Restrict movement to valid moves

Now need to fix valid moves to be accurate

src/game.rs

@@ -167,7 +167,9 @@ impl Board {
             Err(GameError::NullMove)
         } else {
             match self.at(from.clone()) {
-                Some(from_val) => {
+                Some(from_piece) => {
+                    // Check if this is a valid move for this piece
+                    if self.possible_moves(from).contains(&to) {
                         // The current epoch is the last epoch + 1
                         let epoch = self.current_epoch();
 
@@ -190,12 +192,15 @@ impl Board {
                             to: Some(to.clone()),
                         });
 
-                    self.inner[to.y][to.x] = Some(*from_val);
+                        self.inner[to.y][to.x] = Some(*from_piece);
                         self.inner[from.y][from.x] = None;
 
                         self.moves.extend(moves.clone());
 
                         Ok(moves)
+                    } else {
+                        Err(GameError::InvalidIndex)
+                    }
                 }
                 None => Err(GameError::NullMove),
             }
@@ -212,6 +217,7 @@ impl Board {
     }
 
     /// Returns the possible moves the piece at this tile can make.
+    /// !!TODO: exclude pieces on your own side!!
     pub(crate) fn possible_moves(&self, BoardIndex { x, y }: BoardIndex) -> HashSet<BoardIndex> {
         let f = |(a, b): (Option<usize>, Option<usize>)| {
             if let (Some(x), Some(y)) = (a, b) {