optimize chatter list (#2814)

* optimize chatter list

* changelog

* Fix tests

Co-authored-by: Rasmus Karlsson <rasmus.karlsson@pajlada.com>

src/common/ChatterSet.cpp

@@ -0,0 +1,58 @@
+#include "common/ChatterSet.hpp"
+
+#include <tuple>
+#include "debug/Benchmark.hpp"
+
+namespace chatterino {
+
+ChatterSet::ChatterSet()
+    : items(chatterLimit)
+{
+}
+
+void ChatterSet::addRecentChatter(const QString &userName)
+{
+    this->items.put(userName.toLower(), userName);
+}
+
+void ChatterSet::updateOnlineChatters(
+    const std::unordered_set<QString> &lowerCaseUsernames)
+{
+    BenchmarkGuard bench("update online chatters");
+
+    // Create a new lru cache without the users that are not present anymore.
+    cache::lru_cache<QString, QString> tmp(chatterLimit);
+
+    for (auto &&chatter : lowerCaseUsernames)
+    {
+        if (this->items.exists(chatter))
+            tmp.put(chatter, this->items.get(chatter));
+
+        // Less chatters than the limit => try to preserve as many as possible.
+        else if (lowerCaseUsernames.size() < chatterLimit)
+            tmp.put(chatter, chatter);
+    }
+
+    this->items = std::move(tmp);
+}
+
+bool ChatterSet::contains(const QString &userName) const
+{
+    return this->items.exists(userName.toLower());
+}
+
+std::vector<QString> ChatterSet::filterByPrefix(const QString &prefix) const
+{
+    QString lowerPrefix = prefix.toLower();
+    std::vector<QString> result;
+
+    for (auto &&item : this->items)
+    {
+        if (item.first.startsWith(lowerPrefix))
+            result.push_back(item.second);
+    }
+
+    return result;
+}
+
+}  // namespace chatterino