# ==================================================================================================================== #
#             _____           _ _               ____                 _                                                 #
#  _ __  _   |_   _|__   ___ | (_)_ __   __ _  / ___|_ __ __ _ _ __ | |__                                              #
# | '_ \| | | || |/ _ \ / _ \| | | '_ \ / _` || |  _| '__/ _` | '_ \| '_ \                                             #
# | |_) | |_| || | (_) | (_) | | | | | | (_| || |_| | | | (_| | |_) | | | |                                            #
# | .__/ \__, ||_|\___/ \___/|_|_|_| |_|\__, (_)____|_|  \__,_| .__/|_| |_|                                            #
# |_|    |___/                          |___/                 |_|                                                      #
# ==================================================================================================================== #
# Authors:                                                                                                             #
#   Patrick Lehmann                                                                                                    #
#                                                                                                                      #
# License:                                                                                                             #
# ==================================================================================================================== #
# Copyright 2017-2026 Patrick Lehmann - Bötzingen, Germany                                                             #
#                                                                                                                      #
# Licensed under the Apache License, Version 2.0 (the "License");                                                      #
# you may not use this file except in compliance with the License.                                                     #
# You may obtain a copy of the License at                                                                              #
#                                                                                                                      #
#   http://www.apache.org/licenses/LICENSE-2.0                                                                         #
#                                                                                                                      #
# Unless required by applicable law or agreed to in writing, software                                                  #
# distributed under the License is distributed on an "AS IS" BASIS,                                                    #
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.                                             #
# See the License for the specific language governing permissions and                                                  #
# limitations under the License.                                                                                       #
#                                                                                                                      #
# SPDX-License-Identifier: Apache-2.0                                                                                  #
# ==================================================================================================================== #
#
"""
A powerful **graph** data structure for Python.

Graph algorithms using all vertices are provided as methods on the graph instance. Whereas graph algorithms based on a
starting vertex are provided as methods on a vertex.

.. admonition:: Example Graph

	.. mermaid::
		 :caption: A directed graph with backward-edges denoted by dotted vertex relations.

		 %%{init: { "flowchart": { "nodeSpacing": 15, "rankSpacing": 30, "curve": "linear", "useMaxWidth": false } } }%%
		 graph LR
			 A(A); B(B); C(C); D(D); E(E); F(F) ; G(G); H(H); I(I)

			 A --> B --> E
			 G --> F
			 A --> C --> G --> H --> D
			 D -.-> A
			 D & F -.-> B
			 I ---> E --> F --> D

			 classDef node fill:#eee,stroke:#777,font-size:smaller;
"""
import heapq
from collections import deque
from itertools   import chain
from typing      import TypeVar, Generic, List, Tuple, Dict, Set, Deque, Union, Optional as Nullable
from typing      import Callable, Iterator as typing_Iterator, Generator, Iterable, Mapping, Hashable

try:
	from pyTooling.Decorators  import export, readonly
	from pyTooling.MetaClasses import ExtendedType
	from pyTooling.Exceptions  import ToolingException
	from pyTooling.Common      import getFullyQualifiedName
	from pyTooling.Tree        import Node
except (ImportError, ModuleNotFoundError):  # pragma: no cover
	print("[pyTooling.Graph] Could not import from 'pyTooling.*'!")

	try:
		from Decorators          import export, readonly
		from MetaClasses         import ExtendedType, mixin
		from Exceptions          import ToolingException
		from Common              import getFullyQualifiedName
		from Tree                import Node
	except (ImportError, ModuleNotFoundError) as ex:  # pragma: no cover
		print("[pyTooling.Graph] Could not import directly!")
		raise ex


DictKeyType = TypeVar("DictKeyType", bound=Hashable)
"""A type variable for dictionary keys."""

DictValueType = TypeVar("DictValueType")
"""A type variable for dictionary values."""

IDType = TypeVar("IDType", bound=Hashable)
"""A type variable for an ID."""

WeightType = TypeVar("WeightType", bound=Union[int, float])
"""A type variable for a weight."""

ValueType = TypeVar("ValueType")
"""A type variable for a value."""

VertexIDType = TypeVar("VertexIDType", bound=Hashable)
"""A type variable for a vertex's ID."""

VertexWeightType = TypeVar("VertexWeightType", bound=Union[int, float])
"""A type variable for a vertex's weight."""

VertexValueType = TypeVar("VertexValueType")
"""A type variable for a vertex's value."""

VertexDictKeyType = TypeVar("VertexDictKeyType", bound=Hashable)
"""A type variable for a vertex's dictionary keys."""

VertexDictValueType = TypeVar("VertexDictValueType")
"""A type variable for a vertex's dictionary values."""

EdgeIDType = TypeVar("EdgeIDType", bound=Hashable)
"""A type variable for an edge's ID."""

EdgeWeightType = TypeVar("EdgeWeightType", bound=Union[int, float])
"""A type variable for an edge's weight."""

EdgeValueType = TypeVar("EdgeValueType")
"""A type variable for an edge's value."""

EdgeDictKeyType = TypeVar("EdgeDictKeyType", bound=Hashable)
"""A type variable for an edge's dictionary keys."""

EdgeDictValueType = TypeVar("EdgeDictValueType")
"""A type variable for an edge's dictionary values."""

LinkIDType = TypeVar("LinkIDType", bound=Hashable)
"""A type variable for an link's ID."""

LinkWeightType = TypeVar("LinkWeightType", bound=Union[int, float])
"""A type variable for an link's weight."""

LinkValueType = TypeVar("LinkValueType")
"""A type variable for an link's value."""

LinkDictKeyType = TypeVar("LinkDictKeyType", bound=Hashable)
"""A type variable for an link's dictionary keys."""

LinkDictValueType = TypeVar("LinkDictValueType")
"""A type variable for an link's dictionary values."""

ComponentDictKeyType = TypeVar("ComponentDictKeyType", bound=Hashable)
"""A type variable for a component's dictionary keys."""

ComponentDictValueType = TypeVar("ComponentDictValueType")
"""A type variable for a component's dictionary values."""

SubgraphDictKeyType = TypeVar("SubgraphDictKeyType", bound=Hashable)
"""A type variable for a component's dictionary keys."""

SubgraphDictValueType = TypeVar("SubgraphDictValueType")
"""A type variable for a component's dictionary values."""

ViewDictKeyType = TypeVar("ViewDictKeyType", bound=Hashable)
"""A type variable for a component's dictionary keys."""

ViewDictValueType = TypeVar("ViewDictValueType")
"""A type variable for a component's dictionary values."""

GraphDictKeyType = TypeVar("GraphDictKeyType", bound=Hashable)
"""A type variable for a graph's dictionary keys."""

GraphDictValueType = TypeVar("GraphDictValueType")
"""A type variable for a graph's dictionary values."""


@export
class GraphException(ToolingException):
	"""Base exception of all exceptions raised by :mod:`pyTooling.Graph`."""


@export
class InternalError(GraphException):
	"""
	The exception is raised when a data structure corruption is detected.

	.. danger::

	   This exception should never be raised.

	   If so, please create an issue at GitHub so the data structure corruption can be investigated and fixed. |br|
	   `⇒ Bug Tracker at GitHub <https://github.com/pyTooling/pyTooling/issues>`__
	"""


@export
class NotInSameGraph(GraphException):
	"""The exception is raised when creating an edge between two vertices, but these are not in the same graph."""


@export
class DuplicateVertexError(GraphException):
	"""The exception is raised when the vertex already exists in the graph."""


@export
class DuplicateEdgeError(GraphException):
	"""The exception is raised when the edge already exists in the graph."""


@export
class DestinationNotReachable(GraphException):
	"""The exception is raised when a destination vertex is not reachable."""


@export
class NotATreeError(GraphException):
	"""
	The exception is raised when a subgraph is not a tree.

	Either the subgraph has a cycle (backward edge) or links between branches (cross-edge).
	"""


@export
class CycleError(GraphException):
	"""The exception is raised when a not permitted cycle is found."""


@export
class Base(
	Generic[DictKeyType, DictValueType],
	metaclass=ExtendedType, slots=True
):
	_dict: Dict[DictKeyType, DictValueType]  #: A dictionary to store arbitrary key-value-pairs.

	def __init__(
		self,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::Base::init Needs documentation.

		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		self._dict = {key: value for key, value in keyValuePairs.items()} if keyValuePairs is not None else {}

	def __del__(self) -> None:
		"""
		.. todo:: GRAPH::Base::del Needs documentation.

		"""
		try:
			del self._dict
		except AttributeError:
			pass

	def Delete(self) -> None:
		self._dict = None

	def __getitem__(self, key: DictKeyType) -> DictValueType:
		"""
		Read a vertex's attached attributes (key-value-pairs) by key.

		:param key: The key to look for.
		:returns:   The value associated to the given key.
		"""
		return self._dict[key]

	def __setitem__(self, key: DictKeyType, value: DictValueType) -> None:
		"""
		Create or update a vertex's attached attributes (key-value-pairs) by key.

		If a key doesn't exist yet, a new key-value-pair is created.

		:param key: The key to create or update.
		:param value: The value to associate to the given key.
		"""
		self._dict[key] = value

	def __delitem__(self, key: DictKeyType) -> None:
		"""
		Remove an entry from vertex's attached attributes (key-value-pairs) by key.

		:param key:       The key to remove.
		:raises KeyError: If key doesn't exist in the vertex's attributes.
		"""
		del self._dict[key]

	def __contains__(self, key: DictKeyType) -> bool:
		"""
		Checks if the key is an attached attribute (key-value-pairs) on this vertex.

		:param key: The key to check.
		:returns:   ``True``, if the key is an attached attribute.
		"""
		return key in self._dict

	def __len__(self) -> int:
		"""
		Returns the number of attached attributes (key-value-pairs) on this vertex.

		:returns: Number of attached attributes.
		"""
		return len(self._dict)


@export
class BaseWithIDValueAndWeight(
	Base[DictKeyType, DictValueType],
	Generic[IDType, ValueType, WeightType, DictKeyType, DictValueType]
):
	_id:        Nullable[IDType]      #: Field storing the object's Identifier.
	_value:     Nullable[ValueType]   #: Field storing the object's value of any type.
	_weight:    Nullable[WeightType]  #: Field storing the object's weight.

	def __init__(
		self,
		identifier: Nullable[IDType] = None,
		value: Nullable[ValueType] = None,
		weight: Nullable[WeightType] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::Vertex::init Needs documentation.

		:param identifier:    The optional unique ID.
		:param value:         The optional value.
		:param weight:        The optional weight.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		super().__init__(keyValuePairs)

		self._id = identifier
		self._value = value
		self._weight = weight

	@readonly
	def ID(self) -> Nullable[IDType]:
		"""
		Read-only property to access the unique ID (:attr:`_id`).

		If no ID was given at creation time, ID returns ``None``.

		:returns: Unique ID, if ID was given at creation time, else ``None``.
		"""
		return self._id

	@property
	def Value(self) -> ValueType:
		"""
		Property to get and set the value (:attr:`_value`).

		:returns: The value.
		"""
		return self._value

	@Value.setter
	def Value(self, value: ValueType) -> None:
		self._value = value

	@property
	def Weight(self) -> Nullable[EdgeWeightType]:
		"""
		Property to get and set the weight (:attr:`_weight`) of an edge.

		:returns: The weight of an edge.
		"""
		return self._weight

	@Weight.setter
	def Weight(self, value: Nullable[EdgeWeightType]) -> None:
		self._weight = value


@export
class BaseWithName(
	Base[DictKeyType, DictValueType],
	Generic[DictKeyType, DictValueType]
):
	_name: Nullable[str]  #: Field storing the object's name.

	def __init__(
		self,
		name: Nullable[str] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None,
	) -> None:
		"""
		.. todo:: GRAPH::BaseWithName::init Needs documentation.

		:param name:          The optional name.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		if name is not None and not isinstance(name, str):
			ex = TypeError("Parameter 'name' is not of type 'str'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(name)}'.")
			raise ex

		super().__init__(keyValuePairs)

		self._name = name

	@property
	def Name(self) -> Nullable[str]:
		"""
		Property to get and set the name (:attr:`_name`).

		:returns: The value of a component.
		"""
		return self._name

	@Name.setter
	def Name(self, value: str) -> None:
		if not isinstance(value, str):
			ex = TypeError("Name is not of type 'str'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(value)}'.")
			raise ex

		self._name = value


@export
class BaseWithVertices(
	BaseWithName[DictKeyType, DictValueType],
	Generic[
		DictKeyType, DictValueType,
		GraphDictKeyType, GraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	]
):
	_graph:    'Graph[GraphDictKeyType, GraphDictValueType,' \
								'VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,' \
								'EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,' \
								'LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType' \
								']'   #: Field storing a reference to the graph.
	_vertices: Set['Vertex[GraphDictKeyType, GraphDictValueType,'
								'VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,'
								'EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,'
								'LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType'
								']']  #: Field storing a set of vertices.

	def __init__(
		self,
		graph: 'Graph',
		name: Nullable[str] = None,
		vertices: Nullable[Iterable['Vertex']] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::Component::init Needs documentation.

		:param graph:         The reference to the graph.
		:param name:          The optional name.
		:param vertices:      The optional list of vertices.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		if graph is None:
			raise ValueError("Parameter 'graph' is None.")
		elif not isinstance(graph, Graph):
			ex = TypeError("Parameter 'graph' is not of type 'Graph'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(graph)}'.")
			raise ex

		super().__init__(name, keyValuePairs)

		self._graph = graph
		self._vertices = set() if vertices is None else {v for v in vertices}

	def __del__(self) -> None:
		"""
		.. todo:: GRAPH::BaseWithVertices::del Needs documentation.

		"""
		try:
			del self._vertices
		except AttributeError:
			pass

		super().__del__()

	@readonly
	def Graph(self) -> 'Graph':
		"""
		Read-only property to access the graph, this object is associated to (:attr:`_graph`).

		:returns: The graph this object is associated to.
		"""
		return self._graph

	@readonly
	def Vertices(self) -> Set['Vertex']:
		"""
		Read-only property to access the vertices in this component (:attr:`_vertices`).

		:returns: The set of vertices in this component.
		"""
		return self._vertices

	@readonly
	def VertexCount(self) -> int:
		"""
		Read-only property to access the number of vertices referenced by this object.

		:returns: The number of vertices this object references.
		"""
		return len(self._vertices)


@export
class Vertex(
	BaseWithIDValueAndWeight[VertexIDType, VertexValueType, VertexWeightType, VertexDictKeyType, VertexDictValueType],
	Generic[
		GraphDictKeyType, GraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	]
):
	"""
	A **vertex** can have a unique ID, a value and attached meta information as key-value-pairs. A vertex has references
	to inbound and outbound edges, thus a graph can be traversed in reverse.
	"""
	_graph:     'BaseGraph[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType]'  #: Field storing a reference to the graph.
	_subgraph:  'Subgraph[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType]'   #: Field storing a reference to the subgraph.
	_component: 'Component'
	_views:     Dict[Hashable, 'View']
	_inboundEdges:   List['Edge[EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType]']  #: Field storing a list of inbound edges.
	_outboundEdges:  List['Edge[EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType]']  #: Field storing a list of outbound edges.
	_inboundLinks:   List['Link[EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType]']  #: Field storing a list of inbound links.
	_outboundLinks:  List['Link[EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType]']  #: Field storing a list of outbound links.

	def __init__(
		self,
		vertexID: Nullable[VertexIDType] = None,
		value: Nullable[VertexValueType] = None,
		weight: Nullable[VertexWeightType] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None,
		graph: Nullable['Graph'] = None,
		subgraph: Nullable['Subgraph'] = None
	) -> None:
		"""
		.. todo:: GRAPH::Vertex::init Needs documentation.

		:param vertexID:      The optional ID for the new vertex.
		:param value:         The optional value for the new vertex.
		:param weight:        The optional weight for the new vertex.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		:param graph:         The optional reference to the graph.
		:param subgraph:      undocumented
		"""
		if vertexID is not None and not isinstance(vertexID, Hashable):
			ex = TypeError("Parameter 'vertexID' is not of type 'VertexIDType'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(vertexID)}'.")
			raise ex

		super().__init__(vertexID, value, weight, keyValuePairs)

		if subgraph is None:
			self._graph = graph if graph is not None else Graph()
			self._subgraph = None
			self._component = Component(self._graph, vertices=(self,))

			if vertexID is None:
				self._graph._verticesWithoutID.append(self)
			elif vertexID not in self._graph._verticesWithID:
				self._graph._verticesWithID[vertexID] = self
			else:
				raise DuplicateVertexError(f"Vertex ID '{vertexID}' already exists in this graph.")
		else:
			self._graph = subgraph._graph
			self._subgraph = subgraph
			self._component = Component(self._graph, vertices=(self,))

			if vertexID is None:
				subgraph._verticesWithoutID.append(self)
			elif vertexID not in subgraph._verticesWithID:
				subgraph._verticesWithID[vertexID] = self
			else:
				raise DuplicateVertexError(f"Vertex ID '{vertexID}' already exists in this subgraph.")

		self._views =         {}
		self._inboundEdges =  []
		self._outboundEdges = []
		self._inboundLinks =  []
		self._outboundLinks = []

	def __del__(self) -> None:
		"""
		.. todo:: GRAPH::BaseEdge::del Needs documentation.

		"""
		try:
			del self._views
			del self._inboundEdges
			del self._outboundEdges
			del self._inboundLinks
			del self._outboundLinks
		except AttributeError:
			pass

		super().__del__()

	def Delete(self) -> None:
		for edge in self._outboundEdges:
			edge._destination._inboundEdges.remove(edge)
			edge._Delete()
		for edge in self._inboundEdges:
			edge._source._outboundEdges.remove(edge)
			edge._Delete()
		for link in self._outboundLinks:
			link._destination._inboundLinks.remove(link)
			link._Delete()
		for link in self._inboundLinks:
			link._source._outboundLinks.remove(link)
			link._Delete()

		if self._id is None:
			self._graph._verticesWithoutID.remove(self)
		else:
			del self._graph._verticesWithID[self._id]

		# subgraph

		# component

		# views
		self._views =         None
		self._inboundEdges =  None
		self._outboundEdges = None
		self._inboundLinks =  None
		self._outboundLinks = None

		super().Delete()
		assert getrefcount(self) == 1

	@readonly
	def Graph(self) -> 'Graph':
		"""
		Read-only property to access the graph, this vertex is associated to (:attr:`_graph`).

		:returns: The graph this vertex is associated to.
		"""
		return self._graph

	@readonly
	def Component(self) -> 'Component':
		"""
		Read-only property to access the component, this vertex is associated to (:attr:`_component`).

		:returns: The component this vertex is associated to.
		"""
		return self._component

	@readonly
	def InboundEdges(self) -> Tuple['Edge', ...]:
		"""
		Read-only property to get a tuple of inbound edges (:attr:`_inboundEdges`).

		:returns: Tuple of inbound edges.
		"""
		return tuple(self._inboundEdges)

	@readonly
	def OutboundEdges(self) -> Tuple['Edge', ...]:
		"""
		Read-only property to get a tuple of outbound edges (:attr:`_outboundEdges`).

		:returns: Tuple of outbound edges.
		"""
		return tuple(self._outboundEdges)

	@readonly
	def InboundLinks(self) -> Tuple['Link', ...]:
		"""
		Read-only property to get a tuple of inbound links (:attr:`_inboundLinks`).

		:returns: Tuple of inbound links.
		"""
		return tuple(self._inboundLinks)

	@readonly
	def OutboundLinks(self) -> Tuple['Link', ...]:
		"""
		Read-only property to get a tuple of outbound links (:attr:`_outboundLinks`).

		:returns: Tuple of outbound links.
		"""
		return tuple(self._outboundLinks)

	@readonly
	def EdgeCount(self) -> int:
		"""
		Read-only property to get the number of all edges (inbound and outbound).

		:returns: Number of inbound and outbound edges.
		"""
		return len(self._inboundEdges) + len(self._outboundEdges)

	@readonly
	def InboundEdgeCount(self) -> int:
		"""
		Read-only property to get the number of inbound edges.

		:returns: Number of inbound edges.
		"""
		return len(self._inboundEdges)

	@readonly
	def OutboundEdgeCount(self) -> int:
		"""
		Read-only property to get the number of outbound edges.

		:returns: Number of outbound edges.
		"""
		return len(self._outboundEdges)

	@readonly
	def LinkCount(self) -> int:
		"""
		Read-only property to get the number of all links (inbound and outbound).

		:returns: Number of inbound and outbound links.
		"""
		return len(self._inboundLinks) + len(self._outboundLinks)

	@readonly
	def InboundLinkCount(self) -> int:
		"""
		Read-only property to get the number of inbound links.

		:returns: Number of inbound links.
		"""
		return len(self._inboundLinks)

	@readonly
	def OutboundLinkCount(self) -> int:
		"""
		Read-only property to get the number of outbound links.

		:returns: Number of outbound links.
		"""
		return len(self._outboundLinks)

	@readonly
	def IsRoot(self) -> bool:
		"""
		Read-only property to check if this vertex is a root vertex in the graph.

		A root has no inbound edges (no predecessor vertices).

		:returns: ``True``, if this vertex is a root.

		.. seealso::

		   :meth:`IsLeaf` |br|
		      |rarr| Check if a vertex is a leaf vertex in the graph.
		   :meth:`Graph.IterateRoots <pyTooling.Graph.Graph.IterateRoots>` |br|
		      |rarr| Iterate all roots of a graph.
		   :meth:`Graph.IterateLeafs <pyTooling.Graph.Graph.IterateLeafs>` |br|
		      |rarr| Iterate all leafs of a graph.
		"""
		return len(self._inboundEdges) == 0

	@readonly
	def IsLeaf(self) -> bool:
		"""
		Read-only property to check if this vertex is a leaf vertex in the graph.

		A leaf has no outbound edges (no successor vertices).

		:returns: ``True``, if this vertex is a leaf.

		.. seealso::

		   :meth:`IsRoot` |br|
		      |rarr| Check if a vertex is a root vertex in the graph.
		   :meth:`Graph.IterateRoots <pyTooling.Graph.Graph.IterateRoots>` |br|
		      |rarr| Iterate all roots of a graph.
		   :meth:`Graph.IterateLeafs <pyTooling.Graph.Graph.IterateLeafs>` |br|
		      |rarr| Iterate all leafs of a graph.
		"""
		return len(self._outboundEdges) == 0

	@readonly
	def Predecessors(self) -> Tuple['Vertex', ...]:
		"""
		Read-only property to get a tuple of predecessor vertices.

		:returns: Tuple of predecessor vertices.
		"""
		return tuple([edge.Source for edge in self._inboundEdges])

	@readonly
	def Successors(self) -> Tuple['Vertex', ...]:
		"""
		Read-only property to get a tuple of successor vertices.

		:returns: Tuple of successor vertices.
		"""
		return tuple([edge.Destination for edge in self._outboundEdges])

	def EdgeToVertex(
		self,
		vertex: 'Vertex',
		edgeID: Nullable[EdgeIDType] = None,
		edgeWeight: Nullable[EdgeWeightType] = None,
		edgeValue: Nullable[VertexValueType] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> 'Edge':
		"""
		Create an outbound edge from this vertex to the referenced vertex.

		:param vertex:        The vertex to be linked to.
		:param edgeID:        The edge's optional ID for the new edge object.
		:param edgeWeight:    The edge's optional weight for the new edge object.
		:param edgeValue:     The edge's optional value for the new edge object.
		:param keyValuePairs: An optional mapping (dictionary) of key-value-pairs for the new edge object.
		:returns:             The edge object linking this vertex and the referenced vertex.

		.. seealso::

		   :meth:`EdgeFromVertex` |br|
		      |rarr| Create an inbound edge from the referenced vertex to this vertex.
		   :meth:`EdgeToNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an outbound edge from this vertex.
		   :meth:`EdgeFromNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an inbound edge to this vertex.
		   :meth:`LinkToVertex` |br|
		      |rarr| Create an outbound link from this vertex to the referenced vertex.
		   :meth:`LinkFromVertex` |br|
		      |rarr| Create an inbound link from the referenced vertex to this vertex.

		.. todo:: GRAPH::Vertex::EdgeToVertex Needs possible exceptions to be documented.
		"""
		if self._subgraph is vertex._subgraph:
			edge = Edge(self, vertex, edgeID, edgeValue, edgeWeight, keyValuePairs)

			self._outboundEdges.append(edge)
			vertex._inboundEdges.append(edge)

			if self._subgraph is None:
				# TODO: move into Edge?
				# TODO: keep _graph pointer in edge and then register edge on graph?
				if edgeID is None:
					self._graph._edgesWithoutID.append(edge)
				elif edgeID not in self._graph._edgesWithID:
					self._graph._edgesWithID[edgeID] = edge
				else:
					raise DuplicateEdgeError(f"Edge ID '{edgeID}' already exists in this graph.")
			else:
				# TODO: keep _graph pointer in edge and then register edge on graph?
				if edgeID is None:
					self._subgraph._edgesWithoutID.append(edge)
				elif edgeID not in self._subgraph._edgesWithID:
					self._subgraph._edgesWithID[edgeID] = edge
				else:
					raise DuplicateEdgeError(f"Edge ID '{edgeID}' already exists in this subgraph.")
		else:
			# FIXME: needs an error message
			raise GraphException()

		return edge

	def EdgeFromVertex(
		self,
		vertex: 'Vertex',
		edgeID: Nullable[EdgeIDType] = None,
		edgeWeight: Nullable[EdgeWeightType] = None,
		edgeValue: Nullable[VertexValueType] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> 'Edge':
		"""
		Create an inbound edge from the referenced vertex to this vertex.

		:param vertex:        The vertex to be linked from.
		:param edgeID:        The edge's optional ID for the new edge object.
		:param edgeWeight:    The edge's optional weight for the new edge object.
		:param edgeValue:     The edge's optional value for the new edge object.
		:param keyValuePairs: An optional mapping (dictionary) of key-value-pairs for the new edge object.
		:returns:             The edge object linking the referenced vertex and this vertex.

		.. seealso::

		   :meth:`EdgeToVertex` |br|
		      |rarr| Create an outbound edge from this vertex to the referenced vertex.
		   :meth:`EdgeToNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an outbound edge from this vertex.
		   :meth:`EdgeFromNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an inbound edge to this vertex.
		   :meth:`LinkToVertex` |br|
		      |rarr| Create an outbound link from this vertex to the referenced vertex.
		   :meth:`LinkFromVertex` |br|
		      |rarr| Create an inbound link from the referenced vertex to this vertex.

		.. todo:: GRAPH::Vertex::EdgeFromVertex Needs possible exceptions to be documented.
		"""
		if self._subgraph is vertex._subgraph:
			edge = Edge(vertex, self, edgeID, edgeValue, edgeWeight, keyValuePairs)

			vertex._outboundEdges.append(edge)
			self._inboundEdges.append(edge)

			if self._subgraph is None:
				# TODO: move into Edge?
				# TODO: keep _graph pointer in edge and then register edge on graph?
				if edgeID is None:
					self._graph._edgesWithoutID.append(edge)
				elif edgeID not in self._graph._edgesWithID:
					self._graph._edgesWithID[edgeID] = edge
				else:
					raise DuplicateEdgeError(f"Edge ID '{edgeID}' already exists in this graph.")
			else:
				# TODO: keep _graph pointer in edge and then register edge on graph?
				if edgeID is None:
					self._subgraph._edgesWithoutID.append(edge)
				elif edgeID not in self._graph._edgesWithID:
					self._subgraph._edgesWithID[edgeID] = edge
				else:
					raise DuplicateEdgeError(f"Edge ID '{edgeID}' already exists in this graph.")
		else:
			# FIXME: needs an error message
			raise GraphException()

		return edge

	def EdgeToNewVertex(
		self,
		vertexID: Nullable[VertexIDType] = None,
		vertexValue: Nullable[VertexValueType] = None,
		vertexWeight: Nullable[VertexWeightType] = None,
		vertexKeyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None,
		edgeID: Nullable[EdgeIDType] = None,
		edgeWeight: Nullable[EdgeWeightType] = None,
		edgeValue: Nullable[VertexValueType] = None,
		edgeKeyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> 'Edge':
		"""
		Create a new vertex and link that vertex by an outbound edge from this vertex.

		:param vertexID:            The new vertex' optional ID.
		:param vertexValue:         The new vertex' optional value.
		:param vertexWeight:        The new vertex' optional weight.
		:param vertexKeyValuePairs: An optional mapping (dictionary) of key-value-pairs for the new vertex.
		:param edgeID:              The edge's optional ID for the new edge object.
		:param edgeWeight:          The edge's optional weight for the new edge object.
		:param edgeValue:           The edge's optional value for the new edge object.
		:param edgeKeyValuePairs:   An optional mapping (dictionary) of key-value-pairs for the new edge object.
		:returns:                   The edge object linking this vertex and the created vertex.

		.. seealso::

		   :meth:`EdgeToVertex` |br|
		      |rarr| Create an outbound edge from this vertex to the referenced vertex.
		   :meth:`EdgeFromVertex` |br|
		      |rarr| Create an inbound edge from the referenced vertex to this vertex.
		   :meth:`EdgeFromNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an inbound edge to this vertex.
		   :meth:`LinkToVertex` |br|
		      |rarr| Create an outbound link from this vertex to the referenced vertex.
		   :meth:`LinkFromVertex` |br|
		      |rarr| Create an inbound link from the referenced vertex to this vertex.

		.. todo:: GRAPH::Vertex::EdgeToNewVertex Needs possible exceptions to be documented.
		"""
		vertex = Vertex(vertexID, vertexValue, vertexWeight, vertexKeyValuePairs, graph=self._graph)  # , component=self._component)

		if self._subgraph is vertex._subgraph:
			edge = Edge(self, vertex, edgeID, edgeValue, edgeWeight, edgeKeyValuePairs)

			self._outboundEdges.append(edge)
			vertex._inboundEdges.append(edge)

			if self._subgraph is None:
				# TODO: move into Edge?
				# TODO: keep _graph pointer in edge and then register edge on graph?
				if edgeID is None:
					self._graph._edgesWithoutID.append(edge)
				elif edgeID not in self._graph._edgesWithID:
					self._graph._edgesWithID[edgeID] = edge
				else:
					raise DuplicateEdgeError(f"Edge ID '{edgeID}' already exists in this graph.")
			else:
				# TODO: keep _graph pointer in edge and then register edge on graph?
				if edgeID is None:
					self._subgraph._edgesWithoutID.append(edge)
				elif edgeID not in self._graph._edgesWithID:
					self._subgraph._edgesWithID[edgeID] = edge
				else:
					raise DuplicateEdgeError(f"Edge ID '{edgeID}' already exists in this graph.")
		else:
			# FIXME: needs an error message
			raise GraphException()

		return edge

	def EdgeFromNewVertex(
		self,
		vertexID: Nullable[VertexIDType] = None,
		vertexValue: Nullable[VertexValueType] = None,
		vertexWeight: Nullable[VertexWeightType] = None,
		vertexKeyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None,
		edgeID: Nullable[EdgeIDType] = None,
		edgeWeight: Nullable[EdgeWeightType] = None,
		edgeValue: Nullable[VertexValueType] = None,
		edgeKeyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> 'Edge':
		"""
		Create a new vertex and link that vertex by an inbound edge to this vertex.

		:param vertexID:            The new vertex' optional ID.
		:param vertexValue:         The new vertex' optional value.
		:param vertexWeight:        The new vertex' optional weight.
		:param vertexKeyValuePairs: An optional mapping (dictionary) of key-value-pairs for the new vertex.
		:param edgeID:              The edge's optional ID for the new edge object.
		:param edgeWeight:          The edge's optional weight for the new edge object.
		:param edgeValue:           The edge's optional value for the new edge object.
		:param edgeKeyValuePairs:   An optional mapping (dictionary) of key-value-pairs for the new edge object.
		:returns:                   The edge object linking this vertex and the created vertex.

		.. seealso::

		   :meth:`EdgeToVertex` |br|
		      |rarr| Create an outbound edge from this vertex to the referenced vertex.
		   :meth:`EdgeFromVertex` |br|
		      |rarr| Create an inbound edge from the referenced vertex to this vertex.
		   :meth:`EdgeToNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an outbound edge from this vertex.
		   :meth:`LinkToVertex` |br|
		      |rarr| Create an outbound link from this vertex to the referenced vertex.
		   :meth:`LinkFromVertex` |br|
		      |rarr| Create an inbound link from the referenced vertex to this vertex.

		.. todo:: GRAPH::Vertex::EdgeFromNewVertex Needs possible exceptions to be documented.
		"""
		vertex = Vertex(vertexID, vertexValue, vertexWeight, vertexKeyValuePairs, graph=self._graph)  # , component=self._component)

		if self._subgraph is vertex._subgraph:
			edge = Edge(vertex, self, edgeID, edgeValue, edgeWeight, edgeKeyValuePairs)

			vertex._outboundEdges.append(edge)
			self._inboundEdges.append(edge)

			if self._subgraph is None:
				# TODO: move into Edge?
				# TODO: keep _graph pointer in edge and then register edge on graph?
				if edgeID is None:
					self._graph._edgesWithoutID.append(edge)
				elif edgeID not in self._graph._edgesWithID:
					self._graph._edgesWithID[edgeID] = edge
				else:
					raise DuplicateEdgeError(f"Edge ID '{edgeID}' already exists in this graph.")
			else:
				# TODO: keep _graph pointer in edge and then register edge on graph?
				if edgeID is None:
					self._subgraph._edgesWithoutID.append(edge)
				elif edgeID not in self._graph._edgesWithID:
					self._subgraph._edgesWithID[edgeID] = edge
				else:
					raise DuplicateEdgeError(f"Edge ID '{edgeID}' already exists in this graph.")
		else:
			# FIXME: needs an error message
			raise GraphException()

		return edge

	def LinkToVertex(
		self,
		vertex: 'Vertex',
		linkID: Nullable[EdgeIDType] = None,
		linkWeight: Nullable[EdgeWeightType] = None,
		linkValue: Nullable[VertexValueType] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None,
	) -> 'Link':
		"""
		Create an outbound link from this vertex to the referenced vertex.

		:param vertex:        The vertex to be linked to.
		:param edgeID:        The edge's optional ID for the new link object.
		:param edgeWeight:    The edge's optional weight for the new link object.
		:param edgeValue:     The edge's optional value for the new link object.
		:param keyValuePairs: An optional mapping (dictionary) of key-value-pairs for the new link object.
		:returns:             The link object linking this vertex and the referenced vertex.

		.. seealso::

		   :meth:`EdgeToVertex` |br|
		      |rarr| Create an outbound edge from this vertex to the referenced vertex.
		   :meth:`EdgeFromVertex` |br|
		      |rarr| Create an inbound edge from the referenced vertex to this vertex.
		   :meth:`EdgeToNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an outbound edge from this vertex.
		   :meth:`EdgeFromNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an inbound edge to this vertex.
		   :meth:`LinkFromVertex` |br|
		      |rarr| Create an inbound link from the referenced vertex to this vertex.

		.. todo:: GRAPH::Vertex::LinkToVertex Needs possible exceptions to be documented.
		"""
		if self._subgraph is vertex._subgraph:
			# FIXME: needs an error message
			raise GraphException()
		else:
			link = Link(self, vertex, linkID, linkValue, linkWeight, keyValuePairs)

			self._outboundLinks.append(link)
			vertex._inboundLinks.append(link)

			if self._subgraph is None:
				# TODO: move into Edge?
				# TODO: keep _graph pointer in link and then register link on graph?
				if linkID is None:
					self._graph._linksWithoutID.append(link)
				elif linkID not in self._graph._linksWithID:
					self._graph._linksWithID[linkID] = link
				else:
					raise DuplicateEdgeError(f"Link ID '{linkID}' already exists in this graph.")
			else:
				# TODO: keep _graph pointer in link and then register link on graph?
				if linkID is None:
					self._subgraph._linksWithoutID.append(link)
					vertex._subgraph._linksWithoutID.append(link)
				elif linkID not in self._graph._linksWithID:
					self._subgraph._linksWithID[linkID] = link
					vertex._subgraph._linksWithID[linkID] = link
				else:
					raise DuplicateEdgeError(f"Link ID '{linkID}' already exists in this graph.")

		return link

	def LinkFromVertex(
		self,
		vertex: 'Vertex',
		linkID: Nullable[EdgeIDType] = None,
		linkWeight: Nullable[EdgeWeightType] = None,
		linkValue: Nullable[VertexValueType] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> 'Edge':
		"""
		Create an inbound link from the referenced vertex to this vertex.

		:param vertex:        The vertex to be linked from.
		:param edgeID:        The edge's optional ID for the new link object.
		:param edgeWeight:    The edge's optional weight for the new link object.
		:param edgeValue:     The edge's optional value for the new link object.
		:param keyValuePairs: An optional mapping (dictionary) of key-value-pairs for the new link object.
		:returns:             The link object linking the referenced vertex and this vertex.

		.. seealso::

		   :meth:`EdgeToVertex` |br|
		      |rarr| Create an outbound edge from this vertex to the referenced vertex.
		   :meth:`EdgeFromVertex` |br|
		      |rarr| Create an inbound edge from the referenced vertex to this vertex.
		   :meth:`EdgeToNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an outbound edge from this vertex.
		   :meth:`EdgeFromNewVertex` |br|
		      |rarr| Create a new vertex and link that vertex by an inbound edge to this vertex.
		   :meth:`LinkToVertex` |br|
		      |rarr| Create an outbound link from this vertex to the referenced vertex.

		.. todo:: GRAPH::Vertex::LinkFromVertex Needs possible exceptions to be documented.
		"""
		if self._subgraph is vertex._subgraph:
			# FIXME: needs an error message
			raise GraphException()
		else:
			link = Link(vertex, self, linkID, linkValue, linkWeight, keyValuePairs)

			vertex._outboundLinks.append(link)
			self._inboundLinks.append(link)

			if self._subgraph is None:
				# TODO: move into Edge?
				# TODO: keep _graph pointer in link and then register link on graph?
				if linkID is None:
					self._graph._linksWithoutID.append(link)
				elif linkID not in self._graph._linksWithID:
					self._graph._linksWithID[linkID] = link
				else:
					raise DuplicateEdgeError(f"Link ID '{linkID}' already exists in this graph.")
			else:
				# TODO: keep _graph pointer in link and then register link on graph?
				if linkID is None:
					self._subgraph._linksWithoutID.append(link)
					vertex._subgraph._linksWithoutID.append(link)
				elif linkID not in self._graph._linksWithID:
					self._subgraph._linksWithID[linkID] = link
					vertex._subgraph._linksWithID[linkID] = link
				else:
					raise DuplicateEdgeError(f"Link ID '{linkID}' already exists in this graph.")

		return link

	def HasEdgeToDestination(self, destination: 'Vertex') -> bool:
		"""
		Check if this vertex is linked to another vertex by any outbound edge.

		:param destination: Destination vertex to check.
		:returns:           ``True``, if the destination vertex is a destination on any outbound edge.

		.. seealso::

		   :meth:`HasEdgeFromSource` |br|
		      |rarr| Check if this vertex is linked to another vertex by any inbound edge.
		   :meth:`HasLinkToDestination` |br|
		      |rarr| Check if this vertex is linked to another vertex by any outbound link.
		   :meth:`HasLinkFromSource` |br|
		      |rarr| Check if this vertex is linked to another vertex by any inbound link.
		"""
		for edge in self._outboundEdges:
			if destination is edge.Destination:
				return True

		return False

	def HasEdgeFromSource(self, source: 'Vertex') -> bool:
		"""
		Check if this vertex is linked to another vertex by any inbound edge.

		:param source: Source vertex to check.
		:returns:      ``True``, if the source vertex is a source on any inbound edge.

		.. seealso::

		   :meth:`HasEdgeToDestination` |br|
		      |rarr| Check if this vertex is linked to another vertex by any outbound edge.
		   :meth:`HasLinkToDestination` |br|
		      |rarr| Check if this vertex is linked to another vertex by any outbound link.
		   :meth:`HasLinkFromSource` |br|
		      |rarr| Check if this vertex is linked to another vertex by any inbound link.
		"""
		for edge in self._inboundEdges:
			if source is edge.Source:
				return True

		return False

	def HasLinkToDestination(self, destination: 'Vertex') -> bool:
		"""
		Check if this vertex is linked to another vertex by any outbound link.

		:param destination: Destination vertex to check.
		:returns:           ``True``, if the destination vertex is a destination on any outbound link.

		.. seealso::

		   :meth:`HasEdgeToDestination` |br|
		      |rarr| Check if this vertex is linked to another vertex by any outbound edge.
		   :meth:`HasEdgeFromSource` |br|
		      |rarr| Check if this vertex is linked to another vertex by any inbound edge.
		   :meth:`HasLinkFromSource` |br|
		      |rarr| Check if this vertex is linked to another vertex by any inbound link.
		"""
		for link in self._outboundLinks:
			if destination is link.Destination:
				return True

		return False

	def HasLinkFromSource(self, source: 'Vertex') -> bool:
		"""
		Check if this vertex is linked to another vertex by any inbound link.

		:param source: Source vertex to check.
		:returns:      ``True``, if the source vertex is a source on any inbound link.

		.. seealso::

		   :meth:`HasEdgeToDestination` |br|
		      |rarr| Check if this vertex is linked to another vertex by any outbound edge.
		   :meth:`HasEdgeFromSource` |br|
		      |rarr| Check if this vertex is linked to another vertex by any inbound edge.
		   :meth:`HasLinkToDestination` |br|
		      |rarr| Check if this vertex is linked to another vertex by any outbound link.
		"""
		for link in self._inboundLinks:
			if source is link.Source:
				return True

		return False

	def DeleteEdgeTo(self, destination: 'Vertex') -> None:
		for edge in self._outboundEdges:
			if edge._destination is destination:
				break
		else:
			raise GraphException(f"No outbound edge found to '{destination!r}'.")

		edge.Delete()

	def DeleteEdgeFrom(self, source: 'Vertex') -> None:
		for edge in self._inboundEdges:
			if edge._source is source:
				break
		else:
			raise GraphException(f"No inbound edge found to '{source!r}'.")

		edge.Delete()

	def DeleteLinkTo(self, destination: 'Vertex') -> None:
		for link in self._outboundLinks:
			if link._destination is destination:
				break
		else:
			raise GraphException(f"No outbound link found to '{destination!r}'.")

		link.Delete()

	def DeleteLinkFrom(self, source: 'Vertex') -> None:
		for link in self._inboundLinks:
			if link._source is source:
				break
		else:
			raise GraphException(f"No inbound link found to '{source!r}'.")

		link.Delete()

	def Copy(self, graph: Graph, copyDict: bool = False, linkingKeyToOriginalVertex: Nullable[str] = None, linkingKeyFromOriginalVertex: Nullable[str] = None) -> 'Vertex':
		"""
		Creates a copy of this vertex in another graph.

		Optionally, the vertex's attached attributes (key-value-pairs) can be copied and a linkage between both vertices
		can be established.

		:param graph:                        The graph, the vertex is created in.
		:param copyDict:                     If ``True``, copy all attached attributes into the new vertex.
		:param linkingKeyToOriginalVertex:   If not ``None``, add a key-value-pair using this parameter as key from new vertex to the original vertex.
		:param linkingKeyFromOriginalVertex: If not ``None``, add a key-value-pair using this parameter as key from original vertex to the new vertex.
		:returns:                            The newly created vertex.
		:raises GraphException:              If source graph and destination graph are the same.
		"""
		if graph is self._graph:
			raise GraphException("Graph to copy this vertex to, is the same graph.")

		vertex = Vertex(self._id, self._value, self._weight, graph=graph)
		if copyDict:
			vertex._dict = self._dict.copy()

		if linkingKeyToOriginalVertex is not None:
			vertex._dict[linkingKeyToOriginalVertex] = self
		if linkingKeyFromOriginalVertex is not None:
			self._dict[linkingKeyFromOriginalVertex] = vertex

		return vertex

	def IterateOutboundEdges(self, predicate: Nullable[Callable[['Edge'], bool]] = None) -> Generator['Edge', None, None]:
		"""
		Iterate all or selected outbound edges of this vertex.

		If parameter ``predicate`` is not None, the given filter function is used to skip edges in the generator.

		:param predicate: Filter function accepting any edge and returning a boolean.
		:returns:         A generator to iterate all outbound edges.
		"""
		if predicate is None:
			for edge in self._outboundEdges:
				yield edge
		else:
			for edge in self._outboundEdges:
				if predicate(edge):
					yield edge

	def IterateInboundEdges(self, predicate: Nullable[Callable[['Edge'], bool]] = None) -> Generator['Edge', None, None]:
		"""
		Iterate all or selected inbound edges of this vertex.

		If parameter ``predicate`` is not None, the given filter function is used to skip edges in the generator.

		:param predicate: Filter function accepting any edge and returning a boolean.
		:returns:         A generator to iterate all inbound edges.
		"""
		if predicate is None:
			for edge in self._inboundEdges:
				yield edge
		else:
			for edge in self._inboundEdges:
				if predicate(edge):
					yield edge

	def IterateOutboundLinks(self, predicate: Nullable[Callable[['Link'], bool]] = None) -> Generator['Link', None, None]:
		"""
		Iterate all or selected outbound links of this vertex.

		If parameter ``predicate`` is not None, the given filter function is used to skip links in the generator.

		:param predicate: Filter function accepting any link and returning a boolean.
		:returns:         A generator to iterate all outbound links.
		"""
		if predicate is None:
			for link in self._outboundLinks:
				yield link
		else:
			for link in self._outboundLinks:
				if predicate(link):
					yield link

	def IterateInboundLinks(self, predicate: Nullable[Callable[['Link'], bool]] = None) -> Generator['Link', None, None]:
		"""
		Iterate all or selected inbound links of this vertex.

		If parameter ``predicate`` is not None, the given filter function is used to skip links in the generator.

		:param predicate: Filter function accepting any link and returning a boolean.
		:returns:         A generator to iterate all inbound links.
		"""
		if predicate is None:
			for link in self._inboundLinks:
				yield link
		else:
			for link in self._inboundLinks:
				if predicate(link):
					yield link

	def IterateSuccessorVertices(self, predicate: Nullable[Callable[['Edge'], bool]] = None) -> Generator['Vertex', None, None]:
		"""
		Iterate all or selected successor vertices of this vertex.

		If parameter ``predicate`` is not None, the given filter function is used to skip successors in the generator.

		:param predicate: Filter function accepting any edge and returning a boolean.
		:returns:         A generator to iterate all successor vertices.
		"""
		if predicate is None:
			for edge in self._outboundEdges:
				yield edge.Destination
		else:
			for edge in self._outboundEdges:
				if predicate(edge):
					yield edge.Destination

	def IteratePredecessorVertices(self, predicate: Nullable[Callable[['Edge'], bool]] = None) -> Generator['Vertex', None, None]:
		"""
		Iterate all or selected predecessor vertices of this vertex.

		If parameter ``predicate`` is not None, the given filter function is used to skip predecessors in the generator.

		:param predicate: Filter function accepting any edge and returning a boolean.
		:returns:         A generator to iterate all predecessor vertices.
		"""
		if predicate is None:
			for edge in self._inboundEdges:
				yield edge.Source
		else:
			for edge in self._inboundEdges:
				if predicate(edge):
					yield edge.Source

	def IterateVerticesBFS(self) -> Generator['Vertex', None, None]:
		"""
		A generator to iterate all reachable vertices starting from this node in breadth-first search (BFS) order.

		:returns: A generator to iterate vertices traversed in BFS order.

		.. seealso::

		   :meth:`IterateVerticesDFS` |br|
		      |rarr| Iterate all reachable vertices **depth-first search** order.
		"""
		visited: Set[Vertex] = set()
		queue: Deque[Vertex] = deque()

		yield self
		visited.add(self)
		for edge in self._outboundEdges:
			nextVertex = edge.Destination
			if nextVertex is not self:
				queue.appendleft(nextVertex)
				visited.add(nextVertex)

		while queue:
			vertex = queue.pop()
			yield vertex
			for edge in vertex._outboundEdges:
				nextVertex = edge.Destination
				if nextVertex not in visited:
					queue.appendleft(nextVertex)
					visited.add(nextVertex)

	def IterateVerticesDFS(self) -> Generator['Vertex', None, None]:
		"""
		A generator to iterate all reachable vertices starting from this node in depth-first search (DFS) order.

		:returns: A generator to iterate vertices traversed in DFS order.

		.. seealso::

		   :meth:`IterateVerticesBFS` |br|
		      |rarr| Iterate all reachable vertices **breadth-first search** order.

		   Wikipedia - https://en.wikipedia.org/wiki/Depth-first_search
		"""
		visited: Set[Vertex] = set()
		stack: List[typing_Iterator[Edge]] = list()

		yield self
		visited.add(self)
		stack.append(iter(self._outboundEdges))

		while True:
			try:
				edge = next(stack[-1])
				nextVertex = edge._destination
				if nextVertex not in visited:
					visited.add(nextVertex)
					yield nextVertex
					if len(nextVertex._outboundEdges) != 0:
						stack.append(iter(nextVertex._outboundEdges))
			except StopIteration:
				stack.pop()

				if len(stack) == 0:
					return

	def IterateAllOutboundPathsAsVertexList(self) -> Generator[Tuple['Vertex', ...], None, None]:
		if len(self._outboundEdges) == 0:
			yield (self, )
			return

		visited:       Set[Vertex] =                 set()
		vertexStack:   List[Vertex] =                list()
		iteratorStack: List[typing_Iterator[Edge]] = list()

		visited.add(self)
		vertexStack.append(self)
		iteratorStack.append(iter(self._outboundEdges))

		while True:
			try:
				edge = next(iteratorStack[-1])
				nextVertex = edge._destination
				if nextVertex in visited:
					ex = CycleError(f"Loop detected.")
					ex.add_note(f"First loop is:")
					for i, vertex in enumerate(vertexStack):
						ex.add_note(f"  {i}: {vertex!r}")
					raise ex

				vertexStack.append(nextVertex)
				if len(nextVertex._outboundEdges) == 0:
					yield tuple(vertexStack)
					vertexStack.pop()
				else:
					iteratorStack.append(iter(nextVertex._outboundEdges))

			except StopIteration:
				vertexStack.pop()
				iteratorStack.pop()

				if len(vertexStack) == 0:
					return

	def ShortestPathToByHops(self, destination: 'Vertex') -> Generator['Vertex', None, None]:
		"""
		Compute the shortest path (by hops) between this vertex and the destination vertex.

		A generator is return to iterate all vertices along the path including source and destination vertex.

		The search algorithm is breadth-first search (BFS) based. The found solution, if any, is not unique but deterministic
		as long as the graph was not modified (e.g. ordering of edges on vertices).

		:param destination: The destination vertex to reach.
		:returns:           A generator to iterate all vertices on the path found between this vertex and the destination vertex.
		"""
		# Trivial case if start is destination
		if self is destination:
			yield self
			return

		# Local struct to create multiple linked-lists forming a paths from current node back to the starting point
		# (actually a tree). Each node holds a reference to the vertex it represents.
		# Hint: slotted classes are faster than '@dataclasses.dataclass'.
		class Node(metaclass=ExtendedType, slots=True):
			parent: 'Node'
			ref: Vertex

			def __init__(self, parent: 'Node', ref: Vertex) -> None:
				self.parent = parent
				self.ref = ref

			def __str__(self):
				return f"Vertex: {self.ref.ID}"

		# Initially add all reachable vertices to a queue if vertices to be processed.
		startNode = Node(None, self)
		visited: Set[Vertex] = set()
		queue: Deque[Node] = deque()

		# Add starting vertex and all its children to the processing list.
		# If a child is the destination, break immediately else go into 'else' branch and use BFS algorithm.
		visited.add(self)
		for edge in self._outboundEdges:
			nextVertex = edge.Destination
			if nextVertex is destination:
				# Child is destination, so construct the last node for path traversal and break from loop.
				destinationNode = Node(startNode, nextVertex)
				break
			if nextVertex is not self:
				# Ignore backward-edges and side-edges.
				# Here self-edges, because there is only the starting vertex in the list of visited edges.
				visited.add(nextVertex)
				queue.appendleft(Node(startNode, nextVertex))
		else:
			# Process queue until destination is found or no further vertices are reachable.
			while queue:
				node = queue.pop()
				for edge in node.ref._outboundEdges:
					nextVertex = edge.Destination
					# Next reachable vertex is destination, so construct the last node for path traversal and break from loop.
					if nextVertex is destination:
						destinationNode = Node(node, nextVertex)
						break
					# Ignore backward-edges and side-edges.
					if nextVertex not in visited:
						visited.add(nextVertex)
						queue.appendleft(Node(node, nextVertex))
				# Next 3 lines realize a double-break if break was called in inner loop, otherwise continue with outer loop.
				else:
					continue
				break
			else:
				# All reachable vertices have been processed, but destination was not among them.
				raise DestinationNotReachable(f"Destination is not reachable.")

		# Reverse order of linked list from destinationNode to startNode
		currentNode = destinationNode
		previousNode = destinationNode.parent
		currentNode.parent = None
		while previousNode is not None:
			node = previousNode.parent
			previousNode.parent = currentNode
			currentNode = previousNode
			previousNode = node

		# Scan reversed linked-list and yield referenced vertices
		yield startNode.ref
		node = startNode.parent
		while node is not None:
			yield node.ref
			node = node.parent

	def ShortestPathToByWeight(self, destination: 'Vertex') -> Generator['Vertex', None, None]:
		"""
		Compute the shortest path (by edge weight) between this vertex and the destination vertex.

		A generator is return to iterate all vertices along the path including source and destination vertex.

		The search algorithm is based on Dijkstra algorithm and using :mod:`heapq`. The found solution, if any, is not
		unique but deterministic as long as the graph was not modified (e.g. ordering of edges on vertices).

		:param destination: The destination vertex to reach.
		:returns:           A generator to iterate all vertices on the path found between this vertex and the destination vertex.
		"""
		# Improvements: both-sided Dijkstra (search from start and destination to reduce discovered area.

		# Trivial case if start is destination
		if self is destination:
			yield self
			return

		# Local struct to create multiple-linked lists forming a paths from current node back to the starting point
		# (actually a tree). Each node holds the overall weight from start to current node and a reference to the vertex it
		# represents.
		# Hint: slotted classes are faster than '@dataclasses.dataclass'.
		class Node(metaclass=ExtendedType, slots=True):
			parent: 'Node'
			distance: EdgeWeightType
			ref: Vertex

			def __init__(self, parent: 'Node', distance: EdgeWeightType, ref: Vertex) -> None:
				self.parent = parent
				self.distance = distance
				self.ref = ref

			def __lt__(self, other):
				return self.distance < other.distance

			def __str__(self):
				return f"Vertex: {self.ref.ID}"

		visited: Set['Vertex'] = set()
		startNode = Node(None, 0, self)
		priorityQueue = [startNode]

		# Add starting vertex and all its children to the processing list.
		# If a child is the destination, break immediately else go into 'else' branch and use Dijkstra algorithm.
		visited.add(self)
		for edge in self._outboundEdges:
			nextVertex = edge.Destination
			# Child is destination, so construct the last node for path traversal and break from loop.
			if nextVertex is destination:
				destinationNode = Node(startNode, edge._weight, nextVertex)
				break
			# Ignore backward-edges and side-edges.
			# Here self-edges, because there is only the starting vertex in the list of visited edges.
			if nextVertex is not self:
				visited.add(nextVertex)
				heapq.heappush(priorityQueue, Node(startNode, edge._weight, nextVertex))
		else:
			# Process priority queue until destination is found or no further vertices are reachable.
			while priorityQueue:
				node = heapq.heappop(priorityQueue)
				for edge in node.ref._outboundEdges:
					nextVertex = edge.Destination
					# Next reachable vertex is destination, so construct the last node for path traversal and break from loop.
					if nextVertex is destination:
						destinationNode = Node(node, node.distance + edge._weight, nextVertex)
						break
					# Ignore backward-edges and side-edges.
					if nextVertex not in visited:
						visited.add(nextVertex)
						heapq.heappush(priorityQueue, Node(node, node.distance + edge._weight, nextVertex))
				# Next 3 lines realize a double-break if break was called in inner loop, otherwise continue with outer loop.
				else:
					continue
				break
			else:
				# All reachable vertices have been processed, but destination was not among them.
				raise DestinationNotReachable(f"Destination is not reachable.")

		# Reverse order of linked-list from destinationNode to startNode
		currentNode = destinationNode
		previousNode = destinationNode.parent
		currentNode.parent = None
		while previousNode is not None:
			node = previousNode.parent
			previousNode.parent = currentNode
			currentNode = previousNode
			previousNode = node

		# Scan reversed linked-list and yield referenced vertices
		yield startNode.ref, startNode.distance
		node = startNode.parent
		while node is not None:
			yield node.ref, node.distance
			node = node.parent

		# Other possible algorithms:
		# * Bellman-Ford
		# * Floyd-Warshall

	# def PathExistsTo(self, destination: 'Vertex'):
	# 	raise NotImplementedError()
	# 	# DFS
	# 	# Union find
	#
	# def MaximumFlowTo(self, destination: 'Vertex'):
	# 	raise NotImplementedError()
	# 	# Ford-Fulkerson algorithm
	# 	# Edmons-Karp algorithm
	# 	# Dinic's algorithm

	def ConvertToTree(self) -> Node:
		"""
		Converts all reachable vertices from this starting vertex to a tree of :class:`~pyTooling.Tree.Node` instances.

		The tree is traversed using depths-first-search.

		:returns:
		"""
		visited: Set[Vertex] = set()
		stack: List[Tuple[Node, typing_Iterator[Edge]]] = list()

		root = Node(nodeID=self._id, value=self._value)
		root._dict = self._dict.copy()

		visited.add(self)
		stack.append((root, iter(self._outboundEdges)))

		while True:
			try:
				edge = next(stack[-1][1])
				nextVertex = edge._destination
				if nextVertex not in visited:
					node = Node(nextVertex._id, nextVertex._value, parent=stack[-1][0])
					visited.add(nextVertex)
					if len(nextVertex._outboundEdges) != 0:
						stack.append((node, iter(nextVertex._outboundEdges)))
				else:
					raise NotATreeError(f"The directed subgraph is not a tree.")
					# TODO: compute cycle:
					#       a) branch 1 is described in stack
					#       b) branch 2 can be found by walking from joint to root in the tree
			except StopIteration:
				stack.pop()

				if len(stack) == 0:
					return root

	def __repr__(self) -> str:
		"""
		Returns a detailed string representation of the vertex.

		:returns: The detailed string representation of the vertex.
		"""
		vertexID = value = ""
		sep = ": "
		if self._id is not None:
			vertexID = f"{sep}vertexID='{self._id}'"
			sep = "; "
		if self._value is not None:
			value = f"{sep}value='{self._value}'"

		return f"<vertex{vertexID}{value}>"

	def __str__(self) -> str:
		"""
		Return a string representation of the vertex.

		Order of resolution:

		1. If :attr:`_value` is not None, return the string representation of :attr:`_value`.
		2. If :attr:`_id` is not None, return the string representation of :attr:`_id`.
		3. Else, return :meth:`__repr__`.

		:returns: The resolved string representation of the vertex.
		"""
		if self._value is not None:
			return str(self._value)
		elif self._id is not None:
			return str(self._id)
		else:
			return self.__repr__()


@export
class BaseEdge(
	BaseWithIDValueAndWeight[EdgeIDType, EdgeValueType, EdgeWeightType, EdgeDictKeyType, EdgeDictValueType],
	Generic[EdgeIDType, EdgeValueType, EdgeWeightType, EdgeDictKeyType, EdgeDictValueType]
):
	"""
	An **edge** can have a unique ID, a value, a weight and attached meta information as key-value-pairs. All edges are
	directed.
	"""
	_source:      Vertex
	_destination: Vertex

	def __init__(
		self,
		source: Vertex,
		destination: Vertex,
		edgeID: Nullable[EdgeIDType] = None,
		value: Nullable[EdgeValueType] = None,
		weight: Nullable[EdgeWeightType] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::BaseEdge::init Needs documentation.

		:param source:        The source of the new edge.
		:param destination:   The destination of the new edge.
		:param edgeID:        The optional unique ID for the new edge.
		:param value:         The optional value for the new edge.
		:param weight:        The optional weight for the new edge.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		super().__init__(edgeID, value, weight, keyValuePairs)

		self._source = source
		self._destination = destination

		component = source._component
		if component is not destination._component:
			# TODO: should it be divided into with/without ID?
			oldComponent = destination._component
			for vertex in oldComponent._vertices:
				vertex._component = component
				component._vertices.add(vertex)
			component._graph._components.remove(oldComponent)
			del oldComponent

	@readonly
	def Source(self) -> Vertex:
		"""
		Read-only property to get the source (:attr:`_source`) of an edge.

		:returns: The source of an edge.
		"""
		return self._source

	@readonly
	def Destination(self) -> Vertex:
		"""
		Read-only property to get the destination (:attr:`_destination`) of an edge.

		:returns: The destination of an edge.
		"""
		return self._destination

	def Reverse(self) -> None:
		"""Reverse the direction of this edge."""
		swap = self._source
		self._source = self._destination
		self._destination = swap


@export
class Edge(
	BaseEdge[EdgeIDType, EdgeValueType, EdgeWeightType, EdgeDictKeyType, EdgeDictValueType],
	Generic[EdgeIDType, EdgeValueType, EdgeWeightType, EdgeDictKeyType, EdgeDictValueType]
):
	"""
	An **edge** can have a unique ID, a value, a weight and attached meta information as key-value-pairs. All edges are
	directed.
	"""

	def __init__(
		self,
		source: Vertex,
		destination: Vertex,
		edgeID: Nullable[EdgeIDType] = None,
		value: Nullable[EdgeValueType] = None,
		weight: Nullable[EdgeWeightType] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::Edge::init Needs documentation.

		:param source:        The source of the new edge.
		:param destination:   The destination of the new edge.
		:param edgeID:        The optional unique ID for the new edge.
		:param value:         The optional value for the new edge.
		:param weight:        The optional weight for the new edge.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		if not isinstance(source, Vertex):
			ex = TypeError("Parameter 'source' is not of type 'Vertex'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(source)}'.")
			raise ex
		if not isinstance(destination, Vertex):
			ex = TypeError("Parameter 'destination' is not of type 'Vertex'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(destination)}'.")
			raise ex
		if edgeID is not None and not isinstance(edgeID, Hashable):
			ex = TypeError("Parameter 'edgeID' is not of type 'EdgeIDType'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(edgeID)}'.")
			raise ex
		# if value is not None and  not isinstance(value, Vertex):
		# 	raise TypeError("Parameter 'value' is not of type 'EdgeValueType'.")
		if weight is not None and not isinstance(weight, (int, float)):
			ex = TypeError("Parameter 'weight' is not of type 'EdgeWeightType'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(weight)}'.")
			raise ex
		if source._graph is not destination._graph:
			raise NotInSameGraph(f"Source vertex and destination vertex are not in same graph.")

		super().__init__(source, destination, edgeID, value, weight, keyValuePairs)

	def Delete(self) -> None:
		# Remove from Source and Destination
		self._source._outboundEdges.remove(self)
		self._destination._inboundEdges.remove(self)

		# Remove from Graph and Subgraph
		if self._id is None:
			self._source._graph._edgesWithoutID.remove(self)
			if self._source._subgraph is not None:
				self._source._subgraph._edgesWithoutID.remove(self)
		else:
			del self._source._graph._edgesWithID[self._id]
			if self._source._subgraph is not None:
				del self._source._subgraph._edgesWithID[self]

		self._Delete()

	def _Delete(self) -> None:
		super().Delete()

	def Reverse(self) -> None:
		"""Reverse the direction of this edge."""
		self._source._outboundEdges.remove(self)
		self._source._inboundEdges.append(self)
		self._destination._inboundEdges.remove(self)
		self._destination._outboundEdges.append(self)

		super().Reverse()


@export
class Link(
	BaseEdge[LinkIDType, LinkValueType, LinkWeightType, LinkDictKeyType, LinkDictValueType],
	Generic[LinkIDType, LinkValueType, LinkWeightType, LinkDictKeyType, LinkDictValueType]
):
	"""
	A **link** can have a unique ID, a value, a weight and attached meta information as key-value-pairs. All links are
	directed.
	"""

	def __init__(
		self,
		source: Vertex,
		destination: Vertex,
		linkID: LinkIDType = None,
		value: LinkValueType = None,
		weight: Nullable[LinkWeightType] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::Edge::init Needs documentation.

		:param source:        The source of the new link.
		:param destination:   The destination of the new link.
		:param linkID:        The optional unique ID for the new link.
		:param value:         The optional value for the new v.
		:param weight:        The optional weight for the new link.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		if not isinstance(source, Vertex):
			ex = TypeError("Parameter 'source' is not of type 'Vertex'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(source)}'.")
			raise ex
		if not isinstance(destination, Vertex):
			ex = TypeError("Parameter 'destination' is not of type 'Vertex'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(destination)}'.")
			raise ex
		if linkID is not None and not isinstance(linkID, Hashable):
			ex = TypeError("Parameter 'linkID' is not of type 'LinkIDType'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(linkID)}'.")
			raise ex
		# if value is not None and  not isinstance(value, Vertex):
		# 	raise TypeError("Parameter 'value' is not of type 'EdgeValueType'.")
		if weight is not None and not isinstance(weight, (int, float)):
			ex = TypeError("Parameter 'weight' is not of type 'EdgeWeightType'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(weight)}'.")
			raise ex
		if source._graph is not destination._graph:
			raise NotInSameGraph(f"Source vertex and destination vertex are not in same graph.")

		super().__init__(source, destination, linkID, value, weight, keyValuePairs)

	def Delete(self) -> None:
		self._source._outboundEdges.remove(self)
		self._destination._inboundEdges.remove(self)

		if self._id is None:
			self._source._graph._linksWithoutID.remove(self)
		else:
			del self._source._graph._linksWithID[self._id]

		self._Delete()
		assert getrefcount(self) == 1

	def _Delete(self) -> None:
		super().Delete()

	def Reverse(self) -> None:
		"""Reverse the direction of this link."""
		self._source._outboundEdges.remove(self)
		self._source._inboundEdges.append(self)
		self._destination._inboundEdges.remove(self)
		self._destination._outboundEdges.append(self)

		super().Reverse()


@export
class BaseGraph(
	BaseWithName[GraphDictKeyType, GraphDictValueType],
	Generic[
		GraphDictKeyType, GraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	]
):
	"""
	.. todo:: GRAPH::BaseGraph Needs documentation.

	"""

	_verticesWithID:    Dict[VertexIDType, Vertex[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType]]
	_verticesWithoutID: List[Vertex[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType]]
	_edgesWithID:       Dict[EdgeIDType, Edge[EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType]]
	_edgesWithoutID:    List[Edge[EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType]]
	_linksWithID:       Dict[EdgeIDType, Link[LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType]]
	_linksWithoutID:    List[Link[LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType]]

	def __init__(
		self,
		name: Nullable[str] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
		#, vertices: Nullable[Iterable[Vertex]] = None) -> None:
	) -> None:
		"""
		.. todo:: GRAPH::BaseGraph::init Needs documentation.

		:param name:          The optional name of the graph.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		super().__init__(name, keyValuePairs)

		self._verticesWithoutID = []
		self._verticesWithID = {}
		self._edgesWithoutID = []
		self._edgesWithID = {}
		self._linksWithoutID = []
		self._linksWithID = {}

	def __del__(self) -> None:
		"""
		.. todo:: GRAPH::BaseGraph::del Needs documentation.

		"""
		try:
			del self._verticesWithoutID
			del self._verticesWithID
			del self._edgesWithoutID
			del self._edgesWithID
			del self._linksWithoutID
			del self._linksWithID
		except AttributeError:
			pass

		super().__del__()

	@readonly
	def VertexCount(self) -> int:
		"""Read-only property to access the number of vertices in this graph.

		:returns: The number of vertices in this graph."""
		return len(self._verticesWithoutID) + len(self._verticesWithID)

	@readonly
	def EdgeCount(self) -> int:
		"""Read-only property to access the number of edges in this graph.

		:returns: The number of edges in this graph."""
		return len(self._edgesWithoutID) + len(self._edgesWithID)

	@readonly
	def LinkCount(self) -> int:
		"""Read-only property to access the number of links in this graph.

		:returns: The number of links in this graph."""
		return len(self._linksWithoutID) + len(self._linksWithID)

	def IterateVertices(self, predicate: Nullable[Callable[[Vertex], bool]] = None) -> Generator[Vertex[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType], None, None]:
		"""
		Iterate all or selected vertices of a graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip vertices in the generator.

		:param predicate: Filter function accepting any vertex and returning a boolean.
		:returns:         A generator to iterate all vertices.
		"""
		if predicate is None:
			yield from self._verticesWithoutID
			yield from self._verticesWithID.values()

		else:
			for vertex in self._verticesWithoutID:
				if predicate(vertex):
					yield vertex

			for vertex in self._verticesWithID.values():
				if predicate(vertex):
					yield vertex

	def IterateRoots(self, predicate: Nullable[Callable[[Vertex], bool]] = None) -> Generator[Vertex[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType], None, None]:
		"""
		Iterate all or selected roots (vertices without inbound edges / without predecessors) of a graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip vertices in the generator.

		:param predicate: Filter function accepting any vertex and returning a boolean.
		:returns:         A generator to iterate all vertices without inbound edges.

		.. seealso::

		   :meth:`IterateLeafs` |br|
		      |rarr| Iterate leafs of a graph.
		   :meth:`Vertex.IsRoot <pyTooling.Graph.Vertex.IsRoot>` |br|
		      |rarr| Check if a vertex is a root vertex in the graph.
		   :meth:`Vertex.IsLeaf <pyTooling.Graph.Vertex.IsLeaf>` |br|
		      |rarr| Check if a vertex is a leaf vertex in the graph.
		"""
		if predicate is None:
			for vertex in self._verticesWithoutID:
				if len(vertex._inboundEdges) == 0:
					yield vertex

			for vertex in self._verticesWithID.values():
				if len(vertex._inboundEdges) == 0:
					yield vertex
		else:
			for vertex in self._verticesWithoutID:
				if len(vertex._inboundEdges) == 0 and predicate(vertex):
					yield vertex

			for vertex in self._verticesWithID.values():
				if len(vertex._inboundEdges) == 0 and predicate(vertex):
					yield vertex

	def IterateLeafs(self, predicate: Nullable[Callable[[Vertex], bool]] = None) -> Generator[Vertex[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType], None, None]:
		"""
		Iterate all or selected leafs (vertices without outbound edges / without successors) of a graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip vertices in the generator.

		:param predicate: Filter function accepting any vertex and returning a boolean.
		:returns:         A generator to iterate all vertices without outbound edges.

		.. seealso::

		   :meth:`IterateRoots` |br|
		      |rarr| Iterate roots of a graph.
		   :meth:`Vertex.IsRoot <pyTooling.Graph.Vertex.IsRoot>` |br|
		      |rarr| Check if a vertex is a root vertex in the graph.
		   :meth:`Vertex.IsLeaf <pyTooling.Graph.Vertex.IsLeaf>` |br|
		      |rarr| Check if a vertex is a leaf vertex in the graph.
		"""
		if predicate is None:
			for vertex in self._verticesWithoutID:
				if len(vertex._outboundEdges) == 0:
					yield vertex

			for vertex in self._verticesWithID.values():
				if len(vertex._outboundEdges) == 0:
					yield vertex
		else:
			for vertex in self._verticesWithoutID:
				if len(vertex._outboundEdges) == 0 and predicate(vertex):
					yield vertex

			for vertex in self._verticesWithID.values():
				if len(vertex._outboundEdges) == 0 and predicate(vertex):
					yield vertex

	# def IterateBFS(self, predicate: Nullable[Callable[[Vertex], bool]] = None) -> Generator[Vertex[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType], None, None]:
	# 	raise NotImplementedError()
	#
	# def IterateDFS(self, predicate: Nullable[Callable[[Vertex], bool]] = None) -> Generator[Vertex[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType], None, None]:
	# 	raise NotImplementedError()

	def IterateTopologically(self, predicate: Nullable[Callable[[Vertex], bool]] = None) -> Generator[Vertex[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType], None, None]:
		"""
		Iterate all or selected vertices in topological order.

		If parameter ``predicate`` is not None, the given filter function is used to skip vertices in the generator.

		:param predicate:   Filter function accepting any vertex and returning a boolean.
		:returns:           A generator to iterate all vertices in topological order.
		:except CycleError: Raised if graph is cyclic, thus topological sorting isn't possible.
		"""
		outboundEdgeCounts = {}
		leafVertices = []

		for vertex in self._verticesWithoutID:
			if (count := len(vertex._outboundEdges)) == 0:
				leafVertices.append(vertex)
			else:
				outboundEdgeCounts[vertex] = count

		for vertex in self._verticesWithID.values():
			if (count := len(vertex._outboundEdges)) == 0:
				leafVertices.append(vertex)
			else:
				outboundEdgeCounts[vertex] = count

		if not leafVertices:
			raise CycleError(f"Graph has no leafs. Thus, no topological sorting exists.")

		overallCount = len(outboundEdgeCounts) + len(leafVertices)

		def removeVertex(vertex: Vertex):
			nonlocal overallCount
			overallCount -= 1
			for inboundEdge in vertex._inboundEdges:
				sourceVertex = inboundEdge.Source
				count = outboundEdgeCounts[sourceVertex] - 1
				outboundEdgeCounts[sourceVertex] = count
				if count == 0:
					leafVertices.append(sourceVertex)

		if predicate is None:
			for vertex in leafVertices:
				yield vertex

				removeVertex(vertex)
		else:
			for vertex in leafVertices:
				if predicate(vertex):
					yield vertex

				removeVertex(vertex)

		if overallCount == 0:
			return
		elif overallCount > 0:
			raise CycleError(f"Graph has remaining vertices. Thus, the graph has at least one cycle.")

		raise InternalError(f"Graph data structure is corrupted.")  # pragma: no cover

	def IterateEdges(self, predicate: Nullable[Callable[[Edge], bool]] = None) -> Generator[Edge[EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType], None, None]:
		"""
		Iterate all or selected edges of a graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip edges in the generator.

		:param predicate: Filter function accepting any edge and returning a boolean.
		:returns:         A generator to iterate all edges.
		"""
		if predicate is None:
			yield from self._edgesWithoutID
			yield from self._edgesWithID.values()

		else:
			for edge in self._edgesWithoutID:
				if predicate(edge):
					yield edge

			for edge in self._edgesWithID.values():
				if predicate(edge):
					yield edge

	def IterateLinks(self, predicate: Nullable[Callable[[Link], bool]] = None) -> Generator[Link[LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType], None, None]:
		"""
		Iterate all or selected links of a graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip links in the generator.

		:param predicate: Filter function accepting any link and returning a boolean.
		:returns:         A generator to iterate all links.
		"""
		if predicate is None:
			yield from self._linksWithoutID
			yield from self._linksWithID.values()

		else:
			for link in self._linksWithoutID:
				if predicate(link):
					yield link

			for link in self._linksWithID.values():
				if predicate(link):
					yield link

	def ReverseEdges(self, predicate: Nullable[Callable[[Edge], bool]] = None) -> None:
		"""
		Reverse all or selected edges of a graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip edges.

		:param predicate: Filter function accepting any edge and returning a boolean.
		"""
		if predicate is None:
			for edge in self._edgesWithoutID:
				swap = edge._source
				edge._source = edge._destination
				edge._destination = swap

			for edge in self._edgesWithID.values():
				swap = edge._source
				edge._source = edge._destination
				edge._destination = swap

			for vertex in self._verticesWithoutID:
				swap = vertex._inboundEdges
				vertex._inboundEdges = vertex._outboundEdges
				vertex._outboundEdges = swap

			for vertex in self._verticesWithID.values():
				swap = vertex._inboundEdges
				vertex._inboundEdges = vertex._outboundEdges
				vertex._outboundEdges = swap
		else:
			for edge in self._edgesWithoutID:
				if predicate(edge):
					edge.Reverse()

			for edge in self._edgesWithID.values():
				if predicate(edge):
					edge.Reverse()

	def ReverseLinks(self, predicate: Nullable[Callable[[Link], bool]] = None) -> None:
		"""
		Reverse all or selected links of a graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip links.

		:param predicate: Filter function accepting any link and returning a boolean.
		"""
		if predicate is None:
			for link in self._linksWithoutID:
				swap = link._source
				link._source = link._destination
				link._destination = swap

			for link in self._linksWithID.values():
				swap = link._source
				link._source = link._destination
				link._destination = swap

			for vertex in self._verticesWithoutID:
				swap = vertex._inboundLinks
				vertex._inboundLinks = vertex._outboundLinks
				vertex._outboundLinks = swap

			for vertex in self._verticesWithID.values():
				swap = vertex._inboundLinks
				vertex._inboundLinks = vertex._outboundLinks
				vertex._outboundLinks = swap
		else:
			for link in self._linksWithoutID:
				if predicate(link):
					link.Reverse()

			for link in self._linksWithID.values():
				if predicate(link):
					link.Reverse()

	def RemoveEdges(self, predicate: Nullable[Callable[[Edge], bool]] = None) -> None:
		"""
		Remove all or selected edges of a graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip edges.

		:param predicate: Filter function accepting any edge and returning a boolean.
		"""
		if predicate is None:
			for edge in self._edgesWithoutID:
				edge._Delete()

			for edge in self._edgesWithID.values():
				edge._Delete()

			self._edgesWithoutID = []
			self._edgesWithID = {}

			for vertex in self._verticesWithoutID:
				vertex._inboundEdges = []
				vertex._outboundEdges = []

			for vertex in self._verticesWithID.values():
				vertex._inboundEdges = []
				vertex._outboundEdges = []

		else:
			delEdges = [edge for edge in self._edgesWithID.values() if predicate(edge)]
			for edge in delEdges:
				del self._edgesWithID[edge._id]

				edge._source._outboundEdges.remove(edge)
				edge._destination._inboundEdges.remove(edge)
				edge._Delete()

			for edge in self._edgesWithoutID:
				if predicate(edge):
					self._edgesWithoutID.remove(edge)

					edge._source._outboundEdges.remove(edge)
					edge._destination._inboundEdges.remove(edge)
					edge._Delete()

	def RemoveLinks(self, predicate: Nullable[Callable[[Link], bool]] = None) -> None:
		"""
		Remove all or selected links of a graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip links.

		:param predicate: Filter function accepting any link and returning a boolean.
		"""
		if predicate is None:
			for link in self._linksWithoutID:
				link._Delete()

			for link in self._linksWithID.values():
				link._Delete()

			self._linksWithoutID = []
			self._linksWithID = {}

			for vertex in self._verticesWithoutID:
				vertex._inboundLinks = []
				vertex._outboundLinks = []

			for vertex in self._verticesWithID.values():
				vertex._inboundLinks = []
				vertex._outboundLinks = []

		else:
			delLinks = [link for link in self._linksWithID.values() if predicate(link)]
			for link in delLinks:
				del self._linksWithID[link._id]

				link._source._outboundLinks.remove(link)
				link._destination._inboundLinks.remove(link)
				link._Delete()

			for link in self._linksWithoutID:
				if predicate(link):
					self._linksWithoutID.remove(link)

					link._source._outboundLinks.remove(link)
					link._destination._inboundLinks.remove(link)
					link._Delete()

	def HasCycle(self) -> bool:
		"""
		.. todo:: GRAPH::BaseGraph::HasCycle Needs documentation.

		"""
		# IsAcyclic ?

		# Handle trivial case if graph is empty
		if len(self._verticesWithID) + len(self._verticesWithoutID) == 0:
			return False

		outboundEdgeCounts = {}
		leafVertices = []

		for vertex in self._verticesWithoutID:
			if (count := len(vertex._outboundEdges)) == 0:
				leafVertices.append(vertex)
			else:
				outboundEdgeCounts[vertex] = count

		for vertex in self._verticesWithID.values():
			if (count := len(vertex._outboundEdges)) == 0:
				leafVertices.append(vertex)
			else:
				outboundEdgeCounts[vertex] = count

		# If there are no leafs, then each vertex has at least one inbound and one outbound edges. Thus, there is a cycle.
		if not leafVertices:
			return True

		overallCount = len(outboundEdgeCounts) + len(leafVertices)

		for vertex in leafVertices:
			overallCount -= 1
			for inboundEdge in vertex._inboundEdges:
				sourceVertex = inboundEdge.Source
				count = outboundEdgeCounts[sourceVertex] - 1
				outboundEdgeCounts[sourceVertex] = count
				if count == 0:
					leafVertices.append(sourceVertex)

		# If all vertices were processed, no cycle exists.
		if overallCount == 0:
			return False
		# If there are remaining vertices, then a cycle exists.
		elif overallCount > 0:
			return True

		raise InternalError(f"Graph data structure is corrupted.")  # pragma: no cover


@export
class Subgraph(
	BaseGraph[
		SubgraphDictKeyType, SubgraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	],
	Generic[
		SubgraphDictKeyType, SubgraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	]
):
	"""
	.. todo:: GRAPH::Subgraph Needs documentation.

	"""

	_graph:    'Graph'

	def __init__(
		self,
		graph: 'Graph',
		name: Nullable[str] = None,
		# vertices: Nullable[Iterable[Vertex]] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::Subgraph::init Needs documentation.

		:param graph:         The reference to the graph.
		:param name:          The optional name of the new sub-graph.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		if graph is None:
			raise ValueError("Parameter 'graph' is None.")
		if not isinstance(graph, Graph):
			ex = TypeError("Parameter 'graph' is not of type 'Graph'.")
			ex.add_note(f"Got type '{getFullyQualifiedName(graph)}'.")
			raise ex

		super().__init__(name, keyValuePairs)

		graph._subgraphs.add(self)

		self._graph = graph

	def __del__(self) -> None:
		"""
		.. todo:: GRAPH::Subgraph::del Needs documentation.

		"""
		super().__del__()

	@readonly
	def Graph(self) -> 'Graph':
		"""
		Read-only property to access the graph, this subgraph is associated to (:attr:`_graph`).

		:returns: The graph this subgraph is associated to.
		"""
		return self._graph

	def __str__(self) -> str:
		"""
		.. todo:: GRAPH::Subgraph::str Needs documentation.

		"""
		return self._name if self._name is not None else "Unnamed subgraph"


@export
class View(
	BaseWithVertices[
		ViewDictKeyType, ViewDictValueType,
		GraphDictKeyType, GraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	],
	Generic[
		ViewDictKeyType, ViewDictValueType,
		GraphDictKeyType, GraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	]
):
	"""
	.. todo:: GRAPH::View Needs documentation.

	"""

	def __init__(
		self,
		graph: 'Graph',
		name: Nullable[str] = None,
		vertices: Nullable[Iterable[Vertex]] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::View::init Needs documentation.

		:param graph:         The reference to the graph.
		:param name:          The optional name of the new view.
		:param vertices:      The optional list of vertices in the new view.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		super().__init__(graph, name, vertices, keyValuePairs)

		graph._views.add(self)

	def __del__(self) -> None:
		"""
		.. todo:: GRAPH::View::del Needs documentation.

		"""
		super().__del__()

	def __str__(self) -> str:
		"""
		.. todo:: GRAPH::View::str Needs documentation.

		"""
		return self._name if self._name is not None else "Unnamed view"


@export
class Component(
	BaseWithVertices[
		ComponentDictKeyType, ComponentDictValueType,
		GraphDictKeyType, GraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	],
	Generic[
		ComponentDictKeyType, ComponentDictValueType,
		GraphDictKeyType, GraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	]
):
	"""
	.. todo:: GRAPH::Component Needs documentation.

	"""

	def __init__(
		self,
		graph: 'Graph',
		name: Nullable[str] = None,
		vertices: Nullable[Iterable[Vertex]] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::Component::init Needs documentation.

		:param graph:         The reference to the graph.
		:param name:          The optional name of the new component.
		:param vertices:      The optional list of vertices in the new component.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.
		"""
		super().__init__(graph, name, vertices, keyValuePairs)

		graph._components.add(self)

	def __del__(self) -> None:
		"""
		.. todo:: GRAPH::Component::del Needs documentation.

		"""
		super().__del__()

	def __str__(self) -> str:
		"""
		.. todo:: GRAPH::Component::str Needs documentation.

		"""
		return self._name if self._name is not None else "Unnamed component"


@export
class Graph(
	BaseGraph[
		GraphDictKeyType, GraphDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	],
	Generic[
		GraphDictKeyType, GraphDictValueType,
		ComponentDictKeyType, ComponentDictValueType,
		SubgraphDictKeyType, SubgraphDictValueType,
		ViewDictKeyType, ViewDictValueType,
		VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType,
		EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType,
		LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType
	]
):
	"""
	A **graph** data structure is represented by an instance of :class:`~pyTooling.Graph.Graph` holding references to
	all nodes. Nodes are instances of :class:`~pyTooling.Graph.Vertex` classes and directed links between nodes are
	made of :class:`~pyTooling.Graph.Edge` instances. A graph can have attached meta information as key-value-pairs.
	"""
	_subgraphs:         Set[Subgraph[SubgraphDictKeyType, SubgraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType]]
	_views:             Set[View[ViewDictKeyType, ViewDictValueType, GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType]]
	_components:        Set[Component[ComponentDictKeyType, ComponentDictValueType, GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType]]

	def __init__(
		self,
		name: Nullable[str] = None,
		keyValuePairs: Nullable[Mapping[DictKeyType, DictValueType]] = None
	) -> None:
		"""
		.. todo:: GRAPH::Graph::init Needs documentation.

		:param name:          The optional name of the new graph.
		:param keyValuePairs: The optional mapping (dictionary) of key-value-pairs.#
		"""
		super().__init__(name, keyValuePairs)

		self._subgraphs = set()
		self._views = set()
		self._components = set()

	def __del__(self) -> None:
		"""
		.. todo:: GRAPH::Graph::del Needs documentation.

		"""
		try:
			del self._subgraphs
			del self._views
			del self._components
		except AttributeError:
			pass

		super().__del__()

	@readonly
	def Subgraphs(self) -> Set[Subgraph]:
		"""Read-only property to access the subgraphs in this graph (:attr:`_subgraphs`).

		:returns: The set of subgraphs in this graph."""
		return self._subgraphs

	@readonly
	def Views(self) -> Set[View]:
		"""Read-only property to access the views in this graph (:attr:`_views`).

		:returns: The set of views in this graph."""
		return self._views

	@readonly
	def Components(self) -> Set[Component]:
		"""Read-only property to access the components in this graph (:attr:`_components`).

		:returns: The set of components in this graph."""
		return self._components

	@readonly
	def SubgraphCount(self) -> int:
		"""Read-only property to access the number of subgraphs in this graph.

		:returns: The number of subgraphs in this graph."""
		return len(self._subgraphs)

	@readonly
	def ViewCount(self) -> int:
		"""Read-only property to access the number of views in this graph.

		:returns: The number of views in this graph."""
		return len(self._views)

	@readonly
	def ComponentCount(self) -> int:
		"""Read-only property to access the number of components in this graph.

		:returns: The number of components in this graph."""
		return len(self._components)

	def __iter__(self) -> typing_Iterator[Vertex[GraphDictKeyType, GraphDictValueType, VertexIDType, VertexWeightType, VertexValueType, VertexDictKeyType, VertexDictValueType, EdgeIDType, EdgeWeightType, EdgeValueType, EdgeDictKeyType, EdgeDictValueType, LinkIDType, LinkWeightType, LinkValueType, LinkDictKeyType, LinkDictValueType]]:
		"""
		.. todo:: GRAPH::Graph::iter Needs documentation.

		"""
		def gen():
			yield from self._verticesWithoutID
			yield from self._verticesWithID
		return iter(gen())

	def HasVertexByID(self, vertexID: Nullable[VertexIDType]) -> bool:
		"""
		.. todo:: GRAPH::Graph::HasVertexByID Needs documentation.

		"""
		if vertexID is None:
			return len(self._verticesWithoutID) >= 1
		else:
			return vertexID in self._verticesWithID

	def HasVertexByValue(self, value: Nullable[VertexValueType]) -> bool:
		"""
		.. todo:: GRAPH::Graph::HasVertexByValue Needs documentation.

		"""
		return any(vertex._value == value for vertex in chain(self._verticesWithoutID, self._verticesWithID.values()))

	def GetVertexByID(self, vertexID: Nullable[VertexIDType]) -> Vertex:
		"""
		.. todo:: GRAPH::Graph::GetVertexByID Needs documentation.

		"""
		if vertexID is None:
			if (l := len(self._verticesWithoutID)) == 1:
				return self._verticesWithoutID[0]
			elif l == 0:
				raise KeyError(f"Found no vertex with ID `None`.")
			else:
				raise KeyError(f"Found multiple vertices with ID `None`.")
		else:
			return self._verticesWithID[vertexID]

	def GetVertexByValue(self, value: Nullable[VertexValueType]) -> Vertex:
		"""
		.. todo:: GRAPH::Graph::GetVertexByValue Needs documentation.

		"""
		# FIXME: optimize: iterate only until first item is found and check for a second to produce error
		vertices = [vertex for vertex in chain(self._verticesWithoutID, self._verticesWithID.values()) if vertex._value == value]
		if (l := len(vertices)) == 1:
			return vertices[0]
		elif l == 0:
			raise KeyError(f"Found no vertex with Value == `{value}`.")
		else:
			raise KeyError(f"Found multiple vertices with Value == `{value}`.")

	def CopyGraph(self) -> 'Graph':
		raise NotImplementedError()

	def CopyVertices(self, predicate: Nullable[Callable[[Vertex], bool]] = None, copyGraphDict: bool = True, copyVertexDict: bool = True) -> 'Graph':
		"""
		Create a new graph and copy all or selected vertices of the original graph.

		If parameter ``predicate`` is not None, the given filter function is used to skip vertices.

		:param predicate:      Filter function accepting any vertex and returning a boolean.
		:param copyGraphDict:  If ``True``, copy all graph attached attributes into the new graph.
		:param copyVertexDict: If ``True``, copy all vertex attached attributes into the new vertices.
		"""
		graph = Graph(self._name)
		if copyGraphDict:
			graph._dict = self._dict.copy()

		if predicate is None:
			for vertex in self._verticesWithoutID:
				v = Vertex(None, vertex._value, graph=graph)
				if copyVertexDict:
					v._dict = vertex._dict.copy()

			for vertexID, vertex in self._verticesWithID.items():
				v = Vertex(vertexID, vertex._value, graph=graph)
				if copyVertexDict:
					v._dict = vertex._dict.copy()
		else:
			for vertex in self._verticesWithoutID:
				if predicate(vertex):
					v = Vertex(None, vertex._value, graph=graph)
					if copyVertexDict:
						v._dict = vertex._dict.copy()

			for vertexID, vertex in self._verticesWithID.items():
				if predicate(vertex):
					v = Vertex(vertexID, vertex._value, graph=graph)
					if copyVertexDict:
						v._dict = vertex._dict.copy()

		return graph

		# class Iterator():
		# 	visited = [False for _ in range(self.__len__())]

	# def CheckForNegativeCycles(self):
	# 	raise NotImplementedError()
	# 	# Bellman-Ford
	# 	# Floyd-Warshall
	#
	# def IsStronglyConnected(self):
	# 	raise NotImplementedError()
	#
	# def GetStronglyConnectedComponents(self):
	# 	raise NotImplementedError()
	# 	# Tarjan's and Kosaraju's algorithm
	#
	# def TravelingSalesmanProblem(self):
	# 	raise NotImplementedError()
	# 	# Held-Karp
	# 	# branch and bound
	#
	# def GetBridges(self):
	# 	raise NotImplementedError()
	#
	# def GetArticulationPoints(self):
	# 	raise NotImplementedError()
	#
	# def MinimumSpanningTree(self):
	# 	raise NotImplementedError()
	# 	# Kruskal
	# 	# Prim's algorithm
	# 	# Buruvka's algorithm

	def __repr__(self) -> str:
		"""
		.. todo:: GRAPH::Graph::repr Needs documentation.

		"""
		statistics = f", vertices: {self.VertexCount}, edges: {self.EdgeCount}"
		if self._name is None:
			return f"<graph: unnamed graph{statistics}>"
		else:
			return f"<graph: '{self._name}'{statistics}>"

	def __str__(self) -> str:
		"""
		.. todo:: GRAPH::Graph::str Needs documentation.

		"""
		if self._name is None:
			return f"Graph: unnamed graph"
		else:
			return f"Graph: '{self._name}'"
