This patch creates a constant to represent the
maximum number of timeline event to put in the cache:
`NUMBER_OF_TIMELINE_EVENTS_TO_KEEP_FOR_THE_CACHE`. Verbose, but easily
understandable.
This patch also renames a few variables.
This patch simplifies `SlidingSyncRoom::timeline_queue` from
```rust
Arc<RwLock<ObservableVector<SyncTimelineEvent>>>
```
to
```rust
Vector<SyncTimelineEvent>
```
First, we don't need to be observable. It's never observed since
it's private, and even privately, it's never observed, there is no
subscriber.
Second, no lock is required as updates happen synchronously.
Third, `Arc` is not necessary. We want each clone of `SlidingSyncRoom`
to not share any state across them.
Finally, this patch simplifies the iterator + `.push_back` by a simple
`.extend` to update the `timeline_queue`. Behind the scene, `impl Extend
for Vector` actually does an iterate + `.push_back`; let's keep our code
simple though.
`SlidingSyncRoom::is_cold` is not well-named. This patch introduces an
enum, named `SlidingSyncRoomState` which contains more detailed state:
`NotLoaded`, `Preloaded`, and `Loaded`.
The use of `AtomicBool` is also removed. Thus, we no longer need an
`Arc` for the state, which makes `Clone` more obvious: the state is not
shared across clones anymore.
A `SlidingSyncRoom` receives an Ruma
`api::client::sync::sync_events::v4:SlidingSyncRoom`. This value is
stored in the `SlidingSyncRoom::inner` field. From here, some getters
like `name()`, `is_dm()` etc. are using the `inner` field to compute a
result. There was one exception though: `prev_batch`. This value is part
of `v4::SlidingSyncRoom` but it was copied and updated in its own field:
`SlidingSyncRoom::prev_batch`.
I was wondering why. Turns out, there is no reason. Its getter
`prev_batch()` is public, but it's not used by the FFI bindings, so
basically nobody uses it (as this project is experimental as the time of
writing, we know our users).
This patch removes the `SlidingSyncRoom::prev_batch` field.
This patch also removes the `SlidingSyncRoom::prev_batch()` getter.
This patch finally removes the `FrozenSlidingSyncRoom::prev_batch` field
too.
Prior to this patch, to check a room exists, it was removed from the
collection, then re-added if it exists. Instead of doing this `remove`
+ `insert` dance, we can simply use `get_mut`, which also returns an
`Option`. This patch does that, in addition to rewrite the code to use a
`match` instead of a `if` + `else`.
`SlidingSync::subscribe` and `SlidingSync::unsubscribe` will cancel in-
flight requests, i.e. the `SlidingSyncInternalMessage::ContinueSyncLoop`
will be sent in the internal channel, just like what `SlidingSyncList`s
already do when a parameter is changed.
