feat(editor): support moving cursor with arrow keys

src/editor.rs

@@ -47,6 +47,7 @@ impl Editor {
         let pressed_key = Terminal::read_key()?;
         match pressed_key {
             Key::Ctrl('q') => self.should_quit = true,
+            Key::Up | Key::Left | Key::Right | Key::Down => self.move_cursor(pressed_key),
             _ => (),
         };
         Ok(())
@@ -88,6 +89,29 @@ impl Editor {
             }
         }
     }
+
+    fn move_cursor(&mut self, key: Key) {
+        let Position { mut y, mut x } = self.cursor_position;
+        let size = self.terminal.size();
+        let height = size.height.saturating_sub(1) as usize;
+        let width = size.width.saturating_sub(1) as usize;
+        match key {
+            Key::Up => y = y.saturating_sub(1),
+            Key::Down => {
+                if y < height {
+                    y = y.saturating_add(1);
+                }
+            }
+            Key::Left => x = x.saturating_sub(1),
+            Key::Right => {
+                if x < width {
+                    x = x.saturating_add(1);
+                }
+            }
+            _ => (),
+        }
+        self.cursor_position = Position { x, y }
+    }
 }
 
 fn die(e: std::io::Error) {