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

src/ifcopenshell-python/ifcopenshell/api/group/add_group.py

@@ -0,0 +1,17 @@
+import ifcopenshell
+from ifcopenshell.api.owner.api import create_owner_history
+
+
+class Usecase:
+    def __init__(self, file, settings={}):
+        self.file = file
+        self.settings = {}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        return self.file.create_entity("IfcGroup", **{
+            "GlobalId": ifcopenshell.guid.new(),
+            "OwnerHistory": create_owner_history(),
+            "Name": "Unnamed"
+        })

src/ifcopenshell-python/ifcopenshell/api/group/assign_group.py

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+import ifcopenshell
+from ifcopenshell.api.owner.api import create_owner_history
+from ifcopenshell.api.owner.api import update_owner_history
+
+
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {
+            "product": None,
+            "group": None,
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        if not self.settings["group"].IsGroupedBy:
+            return self.file.create_entity("IfcRelAssignsToGroup", **{
+                "GlobalId": ifcopenshell.guid.new(),
+                "OwnerHistory": create_owner_history(),
+                "RelatedObjects": [self.settings["product"]],
+                "RelatingGroup": self.settings["group"]
+            })
+        rel = self.settings["group"].IsGroupedBy[0]
+        related_objects = set(rel.RelatedObjects) or set()
+        related_objects.add(self.settings["product"])
+        rel.RelatedObjects = list(related_objects)
+        update_owner_history(rel)

src/ifcopenshell-python/ifcopenshell/api/group/data.py

@@ -0,0 +1,24 @@
+class Data:
+    is_loaded = False
+    products = {}
+    groups = {}
+
+    @classmethod
+    def purge(cls):
+        cls.is_loaded = False
+        cls.products = {}
+        cls.groups = {}
+
+    @classmethod
+    def load(cls, file):
+        cls.products = {}
+        cls.groups = {}
+        for group in file.by_type("IfcGroup", include_subtypes=False):
+            if group.IsGroupedBy:
+                for rel in group.IsGroupedBy:
+                    for product in rel.RelatedObjects:
+                        cls.products.setdefault(product.id(), []).append(group.id())
+            data = group.get_info()
+            del data["OwnerHistory"]
+            cls.groups[group.id()] = data
+        cls.is_loaded=True

src/ifcopenshell-python/ifcopenshell/api/group/edit_group.py

@@ -0,0 +1,13 @@
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {
+            "group": None,
+            "attributes": {}
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        for name, value in self.settings["attributes"].items():
+            setattr(self.settings["group"], name, value)

src/ifcopenshell-python/ifcopenshell/api/group/remove_group.py

@@ -0,0 +1,11 @@
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {"group": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        for rel in self.settings["group"].IsGroupedBy or []:
+            self.file.remove(rel)
+        self.file.remove(self.settings["group"])

src/ifcopenshell-python/ifcopenshell/api/group/unassign_group.py

@@ -0,0 +1,25 @@
+import ifcopenshell
+from ifcopenshell.api.owner.api import update_owner_history
+
+
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {
+            "product": None,
+            "group": None,
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        if not self.settings["group"].IsGroupedBy:
+            return
+        rel = self.settings["group"].IsGroupedBy[0]
+        related_objects = set(rel.RelatedObjects) or set()
+        related_objects.remove(self.settings["product"])
+        if len(related_objects):
+            rel.RelatedObjects = list(related_objects)
+            update_owner_history(rel)
+        else:
+            self.file.remove(rel)