mentions: don't lose focus after select mention

Closes: https://github.com/damus-io/notedeck/issues/728

Signed-off-by: kernelkind <kernelkind@gmail.com>

crates/notedeck_columns/src/post.rs

@@ -1,4 +1,8 @@
-use egui::{text::LayoutJob, TextBuffer, TextFormat};
+use egui::{
+    text::{CCursor, CCursorRange, LayoutJob},
+    text_edit::TextEditOutput,
+    TextBuffer, TextEdit, TextFormat,
+};
 use enostr::{FullKeypair, Pubkey};
 use nostrdb::{Note, NoteBuilder, NoteReply};
 use std::{
@@ -270,6 +274,36 @@ impl Default for PostBuffer {
     }
 }
 
+/// New cursor index (indexed by characters) after operation is performed
+#[must_use = "must call MentionSelectedResponse::process"]
+pub struct MentionSelectedResponse {
+    pub next_cursor_index: usize,
+}
+
+impl MentionSelectedResponse {
+    pub fn process(&self, ctx: &egui::Context, text_edit_output: &TextEditOutput) {
+        let text_edit_id = text_edit_output.response.id;
+        let Some(mut before_state) = TextEdit::load_state(ctx, text_edit_id) else {
+            return;
+        };
+
+        let mut new_cursor = text_edit_output
+            .galley
+            .from_ccursor(CCursor::new(self.next_cursor_index));
+        new_cursor.ccursor.prefer_next_row = true;
+
+        before_state
+            .cursor
+            .set_char_range(Some(CCursorRange::one(CCursor::new(
+                self.next_cursor_index,
+            ))));
+
+        ctx.memory_mut(|mem| mem.request_focus(text_edit_id));
+
+        TextEdit::store_state(ctx, text_edit_id, before_state);
+    }
+}
+
 impl PostBuffer {
     pub fn get_new_mentions_key(&mut self) -> usize {
         let prev = self.mentions_key;
@@ -319,15 +353,19 @@ impl PostBuffer {
         mention_key: usize,
         full_name: &str,
         pk: Pubkey,
-    ) {
-        if let Some(info) = self.mentions.get(&mention_key) {
-            let text_start_index = info.start_index + 1;
-            self.delete_char_range(text_start_index..info.end_index);
-            self.insert_text(full_name, text_start_index);
-            self.select_full_mention(mention_key, pk);
-        } else {
+    ) -> Option<MentionSelectedResponse> {
+        let Some(info) = self.mentions.get(&mention_key) else {
             error!("Error selecting mention for index: {mention_key}. Have the following mentions: {:?}", self.mentions);
-        }
+            return None;
+        };
+        let text_start_index = info.start_index + 1; // increment by one to exclude the mention indicator, '@'
+        self.delete_char_range(text_start_index..info.end_index);
+        let text_chars_inserted = self.insert_text(full_name, text_start_index);
+        self.select_full_mention(mention_key, pk);
+
+        Some(MentionSelectedResponse {
+            next_cursor_index: text_start_index + text_chars_inserted,
+        })
     }
 
     pub fn delete_mention(&mut self, mention_key: usize) {

crates/notedeck_columns/src/ui/note/post.rs

@@ -218,6 +218,7 @@ impl<'a, 'd> PostView<'a, 'd> {
         out.response
     }
 
+    // Displays the mention picker and handles when one is selected.
     fn show_mention_hints(
         &mut self,
         txn: &nostrdb::Transaction,
@@ -281,17 +282,22 @@ impl<'a, 'd> PostView<'a, 'd> {
         )
         .show_in_rect(hint_rect, ui);
 
+        let mut selection_made = None;
         match resp {
             ui::mentions_picker::MentionPickerResponse::SelectResult(selection) => {
                 if let Some(hint_index) = selection {
                     if let Some(pk) = res.get(hint_index) {
                         let record = self.note_context.ndb.get_profile_by_pubkey(txn, pk);
 
-                        self.draft.buffer.select_mention_and_replace_name(
-                            mention.index,
-                            get_display_name(record.ok().as_ref()).name(),
-                            Pubkey::new(**pk),
-                        );
+                        if let Some(made_selection) =
+                            self.draft.buffer.select_mention_and_replace_name(
+                                mention.index,
+                                get_display_name(record.ok().as_ref()).name(),
+                                Pubkey::new(**pk),
+                            )
+                        {
+                            selection_made = Some(made_selection);
+                        }
                         self.draft.cur_mention_hint = None;
                     }
                 }
@@ -301,6 +307,10 @@ impl<'a, 'd> PostView<'a, 'd> {
                 self.draft.buffer.delete_mention(mention.index)
             }
         }
+
+        if let Some(selection) = selection_made {
+            selection.process(ui.ctx(), textedit_output);
+        }
     }
 
     fn focused(&self, ui: &egui::Ui) -> bool {