allow move arena to properly handle skipping a move

src/logic/future_moves.rs

@@ -120,16 +120,22 @@ impl FutureMoves {
 
         // use [`Board::all_positions`] here instead of [`Board::possible_moves`]
         // because we use [`Board::what_if`] later and we want to reduce calls to [`Board::propegate_from_dry`]
-        let new: Vec<Move> = Board::all_positions()
+        let mut new: Vec<Move> = Board::all_positions()
             .flat_map(|(i, j)| {
                 parent
                     .board
                     .what_if(i, j, new_color)
                     .map(move |x| (i, j, x))
             })
-            .map(|(i, j, new_board)| Move::new(i, j, new_board, new_color, self.agent_color))
+            .map(|(i, j, new_board)| {
+                Move::new(Some((i, j)), new_board, new_color, self.agent_color)
+            })
             .collect();
 
+        if new.is_empty() {
+            new.push(Move::new(None, parent.board, new_color, self.agent_color));
+        }
+
         let start_idx = self.arena.len();
         self.arena.extend(new);
 
@@ -224,7 +230,7 @@ impl FutureMoves {
                     "selected move color should be the same as the color of the agent"
                 );
             })
-            .map(|&x| self.arena[x].coords())
+            .and_then(|&x| self.arena[x].coord)
     }
 
     /// Updates `FutureMoves` based on the current state of the board
@@ -248,13 +254,8 @@ impl FutureMoves {
     /// Clear the arena and create and set a root which contains a Board
     pub fn set_root_from_board(&mut self, board: Board) {
         self.arena.clear();
-        self.arena.push(Move::new(
+        self.arena
-            0, // dummy
+            .push(Move::new(None, board, !self.agent_color, self.agent_color));
-            0, // dummy
-            board,
-            !self.agent_color,
-            self.agent_color,
-        ));
         // because we have to regenerate root from a [`Board`]
         // we need to reset the current_depth (fixes `skip_move_recovery`)
         self.current_depth = 0;
@@ -275,7 +276,7 @@ impl FutureMoves {
         self.arena
             .iter()
             .enumerate()
-            .find(|(_, node)| node.parent == self.current_root && node.coords() == (i, j))
+            .find(|(_, node)| node.parent == self.current_root && node.coord == Some((i, j)))
             .map(|x| x.0)
             // do raw set so we can prune it on the next move (in `update`)
             .inspect(|&root| self.update_root_idx_raw(root))
@@ -470,8 +471,7 @@ mod tests {
         let mut futm = FutureMoves::new(Piece::Black, FUTURE_MOVES_CONFIG);
 
         futm.arena.push(Move {
-            i: 0,
+            coord: None,
-            j: 0,
             board: Board::new(),
             winner: Winner::None,
             parent: None,
@@ -487,13 +487,12 @@ mod tests {
 
         // child 1
         futm.arena
-            .push(Move::new(0, 0, Board::new(), Piece::White, Piece::Black));
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
         futm.set_parent_child(0, 1);
 
         // dummy (2)
         futm.arena.push(Move::new(
-            1234,
+            Some((1234, 1234)),
-            1234,
             Board::new(),
             Piece::White,
             Piece::Black,
@@ -501,12 +500,12 @@ mod tests {
 
         // 3
         futm.arena
-            .push(Move::new(0, 0, Board::new(), Piece::White, Piece::Black));
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
         futm.set_parent_child(0, 3);
 
         // 4
         futm.arena
-            .push(Move::new(0, 0, Board::new(), Piece::White, Piece::Black));
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
         futm.set_parent_child(0, 4);
 
         assert_eq!(futm.arena_len(), 5);
@@ -515,7 +514,11 @@ mod tests {
         assert_eq!(futm.arena_len(), 4);
         assert_eq!(futm.arena[0].children.len(), 3);
 
-        assert_ne!(futm.arena[2].i, 1234, "dummy value still exists");
+        assert_ne!(
+            futm.arena[2].coord,
+            Some((1234, 1234)),
+            "dummy value still exists"
+        );
     }
 
     #[test]
@@ -524,8 +527,7 @@ mod tests {
         futm.config.max_depth = 1;
 
         futm.arena.push(Move::new(
-            0,
+            None,
-            0,
             Board::new().starting_pos(),
             Piece::Black,
             Piece::Black,
@@ -556,8 +558,7 @@ mod tests {
         let mut futm = FutureMoves::new(Piece::Black, FUTURE_MOVES_CONFIG);
 
         futm.arena.push(Move {
-            i: 0,
+            coord: None,
-            j: 0,
             board: Board::new(),
             winner: Winner::None,
             parent: None,
@@ -573,25 +574,20 @@ mod tests {
 
         // child 1
         futm.arena
-            .push(Move::new(0, 0, Board::new(), Piece::White, Piece::Black));
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
         futm.set_parent_child(0, 1);
 
         // dummy
-        futm.arena.push(Move::new(
+        futm.arena
-            1234,
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
-            1234,
-            Board::new(),
-            Piece::White,
-            Piece::Black,
-        ));
 
         futm.arena
-            .push(Move::new(0, 0, Board::new(), Piece::White, Piece::Black));
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
 
         futm.set_parent_child(1, 3);
 
         futm.arena
-            .push(Move::new(0, 0, Board::new(), Piece::White, Piece::Black));
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
 
         futm.set_parent_child(0, 4);
 
@@ -603,8 +599,7 @@ mod tests {
         let mut futm = FutureMoves::new(Piece::Black, FUTURE_MOVES_CONFIG);
 
         futm.arena.push(Move {
-            i: 0,
+            coord: None,
-            j: 0,
             board: Board::new(),
             winner: Winner::None,
             parent: None,
@@ -620,20 +615,15 @@ mod tests {
 
         // child 1
         futm.arena
-            .push(Move::new(0, 0, Board::new(), Piece::White, Piece::Black));
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
         futm.set_parent_child(0, 1);
 
         // dummy
-        futm.arena.push(Move::new(
+        futm.arena
-            1234,
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
-            1234,
-            Board::new(),
-            Piece::White,
-            Piece::Black,
-        ));
 
         futm.arena
-            .push(Move::new(0, 0, Board::new(), Piece::White, Piece::Black));
+            .push(Move::new(None, Board::new(), Piece::White, Piece::Black));
         futm.set_parent_child(1, 3);
 
         assert_eq!(

src/logic/move.rs

@@ -4,11 +4,8 @@ use lazy_static::lazy_static;
 
 #[derive(Clone, Debug)]
 pub struct Move {
-    /// `i` position of move
+    /// Coordinates (i, j) of the move (if it exists)
-    pub i: usize,
+    pub coord: Option<(usize, usize)>,
-
-    /// `j` position of move
-    pub j: usize,
 
     /// [`Board`] state after move is made
     pub board: Board,
@@ -43,10 +40,14 @@ lazy_static! {
 }
 
 impl Move {
-    pub fn new(i: usize, j: usize, board: Board, color: Piece, agent_color: Piece) -> Self {
+    pub fn new(
+        coord: Option<(usize, usize)>,
+        board: Board,
+        color: Piece,
+        agent_color: Piece,
+    ) -> Self {
         let mut m = Move {
-            i,
+            coord,
-            j,
             board,
             winner: board.game_winner(),
             parent: None,
@@ -61,10 +62,6 @@ impl Move {
         m
     }
 
-    pub const fn coords(&self) -> (usize, usize) {
-        (self.i, self.j)
-    }
-
     fn compute_self_value(&self, agent_color: Piece) -> i64 {
         if self.winner == Winner::Player(!agent_color) {
             // if this board results in the opponent winning, MAJORLY negatively weigh this move