ClipboardHistory: Add a clipboard history applet :^)

It will listen for clipboard content changes in the backgroud. Once you click
on its icon, it will pop up a window listing all recorded clipboard contents.
You can then double-click on an item to copy it again.

MenuApplets/ClipboardHistory/ClipboardHistoryModel.cpp

@@ -0,0 +1,86 @@
+/*
+ * Copyright (c) 2019-2020, Sergey Bugaev <bugaevc@serenityos.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "ClipboardHistoryModel.h"
+
+NonnullRefPtr<ClipboardHistoryModel> ClipboardHistoryModel::create()
+{
+    return adopt(*new ClipboardHistoryModel());
+}
+
+ClipboardHistoryModel::~ClipboardHistoryModel()
+{
+}
+
+String ClipboardHistoryModel::column_name(int column) const
+{
+    switch (column) {
+    case Column::Data:
+        return "Data";
+    case Column::Type:
+        return "Type";
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
+GUI::Model::ColumnMetadata ClipboardHistoryModel::column_metadata(int column) const
+{
+    switch (column) {
+    case Column::Data:
+        return { 200 };
+    case Column::Type:
+        return { 100 };
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
+GUI::Variant ClipboardHistoryModel::data(const GUI::ModelIndex& index, Role) const
+{
+    auto& data_and_type = m_history_items[index.row()];
+    switch (index.column()) {
+    case Column::Data:
+        if (data_and_type.type.starts_with("text/"))
+            return data_and_type.data;
+        return "<...>";
+    case Column::Type:
+        return data_and_type.type;
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
+void ClipboardHistoryModel::update()
+{
+    did_update();
+}
+
+void ClipboardHistoryModel::add_item(const GUI::Clipboard::DataAndType& item)
+{
+    m_history_items.prepend(item);
+    update();
+}