipe['input'].items():
+                src_rate = Fraction(
+                    src_count,
+                    dst_recipe['crafting_time']
+                ) * scale
+                remain.append({src_name: src_rate})
+
+    return required_items
+
+
 # The number of items per minute that each tier of conveyor can carry
 conveyor_rates = [0, 60, 120, 270, 480, 780, 900]
 
@@ -59,8 +71,6 @@ conveyor_rates = [0, 60, 120, 270, 480, 780, 900]
 def main():
     recipes = satisfactory.Cookbook('data/recipes')
 
-    required_items = collections.defaultdict(Fraction)
-
     # Create a list of items we want to make
     # targets = [ 'supercomputer' ]
     targets = recipes.components()