TextEditor: Add live preview for HTML documents :^)

This allows you to edit HTML and see the changes live. This feature is
possibly my favorite feature in the world right now.

Applications/TextEditor/TextEditorWidget.cpp

@@ -74,6 +74,9 @@ TextEditorWidget::TextEditorWidget()
         if (m_markdown_preview_enabled)
             update_markdown_preview();
 
+        if (m_html_preview_enabled)
+            update_html_preview();
+
         // Do not mark as dirty on the first change (When document is first opened.)
         if (m_document_opening) {
             m_document_opening = false;
@@ -390,10 +393,21 @@ TextEditorWidget::TextEditorWidget()
         },
         this);
 
+    m_html_preview_action = GUI::Action::create_checkable(
+        "HTML preview", [this](auto& action) {
+            set_html_preview_enabled(action.is_checked());
+        },
+        this);
+
+    m_preview_actions.add_action(*m_markdown_preview_action);
+    m_preview_actions.add_action(*m_html_preview_action);
+    m_preview_actions.set_exclusive(true);
+
     auto& view_menu = menubar->add_menu("View");
     view_menu.add_action(*m_line_wrapping_setting_action);
     view_menu.add_separator();
     view_menu.add_action(*m_markdown_preview_action);
+    view_menu.add_action(*m_html_preview_action);
     view_menu.add_separator();
 
     auto& font_menu = view_menu.add_submenu("Font");
@@ -481,6 +495,7 @@ void TextEditorWidget::set_path(const LexicalPath& lexical_path)
     }
 
     set_markdown_preview_enabled(m_extension == "md");
+    set_html_preview_enabled(m_extension == "html");
 
     update_title();
 }
@@ -546,6 +561,17 @@ void TextEditorWidget::drop_event(GUI::DropEvent& event)
     }
 }
 
+void TextEditorWidget::set_html_preview_enabled(bool enabled)
+{
+    if (m_html_preview_enabled == enabled)
+        return;
+    m_html_preview_enabled = enabled;
+    m_html_preview_action->set_checked(enabled);
+    m_page_view->set_visible(enabled);
+    if (enabled)
+        update_html_preview();
+}
+
 void TextEditorWidget::set_markdown_preview_enabled(bool enabled)
 {
     if (m_markdown_preview_enabled == enabled)
@@ -565,3 +591,8 @@ void TextEditorWidget::update_markdown_preview()
         m_page_view->load_html(html, URL::create_with_file_protocol(m_path));
     }
 }
+
+void TextEditorWidget::update_html_preview()
+{
+    m_page_view->load_html(m_editor->text(), URL::create_with_file_protocol(m_path));
+}

Applications/TextEditor/TextEditorWidget.h

@@ -45,12 +45,14 @@ public:
     GUI::TextEditor& editor() { return *m_editor; }
 
     void set_markdown_preview_enabled(bool);
+    void set_html_preview_enabled(bool);
 
 private:
     TextEditorWidget();
     void set_path(const LexicalPath& file);
     void update_title();
     void update_markdown_preview();
+    void update_html_preview();
 
     virtual void drop_event(GUI::DropEvent&) override;
 
@@ -64,13 +66,17 @@ private:
     RefPtr<GUI::Action> m_save_as_action;
     RefPtr<GUI::Action> m_find_replace_action;
     RefPtr<GUI::Action> m_line_wrapping_setting_action;
-    RefPtr<GUI::Action> m_markdown_preview_action;
+
     RefPtr<GUI::Action> m_find_next_action;
     RefPtr<GUI::Action> m_find_previous_action;
     RefPtr<GUI::Action> m_replace_next_action;
     RefPtr<GUI::Action> m_replace_previous_action;
     RefPtr<GUI::Action> m_replace_all_action;
 
+    GUI::ActionGroup m_preview_actions;
+    RefPtr<GUI::Action> m_markdown_preview_action;
+    RefPtr<GUI::Action> m_html_preview_action;
+
     RefPtr<GUI::StatusBar> m_statusbar;
 
     RefPtr<GUI::TextBox> m_find_textbox;
@@ -95,4 +101,5 @@ private:
     bool m_document_dirty { false };
     bool m_document_opening { false };
     bool m_markdown_preview_enabled { false };
+    bool m_html_preview_enabled { false };
 };