Add username autocompletion popup menu (#2866)

src/widgets/splits/InputCompletionPopup.hpp

@@ -0,0 +1,43 @@
+#pragma once
+
+#include <functional>
+#include "common/Channel.hpp"
+#include "widgets/BasePopup.hpp"
+#include "widgets/listview/GenericListModel.hpp"
+
+namespace chatterino {
+
+class GenericListView;
+
+class InputCompletionPopup : public BasePopup
+{
+    using ActionCallback = std::function<void(const QString &)>;
+
+    constexpr static int maxEntryCount = 200;
+
+public:
+    InputCompletionPopup(QWidget *parent = nullptr);
+
+    void updateEmotes(const QString &text, ChannelPtr channel);
+    void updateUsers(const QString &text, ChannelPtr channel);
+    virtual bool eventFilter(QObject *, QEvent *event) override;
+
+    void setInputAction(ActionCallback callback);
+
+protected:
+    void showEvent(QShowEvent *event) override;
+    void hideEvent(QHideEvent *event) override;
+
+private:
+    void initLayout();
+
+    struct {
+        GenericListView *listView;
+    } ui_;
+
+    GenericListModel model_;
+    ActionCallback callback_;
+    QTimer redrawTimer_;
+};
+
+}  // namespace chatterino