1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
use crate::{
    render_graph::{
        Edge, Node, NodeRunError, NodeState, RenderGraphContext, RenderGraphError, RenderLabel,
        SlotInfo, SlotLabel,
    },
    renderer::RenderContext,
};
use bevy_ecs::{define_label, intern::Interned, prelude::World, system::Resource};
use bevy_utils::HashMap;
use std::fmt::Debug;

use super::{EdgeExistence, InternedRenderLabel, IntoRenderNodeArray};

pub use bevy_render_macros::RenderSubGraph;

define_label!(
    /// A strongly-typed class of labels used to identify a [`SubGraph`] in a render graph.
    RenderSubGraph,
    RENDER_SUB_GRAPH_INTERNER
);

/// A shorthand for `Interned<dyn RenderSubGraph>`.
pub type InternedRenderSubGraph = Interned<dyn RenderSubGraph>;

/// The render graph configures the modular and re-usable render logic.
/// It is a retained and stateless (nodes themselves may have their own internal state) structure,
/// which can not be modified while it is executed by the graph runner.
///
/// The [`RenderGraphRunner`](crate::renderer::graph_runner::RenderGraphRunner) is responsible for executing the entire graph each frame.
/// It will execute each node in the graph in the correct order, based on the edges between the nodes.
///
/// It consists of three main components: [`Nodes`](Node), [`Edges`](Edge)
/// and [`Slots`](super::SlotType).
///
/// Nodes are responsible for generating draw calls and operating on input and output slots.
/// Edges specify the order of execution for nodes and connect input and output slots together.
/// Slots describe the render resources created or used by the nodes.
///
/// Additionally a render graph can contain multiple sub graphs, which are run by the
/// corresponding nodes. Every render graph can have its own optional input node.
///
/// ## Example
/// Here is a simple render graph example with two nodes connected by a node edge.
/// ```ignore
/// # TODO: Remove when #10645 is fixed
/// # use bevy_app::prelude::*;
/// # use bevy_ecs::prelude::World;
/// # use bevy_render::render_graph::{RenderGraph, RenderLabel, Node, RenderGraphContext, NodeRunError};
/// # use bevy_render::renderer::RenderContext;
/// #
/// #[derive(RenderLabel)]
/// enum Labels {
///     A,
///     B,
/// }
///
/// # struct MyNode;
/// #
/// # impl Node for MyNode {
/// #     fn run(&self, graph: &mut RenderGraphContext, render_context: &mut RenderContext, world: &World) -> Result<(), NodeRunError> {
/// #         unimplemented!()
/// #     }
/// # }
/// #
/// let mut graph = RenderGraph::default();
/// graph.add_node(Labels::A, MyNode);
/// graph.add_node(Labels::B, MyNode);
/// graph.add_node_edge(Labels::B, Labels::A);
/// ```
#[derive(Resource, Default)]
pub struct RenderGraph {
    nodes: HashMap<InternedRenderLabel, NodeState>,
    sub_graphs: HashMap<InternedRenderSubGraph, RenderGraph>,
}

/// The label for the input node of a graph. Used to connect other nodes to it.
#[derive(Debug, Hash, PartialEq, Eq, Clone, RenderLabel)]
pub struct GraphInput;

impl RenderGraph {
    /// Updates all nodes and sub graphs of the render graph. Should be called before executing it.
    pub fn update(&mut self, world: &mut World) {
        for node in self.nodes.values_mut() {
            node.node.update(world);
        }

        for sub_graph in self.sub_graphs.values_mut() {
            sub_graph.update(world);
        }
    }

    /// Creates an [`GraphInputNode`] with the specified slots if not already present.
    pub fn set_input(&mut self, inputs: Vec<SlotInfo>) {
        assert!(
            matches!(
                self.get_node_state(GraphInput),
                Err(RenderGraphError::InvalidNode(_))
            ),
            "Graph already has an input node"
        );

        self.add_node(GraphInput, GraphInputNode { inputs });
    }

    /// Returns the [`NodeState`] of the input node of this graph.
    ///
    /// # See also
    ///
    /// - [`input_node`](Self::input_node) for an unchecked version.
    #[inline]
    pub fn get_input_node(&self) -> Option<&NodeState> {
        self.get_node_state(GraphInput).ok()
    }

    /// Returns the [`NodeState`] of the input node of this graph.
    ///
    /// # Panics
    ///
    /// Panics if there is no input node set.
    ///
    /// # See also
    ///
    /// - [`get_input_node`](Self::get_input_node) for a version which returns an [`Option`] instead.
    #[inline]
    pub fn input_node(&self) -> &NodeState {
        self.get_input_node().unwrap()
    }

    /// Adds the `node` with the `label` to the graph.
    /// If the label is already present replaces it instead.
    pub fn add_node<T>(&mut self, label: impl RenderLabel, node: T)
    where
        T: Node,
    {
        let label = label.intern();
        let node_state = NodeState::new(label, node);
        self.nodes.insert(label, node_state);
    }

    /// Add `node_edge`s based on the order of the given `edges` array.
    ///
    /// Defining an edge that already exists is not considered an error with this api.
    /// It simply won't create a new edge.
    pub fn add_node_edges<const N: usize>(&mut self, edges: impl IntoRenderNodeArray<N>) {
        for window in edges.into_array().windows(2) {
            let [a, b] = window else {
                break;
            };
            if let Err(err) = self.try_add_node_edge(*a, *b) {
                match err {
                    // Already existing edges are very easy to produce with this api
                    // and shouldn't cause a panic
                    RenderGraphError::EdgeAlreadyExists(_) => {}
                    _ => panic!("{err:?}"),
                }
            }
        }
    }

    /// Removes the `node` with the `label` from the graph.
    /// If the label does not exist, nothing happens.
    pub fn remove_node(&mut self, label: impl RenderLabel) -> Result<(), RenderGraphError> {
        let label = label.intern();
        if let Some(node_state) = self.nodes.remove(&label) {
            // Remove all edges from other nodes to this one. Note that as we're removing this
            // node, we don't need to remove its input edges
            for input_edge in node_state.edges.input_edges() {
                match input_edge {
                    Edge::SlotEdge { output_node, .. }
                    | Edge::NodeEdge {
                        input_node: _,
                        output_node,
                    } => {
                        if let Ok(output_node) = self.get_node_state_mut(*output_node) {
                            output_node.edges.remove_output_edge(input_edge.clone())?;
                        }
                    }
                }
            }
            // Remove all edges from this node to other nodes. Note that as we're removing this
            // node, we don't need to remove its output edges
            for output_edge in node_state.edges.output_edges() {
                match output_edge {
                    Edge::SlotEdge {
                        output_node: _,
                        output_index: _,
                        input_node,
                        input_index: _,
                    }
                    | Edge::NodeEdge {
                        output_node: _,
                        input_node,
                    } => {
                        if let Ok(input_node) = self.get_node_state_mut(*input_node) {
                            input_node.edges.remove_input_edge(output_edge.clone())?;
                        }
                    }
                }
            }
        }

        Ok(())
    }

    /// Retrieves the [`NodeState`] referenced by the `label`.
    pub fn get_node_state(&self, label: impl RenderLabel) -> Result<&NodeState, RenderGraphError> {
        let label = label.intern();
        self.nodes
            .get(&label)
            .ok_or(RenderGraphError::InvalidNode(label))
    }

    /// Retrieves the [`NodeState`] referenced by the `label` mutably.
    pub fn get_node_state_mut(
        &mut self,
        label: impl RenderLabel,
    ) -> Result<&mut NodeState, RenderGraphError> {
        let label = label.intern();
        self.nodes
            .get_mut(&label)
            .ok_or(RenderGraphError::InvalidNode(label))
    }

    /// Retrieves the [`Node`] referenced by the `label`.
    pub fn get_node<T>(&self, label: impl RenderLabel) -> Result<&T, RenderGraphError>
    where
        T: Node,
    {
        self.get_node_state(label).and_then(|n| n.node())
    }

    /// Retrieves the [`Node`] referenced by the `label` mutably.
    pub fn get_node_mut<T>(&mut self, label: impl RenderLabel) -> Result<&mut T, RenderGraphError>
    where
        T: Node,
    {
        self.get_node_state_mut(label).and_then(|n| n.node_mut())
    }

    /// Adds the [`Edge::SlotEdge`] to the graph. This guarantees that the `output_node`
    /// is run before the `input_node` and also connects the `output_slot` to the `input_slot`.
    ///
    /// Fails if any invalid [`RenderLabel`]s or [`SlotLabel`]s are given.
    ///
    /// # See also
    ///
    /// - [`add_slot_edge`](Self::add_slot_edge) for an infallible version.
    pub fn try_add_slot_edge(
        &mut self,
        output_node: impl RenderLabel,
        output_slot: impl Into<SlotLabel>,
        input_node: impl RenderLabel,
        input_slot: impl Into<SlotLabel>,
    ) -> Result<(), RenderGraphError> {
        let output_slot = output_slot.into();
        let input_slot = input_slot.into();

        let output_node = output_node.intern();
        let input_node = input_node.intern();

        let output_index = self
            .get_node_state(output_node)?
            .output_slots
            .get_slot_index(output_slot.clone())
            .ok_or(RenderGraphError::InvalidOutputNodeSlot(output_slot))?;
        let input_index = self
            .get_node_state(input_node)?
            .input_slots
            .get_slot_index(input_slot.clone())
            .ok_or(RenderGraphError::InvalidInputNodeSlot(input_slot))?;

        let edge = Edge::SlotEdge {
            output_node,
            output_index,
            input_node,
            input_index,
        };

        self.validate_edge(&edge, EdgeExistence::DoesNotExist)?;

        {
            let output_node = self.get_node_state_mut(output_node)?;
            output_node.edges.add_output_edge(edge.clone())?;
        }
        let input_node = self.get_node_state_mut(input_node)?;
        input_node.edges.add_input_edge(edge)?;

        Ok(())
    }

    /// Adds the [`Edge::SlotEdge`] to the graph. This guarantees that the `output_node`
    /// is run before the `input_node` and also connects the `output_slot` to the `input_slot`.
    ///
    /// # Panics
    ///
    /// Any invalid [`RenderLabel`]s or [`SlotLabel`]s are given.
    ///
    /// # See also
    ///
    /// - [`try_add_slot_edge`](Self::try_add_slot_edge) for a fallible version.
    pub fn add_slot_edge(
        &mut self,
        output_node: impl RenderLabel,
        output_slot: impl Into<SlotLabel>,
        input_node: impl RenderLabel,
        input_slot: impl Into<SlotLabel>,
    ) {
        self.try_add_slot_edge(output_node, output_slot, input_node, input_slot)
            .unwrap();
    }

    /// Removes the [`Edge::SlotEdge`] from the graph. If any nodes or slots do not exist then
    /// nothing happens.
    pub fn remove_slot_edge(
        &mut self,
        output_node: impl RenderLabel,
        output_slot: impl Into<SlotLabel>,
        input_node: impl RenderLabel,
        input_slot: impl Into<SlotLabel>,
    ) -> Result<(), RenderGraphError> {
        let output_slot = output_slot.into();
        let input_slot = input_slot.into();

        let output_node = output_node.intern();
        let input_node = input_node.intern();

        let output_index = self
            .get_node_state(output_node)?
            .output_slots
            .get_slot_index(output_slot.clone())
            .ok_or(RenderGraphError::InvalidOutputNodeSlot(output_slot))?;
        let input_index = self
            .get_node_state(input_node)?
            .input_slots
            .get_slot_index(input_slot.clone())
            .ok_or(RenderGraphError::InvalidInputNodeSlot(input_slot))?;

        let edge = Edge::SlotEdge {
            output_node,
            output_index,
            input_node,
            input_index,
        };

        self.validate_edge(&edge, EdgeExistence::Exists)?;

        {
            let output_node = self.get_node_state_mut(output_node)?;
            output_node.edges.remove_output_edge(edge.clone())?;
        }
        let input_node = self.get_node_state_mut(input_node)?;
        input_node.edges.remove_input_edge(edge)?;

        Ok(())
    }

    /// Adds the [`Edge::NodeEdge`] to the graph. This guarantees that the `output_node`
    /// is run before the `input_node`.
    ///
    /// Fails if any invalid [`RenderLabel`] is given.
    ///
    /// # See also
    ///
    /// - [`add_node_edge`](Self::add_node_edge) for an infallible version.
    pub fn try_add_node_edge(
        &mut self,
        output_node: impl RenderLabel,
        input_node: impl RenderLabel,
    ) -> Result<(), RenderGraphError> {
        let output_node = output_node.intern();
        let input_node = input_node.intern();

        let edge = Edge::NodeEdge {
            output_node,
            input_node,
        };

        self.validate_edge(&edge, EdgeExistence::DoesNotExist)?;

        {
            let output_node = self.get_node_state_mut(output_node)?;
            output_node.edges.add_output_edge(edge.clone())?;
        }
        let input_node = self.get_node_state_mut(input_node)?;
        input_node.edges.add_input_edge(edge)?;

        Ok(())
    }

    /// Adds the [`Edge::NodeEdge`] to the graph. This guarantees that the `output_node`
    /// is run before the `input_node`.
    ///
    /// # Panics
    ///
    /// Panics if any invalid [`RenderLabel`] is given.
    ///
    /// # See also
    ///
    /// - [`try_add_node_edge`](Self::try_add_node_edge) for a fallible version.
    pub fn add_node_edge(&mut self, output_node: impl RenderLabel, input_node: impl RenderLabel) {
        self.try_add_node_edge(output_node, input_node).unwrap();
    }

    /// Removes the [`Edge::NodeEdge`] from the graph. If either node does not exist then nothing
    /// happens.
    pub fn remove_node_edge(
        &mut self,
        output_node: impl RenderLabel,
        input_node: impl RenderLabel,
    ) -> Result<(), RenderGraphError> {
        let output_node = output_node.intern();
        let input_node = input_node.intern();

        let edge = Edge::NodeEdge {
            output_node,
            input_node,
        };

        self.validate_edge(&edge, EdgeExistence::Exists)?;

        {
            let output_node = self.get_node_state_mut(output_node)?;
            output_node.edges.remove_output_edge(edge.clone())?;
        }
        let input_node = self.get_node_state_mut(input_node)?;
        input_node.edges.remove_input_edge(edge)?;

        Ok(())
    }

    /// Verifies that the edge existence is as expected and
    /// checks that slot edges are connected correctly.
    pub fn validate_edge(
        &mut self,
        edge: &Edge,
        should_exist: EdgeExistence,
    ) -> Result<(), RenderGraphError> {
        if should_exist == EdgeExistence::Exists && !self.has_edge(edge) {
            return Err(RenderGraphError::EdgeDoesNotExist(edge.clone()));
        } else if should_exist == EdgeExistence::DoesNotExist && self.has_edge(edge) {
            return Err(RenderGraphError::EdgeAlreadyExists(edge.clone()));
        }

        match *edge {
            Edge::SlotEdge {
                output_node,
                output_index,
                input_node,
                input_index,
            } => {
                let output_node_state = self.get_node_state(output_node)?;
                let input_node_state = self.get_node_state(input_node)?;

                let output_slot = output_node_state
                    .output_slots
                    .get_slot(output_index)
                    .ok_or(RenderGraphError::InvalidOutputNodeSlot(SlotLabel::Index(
                        output_index,
                    )))?;
                let input_slot = input_node_state.input_slots.get_slot(input_index).ok_or(
                    RenderGraphError::InvalidInputNodeSlot(SlotLabel::Index(input_index)),
                )?;

                if let Some(Edge::SlotEdge {
                    output_node: current_output_node,
                    ..
                }) = input_node_state.edges.input_edges().iter().find(|e| {
                    if let Edge::SlotEdge {
                        input_index: current_input_index,
                        ..
                    } = e
                    {
                        input_index == *current_input_index
                    } else {
                        false
                    }
                }) {
                    if should_exist == EdgeExistence::DoesNotExist {
                        return Err(RenderGraphError::NodeInputSlotAlreadyOccupied {
                            node: input_node,
                            input_slot: input_index,
                            occupied_by_node: *current_output_node,
                        });
                    }
                }

                if output_slot.slot_type != input_slot.slot_type {
                    return Err(RenderGraphError::MismatchedNodeSlots {
                        output_node,
                        output_slot: output_index,
                        input_node,
                        input_slot: input_index,
                    });
                }
            }
            Edge::NodeEdge { .. } => { /* nothing to validate here */ }
        }

        Ok(())
    }

    /// Checks whether the `edge` already exists in the graph.
    pub fn has_edge(&self, edge: &Edge) -> bool {
        let output_node_state = self.get_node_state(edge.get_output_node());
        let input_node_state = self.get_node_state(edge.get_input_node());
        if let Ok(output_node_state) = output_node_state {
            if output_node_state.edges.output_edges().contains(edge) {
                if let Ok(input_node_state) = input_node_state {
                    if input_node_state.edges.input_edges().contains(edge) {
                        return true;
                    }
                }
            }
        }

        false
    }

    /// Returns an iterator over the [`NodeStates`](NodeState).
    pub fn iter_nodes(&self) -> impl Iterator<Item = &NodeState> {
        self.nodes.values()
    }

    /// Returns an iterator over the [`NodeStates`](NodeState), that allows modifying each value.
    pub fn iter_nodes_mut(&mut self) -> impl Iterator<Item = &mut NodeState> {
        self.nodes.values_mut()
    }

    /// Returns an iterator over the sub graphs.
    pub fn iter_sub_graphs(&self) -> impl Iterator<Item = (InternedRenderSubGraph, &RenderGraph)> {
        self.sub_graphs.iter().map(|(name, graph)| (*name, graph))
    }

    /// Returns an iterator over the sub graphs, that allows modifying each value.
    pub fn iter_sub_graphs_mut(
        &mut self,
    ) -> impl Iterator<Item = (InternedRenderSubGraph, &mut RenderGraph)> {
        self.sub_graphs
            .iter_mut()
            .map(|(name, graph)| (*name, graph))
    }

    /// Returns an iterator over a tuple of the input edges and the corresponding output nodes
    /// for the node referenced by the label.
    pub fn iter_node_inputs(
        &self,
        label: impl RenderLabel,
    ) -> Result<impl Iterator<Item = (&Edge, &NodeState)>, RenderGraphError> {
        let node = self.get_node_state(label)?;
        Ok(node
            .edges
            .input_edges()
            .iter()
            .map(|edge| (edge, edge.get_output_node()))
            .map(move |(edge, output_node)| (edge, self.get_node_state(output_node).unwrap())))
    }

    /// Returns an iterator over a tuple of the output edges and the corresponding input nodes
    /// for the node referenced by the label.
    pub fn iter_node_outputs(
        &self,
        label: impl RenderLabel,
    ) -> Result<impl Iterator<Item = (&Edge, &NodeState)>, RenderGraphError> {
        let node = self.get_node_state(label)?;
        Ok(node
            .edges
            .output_edges()
            .iter()
            .map(|edge| (edge, edge.get_input_node()))
            .map(move |(edge, input_node)| (edge, self.get_node_state(input_node).unwrap())))
    }

    /// Adds the `sub_graph` with the `label` to the graph.
    /// If the label is already present replaces it instead.
    pub fn add_sub_graph(&mut self, label: impl RenderSubGraph, sub_graph: RenderGraph) {
        self.sub_graphs.insert(label.intern(), sub_graph);
    }

    /// Removes the `sub_graph` with the `label` from the graph.
    /// If the label does not exist then nothing happens.
    pub fn remove_sub_graph(&mut self, label: impl RenderSubGraph) {
        self.sub_graphs.remove(&label.intern());
    }

    /// Retrieves the sub graph corresponding to the `label`.
    pub fn get_sub_graph(&self, label: impl RenderSubGraph) -> Option<&RenderGraph> {
        self.sub_graphs.get(&label.intern())
    }

    /// Retrieves the sub graph corresponding to the `label` mutably.
    pub fn get_sub_graph_mut(&mut self, label: impl RenderSubGraph) -> Option<&mut RenderGraph> {
        self.sub_graphs.get_mut(&label.intern())
    }

    /// Retrieves the sub graph corresponding to the `label`.
    ///
    /// # Panics
    ///
    /// Panics if any invalid subgraph label is given.
    ///
    /// # See also
    ///
    /// - [`get_sub_graph`](Self::get_sub_graph) for a fallible version.
    pub fn sub_graph(&self, label: impl RenderSubGraph) -> &RenderGraph {
        let label = label.intern();
        self.sub_graphs
            .get(&label)
            .unwrap_or_else(|| panic!("Subgraph {label:?} not found"))
    }

    /// Retrieves the sub graph corresponding to the `label` mutably.
    ///
    /// # Panics
    ///
    /// Panics if any invalid subgraph label is given.
    ///
    /// # See also
    ///
    /// - [`get_sub_graph_mut`](Self::get_sub_graph_mut) for a fallible version.
    pub fn sub_graph_mut(&mut self, label: impl RenderSubGraph) -> &mut RenderGraph {
        let label = label.intern();
        self.sub_graphs
            .get_mut(&label)
            .unwrap_or_else(|| panic!("Subgraph {label:?} not found"))
    }
}

impl Debug for RenderGraph {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        for node in self.iter_nodes() {
            writeln!(f, "{:?}", node.label)?;
            writeln!(f, "  in: {:?}", node.input_slots)?;
            writeln!(f, "  out: {:?}", node.output_slots)?;
        }

        Ok(())
    }
}

/// A [`Node`] which acts as an entry point for a [`RenderGraph`] with custom inputs.
/// It has the same input and output slots and simply copies them over when run.
pub struct GraphInputNode {
    inputs: Vec<SlotInfo>,
}

impl Node for GraphInputNode {
    fn input(&self) -> Vec<SlotInfo> {
        self.inputs.clone()
    }

    fn output(&self) -> Vec<SlotInfo> {
        self.inputs.clone()
    }

    fn run(
        &self,
        graph: &mut RenderGraphContext,
        _render_context: &mut RenderContext,
        _world: &World,
    ) -> Result<(), NodeRunError> {
        for i in 0..graph.inputs().len() {
            let input = graph.inputs()[i].clone();
            graph.set_output(i, input)?;
        }
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use crate::{
        render_graph::{
            node::IntoRenderNodeArray, Edge, InternedRenderLabel, Node, NodeRunError, RenderGraph,
            RenderGraphContext, RenderGraphError, RenderLabel, SlotInfo, SlotType,
        },
        renderer::RenderContext,
    };
    use bevy_ecs::world::{FromWorld, World};
    use bevy_utils::HashSet;

    #[derive(Debug, Hash, PartialEq, Eq, Clone, RenderLabel)]
    enum TestLabel {
        A,
        B,
        C,
        D,
    }

    #[derive(Debug)]
    struct TestNode {
        inputs: Vec<SlotInfo>,
        outputs: Vec<SlotInfo>,
    }

    impl TestNode {
        pub fn new(inputs: usize, outputs: usize) -> Self {
            TestNode {
                inputs: (0..inputs)
                    .map(|i| SlotInfo::new(format!("in_{i}"), SlotType::TextureView))
                    .collect(),
                outputs: (0..outputs)
                    .map(|i| SlotInfo::new(format!("out_{i}"), SlotType::TextureView))
                    .collect(),
            }
        }
    }

    impl Node for TestNode {
        fn input(&self) -> Vec<SlotInfo> {
            self.inputs.clone()
        }

        fn output(&self) -> Vec<SlotInfo> {
            self.outputs.clone()
        }

        fn run(
            &self,
            _: &mut RenderGraphContext,
            _: &mut RenderContext,
            _: &World,
        ) -> Result<(), NodeRunError> {
            Ok(())
        }
    }

    fn input_nodes(label: impl RenderLabel, graph: &RenderGraph) -> HashSet<InternedRenderLabel> {
        graph
            .iter_node_inputs(label)
            .unwrap()
            .map(|(_edge, node)| node.label)
            .collect::<HashSet<InternedRenderLabel>>()
    }

    fn output_nodes(label: impl RenderLabel, graph: &RenderGraph) -> HashSet<InternedRenderLabel> {
        graph
            .iter_node_outputs(label)
            .unwrap()
            .map(|(_edge, node)| node.label)
            .collect::<HashSet<InternedRenderLabel>>()
    }

    #[test]
    fn test_graph_edges() {
        let mut graph = RenderGraph::default();
        graph.add_node(TestLabel::A, TestNode::new(0, 1));
        graph.add_node(TestLabel::B, TestNode::new(0, 1));
        graph.add_node(TestLabel::C, TestNode::new(1, 1));
        graph.add_node(TestLabel::D, TestNode::new(1, 0));

        graph.add_slot_edge(TestLabel::A, "out_0", TestLabel::C, "in_0");
        graph.add_node_edge(TestLabel::B, TestLabel::C);
        graph.add_slot_edge(TestLabel::C, 0, TestLabel::D, 0);

        assert!(
            input_nodes(TestLabel::A, &graph).is_empty(),
            "A has no inputs"
        );
        assert_eq!(
            output_nodes(TestLabel::A, &graph),
            HashSet::from_iter((TestLabel::C,).into_array()),
            "A outputs to C"
        );

        assert!(
            input_nodes(TestLabel::B, &graph).is_empty(),
            "B has no inputs"
        );
        assert_eq!(
            output_nodes(TestLabel::B, &graph),
            HashSet::from_iter((TestLabel::C,).into_array()),
            "B outputs to C"
        );

        assert_eq!(
            input_nodes(TestLabel::C, &graph),
            HashSet::from_iter((TestLabel::A, TestLabel::B).into_array()),
            "A and B input to C"
        );
        assert_eq!(
            output_nodes(TestLabel::C, &graph),
            HashSet::from_iter((TestLabel::D,).into_array()),
            "C outputs to D"
        );

        assert_eq!(
            input_nodes(TestLabel::D, &graph),
            HashSet::from_iter((TestLabel::C,).into_array()),
            "C inputs to D"
        );
        assert!(
            output_nodes(TestLabel::D, &graph).is_empty(),
            "D has no outputs"
        );
    }

    #[test]
    fn test_get_node_typed() {
        struct MyNode {
            value: usize,
        }

        impl Node for MyNode {
            fn run(
                &self,
                _: &mut RenderGraphContext,
                _: &mut RenderContext,
                _: &World,
            ) -> Result<(), NodeRunError> {
                Ok(())
            }
        }

        let mut graph = RenderGraph::default();

        graph.add_node(TestLabel::A, MyNode { value: 42 });

        let node: &MyNode = graph.get_node(TestLabel::A).unwrap();
        assert_eq!(node.value, 42, "node value matches");

        let result: Result<&TestNode, RenderGraphError> = graph.get_node(TestLabel::A);
        assert_eq!(
            result.unwrap_err(),
            RenderGraphError::WrongNodeType,
            "expect a wrong node type error"
        );
    }

    #[test]
    fn test_slot_already_occupied() {
        let mut graph = RenderGraph::default();

        graph.add_node(TestLabel::A, TestNode::new(0, 1));
        graph.add_node(TestLabel::B, TestNode::new(0, 1));
        graph.add_node(TestLabel::C, TestNode::new(1, 1));

        graph.add_slot_edge(TestLabel::A, 0, TestLabel::C, 0);
        assert_eq!(
            graph.try_add_slot_edge(TestLabel::B, 0, TestLabel::C, 0),
            Err(RenderGraphError::NodeInputSlotAlreadyOccupied {
                node: TestLabel::C.intern(),
                input_slot: 0,
                occupied_by_node: TestLabel::A.intern(),
            }),
            "Adding to a slot that is already occupied should return an error"
        );
    }

    #[test]
    fn test_edge_already_exists() {
        let mut graph = RenderGraph::default();

        graph.add_node(TestLabel::A, TestNode::new(0, 1));
        graph.add_node(TestLabel::B, TestNode::new(1, 0));

        graph.add_slot_edge(TestLabel::A, 0, TestLabel::B, 0);
        assert_eq!(
            graph.try_add_slot_edge(TestLabel::A, 0, TestLabel::B, 0),
            Err(RenderGraphError::EdgeAlreadyExists(Edge::SlotEdge {
                output_node: TestLabel::A.intern(),
                output_index: 0,
                input_node: TestLabel::B.intern(),
                input_index: 0,
            })),
            "Adding to a duplicate edge should return an error"
        );
    }

    #[test]
    fn test_add_node_edges() {
        struct SimpleNode;
        impl Node for SimpleNode {
            fn run(
                &self,
                _graph: &mut RenderGraphContext,
                _render_context: &mut RenderContext,
                _world: &World,
            ) -> Result<(), NodeRunError> {
                Ok(())
            }
        }
        impl FromWorld for SimpleNode {
            fn from_world(_world: &mut World) -> Self {
                Self
            }
        }

        let mut graph = RenderGraph::default();
        graph.add_node(TestLabel::A, SimpleNode);
        graph.add_node(TestLabel::B, SimpleNode);
        graph.add_node(TestLabel::C, SimpleNode);

        graph.add_node_edges((TestLabel::A, TestLabel::B, TestLabel::C));

        assert_eq!(
            output_nodes(TestLabel::A, &graph),
            HashSet::from_iter((TestLabel::B,).into_array()),
            "A -> B"
        );
        assert_eq!(
            input_nodes(TestLabel::B, &graph),
            HashSet::from_iter((TestLabel::A,).into_array()),
            "A -> B"
        );
        assert_eq!(
            output_nodes(TestLabel::B, &graph),
            HashSet::from_iter((TestLabel::C,).into_array()),
            "B -> C"
        );
        assert_eq!(
            input_nodes(TestLabel::C, &graph),
            HashSet::from_iter((TestLabel::B,).into_array()),
            "B -> C"
        );
    }
}