add deriving board from index

src/logic/future_moves.rs

@@ -293,6 +293,33 @@ impl FutureMoves {
         }
     }
 
+    fn get_board_from_idx(&self, idx: usize) -> Option<Board> {
+        if let Some(root) = self.current_root {
+            let mut hist = Vec::new();
+
+            let mut current = Some(idx);
+            while let Some(parent_idx) = current {
+                if parent_idx == root {
+                    break;
+                }
+
+                let n = &self.arena[parent_idx];
+                hist.push((n.coord, n.color));
+                current = n.parent;
+            }
+
+            let mut board = self.arena[root].board.clone();
+            for (m, c) in hist.into_iter().rev() {
+                if let Some(m) = m {
+                    let _ = board.place(m, c);
+                }
+            }
+            Some(board)
+        } else {
+            None
+        }
+    }
+
     /// Return the best move which is a child of `self.current_root`
     pub fn best_move(&self) -> Option<Option<CoordPair>> {
         self.current_root