First attempt at ripping out agnostic code into ifcopenshell.api namespace. See #1399.

src/ifcopenshell-python/ifcopenshell/api/geometry/unassign_representation.py

@@ -0,0 +1,56 @@
+import ifcopenshell.api.geometry.remove_representation as remove_representation
+import ifcopenshell.util.element
+
+
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {"product": None, "representation": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        if self.settings["product"].is_a("IfcProduct"):
+            self.unassign_product_representation(self.settings["product"], self.settings["representation"])
+        elif self.settings["product"].is_a("IfcTypeProduct"):
+            self.unassign_type_representation()
+
+    def unassign_product_representation(self, product, representation):
+        representations = list(product.Representation.Representations or [])
+        if representation not in representations:
+            return
+        representations.remove(representation)
+        if not representations:
+            self.file.remove(product.Representation)
+        else:
+            product.Representation.Representations = representations
+
+    def unassign_type_representation(self):
+        for representation_map in self.settings["product"].RepresentationMaps or []:
+            if representation_map.MappedRepresentation == self.settings["representation"]:
+                self.unassign_products_using_mapped_representation(representation_map)
+                self.remove_representation_map_only(representation_map)
+                break
+        self.settings["product"].RepresentationMaps = self.settings["product"].RepresentationMaps or None
+
+    def remove_representation_map_only(self, representation_map):
+        dummy_representation = self.file.createIfcShapeRepresentation()
+        representation_map.MappedRepresentation = dummy_representation
+        ifcopenshell.util.element.remove_deep(self.file, representation_map)
+        self.file.remove(representation_map)
+
+    def unassign_products_using_mapped_representation(self, representation_map):
+        mapped_representations = []
+        just_representations = []
+        for map_usage in representation_map.MapUsage or []:
+            for inverse in self.file.get_inverse(map_usage):
+                if not inverse.is_a("IfcShapeRepresentation"):
+                    continue
+                for definition in inverse.OfProductRepresentation or []:
+                    for product in definition.ShapeOfProduct or []:
+                        mapped_representations.append({"product": product, "representation": inverse})
+                        just_representations.append(inverse)
+        for item in mapped_representations:
+            self.unassign_product_representation(item["product"], item["representation"])
+        for representation in just_representations:
+            remove_representation.Usecase(self.file, {"representation": representation}).execute()