Resolve "Change the processing of the `stories` rule to a `height` GEM Taxonomy tag"

Closes #15 (closed)

building/02_process/height_and_floorspace/height_and_floorspace.py

@@ -86,12 +86,9 @@ class HeightAndFloorspaceRule:
         min_stories = self.tag_to_float(tags, "building:min_level")
 
         # Parse the main stories and roof stories.
-        stories = None
-        floorspace = None
+        stories = 0
+        floorspace = 0
         if main_stories or roof_stories:
-            stories = 0
-            floorspace = 0
-
             if main_stories:
                 stories += main_stories
                 floorspace += main_stories * area
@@ -106,32 +103,29 @@ class HeightAndFloorspaceRule:
             # Ceil the number of stories
             stories = ceil(stories)
 
-            # Take a factor of 90% for the floorspace
-            floorspace *= 0.9
-
         # Parse the underground story tag.
         if underground_stories:
             underground_stories = ceil(underground_stories)
+            floorspace += underground_stories * area
+        else:
+            underground_stories = 0
+
+        # Take a factor of 90% for the floorspace
+        floorspace *= 0.9
 
         # Check if anything is wrong with the tags.
         if stories < 0 or underground_stories < 0:
-            raise ValueError("Number of stories cannot be below 0.")
-        elif stories == 0 and not (underground_stories > 0):
-            raise ValueError(
-                "Number of stories cannot be 0, if there are no underground stories."
-            )
-        elif underground_stories == 0 and not (stories > 0):
-            raise ValueError(
-                "Number of underground stories cannot be 0, if there are no stories."
-            )
-        elif stories > 175:
-            raise ValueError("Number of stories cannot be above 175.")
+            return None, None
+        elif stories == 0 and underground_stories == 0:
+            return None, None
+        elif stories + underground_stories > 175:
+            return None, None
 
         # Create the story tag according to the GEM taxonomy.
         story_tags = []
-        if stories:
+        if stories != 0:
             story_tags.append(f"H:{stories}")
-        if underground_stories:
+        if underground_stories != 0:
             story_tags.append(f"HBEX:{underground_stories}")
 
         return "+".join(story_tags), floorspace