Enables selection of bubbles using an invisible text view

src/transcript/transcript-view.vala

@@ -17,10 +17,7 @@ public class TranscriptView : Adw.Bin
             _model = value;
 
             if (value != null) {
-                // Reset scroll position by updating the existing adjustment
-                scrolled_window.vadjustment.value = 0;
-                scrolled_window.vadjustment.upper = 0;
-                scrolled_window.vadjustment.page_size = 0;
+                reset_for_conversation_change();
 
                 weak TranscriptView self = this;
                 messages_changed_handler_id = value.messages_changed.connect(() => {
@@ -44,11 +41,18 @@ public class TranscriptView : Adw.Bin
     private Adw.ToolbarView container;
     private Label title_label = new Label("Messages");
 
+    private Overlay overlay = new Overlay();
     private TranscriptDrawingArea transcript_drawing_area = new TranscriptDrawingArea();
     private ScrolledWindow scrolled_window = new ScrolledWindow();
     private ulong messages_changed_handler_id = 0;
     private bool needs_reload = false;
 
+    private Graphene.Point _hovering_text_view_origin = Graphene.Point() { x = 0, y = 0 };
+    private TextView _hovering_text_view = new TextView();
+
+    private VisibleTextLayout? hovered_text_bubble = null;
+    private VisibleTextLayout? locked_text_bubble = null;
+
     public TranscriptView() {
         container = new Adw.ToolbarView();
         set_child(container);
@@ -56,8 +60,26 @@ public class TranscriptView : Adw.Bin
         // Set minimum width for the transcript view
         set_size_request(330, -1);
 
-        scrolled_window.set_child(transcript_drawing_area);
-        scrolled_window.add_css_class("message-list-scroller");
+        overlay.set_child(transcript_drawing_area);
+
+        weak TranscriptView self = this;
+        overlay.get_child_position.connect((child, out allocation) => {
+            allocation = Gtk.Allocation() { x = 0, y = 0, width = 0, height = 0 };
+            if (self.hovered_text_bubble != null) {
+                var rect = self.hovered_text_bubble.rect;
+                allocation.x = (int)(rect.origin.x + self._hovering_text_view_origin.x);
+                allocation.y = (int)(rect.origin.y - self._hovering_text_view_origin.y);
+                allocation.width = (int)rect.size.width;
+                allocation.height = (int)rect.size.height;
+
+                return true;
+            }
+
+            return true; 
+        });
+
+        scrolled_window.set_child(overlay);
+        scrolled_window.add_css_class("flipped-y-axis");
         transcript_drawing_area.viewport = scrolled_window.vadjustment;
         container.set_content(scrolled_window);
 
@@ -72,6 +94,33 @@ public class TranscriptView : Adw.Bin
         header_bar.set_title_widget(title_label);
         container.add_top_bar(header_bar);
 
+        // This is an invisible text view that's used to handle selection.
+        _hovering_text_view.add_css_class("hovering-text-view");
+        _hovering_text_view.add_css_class("flipped-y-axis");
+        _hovering_text_view.set_editable(false);
+        _hovering_text_view.set_wrap_mode(Gtk.WrapMode.WORD_CHAR);
+        overlay.add_overlay(_hovering_text_view);
+
+        // When the selection changes, lock the text bubble so that if the cursor moves to another bubble we don't clear it. 
+        _hovering_text_view.buffer.mark_set.connect((location, end) => {
+            self.lock_text_bubble(self.hovered_text_bubble);
+        });
+
+        // When the mouse hovers over a text bubble, configure the hovering text view to show the text of the bubble.
+        transcript_drawing_area.on_text_bubble_hover.connect((visible_text_layout) => {
+            if (visible_text_layout != null) {
+                configure_hovering_text_view(visible_text_layout);
+            }
+        });
+
+        // This is triggered when another bubble is currently locked, and the user clicks on a new bubble.
+        transcript_drawing_area.on_text_bubble_click.connect((visible_text_layout) => {
+            if (visible_text_layout != null) {
+                locked_text_bubble = null;
+                configure_hovering_text_view(visible_text_layout);
+            }
+        });
+
         Repository.get_instance().attachment_downloaded.connect((attachment_guid) => {
             debug("Attachment downloaded: %s", attachment_guid);
 
@@ -103,6 +152,35 @@ public class TranscriptView : Adw.Bin
         });
     }
 
+    private void reset_for_conversation_change() {
+        locked_text_bubble = null;
+        hovered_text_bubble = null;
+        _hovering_text_view.buffer.text = "";
+        overlay.queue_allocate();
+
+        // Reset scroll position by updating the existing adjustment
+        scrolled_window.vadjustment.value = 0;
+        scrolled_window.vadjustment.upper = 0;
+        scrolled_window.vadjustment.page_size = 0;
+    }
+
+    private void lock_text_bubble(VisibleTextLayout? visible_text_layout) {
+        if (visible_text_layout != null) {
+            locked_text_bubble = visible_text_layout;
+            configure_hovering_text_view(visible_text_layout);
+        }
+    }
+
+    private void configure_hovering_text_view(VisibleTextLayout? visible_text_layout) {
+        hovered_text_bubble = visible_text_layout;
+
+        if (locked_text_bubble == null) {
+            _hovering_text_view_origin = visible_text_layout.text_bubble.get_text_origin();
+            _hovering_text_view.buffer.text = visible_text_layout.text_bubble.message.text;
+            overlay.queue_allocate();
+        }
+    }
+
     private void reload_messages() {
         transcript_drawing_area.show_sender = _model.is_group_chat;
         transcript_drawing_area.set_messages(_model.messages);