signal_flow_graph.py

        # Traverse output ports for precedence
        curr_iter_ports = first_iter_ports
        precedence_list = []

        while curr_iter_ports:
            # Add the found ports to the current iter
            precedence_list.append(curr_iter_ports)

            next_iter_ports = []

            for outport in curr_iter_ports:
                for signal in outport.signals:
                    new_inport = signal.destination
                    # Do not traverse over delays.
                    if new_inport is not None and not isinstance(
                        new_inport.operation, Delay
                    ):
                        new_op = new_inport.operation
                        remaining_inports_per_operation[new_op] -= 1
                        if remaining_inports_per_operation[new_op] == 0:
                            next_iter_ports.extend(new_op.outputs)

            curr_iter_ports = next_iter_ports

        return precedence_list

    def _add_component_unconnected_copy(
        self, original_component: GraphComponent
    ) -> GraphComponent:
        if original_component in self._original_components_to_new:
            raise ValueError("Tried to add duplicate SFG component")
        new_component = original_component.copy()
        self._original_components_to_new[original_component] = new_component
        if not new_component.graph_id or new_component.graph_id in self._used_ids:
            new_id = self._graph_id_generator.next_id(
                new_component.type_name(), self._used_ids
            )
            new_component.graph_id = new_id
        self._used_ids.add(new_component.graph_id)
        self._components_by_id[new_component.graph_id] = new_component
        self._components_by_name[new_component.name].append(new_component)
        return new_component

    def _add_operation_connected_tree_copy(self, start_op: Operation) -> None:
        op_stack = deque([start_op])
        while op_stack:
            original_op = op_stack.pop()
            # Add or get the new copy of the operation.
            if original_op not in self._original_components_to_new:
                new_op = cast(
                    Operation,
                    self._add_component_unconnected_copy(original_op),
                )
                self._components_dfs_order.append(new_op)
                self._operations_dfs_order.append(new_op)
            else:
                new_op = cast(Operation, self._original_components_to_new[original_op])

            # Connect input ports to new signals.
            for original_input_port in original_op.inputs:
                if original_input_port.signal_count < 1:
                    raise ValueError("Unconnected input port in SFG")

                for original_signal in original_input_port.signals:
                    # Check if the signal is one of the SFG's input signals.
                    if original_signal in self._original_input_signals_to_indices:
                        # New signal already created during first step of constructor.
                        new_signal = cast(
                            Signal,
                            self._original_components_to_new[original_signal],
                        )

                        new_signal.set_destination(
                            new_op.input(original_input_port.index)
                        )

                        source = cast(OutputPort, new_signal.source)
                        self._components_dfs_order.extend(
                            [new_signal, source.operation]
                        )
                        if source.operation not in self._operations_dfs_order:
                            self._operations_dfs_order.append(source.operation)

                    # Check if the signal has not been added before.
                    elif original_signal not in self._original_components_to_new:
                        if original_signal.source is None:
                            dest = (
                                original_signal.destination.operation.name
                                if original_signal.destination is not None
                                else "None"
                            )
                            raise ValueError(
                                "Dangling signal without source in SFG"
                                f" (destination: {dest})"
                            )

                        new_signal = cast(
                            Signal,
                            self._add_component_unconnected_copy(original_signal),
                        )

                        new_signal.set_destination(
                            new_op.input(original_input_port.index)
                        )

                        self._components_dfs_order.append(new_signal)

                        original_connected_op = original_signal.source.operation
                        # Check if connected Operation has been added before.
                        if original_connected_op in self._original_components_to_new:
                            component = cast(
                                Operation,
                                self._original_components_to_new[original_connected_op],
                            )
                            # Set source to the already added operations port.
                            new_signal.set_source(
                                component.output(original_signal.source.index)
                            )
                        else:
                            # Create new operation, set signal source to it.
                            new_connected_op = cast(
                                Operation,
                                self._add_component_unconnected_copy(
                                    original_connected_op
                                ),
                            )
                            new_signal.set_source(
                                new_connected_op.output(original_signal.source.index)
                            )

                            self._components_dfs_order.append(new_connected_op)
                            self._operations_dfs_order.append(new_connected_op)

                            # Add connected operation to queue of operations to visit.
                            op_stack.append(original_connected_op)

            # Connect output ports.
            for original_output_port in original_op.outputs:
                for original_signal in original_output_port.signals:
                    # Check if the signal is one of the SFG's output signals.
                    if original_signal in self._original_output_signals_to_indices:
                        # New signal already created during first step of constructor.
                        new_signal = cast(
                            Signal,
                            self._original_components_to_new[original_signal],
                        )

                        new_signal.set_source(new_op.output(original_output_port.index))

                        destination = cast(InputPort, new_signal.destination)
                        self._components_dfs_order.extend(
                            [new_signal, destination.operation]
                        )
                        self._operations_dfs_order.append(destination.operation)

                    # Check if signal has not been added before.
                    elif original_signal not in self._original_components_to_new:
                        if original_signal.source is None:
                            raise ValueError(
                                "Dangling signal ({original_signal}) without"
                                " source in SFG"
                            )

                        new_signal = cast(
                            Signal,
                            self._add_component_unconnected_copy(original_signal),
                        )
                        new_signal.set_source(new_op.output(original_output_port.index))

                        self._components_dfs_order.append(new_signal)
                        original_destination = cast(
                            InputPort, original_signal.destination
                        )
                        if original_destination is None:
                            raise ValueError(
                                f"Signal ({original_signal}) without destination in SFG"
                            )

                        original_connected_op = original_destination.operation
                        if original_connected_op is None:
                            raise ValueError(
                                "Signal with empty destination port"
                                f" ({original_destination}) in SFG"
                            )
                        # Check if connected operation has been added.
                        if original_connected_op in self._original_components_to_new:
                            # Set destination to the already connected operations port.
                            new_signal.set_destination(
                                cast(
                                    Operation,
                                    self._original_components_to_new[
                                        original_connected_op
                                    ],
                                ).input(original_destination.index)
                            )
                        else:
                            # Create new operation, set destination to it.
                            new_connected_op = cast(
                                Operation,
                                (
                                    self._add_component_unconnected_copy(
                                        original_connected_op
                                    )
                                ),
                            )
                            new_signal.set_destination(
                                new_connected_op.input(original_destination.index)
                            )

                            self._components_dfs_order.append(new_connected_op)
                            self._operations_dfs_order.append(new_connected_op)

                            # Add connected operation to the queue of operations
                            # to visit.
                            op_stack.append(original_connected_op)

    def _evaluate_source(
        self,
        src: OutputPort,
        results: MutableResultMap,
        delays: MutableDelayMap,
        prefix: str,
        bits_override: Optional[int],
        quantize: bool,
        deferred_delays: DelayQueue,
    ) -> Num:
        key_base = (
            (prefix + "." + src.operation.graph_id)
            if prefix
            else src.operation.graph_id
        )
        key = src.operation.key(src.index, key_base)
        if key in results:
            value = results[key]
            if value is None:
                raise RuntimeError(
                    "Direct feedback loop detected when evaluating operation."
                )
            return value

        value = src.operation.current_output(src.index, delays, key_base)
        results[key] = value
        if value is None:
            value = self._do_evaluate_source(
                key_base,
                key,
                src,
                results,
                delays,
                prefix,
                bits_override,
                quantize,
                deferred_delays,
            )
        else:
            # Evaluate later. Use current value for now.
            deferred_delays.append((key_base, key, src))
        return value

    def _do_evaluate_source(
        self,
        key_base: str,
        key: ResultKey,
        src: OutputPort,
        results: MutableResultMap,
        delays: MutableDelayMap,
        prefix: str,
        bits_override: Optional[int],
        quantize: bool,
        deferred_delays: DelayQueue,
    ) -> Num:
        input_values = [
            self._evaluate_source(
                input_port.signals[0].source,
                results,
                delays,
                prefix,
                bits_override,
                quantize,
                deferred_delays,
            )
            for input_port in src.operation.inputs
        ]
        value = src.operation.evaluate_output(
            src.index,
            input_values,
            results,
            delays,
            key_base,
            bits_override,
            quantize,
        )
        results[key] = value
        return value

    def sfg_digraph(self, show_id=False, engine=None) -> Digraph:
        """
        Returns a Digraph of the SFG. Can be directly displayed in IPython.

        Parameters
        ----------
        show_id : Boolean, optional
            If True, the graph_id:s of signals are shown. The default is False.
        engine : string, optional
            Graphviz layout engine to be used, see https://graphviz.org/documentation/.
            Most common are "dot" and "neato". Default is None leading to dot.

        Returns
        -------
        Digraph
            Digraph of the SFG.

        """
        dg = Digraph()
        dg.attr(rankdir="LR")
        if engine is not None:
            dg.engine = engine
        for op in self._components_by_id.values():
            if isinstance(op, Signal):
                source = cast(OutputPort, op.source)
                destination = cast(InputPort, op.destination)
                if show_id:
                    dg.edge(
                        source.operation.graph_id,
                        destination.operation.graph_id,
                        label=op.graph_id,
                    )
                else:
                    dg.edge(
                        source.operation.graph_id,
                        destination.operation.graph_id,
                    )
            else:
                dg.node(op.graph_id, shape=_OPERATION_SHAPE[op.type_name()])
        return dg

    def _repr_mimebundle_(self, include=None, exclude=None):
        return self.sfg_digraph()._repr_mimebundle_(include=include, exclude=exclude)

    def _repr_jpeg_(self):
        return self.sfg_digraph()._repr_mimebundle_(include=["image/jpeg"])[
            "image/jpeg"
        ]

    def _repr_png_(self):
        return self.sfg_digraph()._repr_mimebundle_(include=["image/png"])["image/png"]

    def show(self, fmt=None, show_id=False, engine=None) -> None:
        """
        Shows a visual representation of the SFG using the default system viewer.

        Parameters
        ----------
        fmt : string, optional
            File format of the generated graph. Output formats can be found at
            https://www.graphviz.org/doc/info/output.html
            Most common are "pdf", "eps", "png", and "svg". Default is None which
            leads to PDF.
        show_id : Boolean, optional
            If True, the graph_id:s of signals are shown. The default is False.
        engine : string, optional
            Graphviz layout engine to be used, see https://graphviz.org/documentation/.
            Most common are "dot" and "neato". Default is None leading to dot.
        """

        dg = self.sfg_digraph(show_id=show_id)
        if engine is not None:
            dg.engine = engine
        if fmt is not None:
            dg.format = fmt
        dg.view()

    def critical_path_time(self) -> int:
        """Return the time of the critical path."""
        # Import here needed to avoid circular imports
        from b_asic.schedule import Schedule

        return Schedule(self, scheduling_algorithm="ASAP").schedule_time

    def edit(self) -> None:
        """Edit SFG in GUI."""
        from b_asic.GUI.main_window import start_editor

        start_editor(self)

    def unfold(self, factor: int) -> "SFG":
        """
        Unfold the SFG *factor* times. Return a new SFG without modifying the original.

        Inputs and outputs are ordered with early inputs first. That is for an SFG
        with n inputs, the first n inputs are the inputs at time t, the next n
        inputs are the inputs at time t+1, the next n at t+2 and so on.

        Parameters
        ----------
        factor : string, optional
            Number of times to unfold
        """

        if factor == 0:
            raise ValueError("Unfolding 0 times removes the SFG")

        # Make `factor` copies of the sfg
        new_ops = [
            [cast(Operation, op.copy()) for op in self.operations]
            for _ in range(factor)
        ]

        id_idx_map = {op.graph_id: idx for (idx, op) in enumerate(self.operations)}

        # The rest of the process is easier if we clear the connections of the inputs
        # and outputs of all operations
        for layer, op_list in enumerate(new_ops):
            for op_idx, op in enumerate(op_list):
                for input_ in op.inputs:
                    input_.clear()
                for output in op.outputs:
                    output.clear()

                suffix = layer

                new_ops[layer][op_idx].name = f"{new_ops[layer][op_idx].name}_{suffix}"
                # NOTE: Since these IDs are what show up when printing the graph, it
                # is helpful to set them. However, this can cause name collisions when
                # names in a graph are already suffixed with _n
                new_ops[layer][op_idx].graph_id = GraphID(
                    f"{new_ops[layer][op_idx].graph_id}_{suffix}"
                )

        # Walk through the operations, replacing delay nodes with connections
        for layer in range(factor):
            for op_idx, op in enumerate(self.operations):
                if isinstance(op, Delay):
                    # Port of the operation feeding into this delay
                    source_port = op.inputs[0].connected_source
                    if source_port is None:
                        raise ValueError("Dangling delay input port in sfg")

                    source_op_idx = id_idx_map[source_port.operation.graph_id]
                    source_op_output_index = source_port.index
                    new_source_op = new_ops[layer][source_op_idx]
                    source_op_output = new_source_op.outputs[source_op_output_index]

                    # If this is the last layer, we need to create a new delay element and connect it instead
                    # of the copied port
                    if layer == factor - 1:
                        delay = Delay(name=op.name)
                        delay.graph_id = op.graph_id

                        # Since we're adding a new operation instead of bypassing as in the
                        # common case, we also need to hook up the inputs to the delay.
                        delay.inputs[0].connect(source_op_output)

                        new_source_op = delay
                        new_source_port = new_source_op.outputs[0]
                    else:
                        # The new output port we should connect to
                        new_source_port = source_op_output

                    for out_signal in op.outputs[0].signals:
                        sink_port = out_signal.destination
                        if sink_port is None:
                            # It would be weird if we found a signal that wasn't connected anywhere
                            raise ValueError("Dangling output port in sfg")

                        sink_op_idx = id_idx_map[sink_port.operation.graph_id]
                        sink_op_output_index = sink_port.index

                        target_layer = 0 if layer == factor - 1 else layer + 1

                        new_dest_op = new_ops[target_layer][sink_op_idx]
                        new_destination = new_dest_op.inputs[sink_op_output_index]
                        new_destination.connect(new_source_port)
                else:
                    # Other opreations need to be re-targeted to the corresponding output in the
                    # current layer, as long as that output is not a delay, as that has been solved
                    # above.
                    # To avoid double connections, we'll only re-connect inputs
                    for input_num, original_input in enumerate(op.inputs):
                        original_source = original_input.connected_source
                        # We may not always have something connected to the input, if we don't
                        # we can abort
                        if original_source is None:
                            continue

                        # delay connections are handled elsewhere
                        if not isinstance(original_source.operation, Delay):
                            source_op_idx = id_idx_map[
                                original_source.operation.graph_id
                            ]
                            source_op_output_idx = original_source.index

                            target_output = new_ops[layer][source_op_idx].outputs[
                                source_op_output_idx
                            ]

                            new_ops[layer][op_idx].inputs[input_num].connect(
                                target_output
                            )

        all_ops = [op for op_list in new_ops for op in op_list]

        # To get the input order correct, we need to know the input order in the original
        # sfg and which operations they correspond to
        input_ids = [op.graph_id for op in self.input_operations]
        output_ids = [op.graph_id for op in self.output_operations]

        # Re-order the inputs to the correct order. Internal order of the inputs should
        # be preserved, i.e. for a graph with 2 inputs (in1, in2), in1 must occur before in2,
        # but the "time" order should be reversed. I.e. the input from layer `factor-1` is the
        # first input
        all_inputs = list(
            itertools.chain.from_iterable(
                [
                    [ops[id_idx_map[input_id]] for input_id in input_ids]
                    for ops in new_ops
                ]
            )
        )

        # Outputs are not reversed, but need the same treatment
        all_outputs = list(
            itertools.chain.from_iterable(
                [
                    [ops[id_idx_map[output_id]] for output_id in output_ids]
                    for ops in new_ops
                ]
            )
        )

        # Sanity check to ensure that no duplicate graph IDs have been created
        ids = [op.graph_id for op in all_ops]
        assert len(ids) == len(set(ids))

        return SFG(inputs=all_inputs, outputs=all_outputs)

    @property
    def is_linear(self) -> bool:
        return all(op.is_linear for op in self.split())

    @property
    def is_constant(self) -> bool:
        return all(output.is_constant for output in self._output_operations)