Use Unicode column width when calculating terminal cursor offset

crates/modalkit-ratatui/Cargo.toml

@@ -19,6 +19,7 @@ modalkit = { workspace = true }
 ratatui = { version = "0.28.1" }
 regex = { workspace = true }
 serde = { version = "^1.0", features = ["derive"] }
+unicode-width = "0.2.0"
 
 [dev-dependencies]
 rand = { workspace = true }

crates/modalkit-ratatui/src/textbox.rs

@@ -58,6 +58,8 @@ use modalkit::editing::{
 use modalkit::errors::{EditError, EditResult, UIResult};
 use modalkit::prelude::*;
 
+use unicode_width::UnicodeWidthStr;
+
 use super::{ScrollActions, TerminalCursor, WindowOps};
 
 /// Line annotation shown in the left gutter.
@@ -859,13 +861,19 @@ where
                 }
             }
 
-            let _ = buf.set_stringn(x, y, s, width, self.style);
-
             if cursor_line {
-                let coff = (cursor.x - start) as u16;
+                let coff = s[..s
+                    .char_indices()
+                    .map(|(i, _)| i)
+                    .nth(cursor.x.saturating_sub(start))
+                    .unwrap_or(s.len())]
+                    .width_cjk() as u16;
+
                 state.term_cursor = (x + coff, y);
             }
 
+            let _ = buf.set_stringn(x, y, s, width, self.style);
+
             self._highlight_followers(line, start, end, (x, y), &finfo, buf);
             self._highlight_line(line, start, end, (x, y), &hinfo, buf);
 
@@ -1002,13 +1010,20 @@ where
 
             let s = s.to_string();
             let w = (right - x) as usize;
-            let (xres, _) = buf.set_stringn(x, y, s, w, self.style);
 
             if cursor_line {
-                let coff = cursor.x.saturating_sub(start) as u16;
+                let coff = s[..s
+                    .char_indices()
+                    .map(|(i, _)| i)
+                    .nth(cursor.x.saturating_sub(start))
+                    .unwrap_or(s.len())]
+                    .width_cjk() as u16;
+
                 state.term_cursor = (x + coff, y);
             }
 
+            let (xres, _) = buf.set_stringn(x, y, s, w, self.style);
+
             self._highlight_followers(line, start, end, (x, y), &finfo, buf);
             self._highlight_line(line, start, end, (x, y), &hinfo, buf);
 
@@ -1057,26 +1072,28 @@ where
                     lgi.render(lga, buf);
                 }
 
+                let s = s.slice(CharOff::from(start)..CharOff::from(end)).to_string();
+
+                if line == cursor.y && (start..=end).contains(&cursor.x) {
+                    let coff = s[..s
+                        .char_indices()
+                        .map(|(i, _)| i)
+                        .nth(cursor.x.saturating_sub(start))
+                        .unwrap_or(s.len())]
+                        .width_cjk() as u16;
+
+                    state.term_cursor = (x + coff, y);
+                }
+
                 if cbx < slen {
-                    let _ = buf.set_stringn(
-                        x,
-                        y,
-                        s.slice(CharOff::from(start)..CharOff::from(end)).to_string(),
-                        width,
-                        self.style,
-                    );
+                    let _ = buf.set_stringn(x, y, s, width, self.style);
                 }
 
                 if let Some(rgi) = rgutter {
                     let rga = Rect::new(gutters.1.x, y, gutters.1.width, 0);
                     rgi.render(rga, buf);
                 }
 
-                if line == cursor.y && (start..=end).contains(&cursor.x) {
-                    let coff = (cursor.x - start) as u16;
-                    state.term_cursor = (x + coff, y);
-                }
-
                 self._highlight_followers(line, start, end, (x, y), &finfo, buf);
                 self._highlight_line(line, start, end, (x, y), &hinfo, buf);
 
@@ -1521,4 +1538,46 @@ mod tests {
         assert_eq!(tbox.get_cursor(), Cursor::new(0, 0));
         assert_eq!(tbox.get_term_cursor(), (2, 8).into());
     }
+
+    #[test]
+    fn test_wide_char_cursor() {
+        let (mut tbox, ctx, mut store) = mkboxstr("세계를 향한 대화\n");
+
+        let area = Rect::new(0, 0, 20, 20);
+        let mut buffer = Buffer::empty(area);
+
+        // Prompt should push everything right by 2 characters.
+        TextBox::new().prompt("> ").render(area, &mut buffer, &mut tbox);
+
+        assert_eq!(tbox.viewctx.corner, Cursor::new(0, 0));
+        assert_eq!(tbox.get_cursor(), Cursor::new(0, 0));
+        assert_eq!(tbox.get_term_cursor(), (2, 0).into());
+
+        // Move the cursor to be over "대", just before the last character.
+        let mov = mv!(MoveType::Column(MoveDir1D::Next, false), 7);
+        let act = EditorAction::Edit(EditAction::Motion.into(), mov);
+        tbox.editor_command(&act, &ctx, &mut store).unwrap();
+
+        // Draw again to update our terminal cursor using oneline().
+        TextBox::new().prompt("> ").oneline().render(area, &mut buffer, &mut tbox);
+
+        assert_eq!(tbox.viewctx.corner, Cursor::new(0, 0));
+        assert_eq!(tbox.get_cursor(), Cursor::new(0, 7));
+        assert_eq!(tbox.get_term_cursor(), (14, 0).into());
+        // Draw again to update our terminal cursor using set_wrap(true).
+        tbox.set_wrap(true);
+        TextBox::new().prompt("> ").render(area, &mut buffer, &mut tbox);
+
+        assert_eq!(tbox.viewctx.corner, Cursor::new(0, 0));
+        assert_eq!(tbox.get_cursor(), Cursor::new(0, 7));
+        assert_eq!(tbox.get_term_cursor(), (14, 0).into());
+
+        // Draw again to update our terminal cursor using set_wrap(false).
+        tbox.set_wrap(true);
+        TextBox::new().prompt("> ").render(area, &mut buffer, &mut tbox);
+
+        assert_eq!(tbox.viewctx.corner, Cursor::new(0, 0));
+        assert_eq!(tbox.get_cursor(), Cursor::new(0, 7));
+        assert_eq!(tbox.get_term_cursor(), (14, 0).into());
+    }
 }