Make text input cursor moveable

cove-tui/src/textline.rs

@@ -24,23 +24,64 @@ impl StatefulWidget for TextLine {
 #[derive(Debug, Default)]
 pub struct TextLineState {
     content: String,
+    cursor: usize,
 }
 
 impl TextLineState {
     pub fn set_cursor<B: Backend>(&self, f: &mut Frame<B>, area: Rect) {
-        let x = area.x + (self.content.width() as u16);
-        let x = cmp::min(x, area.x + area.width);
+        let prefix = self.content.chars().take(self.cursor).collect::<String>();
+        let position = prefix.width() as u16;
+        let x = area.x + cmp::min(position, area.width);
         f.set_cursor(x, area.y);
     }
 
+    fn chars(&self) -> usize {
+        self.content.chars().count()
+    }
+
+    fn move_cursor_start(&mut self) {
+        self.cursor = 0;
+    }
+
+    fn move_cursor_left(&mut self) {
+        if self.cursor > 0 {
+            self.cursor -= 1;
+        }
+    }
+
+    fn move_cursor_right(&mut self) {
+        self.cursor = cmp::min(self.cursor + 1, self.chars());
+    }
+
+    fn move_cursor_end(&mut self) {
+        self.cursor = self.chars();
+    }
+
+    fn cursor_byte_offset(&self) -> usize {
+        self.content
+            .char_indices()
+            .nth(self.cursor)
+            .map(|(i, _)| i)
+            .unwrap_or_else(|| self.content.len())
+    }
+
     pub fn process_input(&mut self, event: Event) {
         if let Event::Key(k) = event {
             match k.code {
-                KeyCode::Backspace => {
-                    self.content.pop();
+                KeyCode::Backspace if self.cursor > 0 => {
+                    self.move_cursor_left();
+                    self.content.remove(self.cursor_byte_offset());
+                }
+                KeyCode::Left => self.move_cursor_left(),
+                KeyCode::Right => self.move_cursor_right(),
+                KeyCode::Home => self.move_cursor_start(),
+                KeyCode::End => self.move_cursor_end(),
+                KeyCode::Delete if self.cursor < self.chars() => {
+                    self.content.remove(self.cursor_byte_offset());
                 }
                 KeyCode::Char(c) => {
-                    self.content.push(c);
+                    self.content.insert(self.cursor_byte_offset(), c);
+                    self.move_cursor_right();
                 }
                 _ => {}
             }