Update presence dynamically and reduce allocations

src/timeline/PresenceEmitter.cpp

@@ -0,0 +1,73 @@
+#include "PresenceEmitter.h"
+
+#include <QCache>
+#include <Utils.h>
+
+#include "Cache.h"
+
+namespace {
+struct CacheEntry
+{
+    QString status;
+    mtx::presence::PresenceState state;
+};
+}
+
+static QCache<QString, CacheEntry> presences;
+
+static QString
+presenceToStr(mtx::presence::PresenceState state)
+{
+    switch (state) {
+    case mtx::presence::PresenceState::offline:
+        return QStringLiteral("offline");
+    case mtx::presence::PresenceState::unavailable:
+        return QStringLiteral("unavailable");
+    case mtx::presence::PresenceState::online:
+    default:
+        return QStringLiteral("online");
+    }
+}
+
+static CacheEntry *
+pullPresence(const QString &id)
+{
+    auto p = cache::presence(id.toStdString());
+    auto c = new CacheEntry{
+      utils::replaceEmoji(QString::fromStdString(p.status_msg).toHtmlEscaped()), p.presence};
+    presences.insert(id, c);
+    return c;
+}
+
+void
+PresenceEmitter::sync(
+  const std::vector<mtx::events::Event<mtx::events::presence::Presence>> &presences_)
+{
+    for (const auto &p : presences_) {
+        auto id = QString::fromStdString(p.sender);
+        presences.remove(id);
+        emit presenceChanged(std::move(id));
+    }
+}
+
+QString
+PresenceEmitter::userPresence(QString id) const
+{
+    if (id.isEmpty())
+        return {};
+    else if (auto p = presences[id])
+        return presenceToStr(p->state);
+    else
+        return presenceToStr(pullPresence(id)->state);
+}
+
+QString
+PresenceEmitter::userStatus(QString id) const
+{
+    if (id.isEmpty())
+        return {};
+    else if (auto p = presences[id])
+        return p->status;
+    else
+        return pullPresence(id)->status;
+}