make group io nodes 'optional' (#167)

Reviewed-on: https://codeberg.org/StreamGraph/StreamGraph/pulls/167
Co-authored-by: Lera Elvoé <yagich@poto.cafe>
Co-committed-by: Lera Elvoé <yagich@poto.cafe>

classes/deck/deck.gd

@@ -50,10 +50,6 @@ var _belonging_to: String = "" # for groups
 var group_input_node: String
 ## The ID of this group's input node. Used only if [member is_group] is [code]true[/code].
 var group_output_node: String
-## The ID of the group node this group is represented by, contained in this deck's parent deck.
-## Used only if [member is_group] is [code]true[/code].
-## @experimental
-#var group_node: String
 
 var emit_group_signals: bool = true
 var emit_node_added_signal: bool = true
@@ -97,8 +93,17 @@ func add_node_type(type: String, assign_id: String = "", assign_to_self: bool =
 ## If [param assign_id] is empty, the node will get its' ID (re-)assigned.
 ## Otherwise, it will be assigned to be that value.[br]
 ## If [param assign_to_self] is [code]true[/code], the node's
-## [member DeckNode._belonging_to] property will be set to [code]self[/code].
+## [member DeckNode._belonging_to] property will be set to [code]self[/code].[br]
+## Returns [code]null[/code] if the node cannot be insantiated.
 func add_node_inst(node: DeckNode, assign_id: String = "", assign_to_self: bool = true) -> DeckNode:
+	if node.node_type == "group_input" and not group_input_node.is_empty():
+		DeckHolder.logger.toast_error("Cannot add group input node, one already exists!")
+		node.free()
+		return null
+	if node.node_type == "group_output" and not group_output_node.is_empty():
+		DeckHolder.logger.toast_error("Cannot add group output node, one already exists!")
+		node.free()
+		return null
 	if assign_to_self:
 		node._belonging_to = self
 		#node._belonging_to_instance = instance_id
@@ -113,9 +118,17 @@ func add_node_inst(node: DeckNode, assign_id: String = "", assign_to_self: bool
 
 	if node.node_type == "group_input":
 		group_input_node = node._id
+		node.about_to_free.connect(
+			func():
+				group_input_node = ""
+		)
 	
 	if node.node_type == "group_output":
 		group_output_node = node._id
+		node.about_to_free.connect(
+			func():
+				group_output_node = ""
+		)
 
 	if emit_node_added_signal:
 		node_added.emit(node)
@@ -702,8 +715,10 @@ static func from_dict(data: Dictionary, path: String = "") -> Deck:
 				node.group_instance_id
 			)
 		
-		group.get_node(node.input_node_id).group_node = node
-		group.get_node(node.output_node_id).group_node = node
+		if not node.input_node_id.is_empty():
+			group.get_node(node.input_node_id).group_node = node
+		if not node.output_node_id.is_empty():
+			group.get_node(node.output_node_id).group_node = node
 		node.init_io()
 
 	return deck

classes/deck/nodes/group/group_node.gd

@@ -60,6 +60,17 @@ func init_io() -> void:
 	input_node = group.get_node(input_node_id)
 	output_node = group.get_node(output_node_id)
 
+	if input_node:
+		input_node.about_to_free.connect(
+			func():
+				input_node_id = ""
+		)
+	if output_node:
+		output_node.about_to_free.connect(
+			func():
+				output_node_id = ""
+		)
+
 	recalculate_ports()
 	setup_connections()
 

graph_node_renderer/deck_renderer_graph_edit.gd

@@ -345,6 +345,9 @@ func _on_add_node_menu_node_selected(type: String) -> void:
 		# deck.add_node_inst(node)
 		var node := deck.add_node_type(type)
 		
+		if node == null:
+			return
+
 		get_node_renderer(node).position_offset = node_pos
 	else:
 		var node := deck.add_lib_group_node(type)