replace HybridSet with NoteUnits

This will unify the collections that hold the notes to timelines
and threads and allow the notifications timeline to have grouped
notifications, among other things

Signed-off-by: kernelkind <kernelkind@gmail.com>

crates/notedeck_columns/src/actionbar.rs

@@ -385,7 +385,7 @@ pub fn process_thread_notes(
             created_at,
         };
 
-        if thread.replies.contains(&note_ref) {
+        if thread.replies.contains_key(&note_ref.key) {
             continue;
         }
 

crates/notedeck_columns/src/timeline/hybrid_set.rs

@@ -1,99 +0,0 @@
-use std::{
-    collections::{BTreeSet, HashSet},
-    hash::Hash,
-};
-
-use crate::timeline::MergeKind;
-
-/// Affords:
-/// - O(1) contains
-/// - O(log n) sorted insertion
-pub struct HybridSet<T> {
-    reversed: bool,
-    lookup: HashSet<T>,   // fast deduplication
-    ordered: BTreeSet<T>, // sorted iteration
-}
-
-impl<T> Default for HybridSet<T> {
-    fn default() -> Self {
-        Self {
-            reversed: Default::default(),
-            lookup: Default::default(),
-            ordered: Default::default(),
-        }
-    }
-}
-
-pub enum InsertionResponse {
-    AlreadyExists,
-    Merged(MergeKind),
-}
-
-impl<T: Copy + Ord + Eq + Hash> HybridSet<T> {
-    pub fn insert(&mut self, val: T) -> InsertionResponse {
-        if !self.lookup.insert(val) {
-            return InsertionResponse::AlreadyExists;
-        }
-
-        let front_insertion = match self.ordered.iter().next() {
-            Some(first) => (val >= *first) == self.reversed,
-            None => true,
-        };
-
-        self.ordered.insert(val); // O(log n)
-
-        InsertionResponse::Merged(if front_insertion {
-            MergeKind::FrontInsert
-        } else {
-            MergeKind::Spliced
-        })
-    }
-}
-
-impl<T: Eq + Hash> HybridSet<T> {
-    pub fn contains(&self, val: &T) -> bool {
-        self.lookup.contains(val) // O(1)
-    }
-}
-
-impl<T> HybridSet<T> {
-    pub fn iter(&self) -> HybridIter<'_, T> {
-        HybridIter {
-            inner: self.ordered.iter(),
-            reversed: self.reversed,
-        }
-    }
-
-    pub fn new(reversed: bool) -> Self {
-        Self {
-            reversed,
-            ..Default::default()
-        }
-    }
-}
-
-impl<'a, T> IntoIterator for &'a HybridSet<T> {
-    type Item = &'a T;
-    type IntoIter = HybridIter<'a, T>;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.iter()
-    }
-}
-
-pub struct HybridIter<'a, T> {
-    inner: std::collections::btree_set::Iter<'a, T>,
-    reversed: bool,
-}
-
-impl<'a, T> Iterator for HybridIter<'a, T> {
-    type Item = &'a T;
-
-    fn next(&mut self) -> Option<Self::Item> {
-        if self.reversed {
-            self.inner.next_back()
-        } else {
-            self.inner.next()
-        }
-    }
-}

crates/notedeck_columns/src/timeline/mod.rs

@@ -26,14 +26,16 @@ use std::{rc::Rc, time::SystemTime};
 use tracing::{debug, error, info, warn};
 
 pub mod cache;
-mod hybrid_set;
 pub mod kind;
+mod note_units;
 pub mod route;
 pub mod thread;
+mod unit;
 
 pub use cache::TimelineCache;
-pub use hybrid_set::{HybridSet, InsertionResponse};
 pub use kind::{ColumnTitle, PubkeySource, ThreadSelection, TimelineKind};
+pub use note_units::{InsertionResponse, NoteUnits};
+pub use unit::{CompositeUnit, NoteUnit, ReactionUnit};
 
 #[derive(Copy, Clone, Eq, PartialEq, Debug, Default)]
 pub enum ViewFilter {

crates/notedeck_columns/src/timeline/note_units.rs

@@ -0,0 +1,511 @@
+use std::collections::{HashMap, HashSet};
+
+use nostrdb::NoteKey;
+use notedeck::NoteRef;
+
+use crate::timeline::{
+    unit::{CompositeUnit, NoteUnit, NoteUnitFragment},
+    MergeKind,
+};
+
+type StorageIndex = usize;
+
+/// Provides efficient access to `NoteUnit`s
+/// Useful for threads and timelines
+/// when reversed=false, sorts from newest to oldest
+#[derive(Debug, Default)]
+pub struct NoteUnits {
+    reversed: bool,
+    storage: Vec<NoteUnit>,
+    lookup: HashMap<NoteKey, StorageIndex>, // `NoteKey` to index in `NoteUnits::storage`
+    order: Vec<StorageIndex>, // the sorted order of the `NoteUnit`s in `NoteUnits::storage`
+}
+
+impl NoteUnits {
+    pub fn values(&self) -> Values<'_> {
+        Values {
+            set: self,
+            front: 0,
+            back: self.order.len(),
+        }
+    }
+
+    pub fn contains_key(&self, k: &NoteKey) -> bool {
+        self.lookup.contains_key(k)
+    }
+
+    pub fn new_with_cap(cap: usize, reversed: bool) -> Self {
+        Self {
+            reversed,
+            storage: Vec::with_capacity(cap),
+            lookup: HashMap::with_capacity(cap),
+            order: Vec::with_capacity(cap),
+        }
+    }
+
+    pub fn len(&self) -> usize {
+        self.storage.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.storage.is_empty()
+    }
+
+    /// Get the kth index from 0..Self::len
+    pub fn kth(&self, k: usize) -> Option<&NoteUnit> {
+        if k >= self.order.len() {
+            return None;
+        }
+        let idx = if self.reversed {
+            self.order[self.order.len() - 1 - k]
+        } else {
+            self.order[k]
+        };
+        Some(&self.storage[idx])
+    }
+
+    /// Core bulk insert for already-built `NoteUnit`s
+    /// Merges new `NoteUnit`s into `Self::storage`
+    /// Updates `Self::order`
+    fn merge_many_internal(
+        &mut self,
+        mut units: Vec<NoteUnit>,
+        touched_indices: &[usize],
+    ) -> InsertManyResponse {
+        units.retain(|e| !self.lookup.contains_key(&e.key()));
+        if units.is_empty() && touched_indices.is_empty() {
+            return InsertManyResponse::Zero;
+        }
+
+        if !touched_indices.is_empty() {
+            self.order.retain(|i| !touched_indices.contains(i));
+        }
+
+        units.sort_unstable();
+        units.dedup_by_key(|u| u.key());
+
+        let base = self.storage.len();
+        let mut new_order = Vec::with_capacity(units.len());
+        self.storage.reserve(units.len());
+        for (i, unit) in units.into_iter().enumerate() {
+            let idx = base + i;
+            let key = unit.key();
+            self.storage.push(unit);
+            self.lookup.insert(key, idx);
+            new_order.push(idx);
+        }
+
+        let front_insertion = if self.order.is_empty() || new_order.is_empty() {
+            true
+        } else if !self.reversed {
+            let first_new = *new_order.first().unwrap();
+            let last_old = *self.order.last().unwrap();
+            self.storage[first_new] >= self.storage[last_old]
+        } else {
+            let last_new = *new_order.last().unwrap();
+            let first_old = *self.order.first().unwrap();
+            self.storage[last_new] <= self.storage[first_old]
+        };
+
+        let mut merged = Vec::with_capacity(self.order.len() + new_order.len());
+        let (mut i, mut j) = (0, 0);
+        while i < self.order.len() && j < new_order.len() {
+            let index_left = self.order[i];
+            let index_right = new_order[j];
+            let left_item = &self.storage[index_left];
+            let right_item = &self.storage[index_right];
+            if left_item <= right_item {
+                // left_item is newer than right_item
+                merged.push(index_left);
+                i += 1;
+            } else {
+                merged.push(index_right);
+                j += 1;
+            }
+        }
+        merged.extend_from_slice(&self.order[i..]);
+        merged.extend_from_slice(&new_order[j..]);
+
+        for &touched_index in touched_indices {
+            let pos = merged
+                .binary_search_by(|&i2| self.storage[i2].cmp(&self.storage[touched_index]))
+                .unwrap_or_else(|p| p);
+            merged.insert(pos, touched_index);
+        }
+
+        let inserted = merged.len() - self.order.len();
+        self.order = merged;
+
+        if inserted == 0 {
+            InsertManyResponse::Zero
+        } else if front_insertion {
+            InsertManyResponse::Some {
+                entries_merged: inserted,
+                merge_kind: MergeKind::FrontInsert,
+            }
+        } else {
+            InsertManyResponse::Some {
+                entries_merged: inserted,
+                merge_kind: MergeKind::Spliced,
+            }
+        }
+    }
+
+    /// Merges `NoteUnitFragment`s
+    /// `NoteUnitFragment::Single` is added normally
+    /// if `NoteUnitFragment::Composite` exists already, it will fold the fragment into the `CompositeUnit`
+    /// otherwise, it will generate the `NoteUnit::CompositeUnit` from the `NoteUnitFragment::Composite`
+    pub fn merge_fragments(&mut self, frags: Vec<NoteUnitFragment>) -> InsertManyResponse {
+        let mut to_build: HashMap<NoteKey, CompositeUnit> = HashMap::new(); // new composites by key
+        let mut singles_to_build: Vec<NoteRef> = Vec::new();
+        let mut singles_seen: HashSet<NoteKey> = HashSet::new();
+
+        let mut touched = Vec::new();
+        for frag in frags {
+            match frag {
+                NoteUnitFragment::Single(note_ref) => {
+                    let key = note_ref.key;
+                    if self.lookup.contains_key(&key) {
+                        continue;
+                    }
+                    if singles_seen.insert(key) {
+                        singles_to_build.push(note_ref);
+                    }
+                }
+                NoteUnitFragment::Composite(c_frag) => {
+                    let key = c_frag.get_underlying_noteref().key;
+
+                    if let Some(&storage_idx) = self.lookup.get(&key) {
+                        if let Some(NoteUnit::Composite(c_unit)) = self.storage.get_mut(storage_idx)
+                        {
+                            if c_frag.get_latest_ref() < c_unit.get_latest_ref() {
+                                touched.push(storage_idx);
+                            }
+                            c_frag.fold_into(c_unit);
+                            continue;
+                        }
+                    }
+                    // aggregate for new composite
+                    use std::collections::hash_map::Entry;
+                    match to_build.entry(key) {
+                        Entry::Occupied(mut o) => {
+                            c_frag.fold_into(o.get_mut());
+                        }
+                        Entry::Vacant(v) => {
+                            v.insert(c_frag.into());
+                        }
+                    }
+                }
+            }
+        }
+
+        let mut items: Vec<NoteUnit> = Vec::with_capacity(singles_to_build.len() + to_build.len());
+        items.extend(singles_to_build.into_iter().map(NoteUnit::Single));
+        items.extend(to_build.into_values().map(NoteUnit::Composite));
+
+        self.merge_many_internal(items, &touched)
+    }
+
+    /// Convienience method to merge a single note
+    pub fn merge_single_unit(&mut self, note_ref: NoteRef) -> InsertionResponse {
+        match self.merge_many_internal(vec![NoteUnit::Single(note_ref)], &[]) {
+            InsertManyResponse::Zero => InsertionResponse::AlreadyExists,
+            InsertManyResponse::Some {
+                entries_merged: _,
+                merge_kind,
+            } => InsertionResponse::Merged(merge_kind),
+        }
+    }
+
+    pub fn latest_ref(&self) -> Option<&NoteRef> {
+        if self.reversed {
+            self.order.last().map(|&i| &self.storage[i])
+        } else {
+            self.order.first().map(|&i| &self.storage[i])
+        }
+        .map(NoteUnit::get_latest_ref)
+    }
+}
+
+pub enum InsertManyResponse {
+    Zero,
+    Some {
+        entries_merged: usize,
+        merge_kind: MergeKind,
+    },
+}
+
+pub struct Values<'a> {
+    set: &'a NoteUnits,
+    front: usize,
+    back: usize,
+}
+
+impl<'a> Iterator for Values<'a> {
+    type Item = &'a NoteUnit;
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.front >= self.back {
+            return None;
+        }
+        let idx = if !self.set.reversed {
+            let i = self.front;
+            self.front += 1;
+            self.set.order[i]
+        } else {
+            self.back -= 1;
+            self.set.order[self.back]
+        };
+        Some(&self.set.storage[idx])
+    }
+}
+
+impl<'a> DoubleEndedIterator for Values<'a> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        if self.front >= self.back {
+            return None;
+        }
+        let idx = if !self.set.reversed {
+            self.back -= 1;
+            self.set.order[self.back]
+        } else {
+            let i = self.front;
+            self.front += 1;
+            self.set.order[i]
+        };
+        Some(&self.set.storage[idx])
+    }
+}
+
+pub enum InsertionResponse {
+    AlreadyExists,
+    Merged(MergeKind),
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::{BTreeMap, HashSet};
+
+    use egui::ahash::HashMap;
+    use enostr::Pubkey;
+    use nostrdb::NoteKey;
+    use notedeck::NoteRef;
+    use pretty_assertions::assert_eq;
+
+    use uuid::Uuid;
+
+    use crate::timeline::{
+        unit::{
+            CompositeFragment, CompositeUnit, NoteUnit, NoteUnitFragment, Reaction,
+            ReactionFragment, ReactionUnit,
+        },
+        NoteUnits,
+    };
+
+    #[derive(Default)]
+    struct UnitBuilder {
+        counter: u64,
+        frags: HashMap<String, NoteUnitFragment>,
+        units: NoteUnits,
+    }
+
+    impl UnitBuilder {
+        fn counter(&mut self) -> u64 {
+            let res = self.counter;
+            self.counter += 1;
+            res
+        }
+
+        fn random_sender(&mut self) -> Pubkey {
+            let mut out = [0u8; 32];
+            out[..8].copy_from_slice(&self.counter().to_le_bytes());
+
+            Pubkey::new(out)
+        }
+
+        fn fragment(&mut self, reacted_to: NoteRef) -> String {
+            let frag = NoteUnitFragment::Composite(CompositeFragment::Reaction(ReactionFragment {
+                noteref_reacted_to: reacted_to,
+                reaction_note_ref: NoteRef {
+                    key: NoteKey::new(self.counter()),
+                    created_at: self.counter(),
+                },
+                reaction: Reaction {
+                    reaction: "+".to_owned(),
+                    sender: self.random_sender(),
+                },
+            }));
+            let id = Uuid::new_v4().to_string();
+            self.frags.insert(id.clone(), frag.clone());
+
+            self.units.merge_fragments(vec![frag]);
+
+            id
+        }
+
+        fn generate_reaction_note(&mut self) -> NoteRef {
+            NoteRef {
+                key: NoteKey::new(self.counter()),
+                created_at: self.counter(),
+            }
+        }
+
+        fn insert_note(&mut self) -> String {
+            let note_ref = NoteRef {
+                key: NoteKey::new(self.counter()),
+                created_at: self.counter(),
+            };
+
+            let id = Uuid::new_v4().to_string();
+            self.frags
+                .insert(id.clone(), NoteUnitFragment::Single(note_ref.clone()));
+
+            self.units.merge_single_unit(note_ref);
+
+            id
+        }
+
+        fn expected_reactions(&mut self, ids: Vec<&String>) -> NoteUnit {
+            let mut reactions = BTreeMap::new();
+            let mut reaction_id = None;
+            let mut senders = HashSet::new();
+            for id in ids {
+                let NoteUnitFragment::Composite(CompositeFragment::Reaction(reac)) =
+                    self.frags.get(id).unwrap()
+                else {
+                    panic!("got something other than reaction");
+                };
+
+                if let Some(prev_reac_id) = reaction_id {
+                    if prev_reac_id != reac.noteref_reacted_to {
+                        panic!("internal error");
+                    }
+                }
+
+                reaction_id = Some(reac.noteref_reacted_to);
+
+                reactions.insert(reac.reaction_note_ref, reac.reaction.clone());
+                senders.insert(reac.reaction.sender);
+            }
+
+            NoteUnit::Composite(CompositeUnit::Reaction(ReactionUnit {
+                note_reacted_to: reaction_id.unwrap(),
+                reactions,
+                senders: senders,
+            }))
+        }
+
+        fn expected_single(&mut self, id: &String) -> NoteUnit {
+            let Some(NoteUnitFragment::Single(note_ref)) = self.frags.get(id) else {
+                panic!("fail");
+            };
+
+            NoteUnit::Single(*note_ref)
+        }
+
+        fn asserted_at(&self, index: usize) -> NoteUnit {
+            self.units.kth(index).unwrap().clone()
+        }
+
+        fn aeq(&mut self, units_kth: usize, expect: Expect) {
+            assert_eq!(
+                self.asserted_at(units_kth),
+                match expect {
+                    Expect::Single(id) => self.expected_single(id),
+                    Expect::Reaction(items) => self.expected_reactions(items),
+                }
+            );
+        }
+    }
+
+    enum Expect<'a> {
+        Single(&'a String),
+        Reaction(Vec<&'a String>),
+    }
+
+    #[test]
+    fn test() {
+        let mut builder = UnitBuilder::default();
+        let reaction_note = builder.generate_reaction_note();
+
+        let single0 = builder.insert_note();
+        builder.aeq(0, Expect::Single(&single0));
+
+        let reac1 = builder.fragment(reaction_note);
+        builder.aeq(0, Expect::Reaction(vec![&reac1]));
+        builder.aeq(1, Expect::Single(&single0));
+
+        let single1 = builder.insert_note();
+        builder.aeq(0, Expect::Single(&single1));
+        builder.aeq(1, Expect::Reaction(vec![&reac1]));
+        builder.aeq(2, Expect::Single(&single0));
+
+        let reac2 = builder.fragment(reaction_note);
+        builder.aeq(0, Expect::Reaction(vec![&reac2, &reac1]));
+        builder.aeq(1, Expect::Single(&single1));
+        builder.aeq(2, Expect::Single(&single0));
+
+        let single2 = builder.insert_note();
+        builder.aeq(0, Expect::Single(&single2));
+        builder.aeq(1, Expect::Reaction(vec![&reac2, &reac1]));
+        builder.aeq(2, Expect::Single(&single1));
+        builder.aeq(3, Expect::Single(&single0));
+
+        let reac3 = builder.fragment(reaction_note);
+        builder.aeq(0, Expect::Reaction(vec![&reac1, &reac2, &reac3]));
+        builder.aeq(1, Expect::Single(&single2));
+        builder.aeq(2, Expect::Single(&single1));
+        builder.aeq(3, Expect::Single(&single0));
+    }
+
+    #[test]
+    fn test2() {
+        let mut builder = UnitBuilder::default();
+        let reaction_note1 = builder.generate_reaction_note();
+        let reaction_note2 = builder.generate_reaction_note();
+
+        let single0 = builder.insert_note();
+        builder.aeq(0, Expect::Single(&single0));
+
+        let reac1_1 = builder.fragment(reaction_note1);
+        builder.aeq(0, Expect::Reaction(vec![&reac1_1]));
+        builder.aeq(1, Expect::Single(&single0));
+
+        let reac2_1 = builder.fragment(reaction_note2);
+        builder.aeq(0, Expect::Reaction(vec![&reac2_1]));
+        builder.aeq(1, Expect::Reaction(vec![&reac1_1]));
+        builder.aeq(2, Expect::Single(&single0));
+
+        let single1 = builder.insert_note();
+        builder.aeq(0, Expect::Single(&single1));
+        builder.aeq(1, Expect::Reaction(vec![&reac2_1]));
+        builder.aeq(2, Expect::Reaction(vec![&reac1_1]));
+        builder.aeq(3, Expect::Single(&single0));
+
+        let reac1_2 = builder.fragment(reaction_note1);
+        builder.aeq(0, Expect::Reaction(vec![&reac1_2, &reac1_1]));
+        builder.aeq(1, Expect::Single(&single1));
+        builder.aeq(2, Expect::Reaction(vec![&reac2_1]));
+        builder.aeq(3, Expect::Single(&single0));
+
+        let single2 = builder.insert_note();
+        builder.aeq(0, Expect::Single(&single2));
+        builder.aeq(1, Expect::Reaction(vec![&reac1_2, &reac1_1]));
+        builder.aeq(2, Expect::Single(&single1));
+        builder.aeq(3, Expect::Reaction(vec![&reac2_1]));
+        builder.aeq(4, Expect::Single(&single0));
+
+        let reac1_3 = builder.fragment(reaction_note1);
+        builder.aeq(0, Expect::Reaction(vec![&reac1_2, &reac1_1, &reac1_3]));
+        builder.aeq(1, Expect::Single(&single2));
+        builder.aeq(2, Expect::Single(&single1));
+        builder.aeq(3, Expect::Reaction(vec![&reac2_1]));
+        builder.aeq(4, Expect::Single(&single0));
+
+        let reac2_2 = builder.fragment(reaction_note2);
+        builder.aeq(0, Expect::Reaction(vec![&reac2_1, &reac2_2]));
+        builder.aeq(1, Expect::Reaction(vec![&reac1_2, &reac1_1, &reac1_3]));
+        builder.aeq(2, Expect::Single(&single2));
+        builder.aeq(3, Expect::Single(&single1));
+        builder.aeq(4, Expect::Single(&single0));
+    }
+}

crates/notedeck_columns/src/timeline/thread.rs

@@ -8,13 +8,13 @@ use notedeck::{NoteCache, NoteRef, UnknownIds};
 use crate::{
     actionbar::{process_thread_notes, NewThreadNotes},
     multi_subscriber::ThreadSubs,
-    timeline::hybrid_set::HybridSet,
+    timeline::{note_units::NoteUnits, unit::NoteUnit, InsertionResponse},
 };
 
 use super::ThreadSelection;
 
 pub struct ThreadNode {
-    pub replies: HybridSet<NoteRef>,
+    pub replies: SingleNoteUnits,
     pub prev: ParentState,
     pub have_all_ancestors: bool,
     pub list: VirtualList,
@@ -31,7 +31,7 @@ pub enum ParentState {
 impl ThreadNode {
     pub fn new(parent: ParentState) -> Self {
         Self {
-            replies: HybridSet::new(true),
+            replies: SingleNoteUnits::new(true),
             prev: parent,
             have_all_ancestors: false,
             list: VirtualList::new(),
@@ -389,3 +389,34 @@ impl NoteSeenFlags {
         self.flags.contains_key(&note_id)
     }
 }
+
+#[derive(Default)]
+pub struct SingleNoteUnits {
+    units: NoteUnits,
+}
+
+impl SingleNoteUnits {
+    pub fn new(reversed: bool) -> Self {
+        Self {
+            units: NoteUnits::new_with_cap(0, reversed),
+        }
+    }
+
+    pub fn insert(&mut self, note_ref: NoteRef) -> InsertionResponse {
+        self.units.merge_single_unit(note_ref)
+    }
+
+    pub fn values(&self) -> impl Iterator<Item = &NoteRef> {
+        self.units.values().filter_map(|entry| {
+            if let NoteUnit::Single(note_ref) = entry {
+                Some(note_ref)
+            } else {
+                None
+            }
+        })
+    }
+
+    pub fn contains_key(&self, k: &NoteKey) -> bool {
+        self.units.contains_key(k)
+    }
+}

crates/notedeck_columns/src/timeline/unit.rs

@@ -0,0 +1,205 @@
+use std::collections::{BTreeMap, HashSet};
+
+use enostr::Pubkey;
+use nostrdb::NoteKey;
+use notedeck::NoteRef;
+
+/// A `NoteUnit` represents a cohesive piece of data derived from notes
+#[derive(Debug, Clone)]
+pub enum NoteUnit {
+    Single(NoteRef), // A single note
+    Composite(CompositeUnit),
+}
+
+impl NoteUnit {
+    pub fn key(&self) -> NoteKey {
+        match self {
+            NoteUnit::Single(note_ref) => note_ref.key,
+            NoteUnit::Composite(clustered_entry) => clustered_entry.key(),
+        }
+    }
+
+    pub fn get_underlying_noteref(&self) -> &NoteRef {
+        match self {
+            NoteUnit::Single(note_ref) => note_ref,
+            NoteUnit::Composite(clustered) => match clustered {
+                CompositeUnit::Reaction(reaction_entry) => &reaction_entry.note_reacted_to,
+            },
+        }
+    }
+
+    pub fn get_latest_ref(&self) -> &NoteRef {
+        match self {
+            NoteUnit::Single(note_ref) => note_ref,
+            NoteUnit::Composite(composite_unit) => composite_unit.get_latest_ref(),
+        }
+    }
+}
+
+impl Ord for NoteUnit {
+    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
+        self.get_latest_ref().cmp(other.get_latest_ref())
+    }
+}
+
+impl PartialEq for NoteUnit {
+    fn eq(&self, other: &Self) -> bool {
+        self.get_latest_ref() == other.get_latest_ref()
+    }
+}
+
+impl Eq for NoteUnit {}
+
+impl PartialOrd for NoteUnit {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+/// Combines potentially many notes into one cohesive piece of data
+#[derive(Debug, Clone)]
+pub enum CompositeUnit {
+    Reaction(ReactionUnit),
+}
+
+impl CompositeUnit {
+    pub fn get_latest_ref(&self) -> &NoteRef {
+        match self {
+            CompositeUnit::Reaction(reaction_unit) => reaction_unit.get_latest_ref(),
+        }
+    }
+}
+
+impl PartialEq for CompositeUnit {
+    fn eq(&self, other: &Self) -> bool {
+        match (self, other) {
+            (Self::Reaction(l0), Self::Reaction(r0)) => l0 == r0,
+        }
+    }
+}
+
+impl CompositeUnit {
+    pub fn key(&self) -> NoteKey {
+        match self {
+            CompositeUnit::Reaction(reaction_entry) => reaction_entry.note_reacted_to.key,
+        }
+    }
+}
+
+impl From<CompositeFragment> for CompositeUnit {
+    fn from(value: CompositeFragment) -> Self {
+        match value {
+            CompositeFragment::Reaction(reaction_fragment) => {
+                CompositeUnit::Reaction(reaction_fragment.into())
+            }
+        }
+    }
+}
+
+/// Represents all the reactions to a specific note `ReactionUnit::note_reacted_to`
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct ReactionUnit {
+    pub note_reacted_to: NoteRef, // NOTE: this should not be modified after it's created
+    pub reactions: BTreeMap<NoteRef, Reaction>,
+    pub senders: HashSet<Pubkey>, // useful for making sure the same user can't add more than one reaction to a note
+}
+
+impl ReactionUnit {
+    pub fn get_latest_ref(&self) -> &NoteRef {
+        self.reactions
+            .first_key_value()
+            .map(|(r, _)| r)
+            .unwrap_or(&self.note_reacted_to)
+    }
+}
+
+impl From<ReactionFragment> for ReactionUnit {
+    fn from(frag: ReactionFragment) -> Self {
+        let mut senders = HashSet::new();
+        senders.insert(frag.reaction.sender);
+
+        let mut reactions = BTreeMap::new();
+        reactions.insert(frag.reaction_note_ref, frag.reaction);
+
+        Self {
+            note_reacted_to: frag.noteref_reacted_to,
+            reactions,
+            senders,
+        }
+    }
+}
+
+#[derive(Clone)]
+pub enum NoteUnitFragment {
+    Single(NoteRef),
+    Composite(CompositeFragment),
+}
+
+#[derive(Debug, Clone)]
+pub enum CompositeFragment {
+    Reaction(ReactionFragment),
+}
+
+impl CompositeFragment {
+    pub fn fold_into(self, unit: &mut CompositeUnit) {
+        match self {
+            CompositeFragment::Reaction(reaction_fragment) => reaction_fragment.fold_into(unit),
+        }
+    }
+
+    pub fn key(&self) -> NoteKey {
+        match self {
+            CompositeFragment::Reaction(reaction_fragment) => {
+                reaction_fragment.reaction_note_ref.key
+            }
+        }
+    }
+
+    pub fn get_underlying_noteref(&self) -> &NoteRef {
+        match self {
+            CompositeFragment::Reaction(reaction_fragment) => &reaction_fragment.noteref_reacted_to,
+        }
+    }
+
+    pub fn get_latest_ref(&self) -> &NoteRef {
+        match self {
+            CompositeFragment::Reaction(reaction_fragment) => &reaction_fragment.reaction_note_ref,
+        }
+    }
+}
+
+/// A singluar reaction to a note
+#[derive(Debug, Clone)]
+pub struct ReactionFragment {
+    pub noteref_reacted_to: NoteRef,
+    pub reaction_note_ref: NoteRef,
+    pub reaction: Reaction,
+}
+
+impl ReactionFragment {
+    /// Add all the contents of Self into `CompositeUnit`
+    pub fn fold_into(self, unit: &mut CompositeUnit) {
+        match unit {
+            CompositeUnit::Reaction(reaction_unit) => {
+                if self.noteref_reacted_to != reaction_unit.note_reacted_to {
+                    return;
+                }
+
+                if reaction_unit.senders.contains(&self.reaction.sender) {
+                    return;
+                }
+
+                reaction_unit.senders.insert(self.reaction.sender);
+                reaction_unit
+                    .reactions
+                    .insert(self.reaction_note_ref, self.reaction);
+            }
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct Reaction {
+    pub reaction: String, // can't use char because some emojis are 'grapheme clusters'
+    pub sender: Pubkey,
+}

crates/notedeck_columns/src/ui/thread.rs

@@ -111,7 +111,7 @@ impl<'a, 'd> ThreadView<'a, 'd> {
             parent_state = ParentState::Unknown;
         }
 
-        for note_ref in &cur_node.replies {
+        for note_ref in cur_node.replies.values() {
             if let Ok(note) = self.note_context.ndb.get_note_by_key(txn, note_ref.key) {
                 note_builder.add_reply(note);
             }