darkfi/event_graph/
mod.rs

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
/* This file is part of DarkFi (https://dark.fi)
 *
 * Copyright (C) 2020-2024 Dyne.org foundation
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

use std::{
    collections::{BTreeMap, HashMap, HashSet, VecDeque},
    path::PathBuf,
    sync::Arc,
};

use darkfi_serial::{deserialize_async, serialize_async};
use log::{debug, error, info, warn};
use num_bigint::BigUint;
use sled_overlay::{sled, SledTreeOverlay};
use smol::{
    lock::{OnceCell, RwLock},
    Executor,
};
use tinyjson::JsonValue::{self};

use crate::{
    event_graph::util::replayer_log,
    net::P2pPtr,
    rpc::{
        jsonrpc::{JsonResponse, JsonResult},
        util::json_map,
    },
    system::{msleep, Publisher, PublisherPtr, StoppableTask, StoppableTaskPtr, Subscription},
    Error, Result,
};

/// An event graph event
pub mod event;
pub use event::Event;

/// P2P protocol implementation for the Event Graph
pub mod proto;
use proto::{EventRep, EventReq, TipRep, TipReq};

/// Utility functions
pub mod util;
use util::{generate_genesis, millis_until_next_rotation, next_rotation_timestamp};

// Debugging event graph
pub mod deg;
use deg::DegEvent;

#[cfg(test)]
mod tests;

/// Initial genesis timestamp in millis (07 Sep 2023, 00:00:00 UTC)
/// Must always be UTC midnight.
pub const INITIAL_GENESIS: u64 = 1_694_044_800_000;
/// Genesis event contents
pub const GENESIS_CONTENTS: &[u8] = &[0x47, 0x45, 0x4e, 0x45, 0x53, 0x49, 0x53];

/// The number of parents an event is supposed to have.
pub const N_EVENT_PARENTS: usize = 5;
/// Allowed timestamp drift in milliseconds
const EVENT_TIME_DRIFT: u64 = 60_000;
/// Null event ID
pub const NULL_ID: blake3::Hash = blake3::Hash::from_bytes([0x00; blake3::OUT_LEN]);

/// Atomic pointer to an [`EventGraph`] instance.
pub type EventGraphPtr = Arc<EventGraph>;

/// An Event Graph instance
pub struct EventGraph {
    /// Pointer to the P2P network instance
    p2p: P2pPtr,
    /// Sled tree containing the DAG
    dag: sled::Tree,
    /// Replay logs path.
    datastore: PathBuf,
    /// Run in replay_mode where if set we log Sled DB instructions
    /// into `datastore`, useful to reacreate a faulty DAG to debug.
    replay_mode: bool,
    /// The set of unreferenced DAG tips
    unreferenced_tips: RwLock<BTreeMap<u64, HashSet<blake3::Hash>>>,
    /// A `HashSet` containg event IDs and their 1-level parents.
    /// These come from the events we've sent out using `EventPut`.
    /// They are used with `EventReq` to decide if we should reply
    /// or not. Additionally it is also used when we broadcast the
    /// `TipRep` message telling peers about our unreferenced tips.
    broadcasted_ids: RwLock<HashSet<blake3::Hash>>,
    /// DAG Pruning Task
    pub prune_task: OnceCell<StoppableTaskPtr>,
    /// Event publisher, this notifies whenever an event is
    /// inserted into the DAG
    pub event_pub: PublisherPtr<Event>,
    /// Current genesis event
    current_genesis: RwLock<Event>,
    /// Currently configured DAG rotation, in days
    days_rotation: u64,
    /// Flag signalling DAG has finished initial sync
    pub synced: RwLock<bool>,
    /// Enable graph debugging
    pub deg_enabled: RwLock<bool>,
    /// The publisher for which we can give deg info over
    deg_publisher: PublisherPtr<DegEvent>,
}

impl EventGraph {
    /// Create a new [`EventGraph`] instance, creates a new Genesis
    /// event and checks if it
    /// is containd in DAG, if not prunes DAG, may also start a pruning
    /// task based on `days_rotation`, and return an atomic instance of
    /// `Self`
    /// * `p2p` atomic pointer to p2p.
    /// * `sled_db` sled DB instance.
    /// * `datastore` path where we should log db instrucion if run in
    ///   replay mode.
    /// * `replay_mode` set the flag to keep a log of db instructions.
    /// * `dag_tree_name` the name of disk-backed tree (or DAG name).
    /// * `days_rotation` marks the lifetime of the DAG before it's
    ///   pruned.
    pub async fn new(
        p2p: P2pPtr,
        sled_db: sled::Db,
        datastore: PathBuf,
        replay_mode: bool,
        dag_tree_name: &str,
        days_rotation: u64,
        ex: Arc<Executor<'_>>,
    ) -> Result<EventGraphPtr> {
        let dag = sled_db.open_tree(dag_tree_name)?;
        let unreferenced_tips = RwLock::new(BTreeMap::new());
        let broadcasted_ids = RwLock::new(HashSet::new());
        let event_pub = Publisher::new();

        // Create the current genesis event based on the `days_rotation`
        let current_genesis = generate_genesis(days_rotation);
        let self_ = Arc::new(Self {
            p2p,
            dag: dag.clone(),
            datastore,
            replay_mode,
            unreferenced_tips,
            broadcasted_ids,
            prune_task: OnceCell::new(),
            event_pub,
            current_genesis: RwLock::new(current_genesis.clone()),
            days_rotation,
            synced: RwLock::new(false),
            deg_enabled: RwLock::new(false),
            deg_publisher: Publisher::new(),
        });

        // Check if we have it in our DAG.
        // If not, we can prune the DAG and insert this new genesis event.
        if !dag.contains_key(current_genesis.id().as_bytes())? {
            info!(
                target: "event_graph::new()",
                "[EVENTGRAPH] DAG does not contain current genesis, pruning existing data",
            );
            self_.dag_prune(current_genesis).await?;
        }

        // Find the unreferenced tips in the current DAG state.
        *self_.unreferenced_tips.write().await = self_.find_unreferenced_tips().await;

        // Spawn the DAG pruning task
        if days_rotation > 0 {
            let prune_task = StoppableTask::new();
            let _ = self_.prune_task.set(prune_task.clone()).await;

            prune_task.clone().start(
                self_.clone().dag_prune_task(days_rotation),
                |res| async move {
                    match res {
                        Ok(()) | Err(Error::DetachedTaskStopped) => { /* Do nothing */ }
                        Err(e) => error!(target: "event_graph::_handle_stop()", "[EVENTGRAPH] Failed stopping prune task: {e}")
                    }
                },
                Error::DetachedTaskStopped,
                ex.clone(),
            );
        }

        Ok(self_)
    }

    pub fn days_rotation(&self) -> u64 {
        self.days_rotation
    }

    /// Sync the DAG from connected peers
    pub async fn dag_sync(&self) -> Result<()> {
        // We do an optimistic sync where we ask all our connected peers for
        // the latest layer DAG tips (unreferenced events) and then we accept
        // the ones we see the most times.
        // * Compare received tips with local ones, identify which we are missing.
        // * Request these from peers
        // * Recursively request these backward
        //
        // Verification:
        // * Timestamps should go backwards
        // * Cross-check with multiple peers, this means we should request the
        //   same event from multiple peers and make sure it is the same.
        // * Since we should be pruning, if we're not synced after some reasonable
        //   amount of iterations, these could be faulty peers and we can try again
        //   from the beginning

        // Get references to all our peers.
        let channels = self.p2p.hosts().peers();
        let mut communicated_peers = channels.len();
        info!(
            target: "event_graph::dag_sync()",
            "[EVENTGRAPH] Syncing DAG from {} peers...", communicated_peers,
        );

        // Here we keep track of the tips, their layers and how many time we've seen them.
        let mut tips: HashMap<blake3::Hash, (u64, usize)> = HashMap::new();

        // Let's first ask all of our peers for their tips and collect them
        // in our hashmap above.
        for channel in channels.iter() {
            let url = channel.address();

            let tip_rep_sub = match channel.subscribe_msg::<TipRep>().await {
                Ok(v) => v,
                Err(e) => {
                    error!(
                        target: "event_graph::dag_sync()",
                        "[EVENTGRAPH] Sync: Couldn't subscribe TipReq for peer {}, skipping ({})",
                        url, e,
                    );
                    communicated_peers -= 1;
                    continue
                }
            };

            if let Err(e) = channel.send(&TipReq {}).await {
                error!(
                    target: "event_graph::dag_sync()",
                    "[EVENTGRAPH] Sync: Couldn't contact peer {}, skipping ({})", url, e,
                );
                communicated_peers -= 1;
                continue
            };

            // Node waits for response
            let Ok(peer_tips) = tip_rep_sub
                .receive_with_timeout(self.p2p.settings().read().await.outbound_connect_timeout)
                .await
            else {
                error!(
                    target: "event_graph::dag_sync()",
                    "[EVENTGRAPH] Sync: Peer {} didn't reply with tips in time, skipping", url,
                );
                communicated_peers -= 1;
                continue
            };

            let peer_tips = &peer_tips.0;

            // Note down the seen tips
            for (layer, layer_tips) in peer_tips {
                for tip in layer_tips {
                    if let Some(seen_tip) = tips.get_mut(tip) {
                        seen_tip.1 += 1;
                    } else {
                        tips.insert(*tip, (*layer, 1));
                    }
                }
            }
        }

        // After we've communicated all the peers, let's see what happened.
        if tips.is_empty() {
            error!(
                target: "event_graph::dag_sync()",
                "[EVENTGRAPH] Sync: Could not find any DAG tips",
            );
            return Err(Error::DagSyncFailed)
        }

        // We know the number of peers we've communicated with,
        // so we will consider events we saw at more than 2/3 of
        // those peers.
        let consideration_threshold = communicated_peers * 2 / 3;
        let mut considered_tips = HashSet::new();
        for (tip, (_, amount)) in tips.iter() {
            if amount > &consideration_threshold {
                considered_tips.insert(*tip);
            }
        }
        drop(tips);

        // Now begin fetching the events backwards.
        let mut missing_parents = HashSet::new();
        for tip in considered_tips.iter() {
            assert!(tip != &NULL_ID);

            if !self.dag.contains_key(tip.as_bytes()).unwrap() {
                missing_parents.insert(*tip);
            }
        }

        if missing_parents.is_empty() {
            *self.synced.write().await = true;
            info!(target: "event_graph::dag_sync()", "[EVENTGRAPH] DAG synced successfully!");
            return Ok(())
        }

        info!(target: "event_graph::dag_sync()", "[EVENTGRAPH] Fetching events");
        let mut received_events: BTreeMap<u64, Vec<Event>> = BTreeMap::new();
        let mut received_events_hashes = HashSet::new();

        while !missing_parents.is_empty() {
            let mut found_event = false;

            for channel in channels.iter() {
                let url = channel.address();

                debug!(
                    target: "event_graph::dag_sync()",
                    "Requesting {:?} from {}...", missing_parents, url,
                );

                let ev_rep_sub = match channel.subscribe_msg::<EventRep>().await {
                    Ok(v) => v,
                    Err(e) => {
                        error!(
                            target: "event_graph::dag_sync()",
                            "[EVENTGRAPH] Sync: Couldn't subscribe EventRep for peer {}, skipping ({})",
                            url, e,
                        );
                        continue
                    }
                };

                let request_missing_events = missing_parents.clone().into_iter().collect();
                if let Err(e) = channel.send(&EventReq(request_missing_events)).await {
                    error!(
                        target: "event_graph::dag_sync()",
                        "[EVENTGRAPH] Sync: Failed communicating EventReq({:?}) to {}: {}",
                        missing_parents, url, e,
                    );
                    continue
                }

                // Node waits for response
                let Ok(parent) = ev_rep_sub
                    .receive_with_timeout(self.p2p.settings().read().await.outbound_connect_timeout)
                    .await
                else {
                    error!(
                        target: "event_graph::dag_sync()",
                        "[EVENTGRAPH] Sync: Timeout waiting for parents {:?} from {}",
                        missing_parents, url,
                    );
                    continue
                };

                let parents = parent.0.clone();

                for parent in parents {
                    let parent_id = parent.id();
                    if !missing_parents.contains(&parent_id) {
                        error!(
                            target: "event_graph::dag_sync()",
                            "[EVENTGRAPH] Sync: Peer {} replied with a wrong event: {}",
                            url, parent.id(),
                        );
                        continue
                    }

                    debug!(
                        target: "event_graph::dag_sync()",
                        "Got correct parent event {}", parent_id,
                    );

                    if let Some(layer_events) = received_events.get_mut(&parent.layer) {
                        layer_events.push(parent.clone());
                    } else {
                        let layer_events = vec![parent.clone()];
                        received_events.insert(parent.layer, layer_events);
                    }
                    received_events_hashes.insert(parent_id);

                    missing_parents.remove(&parent_id);
                    found_event = true;

                    // See if we have the upper parents
                    for upper_parent in parent.parents.iter() {
                        if upper_parent == &NULL_ID {
                            continue
                        }

                        if !missing_parents.contains(upper_parent) &&
                            !received_events_hashes.contains(upper_parent) &&
                            !self.dag.contains_key(upper_parent.as_bytes()).unwrap()
                        {
                            debug!(
                                target: "event_graph::dag_sync()",
                                "Found upper missing parent event{}", upper_parent,
                            );
                            missing_parents.insert(*upper_parent);
                        }
                    }
                }

                break
            }

            if !found_event {
                error!(
                    target: "event_graph::dag_sync()",
                    "[EVENTGRAPH] Sync: Failed to get all events",
                );
                return Err(Error::DagSyncFailed)
            }
        } // <-- while !missing_parents.is_empty

        // At this point we should've got all the events.
        // We should add them to the DAG.
        let mut events = vec![];
        for (_, tips) in received_events {
            for tip in tips {
                events.push(tip);
            }
        }
        self.dag_insert(&events).await?;

        *self.synced.write().await = true;

        info!(target: "event_graph::dag_sync()", "[EVENTGRAPH] DAG synced successfully!");
        Ok(())
    }

    /// Atomically prune the DAG and insert the given event as genesis.
    async fn dag_prune(&self, genesis_event: Event) -> Result<()> {
        debug!(target: "event_graph::dag_prune()", "Pruning DAG...");

        // Acquire exclusive locks to unreferenced_tips, broadcasted_ids and
        // current_genesis while this operation is happening. We do this to
        // ensure that during the pruning operation, no other operations are
        // able to access the intermediate state which could lead to producing
        // the wrong state after pruning.
        let mut unreferenced_tips = self.unreferenced_tips.write().await;
        let mut broadcasted_ids = self.broadcasted_ids.write().await;
        let mut current_genesis = self.current_genesis.write().await;

        // Atomically clear the DAG and write the new genesis event.
        let mut batch = sled::Batch::default();
        for key in self.dag.iter().keys() {
            batch.remove(key.unwrap());
        }
        batch.insert(genesis_event.id().as_bytes(), serialize_async(&genesis_event).await);

        debug!(target: "event_graph::dag_prune()", "Applying batch...");
        if let Err(e) = self.dag.apply_batch(batch) {
            panic!("Failed pruning DAG, sled apply_batch error: {}", e);
        }

        // Clear unreferenced tips and bcast ids
        *unreferenced_tips = BTreeMap::new();
        unreferenced_tips.insert(0, HashSet::from([genesis_event.id()]));
        *current_genesis = genesis_event;
        *broadcasted_ids = HashSet::new();
        drop(unreferenced_tips);
        drop(broadcasted_ids);
        drop(current_genesis);

        debug!(target: "event_graph::dag_prune()", "DAG pruned successfully");
        Ok(())
    }

    /// Background task periodically pruning the DAG.
    async fn dag_prune_task(self: Arc<Self>, days_rotation: u64) -> Result<()> {
        // The DAG should periodically be pruned. This can be a configurable
        // parameter. By pruning, we should deterministically replace the
        // genesis event (can use a deterministic timestamp) and drop everything
        // in the DAG, leaving just the new genesis event.
        debug!(target: "event_graph::dag_prune_task()", "Spawned background DAG pruning task");

        loop {
            // Find the next rotation timestamp:
            let next_rotation = next_rotation_timestamp(INITIAL_GENESIS, days_rotation);

            // Prepare the new genesis event
            let current_genesis = Event {
                timestamp: next_rotation,
                content: GENESIS_CONTENTS.to_vec(),
                parents: [NULL_ID; N_EVENT_PARENTS],
                layer: 0,
            };

            // Sleep until it's time to rotate.
            let s = millis_until_next_rotation(next_rotation);

            debug!(target: "event_graph::dag_prune_task()", "Sleeping {}ms until next DAG prune", s);
            msleep(s).await;
            debug!(target: "event_graph::dag_prune_task()", "Rotation period reached");

            // Trigger DAG prune
            self.dag_prune(current_genesis).await?;
        }
    }

    /// Atomically insert given events into the DAG and return the event IDs.
    /// All provided events must be valid. An overlay is used over the DAG tree,
    /// temporary writting each event in order. After all events have been
    /// validated and inserted successfully, we write the overlay to sled.
    /// This will append the new events into the unreferenced tips set, and
    /// remove the events' parents from it. It will also append the events'
    /// level-1 parents to the `broadcasted_ids` set, so the P2P protocol
    /// knows that any requests for them are actually legitimate.
    /// TODO: The `broadcasted_ids` set should periodically be pruned, when
    /// some sensible time has passed after broadcasting the event.
    pub async fn dag_insert(&self, events: &[Event]) -> Result<Vec<blake3::Hash>> {
        // Sanity check
        if events.is_empty() {
            return Ok(vec![])
        }

        // Acquire exclusive locks to `unreferenced_tips and broadcasted_ids`
        let mut unreferenced_tips = self.unreferenced_tips.write().await;
        let mut broadcasted_ids = self.broadcasted_ids.write().await;

        // Here we keep the IDs to return
        let mut ids = Vec::with_capacity(events.len());

        // Create an overlay over the DAG tree
        let mut overlay = SledTreeOverlay::new(&self.dag);

        // Grab genesis timestamp
        let genesis_timestamp = self.current_genesis.read().await.timestamp;

        // Iterate over given events to validate them and
        // write them to the overlay
        for event in events {
            let event_id = event.id();
            debug!(
                target: "event_graph::dag_insert()",
                "Inserting event {} into the DAG", event_id,
            );

            if !event
                .validate(&self.dag, genesis_timestamp, self.days_rotation, Some(&overlay))
                .await?
            {
                error!(target: "event_graph::dag_insert()", "Event {} is invalid!", event_id);
                return Err(Error::EventIsInvalid)
            }

            let event_se = serialize_async(event).await;

            // Add the event to the overlay
            overlay.insert(event_id.as_bytes(), &event_se)?;

            if self.replay_mode {
                replayer_log(&self.datastore, "insert".to_owned(), event_se)?;
            }
            // Note down the event ID to return
            ids.push(event_id);
        }

        // Aggregate changes into a single batch
        let batch = overlay.aggregate().unwrap();

        // Atomically apply the batch.
        // Panic if something is corrupted.
        if let Err(e) = self.dag.apply_batch(batch) {
            panic!("Failed applying dag_insert batch to sled: {}", e);
        }

        // Iterate over given events to update references and
        // send out notifications about them
        for event in events {
            let event_id = event.id();

            // Update the unreferenced DAG tips set
            debug!(
                target: "event_graph::dag_insert()",
                "Event {} parents {:#?}", event_id, event.parents,
            );
            for parent_id in event.parents.iter() {
                if parent_id != &NULL_ID {
                    debug!(
                        target: "event_graph::dag_insert()",
                        "Removing {} from unreferenced_tips", parent_id,
                    );

                    // Iterate over unreferenced tips in previous layers
                    // and remove the parent
                    // NOTE: this might be too exhaustive, but the
                    // assumption is that previous layers unreferenced
                    // tips will be few.
                    for (layer, tips) in unreferenced_tips.iter_mut() {
                        if layer >= &event.layer {
                            continue
                        }
                        tips.remove(parent_id);
                    }
                    broadcasted_ids.insert(*parent_id);
                }
            }
            unreferenced_tips.retain(|_, tips| !tips.is_empty());
            debug!(
                target: "event_graph::dag_insert()",
                "Adding {} to unreferenced tips", event_id,
            );

            if let Some(layer_tips) = unreferenced_tips.get_mut(&event.layer) {
                layer_tips.insert(event_id);
            } else {
                let mut layer_tips = HashSet::new();
                layer_tips.insert(event_id);
                unreferenced_tips.insert(event.layer, layer_tips);
            }

            // Send out notifications about the new event
            self.event_pub.notify(event.clone()).await;
        }

        // Drop the exclusive locks
        drop(unreferenced_tips);
        drop(broadcasted_ids);

        Ok(ids)
    }

    /// Fetch an event from the DAG
    pub async fn dag_get(&self, event_id: &blake3::Hash) -> Result<Option<Event>> {
        let Some(bytes) = self.dag.get(event_id.as_bytes())? else { return Ok(None) };
        let event: Event = deserialize_async(&bytes).await?;

        Ok(Some(event))
    }

    /// Get next layer along with its N_EVENT_PARENTS from the unreferenced
    /// tips of the DAG. Since tips are mapped by their layer, we go backwards
    /// until we fill the vector, ensuring we always use latest layers tips as
    /// parents.
    async fn get_next_layer_with_parents(&self) -> (u64, [blake3::Hash; N_EVENT_PARENTS]) {
        let unreferenced_tips = self.unreferenced_tips.read().await;

        let mut parents = [NULL_ID; N_EVENT_PARENTS];
        let mut index = 0;
        'outer: for (_, tips) in unreferenced_tips.iter().rev() {
            for tip in tips.iter() {
                parents[index] = *tip;
                index += 1;
                if index >= N_EVENT_PARENTS {
                    break 'outer
                }
            }
        }

        let next_layer = unreferenced_tips.last_key_value().unwrap().0 + 1;

        assert!(parents.iter().any(|x| x != &NULL_ID));
        (next_layer, parents)
    }

    /// Find the unreferenced tips in the current DAG state, mapped by their layers.
    async fn find_unreferenced_tips(&self) -> BTreeMap<u64, HashSet<blake3::Hash>> {
        // First get all the event IDs
        let mut tips = HashSet::new();
        for iter_elem in self.dag.iter() {
            let (id, _) = iter_elem.unwrap();
            let id = blake3::Hash::from_bytes((&id as &[u8]).try_into().unwrap());
            tips.insert(id);
        }

        // Iterate again to find unreferenced IDs
        for iter_elem in self.dag.iter() {
            let (_, event) = iter_elem.unwrap();
            let event: Event = deserialize_async(&event).await.unwrap();
            for parent in event.parents.iter() {
                tips.remove(parent);
            }
        }

        // Build the layers map
        let mut map: BTreeMap<u64, HashSet<blake3::Hash>> = BTreeMap::new();
        for tip in tips {
            let event = self.dag_get(&tip).await.unwrap().unwrap();
            if let Some(layer_tips) = map.get_mut(&event.layer) {
                layer_tips.insert(tip);
            } else {
                let mut layer_tips = HashSet::new();
                layer_tips.insert(tip);
                map.insert(event.layer, layer_tips);
            }
        }

        map
    }

    /// Internal function used for DAG sorting.
    async fn get_unreferenced_tips_sorted(&self) -> [blake3::Hash; N_EVENT_PARENTS] {
        let (_, tips) = self.get_next_layer_with_parents().await;

        // Convert the hash to BigUint for sorting
        let mut sorted: Vec<_> =
            tips.iter().map(|x| BigUint::from_bytes_be(x.as_bytes())).collect();
        sorted.sort_unstable();

        // Convert back to blake3
        let mut tips_sorted = [NULL_ID; N_EVENT_PARENTS];
        for (i, id) in sorted.iter().enumerate() {
            let mut bytes = id.to_bytes_be();

            // Ensure we have 32 bytes
            while bytes.len() < blake3::OUT_LEN {
                bytes.insert(0, 0);
            }

            tips_sorted[i] = blake3::Hash::from_bytes(bytes.try_into().unwrap());
        }

        tips_sorted
    }

    /// Perform a topological sort of the DAG.
    pub async fn order_events(&self) -> Vec<Event> {
        let mut ordered_events = VecDeque::new();
        let mut visited = HashSet::new();

        for tip in self.get_unreferenced_tips_sorted().await {
            if !visited.contains(&tip) && tip != NULL_ID {
                let tip = self.dag_get(&tip).await.unwrap().unwrap();
                ordered_events.extend(self.dfs_topological_sort(tip, &mut visited).await);
            }
        }

        let mut ord_events_vec = ordered_events.make_contiguous().to_vec();
        // Order events based on thier layer numbers, or based on timestamp if they are equal
        ord_events_vec
            .sort_unstable_by(|a, b| a.0.cmp(&b.0).then(b.1.timestamp.cmp(&a.1.timestamp)));

        ord_events_vec.iter().map(|a| a.1.clone()).collect::<Vec<Event>>()
    }

    /// We do a non-recursive DFS (<https://en.wikipedia.org/wiki/Depth-first_search>),
    /// and additionally we consider the timestamps.
    async fn dfs_topological_sort(
        &self,
        event: Event,
        visited: &mut HashSet<blake3::Hash>,
    ) -> VecDeque<(u64, Event)> {
        let mut ordered_events = VecDeque::new();
        let mut stack = VecDeque::new();
        let event_id = event.id();
        stack.push_back(event_id);

        while let Some(event_id) = stack.pop_front() {
            if !visited.contains(&event_id) && event_id != NULL_ID {
                visited.insert(event_id);
                if let Some(event) = self.dag_get(&event_id).await.unwrap() {
                    for parent in event.parents.iter() {
                        stack.push_back(*parent);
                    }

                    ordered_events.push_back((event.layer, event))
                }
            }
        }

        ordered_events
    }

    /// Enable graph debugging
    pub async fn deg_enable(&self) {
        *self.deg_enabled.write().await = true;
        warn!("[EVENTGRAPH] Graph debugging enabled!");
    }

    /// Disable graph debugging
    pub async fn deg_disable(&self) {
        *self.deg_enabled.write().await = false;
        warn!("[EVENTGRAPH] Graph debugging disabled!");
    }

    /// Subscribe to deg events
    pub async fn deg_subscribe(&self) -> Subscription<DegEvent> {
        self.deg_publisher.clone().subscribe().await
    }

    /// Send a deg notification over the publisher
    pub async fn deg_notify(&self, event: DegEvent) {
        self.deg_publisher.notify(event).await;
    }

    pub async fn eventgraph_info(&self, id: u16, _params: JsonValue) -> JsonResult {
        let mut graph = HashMap::new();
        for iter_elem in self.dag.iter() {
            let (id, val) = iter_elem.unwrap();
            let id = blake3::Hash::from_bytes((&id as &[u8]).try_into().unwrap());
            let val: Event = deserialize_async(&val).await.unwrap();
            graph.insert(id, val);
        }

        let json_graph = graph
            .into_iter()
            .map(|(k, v)| {
                let key = k.to_string();
                let value = JsonValue::from(v);
                (key, value)
            })
            .collect();
        let values = json_map([("dag", JsonValue::Object(json_graph))]);

        let result = JsonValue::Object(HashMap::from([("eventgraph_info".to_string(), values)]));

        JsonResponse::new(result, id).into()
    }

    /// Fetch all the events that are on a higher layers than the
    /// provided ones.
    pub async fn fetch_successors_of(
        &self,
        tips: BTreeMap<u64, HashSet<blake3::Hash>>,
    ) -> Result<Vec<Event>> {
        debug!(
             target: "event_graph::fetch_successors_of()",
             "fetching successors of {tips:?}"
        );

        let mut graph = HashMap::new();
        for iter_elem in self.dag.iter() {
            let (id, val) = iter_elem.unwrap();
            let hash = blake3::Hash::from_bytes((&id as &[u8]).try_into().unwrap());
            let event: Event = deserialize_async(&val).await.unwrap();
            graph.insert(hash, event);
        }

        let mut result = vec![];

        'outer: for tip in tips.iter() {
            for i in tip.1.iter() {
                if !graph.contains_key(i) {
                    continue 'outer;
                }
            }

            for (_, ev) in graph.iter() {
                if ev.layer > *tip.0 && !result.contains(ev) {
                    result.push(ev.clone())
                }
            }
        }

        result.sort_by(|a, b| a.layer.cmp(&b.layer));

        Ok(result)
    }
}