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

src/ifcopenshell-python/ifcopenshell/api/layer/add_layer.py

@@ -0,0 +1,11 @@
+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("IfcPresentationLayerAssignment", **{
+            "Name": "Unnamed"
+        })

src/ifcopenshell-python/ifcopenshell/api/layer/assign_layer.py

@@ -0,0 +1,17 @@
+import ifcopenshell
+
+
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {
+            "item": None,
+            "layer": None,
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        assigned_items = set(self.settings["layer"].AssignedItems) or set()
+        assigned_items.add(self.settings["item"])
+        self.settings["layer"].AssignedItems = list(assigned_items)

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

@@ -0,0 +1,35 @@
+import ifcopenshell
+import ifcopenshell.util.date
+from datetime import datetime
+
+
+class Data:
+    is_loaded = False
+    items = {}
+    layers = {}
+
+    @classmethod
+    def purge(cls):
+        cls.is_loaded = False
+        cls.items = {}
+        cls.layers = {}
+
+    @classmethod
+    def load(cls, file):
+        cls._file = file
+        if not cls._file:
+            return
+        cls.load_layers()
+        cls.is_loaded = True
+
+    @classmethod
+    def load_layers(cls):
+        cls.layers = {}
+        cls.items = {}
+        for layer in cls._file.by_type("IfcPresentationLayerAssignment"):
+            data = layer.get_info()
+            if layer.AssignedItems:
+                for item in layer.AssignedItems:
+                    cls.items.setdefault(item.id(), []).append(layer.id())
+            del data["AssignedItems"]
+            cls.layers[layer.id()] = data

src/ifcopenshell-python/ifcopenshell/api/layer/edit_layer.py

@@ -0,0 +1,13 @@
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {
+            "layer": 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["layer"], name, value)

src/ifcopenshell-python/ifcopenshell/api/layer/remove_layer.py

@@ -0,0 +1,9 @@
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {"layer": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        self.file.remove(self.settings["layer"])

src/ifcopenshell-python/ifcopenshell/api/layer/unassign_layer.py

@@ -0,0 +1,17 @@
+import ifcopenshell
+
+
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {
+            "item": None,
+            "layer": None,
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        assigned_items = set(self.settings["layer"].AssignedItems) or set()
+        assigned_items.remove(self.settings["item"])
+        self.settings["layer"].AssignedItems = list(assigned_items)