event cache/timeline: reuse the Paginator when running back-paginat…

…ions (#3373)

* event cache: reuse the paginator internally

Fixes #3355.

* event cache: move the `pagination_token_notifier` into the `RoomPaginationData` as well

* event cache: introduce a `RoomPagination` API object and move code around

Only code motion. No changes in functionality.

* event cache: remove "paginate" (et al.) in `RoomPagination` method names

No changes in functionality, just renamings.

* event_cache/timeline: have the event cache handle restarting a back-pagination that failed under our feet

When a timeline reset happens while we're back-paginating, the event
cache method to run back pagination would return an success result
indicating that the pagination token disappeared. After thinking about
it, it's not the best API in the world; ideally, the backpagination
mechanism would restart automatically.

Now, this was handled in the timeline before, and the reason it was
handled there was because it was possible to back-paginate and ask for a
certain number of events. I've removed that feature, so that
back-pagination on a live timeline matches the capabilities of a
focused-timeline back-pagination: one can only ask for a given number of
*events*, not timeline items.

As a matter of fact, this simplifies the code a lot by removing many
data structures, that were also exposed (and unused, since recent
changes) in the FFI layer.

* Address review comments

bindings/matrix-sdk-ffi/src/timeline/mod.rs

@@ -17,12 +17,15 @@ use std::{collections::HashMap, fmt::Write as _, fs, sync::Arc};
 use anyhow::{Context, Result};
 use as_variant::as_variant;
 use eyeball_im::VectorDiff;
-use futures_util::{pin_mut, StreamExt};
-use matrix_sdk::attachment::{
-    AttachmentConfig, AttachmentInfo, BaseAudioInfo, BaseFileInfo, BaseImageInfo,
-    BaseThumbnailInfo, BaseVideoInfo, Thumbnail,
+use futures_util::{pin_mut, StreamExt as _};
+use matrix_sdk::{
+    attachment::{
+        AttachmentConfig, AttachmentInfo, BaseAudioInfo, BaseFileInfo, BaseImageInfo,
+        BaseThumbnailInfo, BaseVideoInfo, Thumbnail,
+    },
+    event_cache::paginator::PaginatorState,
 };
-use matrix_sdk_ui::timeline::{EventItemOrigin, PaginationStatus, Profile, TimelineDetails};
+use matrix_sdk_ui::timeline::{EventItemOrigin, Profile, TimelineDetails};
 use mime::Mime;
 use ruma::{
     events::{
@@ -164,11 +167,11 @@ impl Timeline {
         &self,
         listener: Box<dyn PaginationStatusListener>,
     ) -> Result<Arc<TaskHandle>, ClientError> {
-        let mut subscriber = self.inner.back_pagination_status();
+        let (initial, mut subscriber) = self.inner.back_pagination_status();
 
         Ok(Arc::new(TaskHandle::new(RUNTIME.spawn(async move {
             // Send the current state even if it hasn't changed right away.
-            listener.on_update(subscriber.next_now());
+            listener.on_update(initial);
 
             while let Some(status) = subscriber.next().await {
                 listener.on_update(status);
@@ -588,7 +591,7 @@ pub trait TimelineListener: Sync + Send {
 
 #[uniffi::export(callback_interface)]
 pub trait PaginationStatusListener: Sync + Send {
-    fn on_update(&self, status: PaginationStatus);
+    fn on_update(&self, status: PaginatorState);
 }
 
 #[derive(Clone, uniffi::Object)]
@@ -978,32 +981,6 @@ impl SendAttachmentJoinHandle {
     }
 }
 
-#[derive(uniffi::Enum)]
-pub enum PaginationOptions {
-    SimpleRequest { event_limit: u16, wait_for_token: bool },
-    UntilNumItems { event_limit: u16, items: u16, wait_for_token: bool },
-}
-
-impl From<PaginationOptions> for matrix_sdk_ui::timeline::PaginationOptions<'static> {
-    fn from(value: PaginationOptions) -> Self {
-        use matrix_sdk_ui::timeline::PaginationOptions as Opts;
-        let (wait_for_token, mut opts) = match value {
-            PaginationOptions::SimpleRequest { event_limit, wait_for_token } => {
-                (wait_for_token, Opts::simple_request(event_limit))
-            }
-            PaginationOptions::UntilNumItems { event_limit, items, wait_for_token } => {
-                (wait_for_token, Opts::until_num_items(event_limit, items))
-            }
-        };
-
-        if wait_for_token {
-            opts = opts.wait_for_token();
-        }
-
-        opts
-    }
-}
-
 /// A [`TimelineItem`](super::TimelineItem) that doesn't correspond to an event.
 #[derive(uniffi::Enum)]
 pub enum VirtualTimelineItem {

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

@@ -14,7 +14,6 @@
 
 use std::{collections::BTreeSet, sync::Arc};
 
-use eyeball::SharedObservable;
 use futures_util::{pin_mut, StreamExt};
 use matrix_sdk::{event_cache::RoomEventCacheUpdate, executor::spawn, Room};
 use ruma::{events::AnySyncTimelineEvent, RoomVersionId};
@@ -28,10 +27,7 @@ use super::{
     queue::send_queued_messages,
     Error, Timeline, TimelineDropHandle, TimelineFocus,
 };
-use crate::{
-    timeline::{event_item::RemoteEventOrigin, PaginationStatus},
-    unable_to_decrypt_hook::UtdHookManager,
-};
+use crate::{timeline::event_item::RemoteEventOrigin, unable_to_decrypt_hook::UtdHookManager};
 
 /// Builder that allows creating and configuring various parts of a
 /// [`Timeline`].
@@ -299,7 +295,6 @@ impl TimelineBuilder {
 
         let timeline = Timeline {
             inner,
-            back_pagination_status: SharedObservable::new(PaginationStatus::Idle),
             msg_sender,
             event_cache: room_event_cache,
             drop_handle: Arc::new(TimelineDropHandle {

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

@@ -18,7 +18,6 @@
 
 use std::{path::PathBuf, pin::Pin, sync::Arc, task::Poll};
 
-use eyeball::SharedObservable;
 use eyeball_im::VectorDiff;
 use futures_core::Stream;
 use imbl::Vector;
@@ -96,7 +95,6 @@ pub use self::{
     event_type_filter::TimelineEventTypeFilter,
     inner::default_event_filter,
     item::{TimelineItem, TimelineItemKind},
-    pagination::{PaginationOptions, PaginationOutcome, PaginationStatus},
     polls::PollResult,
     reactions::ReactionSenderData,
     sliding_sync_ext::SlidingSyncRoomExt,
@@ -130,9 +128,6 @@ pub struct Timeline {
 
     /// References to long-running tasks held by the timeline.
     drop_handle: Arc<TimelineDropHandle>,
-
-    /// Observable for whether a backward pagination is currently running.
-    pub(crate) back_pagination_status: SharedObservable<PaginationStatus>,
 }
 
 // Implements hash etc