Cura/cura/Machines/MaterialManager.py

# Copyright (c) 2018 Ultimaker B.V.
# Cura is released under the terms of the LGPLv3 or higher.

from collections import defaultdict, OrderedDict
import copy
import uuid
from typing import Dict, Optional, TYPE_CHECKING

from PyQt5.Qt import QTimer, QObject, pyqtSignal, pyqtSlot

from UM.Application import Application
from UM.ConfigurationErrorMessage import ConfigurationErrorMessage
from UM.Logger import Logger
from UM.Settings.ContainerRegistry import ContainerRegistry
from UM.Settings.SettingFunction import SettingFunction
from UM.Util import parseBool

from .MaterialNode import MaterialNode
from .MaterialGroup import MaterialGroup
from .VariantType import VariantType

if TYPE_CHECKING:
    from UM.Settings.DefinitionContainer import DefinitionContainer
    from UM.Settings.InstanceContainer import InstanceContainer
    from cura.Settings.GlobalStack import GlobalStack
    from cura.Settings.ExtruderStack import ExtruderStack


#
# MaterialManager maintains a number of maps and trees for material lookup.
# The models GUI and QML use are now only dependent on the MaterialManager. That means as long as the data in
# MaterialManager gets updated correctly, the GUI models should be updated correctly too, and the same goes for GUI.
#
# For now, updating the lookup maps and trees here is very simple: we discard the old data completely and recreate them
# again. This means the update is exactly the same as initialization. There are performance concerns about this approach
# but so far the creation of the tables and maps is very fast and there is no noticeable slowness, we keep it like this
# because it's simple.
#
class MaterialManager(QObject):

    materialsUpdated = pyqtSignal()  # Emitted whenever the material lookup tables are updated.

    def __init__(self, container_registry, parent = None):
        super().__init__(parent)
        self._application = Application.getInstance()
        self._container_registry = container_registry  # type: ContainerRegistry

        self._fallback_materials_map = dict()  # material_type -> generic material metadata
        self._material_group_map = dict()  # root_material_id -> MaterialGroup
        self._diameter_machine_nozzle_buildplate_material_map = dict()  # approximate diameter str -> dict(machine_definition_id -> MaterialNode)

        # We're using these two maps to convert between the specific diameter material id and the generic material id
        # because the generic material ids are used in qualities and definitions, while the specific diameter material is meant
        # i.e. generic_pla -> generic_pla_175
        self._material_diameter_map = defaultdict(dict)  # root_material_id -> approximate diameter str -> root_material_id for that diameter
        self._diameter_material_map = dict()  # material id including diameter (generic_pla_175) -> material root id (generic_pla)

        # This is used in Legacy UM3 send material function and the material management page.
        self._guid_material_groups_map = defaultdict(list)  # GUID -> a list of material_groups

        # The machine definition ID for the non-machine-specific materials.
        # This is used as the last fallback option if the given machine-specific material(s) cannot be found.
        self._default_machine_definition_id = "fdmprinter"
        self._default_approximate_diameter_for_quality_search = "3"

        # When a material gets added/imported, there can be more than one InstanceContainers. In those cases, we don't
        # want to react on every container/metadata changed signal. The timer here is to buffer it a bit so we don't
        # react too many time.
        self._update_timer = QTimer(self)
        self._update_timer.setInterval(300)
        self._update_timer.setSingleShot(True)
        self._update_timer.timeout.connect(self._updateMaps)

        self._container_registry.containerMetaDataChanged.connect(self._onContainerMetadataChanged)
        self._container_registry.containerAdded.connect(self._onContainerMetadataChanged)
        self._container_registry.containerRemoved.connect(self._onContainerMetadataChanged)

    def initialize(self):
        # Find all materials and put them in a matrix for quick search.
        material_metadatas = {metadata["id"]: metadata for metadata in
                              self._container_registry.findContainersMetadata(type = "material") if
                              metadata.get("GUID")}

        self._material_group_map = dict()
                
        # Map #1
        #    root_material_id -> MaterialGroup
        for material_id, material_metadata in material_metadatas.items():
            # We don't store empty material in the lookup tables
            if material_id == "empty_material":
                continue

            root_material_id = material_metadata.get("base_file")
            if root_material_id not in self._material_group_map:
                self._material_group_map[root_material_id] = MaterialGroup(root_material_id, MaterialNode(material_metadatas[root_material_id]))
                self._material_group_map[root_material_id].is_read_only = self._container_registry.isReadOnly(root_material_id)
            group = self._material_group_map[root_material_id]

            # Store this material in the group of the appropriate root material.
            if material_id != root_material_id:
                new_node = MaterialNode(material_metadata)
                group.derived_material_node_list.append(new_node)

        # Order this map alphabetically so it's easier to navigate in a debugger
        self._material_group_map = OrderedDict(sorted(self._material_group_map.items(), key = lambda x: x[0]))

        # Map #1.5
        #    GUID -> material group list
        self._guid_material_groups_map = defaultdict(list)
        for root_material_id, material_group in self._material_group_map.items():
            guid = material_group.root_material_node.metadata["GUID"]
            self._guid_material_groups_map[guid].append(material_group)

        # Map #2
        # Lookup table for material type -> fallback material metadata, only for read-only materials
        grouped_by_type_dict = dict()
        material_types_without_fallback = set()
        for root_material_id, material_node in self._material_group_map.items():
            material_type = material_node.root_material_node.metadata["material"]
            if material_type not in grouped_by_type_dict:
                grouped_by_type_dict[material_type] = {"generic": None,
                                                       "others": []}
                material_types_without_fallback.add(material_type)
            brand = material_node.root_material_node.metadata["brand"]
            if brand.lower() == "generic":
                to_add = True
                if material_type in grouped_by_type_dict:
                    diameter = material_node.root_material_node.metadata.get("approximate_diameter")
                    if diameter != self._default_approximate_diameter_for_quality_search:
                        to_add = False  # don't add if it's not the default diameter

                if to_add:
                    # Checking this first allow us to differentiate between not read only materials:
                    #  - if it's in the list, it means that is a new material without fallback
                    #  - if it is not, then it is a custom material with a fallback material (parent)
                    if material_type in material_types_without_fallback:
                        grouped_by_type_dict[material_type] = material_node.root_material_node.metadata
                        material_types_without_fallback.remove(material_type)

        # Remove the materials that have no fallback materials
        for material_type in material_types_without_fallback:
            del grouped_by_type_dict[material_type]
        self._fallback_materials_map = grouped_by_type_dict

        # Map #3
        # There can be multiple material profiles for the same material with different diameters, such as "generic_pla"
        # and "generic_pla_175". This is inconvenient when we do material-specific quality lookup because a quality can
        # be for either "generic_pla" or "generic_pla_175", but not both. This map helps to get the correct material ID
        # for quality search.
        self._material_diameter_map = defaultdict(dict)
        self._diameter_material_map = dict()

        # Group the material IDs by the same name, material, brand, and color but with different diameters.
        material_group_dict = dict()
        keys_to_fetch = ("name", "material", "brand", "color")
        for root_material_id, machine_node in self._material_group_map.items():
            root_material_metadata = machine_node.root_material_node.metadata

            key_data = []
            for key in keys_to_fetch:
                key_data.append(root_material_metadata.get(key))
            key_data = tuple(key_data)

            # If the key_data doesn't exist, it doesn't matter if the material is read only...
            if key_data not in material_group_dict:
                material_group_dict[key_data] = dict()
            else:
                # ...but if key_data exists, we just overwrite it if the material is read only, otherwise we skip it
                if not machine_node.is_read_only:
                    continue
            approximate_diameter = root_material_metadata.get("approximate_diameter")
            material_group_dict[key_data][approximate_diameter] = root_material_metadata["id"]

        # Map [root_material_id][diameter] -> root_material_id for this diameter
        for data_dict in material_group_dict.values():
            for root_material_id1 in data_dict.values():
                if root_material_id1 in self._material_diameter_map:
                    continue
                diameter_map = data_dict
                for root_material_id2 in data_dict.values():
                    self._material_diameter_map[root_material_id2] = diameter_map

            default_root_material_id = data_dict.get(self._default_approximate_diameter_for_quality_search)
            if default_root_material_id is None:
                default_root_material_id = list(data_dict.values())[0]  # no default diameter present, just take "the" only one
            for root_material_id in data_dict.values():
                self._diameter_material_map[root_material_id] = default_root_material_id

        # Map #4
        # "machine" -> "nozzle name" -> "buildplate name" -> "root material ID" -> specific material InstanceContainer
        self._diameter_machine_nozzle_buildplate_material_map = dict()
        for material_metadata in material_metadatas.values():
            self.__addMaterialMetadataIntoLookupTree(material_metadata)

        self.materialsUpdated.emit()

    def __addMaterialMetadataIntoLookupTree(self, material_metadata: dict) -> None:
        material_id = material_metadata["id"]

        # We don't store empty material in the lookup tables
        if material_id == "empty_material":
            return

        root_material_id = material_metadata["base_file"]
        definition = material_metadata["definition"]
        approximate_diameter = material_metadata["approximate_diameter"]

        if approximate_diameter not in self._diameter_machine_nozzle_buildplate_material_map:
            self._diameter_machine_nozzle_buildplate_material_map[approximate_diameter] = {}

        machine_nozzle_buildplate_material_map = self._diameter_machine_nozzle_buildplate_material_map[
            approximate_diameter]
        if definition not in machine_nozzle_buildplate_material_map:
            machine_nozzle_buildplate_material_map[definition] = MaterialNode()

        # This is a list of information regarding the intermediate nodes:
        #    nozzle -> buildplate
        nozzle_name = material_metadata.get("variant_name")
        buildplate_name = material_metadata.get("buildplate_name")
        intermediate_node_info_list = [(nozzle_name, VariantType.NOZZLE),
                                       (buildplate_name, VariantType.BUILD_PLATE),
                                       ]

        variant_manager = self._application.getVariantManager()

        machine_node = machine_nozzle_buildplate_material_map[definition]
        current_node = machine_node
        current_intermediate_node_info_idx = 0
        error_message = None  # type: Optional[str]
        while current_intermediate_node_info_idx < len(intermediate_node_info_list):
            variant_name, variant_type = intermediate_node_info_list[current_intermediate_node_info_idx]
            if variant_name is not None:
                # The new material has a specific variant, so it needs to be added to that specific branch in the tree.
                variant = variant_manager.getVariantNode(definition, variant_name, variant_type)
                if variant is None:
                    error_message = "Material {id} contains a variant {name} that does not exist.".format(
                        id = material_metadata["id"], name = variant_name)
                    break

                # Update the current node to advance to a more specific branch
                if variant_name not in current_node.children_map:
                    current_node.children_map[variant_name] = MaterialNode()
                current_node = current_node.children_map[variant_name]

            current_intermediate_node_info_idx += 1

        if error_message is not None:
            Logger.log("e", "%s It will not be added into the material lookup tree.", error_message)
            self._container_registry.addWrongContainerId(material_metadata["id"])
            return

        # Add the material to the current tree node, which is the deepest (the most specific) branch we can find.
        # Sanity check: Make sure that there is no duplicated materials.
        if root_material_id in current_node.material_map:
            Logger.log("e", "Duplicated material [%s] with root ID [%s]. It has already been added.",
                       material_id, root_material_id)
            ConfigurationErrorMessage.getInstance().addFaultyContainers(root_material_id)
            return

        current_node.material_map[root_material_id] = MaterialNode(material_metadata)

    def _updateMaps(self):
        Logger.log("i", "Updating material lookup data ...")
        self.initialize()

    def _onContainerMetadataChanged(self, container):
        self._onContainerChanged(container)

    def _onContainerChanged(self, container):
        container_type = container.getMetaDataEntry("type")
        if container_type != "material":
            return

        # update the maps
        self._update_timer.start()

    def getMaterialGroup(self, root_material_id: str) -> Optional[MaterialGroup]:
        return self._material_group_map.get(root_material_id)

    def getRootMaterialIDForDiameter(self, root_material_id: str, approximate_diameter: str) -> str:
        return self._material_diameter_map.get(root_material_id, {}).get(approximate_diameter, root_material_id)

    def getRootMaterialIDWithoutDiameter(self, root_material_id: str) -> str:
        return self._diameter_material_map.get(root_material_id)

    def getMaterialGroupListByGUID(self, guid: str) -> Optional[list]:
        return self._guid_material_groups_map.get(guid)

    #
    # Return a dict with all root material IDs (k) and ContainerNodes (v) that's suitable for the given setup.
    #
    def getAvailableMaterials(self, machine_definition: "DefinitionContainer", nozzle_name: Optional[str],
                              buildplate_name: Optional[str], diameter: float) -> Dict[str, MaterialNode]:
        # round the diameter to get the approximate diameter
        rounded_diameter = str(round(diameter))
        if rounded_diameter not in self._diameter_machine_nozzle_buildplate_material_map:
            Logger.log("i", "Cannot find materials with diameter [%s] (rounded to [%s])", diameter, rounded_diameter)
            return dict()

        machine_definition_id = machine_definition.getId()

        # If there are nozzle-and-or-buildplate materials, get the nozzle-and-or-buildplate material
        machine_nozzle_buildplate_material_map = self._diameter_machine_nozzle_buildplate_material_map[rounded_diameter]
        machine_node = machine_nozzle_buildplate_material_map.get(machine_definition_id)
        default_machine_node = machine_nozzle_buildplate_material_map.get(self._default_machine_definition_id)
        nozzle_node = None
        buildplate_node = None
        if nozzle_name is not None and machine_node is not None:
            nozzle_node = machine_node.getChildNode(nozzle_name)
            # Get buildplate node if possible
            if nozzle_node is not None and buildplate_name is not None:
                buildplate_node = nozzle_node.getChildNode(buildplate_name)

        nodes_to_check = [buildplate_node, nozzle_node, machine_node, default_machine_node]

        # Fallback mechanism of finding materials:
        #  1. buildplate-specific material
        #  2. nozzle-specific material
        #  3. machine-specific material
        #  4. generic material (for fdmprinter)
        machine_exclude_materials = machine_definition.getMetaDataEntry("exclude_materials", [])

        material_id_metadata_dict = dict()  # type: Dict[str, MaterialNode]
        for current_node in nodes_to_check:
            if current_node is None:
                continue

            # Only exclude the materials that are explicitly specified in the "exclude_materials" field.
            # Do not exclude other materials that are of the same type.
            for material_id, node in current_node.material_map.items():
                if material_id in machine_exclude_materials:
                    Logger.log("d", "Exclude material [%s] for machine [%s]",
                               material_id, machine_definition.getId())
                    continue

                if material_id not in material_id_metadata_dict:
                    material_id_metadata_dict[material_id] = node

        return material_id_metadata_dict

    #
    # A convenience function to get available materials for the given machine with the extruder position.
    #
    def getAvailableMaterialsForMachineExtruder(self, machine: "GlobalStack",
                                                extruder_stack: "ExtruderStack") -> Optional[dict]:
        buildplate_name = machine.getBuildplateName()
        nozzle_name = None
        if extruder_stack.variant.getId() != "empty_variant":
            nozzle_name = extruder_stack.variant.getName()
        diameter = extruder_stack.approximateMaterialDiameter

        # Fetch the available materials (ContainerNode) for the current active machine and extruder setup.
        return self.getAvailableMaterials(machine.definition, nozzle_name, buildplate_name, diameter)

    #
    # Gets MaterialNode for the given extruder and machine with the given material name.
    # Returns None if:
    #  1. the given machine doesn't have materials;
    #  2. cannot find any material InstanceContainers with the given settings.
    #
    def getMaterialNode(self, machine_definition_id: str, nozzle_name: Optional[str],
                        buildplate_name: Optional[str], diameter: float, root_material_id: str) -> Optional["InstanceContainer"]:
        # round the diameter to get the approximate diameter
        rounded_diameter = str(round(diameter))
        if rounded_diameter not in self._diameter_machine_nozzle_buildplate_material_map:
            Logger.log("i", "Cannot find materials with diameter [%s] (rounded to [%s]) for root material id [%s]",
                       diameter, rounded_diameter, root_material_id)
            return None

        # If there are nozzle materials, get the nozzle-specific material
        machine_nozzle_buildplate_material_map = self._diameter_machine_nozzle_buildplate_material_map[rounded_diameter]
        machine_node = machine_nozzle_buildplate_material_map.get(machine_definition_id)
        nozzle_node = None
        buildplate_node = None

        # Fallback for "fdmprinter" if the machine-specific materials cannot be found
        if machine_node is None:
            machine_node = machine_nozzle_buildplate_material_map.get(self._default_machine_definition_id)
        if machine_node is not None and nozzle_name is not None:
            nozzle_node = machine_node.getChildNode(nozzle_name)
        if nozzle_node is not None and buildplate_name is not None:
            buildplate_node = nozzle_node.getChildNode(buildplate_name)

        # Fallback mechanism of finding materials:
        #  1. buildplate-specific material
        #  2. nozzle-specific material
        #  3. machine-specific material
        #  4. generic material (for fdmprinter)
        nodes_to_check = [buildplate_node, nozzle_node, machine_node,
                          machine_nozzle_buildplate_material_map.get(self._default_machine_definition_id)]

        material_node = None
        for node in nodes_to_check:
            if node is not None:
                material_node = node.material_map.get(root_material_id)
                if material_node:
                    break

        return material_node

    #
    # Gets MaterialNode for the given extruder and machine with the given material type.
    # Returns None if:
    #  1. the given machine doesn't have materials;
    #  2. cannot find any material InstanceContainers with the given settings.
    #
    def getMaterialNodeByType(self, global_stack: "GlobalStack", position: str, nozzle_name: str,
                              buildplate_name: Optional[str], material_guid: str) -> Optional["MaterialNode"]:
        node = None
        machine_definition = global_stack.definition
        extruder_definition = global_stack.extruders[position].definition
        if parseBool(machine_definition.getMetaDataEntry("has_materials", False)):
            material_diameter = extruder_definition.getProperty("material_diameter", "value")
            if isinstance(material_diameter, SettingFunction):
                material_diameter = material_diameter(global_stack)

            # Look at the guid to material dictionary
            root_material_id = None
            for material_group in self._guid_material_groups_map[material_guid]:
                root_material_id = material_group.root_material_node.metadata["id"]
                break

            if not root_material_id:
                Logger.log("i", "Cannot find materials with guid [%s] ", material_guid)
                return None

            node = self.getMaterialNode(machine_definition.getId(), nozzle_name, buildplate_name,
                                        material_diameter, root_material_id)
        return node

    #
    # Used by QualityManager. Built-in quality profiles may be based on generic material IDs such as "generic_pla".
    # For materials such as ultimaker_pla_orange, no quality profiles may be found, so we should fall back to use
    # the generic material IDs to search for qualities.
    #
    # An example would be, suppose we have machine with preferred material set to "filo3d_pla" (1.75mm), but its
    # extruders only use 2.85mm materials, then we won't be able to find the preferred material for this machine.
    # A fallback would be to fetch a generic material of the same type "PLA" as "filo3d_pla", and in this case it will
    # be "generic_pla". This function is intended to get a generic fallback material for the given material type.
    #
    # This function returns the generic root material ID for the given material type, where material types are "PLA",
    # "ABS", etc.
    #
    def getFallbackMaterialIdByMaterialType(self, material_type: str) -> Optional[str]:
        # For safety
        if material_type not in self._fallback_materials_map:
            Logger.log("w", "The material type [%s] does not have a fallback material" % material_type)
            return None
        fallback_material = self._fallback_materials_map[material_type]
        if fallback_material:
            return self.getRootMaterialIDWithoutDiameter(fallback_material["id"])
        else:
            return None

    ##  Get default material for given global stack, extruder position and extruder nozzle name
    #   you can provide the extruder_definition and then the position is ignored (useful when building up global stack in CuraStackBuilder)
    def getDefaultMaterial(self, global_stack: "GlobalStack", position: str, nozzle_name: Optional[str],
                           extruder_definition: Optional["DefinitionContainer"] = None) -> Optional["MaterialNode"]:
        node = None

        buildplate_name = global_stack.getBuildplateName()
        machine_definition = global_stack.definition
        if extruder_definition is None:
            extruder_definition = global_stack.extruders[position].definition

        if extruder_definition and parseBool(global_stack.getMetaDataEntry("has_materials", False)):
            # At this point the extruder_definition is not None
            material_diameter = extruder_definition.getProperty("material_diameter", "value")
            if isinstance(material_diameter, SettingFunction):
                material_diameter = material_diameter(global_stack)
            approximate_material_diameter = str(round(material_diameter))
            root_material_id = machine_definition.getMetaDataEntry("preferred_material")
            root_material_id = self.getRootMaterialIDForDiameter(root_material_id, approximate_material_diameter)
            node = self.getMaterialNode(machine_definition.getId(), nozzle_name, buildplate_name,
                                        material_diameter, root_material_id)
        return node

    def removeMaterialByRootId(self, root_material_id: str):
        material_group = self.getMaterialGroup(root_material_id)
        if not material_group:
            Logger.log("i", "Unable to remove the material with id %s, because it doesn't exist.", root_material_id)
            return

        nodes_to_remove = [material_group.root_material_node] + material_group.derived_material_node_list
        for node in nodes_to_remove:
            self._container_registry.removeContainer(node.getMetaDataEntry("id", ""))

    #
    # Methods for GUI
    #

    #
    # Sets the new name for the given material.
    #
    @pyqtSlot("QVariant", str)
    def setMaterialName(self, material_node: "MaterialNode", name: str):
        root_material_id = material_node.getMetaDataEntry("base_file")
        if root_material_id is None:
            return
        if self._container_registry.isReadOnly(root_material_id):
            Logger.log("w", "Cannot set name of read-only container %s.", root_material_id)
            return

        material_group = self.getMaterialGroup(root_material_id)
        if material_group:
            container = material_group.root_material_node.getContainer()
            if container:
                container.setName(name)

    #
    # Removes the given material.
    #
    @pyqtSlot("QVariant")
    def removeMaterial(self, material_node: "MaterialNode"):
        root_material_id = material_node.getMetaDataEntry("base_file")
        if root_material_id is not None:
            self.removeMaterialByRootId(root_material_id)

    #
    # Creates a duplicate of a material, which has the same GUID and base_file metadata.
    # Returns the root material ID of the duplicated material if successful.
    #
    @pyqtSlot("QVariant", result = str)
    def duplicateMaterial(self, material_node, new_base_id = None, new_metadata = None) -> Optional[str]:
        root_material_id = material_node.metadata["base_file"]

        material_group = self.getMaterialGroup(root_material_id)
        if not material_group:
            Logger.log("i", "Unable to duplicate the material with id %s, because it doesn't exist.", root_material_id)
            return None

        base_container = material_group.root_material_node.getContainer()
        if not base_container:
            return None

        # Ensure all settings are saved.
        self._application.saveSettings()

        # Create a new ID & container to hold the data.
        new_containers = []
        if new_base_id is None:
            new_base_id = self._container_registry.uniqueName(base_container.getId())
        new_base_container = copy.deepcopy(base_container)
        new_base_container.getMetaData()["id"] = new_base_id
        new_base_container.getMetaData()["base_file"] = new_base_id
        if new_metadata is not None:
            for key, value in new_metadata.items():
                new_base_container.getMetaData()[key] = value
        new_containers.append(new_base_container)

        # Clone all of them.
        for node in material_group.derived_material_node_list:
            container_to_copy = node.getContainer()
            if not container_to_copy:
                continue
            # Create unique IDs for every clone.
            new_id = new_base_id
            if container_to_copy.getMetaDataEntry("definition") != "fdmprinter":
                new_id += "_" + container_to_copy.getMetaDataEntry("definition")
                if container_to_copy.getMetaDataEntry("variant_name"):
                    nozzle_name = container_to_copy.getMetaDataEntry("variant_name")
                    new_id += "_" + nozzle_name.replace(" ", "_")

            new_container = copy.deepcopy(container_to_copy)
            new_container.getMetaData()["id"] = new_id
            new_container.getMetaData()["base_file"] = new_base_id
            if new_metadata is not None:
                for key, value in new_metadata.items():
                    new_container.getMetaData()[key] = value

            new_containers.append(new_container)

        for container_to_add in new_containers:
            container_to_add.setDirty(True)
            self._container_registry.addContainer(container_to_add)
        return new_base_id

    #
    # Create a new material by cloning Generic PLA for the current material diameter and generate a new GUID.
    #
    @pyqtSlot(result = str)
    def createMaterial(self) -> str:
        from UM.i18n import i18nCatalog
        catalog = i18nCatalog("cura")
        # Ensure all settings are saved.
        self._application.saveSettings()

        machine_manager = self._application.getMachineManager()
        extruder_stack = machine_manager.activeStack

        approximate_diameter = str(extruder_stack.approximateMaterialDiameter)
        root_material_id = "generic_pla"
        root_material_id = self.getRootMaterialIDForDiameter(root_material_id, approximate_diameter)
        material_group = self.getMaterialGroup(root_material_id)

        if not material_group:  # This should never happen
            Logger.log("w", "Cannot get the material group of %s.", root_material_id)
            return ""

        # Create a new ID & container to hold the data.
        new_id = self._container_registry.uniqueName("custom_material")
        new_metadata = {"name": catalog.i18nc("@label", "Custom Material"),
                        "brand": catalog.i18nc("@label", "Custom"),
                        "GUID": str(uuid.uuid4()),
                        }

        self.duplicateMaterial(material_group.root_material_node,
                               new_base_id = new_id,
                               new_metadata = new_metadata)
        return new_id