From 56b5ab3212e4f9767941851cde99cc657e41f21f Mon Sep 17 00:00:00 2001
From: Alexey Rusakov <Kitsune-Ral@users.sf.net>
Date: Fri, 13 Dec 2024 21:23:48 +0100
Subject: [PATCH] Room::getEvent()

You can now request an arbitrary event in the room, and save it for
future use (within a single running session, same as timeline).
---
 Quotient/room.cpp | 45 +++++++++++++++++++++++++++++++++++++++------
 Quotient/room.h   |  9 +++++++++
 2 files changed, 48 insertions(+), 6 deletions(-)

diff --git a/Quotient/room.cpp b/Quotient/room.cpp
index a6f55cb9..acafcc79 100644
--- a/Quotient/room.cpp
+++ b/Quotient/room.cpp
@@ -119,6 +119,8 @@ class Q_DECL_HIDDEN Room::Private {
 
     Timeline timeline;
     PendingEvents unsyncedEvents;
+    std::unordered_map<EventId, event_ptr_tt<const RoomEvent>> cachedEvents;
+    std::unordered_map<EventId, std::vector<EventPromise>> cachedEventPromises;
     QHash<QString, TimelineItem::index_t> eventsIndex;
     // A map from event id/relation type pairs to a vector of event pointers. Not using QMultiHash,
     // because we want to quickly return a number of relations for a given event without enumerating
@@ -258,11 +260,23 @@ class Q_DECL_HIDDEN Room::Private {
         return changes;
     }
     void addRelation(const ReactionEvent& reactionEvt);
-    void addRelations(auto from, auto to)
+    void finishEventPromises(const RoomEvent& evt)
     {
-        for (auto it = from; it != to; ++it)
-            if (const auto* reaction = it->template viewAs<ReactionEvent>())
-                addRelation(*reaction);
+        if (auto it = cachedEventPromises.find(evt.id()); it != cachedEventPromises.cend()) {
+            for (auto& p : it->second) {
+                p.addResult(std::cref(evt));
+                p.finish();
+            }
+            cachedEventPromises.erase(it);
+        }
+    }
+    void afterAddedMessages(auto from, auto to)
+    {
+        for (const auto& ti : std::ranges::subrange(from, to)) {
+            switchOnType(*ti, std::bind_front(&Private::addRelation, this));
+            finishEventPromises(*ti);
+            cachedEvents.erase(ti->id());
+        }
     }
 
     Changes addNewMessageEvents(RoomEvents&& events);
@@ -2382,6 +2396,25 @@ JobHandle<GetRoomEventsJob> Room::getPreviousContent(int limit, const QString& f
     return d->getPreviousContent(limit, filter);
 }
 
+EventFuture Room::getEvent(const QString& eventId)
+{
+    if (auto timelineIt = findInTimeline(eventId); timelineIt != historyEdge())
+        return makeReadyValueFuture(std::cref(**timelineIt));
+    auto baseStateObjects = d->baseState | std::views::values;
+    if (auto stateIt = std::ranges::find(baseStateObjects, eventId, &RoomEvent::id);
+        stateIt != end(baseStateObjects))
+        return makeReadyValueFuture(std::cref<RoomEvent>(**stateIt));
+    if (auto cachedIt = d->cachedEvents.find(eventId); cachedIt != d->cachedEvents.end())
+        return makeReadyValueFuture(std::cref(*cachedIt->second));
+
+    connection()->callApi<GetOneRoomEventJob>(id(), eventId).then([this](RoomEventPtr&& pEvt) {
+        const auto [it, cachedEventInserted] = d->cachedEvents.emplace(pEvt->id(), std::move(pEvt));
+        QUO_CHECK(cachedEventInserted);
+        d->finishEventPromises(*(it->second));
+    });
+    return d->cachedEventPromises[eventId].emplace_back().future();
+}
+
 EventFuture Room::ensureEvent(const QString& eventId, quint16 maxWaitSeconds)
 {
     if (auto eventIt = findInTimeline(eventId); eventIt != historyEdge())
@@ -3058,7 +3091,7 @@ Room::Changes Room::Private::addNewMessageEvents(RoomEvents&& events)
     }
 
     if (totalInserted > 0) {
-        addRelations(from, syncEdge());
+        afterAddedMessages(from, syncEdge());
 
         qCDebug(MESSAGES) << "Room" << q->objectName() << "received"
                        << totalInserted << "new events; the last event is now"
@@ -3117,7 +3150,7 @@ std::pair<Room::Changes, Room::rev_iter_t> Room::Private::addHistoricalMessageEv
     q->onAddHistoricalTimelineEvents(from);
     emit q->addedMessages(timeline.front().index(), from->index());
 
-    addRelations(from, historyEdge());
+    afterAddedMessages(from, historyEdge());
     Q_ASSERT(timeline.size() == timelineSize + insertedSize);
     if (insertedSize > 9 || et.nsecsElapsed() >= ProfilerMinNsecs)
         qCDebug(PROFILER) << "Added" << insertedSize << "historical event(s) to" << q->objectName()
diff --git a/Quotient/room.h b/Quotient/room.h
index d5a5898b..0b0ab8f9 100644
--- a/Quotient/room.h
+++ b/Quotient/room.h
@@ -750,6 +750,15 @@ class QUOTIENT_API Room : public QObject {
 
     QJsonArray exportMegolmSessions();
 
+    //! \brief Obtain an arbitrary room event by its id
+    //!
+    //! Looks through the timeline, state events that arrived out of the timeline, and finally
+    //! cached individual events; if the event is not found locally, requests this one event from
+    //! the homeserver.
+    //! \return a ready future with the event reference if an event with \p eventId is found locally;
+    //!         otherwise, a running future connected to the homeserver request
+    EventFuture getEvent(const QString& eventId);
+
     //! \brief Loads the message history until the specified event id is found
     //!
     //! This is potentially heavy; clients should use this sparingly. One intended use case is