Add play/pause button and toggle cell

src/lib.rs

@@ -28,6 +28,15 @@ pub enum Cell {
     Alive = 1,
 }
 
+impl Cell {
+    fn toggle(&mut self) {
+        *self = match *self {
+            Cell::Dead => Cell::Alive,
+            Cell::Alive => Cell::Dead,
+        }
+    }
+}
+
 #[wasm_bindgen]
 pub struct Universe {
     width: u32,
@@ -151,13 +160,20 @@ impl Universe {
         self.height = height;
         self.cells = (0..height * self.height).map(|_i| Cell::Dead).collect();
     }
+
+    pub fn toggle_cell(&mut self, row: u32, col: u32) {
+        let idx = self.get_index(row, col);
+        self.cells[idx].toggle();
+    }
 }
 
 impl Universe {
+    // for test
     pub fn get_cells(&self) -> &[Cell] {
         &self.cells
     }
 
+    // for test
     pub fn set_cells(&mut self, cells: &[(u32, u32)]) {
         for (row, col) in cells.iter().cloned() {
             let idx = self.get_index(row, col);