refactor(ui): Introduce the AllRemoteEvents type.

This patch replaces `VecDeque<EventMeta>` by `AllRemoteEvents` which
is a wrapper type around `VecDeque<EventMeta>`, but this new type aims
at adding semantics API rather than a generic API. It also helps to
isolate the use of these values and to know precisely when and how they
are used.

As a first step, `AllRemoteEvents` implements a generic API to not break
the existing code. Next patches will revisit that a little bit step
by step.

crates/matrix-sdk-ui/src/timeline/controller/mod.rs

@@ -52,7 +52,7 @@ use tracing::{
 };
 
 pub(super) use self::state::{
-    EventMeta, FullEventMeta, PendingEdit, PendingEditKind, TimelineMetadata,
+    AllRemoteEvents, FullEventMeta, PendingEdit, PendingEditKind, TimelineMetadata,
     TimelineNewItemPosition, TimelineState, TimelineStateTransaction,
 };
 use super::{

crates/matrix-sdk-ui/src/timeline/controller/state.rs

@@ -13,7 +13,10 @@
 // limitations under the License.
 
 use std::{
-    collections::{HashMap, VecDeque},
+    collections::{
+        vec_deque::{Iter, IterMut},
+        HashMap, VecDeque,
+    },
     future::Future,
     num::NonZeroUsize,
     sync::{Arc, RwLock},
@@ -715,7 +718,7 @@ impl TimelineStateTransaction<'_> {
         // Returns its position, in this case.
         fn event_already_exists(
             new_event_id: &EventId,
-            all_remote_events: &VecDeque<EventMeta>,
+            all_remote_events: &AllRemoteEvents,
         ) -> Option<usize> {
             all_remote_events.iter().position(|EventMeta { event_id, .. }| event_id == new_event_id)
         }
@@ -924,7 +927,7 @@ pub(in crate::timeline) struct TimelineMetadata {
     ///
     /// This is useful to get this for the moment as it helps the `Timeline` to
     /// compute read receipts and read markers.
-    pub all_remote_events: VecDeque<EventMeta>,
+    pub all_remote_events: AllRemoteEvents,
 
     /// State helping matching reactions to their associated events, and
     /// stashing pending reactions.
@@ -1139,6 +1142,52 @@ impl TimelineMetadata {
     }
 }
 
+/// A type for all remote events.
+///
+/// Having this type helps to know exactly which parts of the code and how they
+/// use all remote events. It also helps to give a bit of semantics on top of
+/// them.
+#[derive(Clone, Debug, Default)]
+pub(crate) struct AllRemoteEvents(VecDeque<EventMeta>);
+
+impl AllRemoteEvents {
+    /// Return a front-to-back iterator over all remote events.
+    pub fn iter(&self) -> Iter<'_, EventMeta> {
+        self.0.iter()
+    }
+
+    /// Return a front-to-back iterator over all remote events as mutable
+    /// references.
+    pub fn iter_mut(&mut self) -> IterMut<'_, EventMeta> {
+        self.0.iter_mut()
+    }
+
+    /// Remove all remote events.
+    pub fn clear(&mut self) {
+        self.0.clear();
+    }
+
+    /// Insert a new remote event at the front of all the others.
+    pub fn push_front(&mut self, event_meta: EventMeta) {
+        self.0.push_front(event_meta)
+    }
+
+    /// Insert a new remote event at the back of all the others.
+    pub fn push_back(&mut self, event_meta: EventMeta) {
+        self.0.push_back(event_meta)
+    }
+
+    /// Remove one remote event at a specific index, and return it if it exists.
+    pub fn remove(&mut self, event_index: usize) -> Option<EventMeta> {
+        self.0.remove(event_index)
+    }
+
+    /// Return a reference to the last remote event if it exists.
+    pub fn back(&self) -> Option<&EventMeta> {
+        self.0.back()
+    }
+}
+
 /// Full metadata about an event.
 ///
 /// Only used to group function parameters.

crates/matrix-sdk-ui/src/timeline/read_receipts.rs

@@ -12,11 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use std::{
-    cmp::Ordering,
-    collections::{HashMap, VecDeque},
-    sync::Arc,
-};
+use std::{cmp::Ordering, collections::HashMap, sync::Arc};
 
 use eyeball_im::ObservableVectorTransaction;
 use futures_core::Stream;
@@ -31,7 +27,7 @@ use tracing::{debug, error, warn};
 
 use super::{
     controller::{
-        EventMeta, FullEventMeta, TimelineMetadata, TimelineState, TimelineStateTransaction,
+        AllRemoteEvents, FullEventMeta, TimelineMetadata, TimelineState, TimelineStateTransaction,
     },
     traits::RoomDataProvider,
     util::{rfind_event_by_id, RelativePosition},
@@ -103,7 +99,7 @@ impl ReadReceipts {
         &mut self,
         new_receipt: FullReceipt<'_>,
         is_own_user_id: bool,
-        all_events: &VecDeque<EventMeta>,
+        all_events: &AllRemoteEvents,
         timeline_items: &mut ObservableVectorTransaction<'_, Arc<TimelineItem>>,
     ) {
         // Get old receipt.
@@ -243,7 +239,7 @@ impl ReadReceipts {
     pub(super) fn compute_event_receipts(
         &self,
         event_id: &EventId,
-        all_events: &VecDeque<EventMeta>,
+        all_events: &AllRemoteEvents,
         at_end: bool,
     ) -> IndexMap<OwnedUserId, Receipt> {
         let mut all_receipts = self.get_event_receipts(event_id).cloned().unwrap_or_default();