rules: handle pawn promotion

src/board.rs

@@ -180,8 +180,8 @@ pub fn find_king(board: &Board, color: u8) -> Pos {
     (0, 0)
 }
 
-/// A movement, with before/after positions.
+/// A movement, with before/after positions and optional promotion.
-pub type Move = (Pos, Pos);
+pub type Move = (Pos, Pos, Option<u8>);
 
 /// Apply a move `m` to a copy of `board`.
 pub fn apply(board: &Board, m: &Move) -> Board {
@@ -307,12 +307,12 @@ mod tests {
         set_square(&mut b, &pos("d4"), SQ_WH_N);
         set_square(&mut b, &pos("f4"), SQ_BL_N);
         // Move white knight in a position attacked by black knight.
-        apply_into(&mut b, &((pos("d4"), pos("e6"))));
+        apply_into(&mut b, &(pos("d4"), pos("e6"), None));
         assert_eq!(get_square(&b, &pos("d4")), SQ_E);
         assert_eq!(get_square(&b, &pos("e6")), SQ_WH_N);
         assert_eq!(num_pieces(&b), 2);
         // Sack it with black knight
-        apply_into(&mut b, &((pos("f4"), pos("e6"))));
+        apply_into(&mut b, &(pos("f4"), pos("e6"), None));
         assert_eq!(get_square(&b, &pos("e6")), SQ_BL_N);
         assert_eq!(num_pieces(&b), 1);
     }

src/cli.rs

@@ -48,7 +48,7 @@ fn get_player_move() -> board::Move {
         let from = if let Some(s) = get_input("From: ") { board::pos(&s) } else { continue };
         let to = if let Some(s) = get_input("To: ") { board::pos(&s) } else { continue };
         if board::is_valid_pos(from) && board::is_valid_pos(to) {
-            return (from, to)
+            return (from, to, None)  // TODO this does not handle promotion.
         }
         println!("Bad input.");
     }

src/engine.rs

@@ -289,7 +289,7 @@ fn analyze(
     let moves = rules::get_player_legal_moves(&state.board, state.color);
     let mut rng = rand::thread_rng();
     let best_move = moves.iter().choose(&mut rng).and_then(|m| Some(*m));
-    thread::sleep(time::Duration::from_millis(1000u64));
+    thread::sleep(time::Duration::from_millis(300u64));
     tx.send(Cmd::TmpBestMove(best_move)).unwrap();
 
     // thread::sleep(time::Duration::from_secs(1));

src/notation.rs

@@ -8,11 +8,31 @@ pub fn move_to_string(m: &board::Move) -> String {
     let mut move_string = String::new();
     move_string.push_str(&board::pos_string(&m.0));
     move_string.push_str(&board::pos_string(&m.1));
+    if let Some(prom) = m.2 {
+        move_string.push(match prom {
+            board::SQ_Q => 'q',
+            board::SQ_B => 'b',
+            board::SQ_N => 'n',
+            board::SQ_R => 'r',
+            _ => panic!("What are you doing? Promote to a legal piece.")
+        });
+    }
     move_string
 }
 
 pub fn parse_move(m_str: &str) -> board::Move {
-    (board::pos(&m_str[0..2]), board::pos(&m_str[2..4]))
+    let prom = if m_str.len() == 5 {
+        Some(match m_str.as_bytes()[4] {
+            b'b' => board::SQ_B,
+            b'n' => board::SQ_N,
+            b'r' => board::SQ_R,
+            b'q' => board::SQ_Q,
+            _ => panic!("What is the opponent doing? This is illegal, I'm out."),
+        })
+    } else {
+        None
+    };
+    (board::pos(&m_str[0..2]), board::pos(&m_str[2..4]), prom)
 }
 
 pub const FEN_START: &str = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1";
@@ -53,13 +73,17 @@ mod tests {
 
     #[test]
     fn test_move_to_string() {
-        assert_eq!(move_to_string(&((0, 0), (3, 3))), "a1d4");
+        assert_eq!(move_to_string(&((0, 0), (3, 3), None)), "a1d4");
-        assert_eq!(move_to_string(&((7, 7), (0, 7))), "h8a8");
+        assert_eq!(move_to_string(&((7, 7), (0, 7), None)), "h8a8");
+        assert_eq!(move_to_string(&((7, 6), (7, 7), Some(board::SQ_Q))), "h7h8q");
+        assert_eq!(move_to_string(&((7, 6), (7, 7), Some(board::SQ_N))), "h7h8n");
     }
 
     #[test]
     fn test_parse_move() {
-        assert_eq!(parse_move("a1d4"), ((0, 0), (3, 3)));
+        assert_eq!(parse_move("a1d4"), ((0, 0), (3, 3), None));
+        assert_eq!(parse_move("a7a8q"), ((0, 6), (0, 7), Some(board::SQ_Q)));
+        assert_eq!(parse_move("a7a8r"), ((0, 6), (0, 7), Some(board::SQ_R)));
     }
 
     #[test]

src/rules.rs

@@ -40,21 +40,28 @@ pub fn get_piece_moves(board: &Board, at: &Pos) -> Vec<Move> {
 fn get_pawn_moves(board: &Board, at: &Pos, piece: u8) -> Vec<Move> {
     let (f, r) = *at;
     let mut moves = vec!();
-    let movement: i8 = if is_white(piece) { 1 } else { -1 };
+    // Direction: positive for white, negative for black.
+    let dir: i8 = if is_white(piece) { 1 } else { -1 };
     // Check 1 or 2 square forward.
     let move_len = if (is_white(piece) && r == 1) || (is_black(piece) && r == 6) { 2 } else { 1 };
     for i in 1..=move_len {
-        let forward_r = r + movement * i;
+        let forward_r = r + dir * i;
-        if movement > 0 && forward_r > POS_MAX {
+        if dir > 0 && forward_r > POS_MAX {
             return moves
         }
-        if movement < 0 && forward_r < POS_MIN {
+        if dir < 0 && forward_r < POS_MIN {
             return moves
         }
         let forward: Pos = (f, forward_r);
         // If forward square is empty (and we are not jumping over an occupied square), add it.
-        if is_empty(board, &forward) && (i == 1 || is_empty(board, &(f, forward_r - 1))) {
+        if is_empty(board, &forward) && (i == 1 || is_empty(board, &(f, forward_r - dir))) {
-            moves.push((*at, forward))
+            // Pawns that get to the opposite rank automatically promote as queens.
+            let prom = if (dir > 0 && forward_r == POS_MAX) || (dir < 0 && forward_r == POS_MIN) {
+                Some(SQ_Q)
+            } else {
+                None
+            };
+            moves.push((*at, forward, prom))
         }
         // Check diagonals for pieces to attack.
         if i == 1 {
@@ -92,7 +99,7 @@ fn get_bishop_moves(board: &Board, at: &Pos, piece: u8) -> Vec<Move> {
                 continue
             }
             if is_empty(board, &p) {
-                moves.push((*at, p));
+                moves.push((*at, p, None));
             } else {
                 if let Some(m) = move_on_enemy(piece, at, get_square(board, &p), &p) {
                     moves.push(m);
@@ -113,7 +120,7 @@ fn get_knight_moves(board: &Board, at: &Pos, piece: u8) -> Vec<Move> {
             continue
         }
         if is_empty(board, &p) {
-            moves.push((*at, p));
+            moves.push((*at, p, None));
         } else if let Some(m) = move_on_enemy(piece, at, get_square(board, &p), &p) {
             moves.push(m);
         }
@@ -135,7 +142,7 @@ fn get_rook_moves(board: &Board, at: &Pos, piece: u8) -> Vec<Move> {
                 continue
             }
             if is_empty(board, &p) {
-                moves.push((*at, p));
+                moves.push((*at, p, None));
             } else {
                 if let Some(m) = move_on_enemy(piece, at, get_square(board, &p), &p) {
                     moves.push(m);
@@ -164,7 +171,7 @@ fn get_king_moves(board: &Board, at: &Pos, piece: u8) -> Vec<Move> {
             continue
         }
         if is_empty(board, &p) {
-            moves.push((*at, p));
+            moves.push((*at, p, None));
         } else if let Some(m) = move_on_enemy(piece, at, get_square(board, &p), &p) {
             moves.push(m);
         }
@@ -177,7 +184,16 @@ fn get_king_moves(board: &Board, at: &Pos, piece: u8) -> Vec<Move> {
 fn move_on_enemy(piece1: u8, pos1: &Pos, piece2: u8, pos2: &Pos) -> Option<Move> {
     let color1 = get_color(piece1);
     if is_color(piece2, opposite(color1)) {
-        Some((*pos1, *pos2))
+        // Automatic queen promotion for pawns moving to the opposite rank.
+        let prom = if
+            is_piece(piece1, SQ_P) &&
+            ((is_white(piece1) && pos2.1 == POS_MAX) || (is_black(piece1) && pos2.1 == POS_MIN))
+        {
+            Some(SQ_Q)
+        } else {
+            None
+        };
+        Some((*pos1, *pos2, prom))
     } else {
         None
     }
@@ -231,20 +247,20 @@ mod tests {
         // Check that a pawn (here white queen's pawn) can move forward if the road is free.
         set_square(&mut b, &pos("d3"), SQ_WH_P);
         let moves = get_piece_moves(&b, &pos("d3"));
-        assert!(moves.len() == 1 && moves.contains( &(pos("d3"), pos("d4")) ));
+        assert!(moves.len() == 1 && moves.contains( &(pos("d3"), pos("d4"), None) ));
 
         // Check that a pawn (here white king's pawn) can move 2 square forward on first move.
         set_square(&mut b, &pos("e2"), SQ_WH_P);
         let moves = get_piece_moves(&b, &pos("e2"));
         assert_eq!(moves.len(), 2);
-        assert!(moves.contains( &(pos("e2"), pos("e3")) ));
+        assert!(moves.contains( &(pos("e2"), pos("e3"), None) ));
-        assert!(moves.contains( &(pos("e2"), pos("e4")) ));
+        assert!(moves.contains( &(pos("e2"), pos("e4"), None) ));
 
         // Check that a pawn cannot move forward if a piece is blocking its path.
         // 1. black pawn 2 square forward; only 1 square forward available from start pos.
         set_square(&mut b, &pos("e4"), SQ_BL_P);
         let moves = get_piece_moves(&b, &pos("e2"));
-        assert!(moves.len() == 1 && moves.contains( &(pos("e2"), pos("e3")) ));
+        assert!(moves.len() == 1 && moves.contains( &(pos("e2"), pos("e3"), None) ));
         // 2. black pawn 1 square forward; no square available.
         set_square(&mut b, &pos("e3"), SQ_BL_P);
         let moves = get_piece_moves(&b, &pos("e2"));
@@ -257,12 +273,18 @@ mod tests {
         // Check that a pawn can take a piece diagonally.
         set_square(&mut b, &pos("f3"), SQ_BL_P);
         let moves = get_piece_moves(&b, &pos("e2"));
-        assert!(moves.len() == 1 && moves.contains( &(pos("e2"), pos("f3")) ));
+        assert!(moves.len() == 1 && moves.contains( &(pos("e2"), pos("f3"), None) ));
         set_square(&mut b, &pos("d3"), SQ_BL_P);
         let moves = get_piece_moves(&b, &pos("e2"));
         assert_eq!(moves.len(), 2);
-        assert!(moves.contains( &(pos("e2"), pos("f3")) ));
+        assert!(moves.contains( &(pos("e2"), pos("f3"), None) ));
-        assert!(moves.contains( &(pos("e2"), pos("d3")) ));
+        assert!(moves.contains( &(pos("e2"), pos("d3"), None) ));
+
+        // Check that a pawn moving to the last rank leads to queen promotion.
+        // 1. by simply moving forward.
+        set_square(&mut b, &pos("a7"), SQ_WH_P);
+        let moves = get_piece_moves(&b, &pos("a7"));
+        assert!(moves.len() == 1 && moves.contains( &(pos("a7"), pos("a8"), Some(SQ_Q)) ));
     }
 
     #[test]
@@ -274,22 +296,22 @@ mod tests {
         let moves = get_piece_moves(&b, &pos("d4"));
         assert_eq!(moves.len(), 13);
         // Going top-right.
-        assert!(moves.contains( &(pos("d4"), pos("e5")) ));
+        assert!(moves.contains( &(pos("d4"), pos("e5"), None) ));
-        assert!(moves.contains( &(pos("d4"), pos("f6")) ));
+        assert!(moves.contains( &(pos("d4"), pos("f6"), None) ));
-        assert!(moves.contains( &(pos("d4"), pos("g7")) ));
+        assert!(moves.contains( &(pos("d4"), pos("g7"), None) ));
-        assert!(moves.contains( &(pos("d4"), pos("h8")) ));
+        assert!(moves.contains( &(pos("d4"), pos("h8"), None) ));
         // Going bottom-right.
-        assert!(moves.contains( &(pos("d4"), pos("e3")) ));
+        assert!(moves.contains( &(pos("d4"), pos("e3"), None) ));
-        assert!(moves.contains( &(pos("d4"), pos("f2")) ));
+        assert!(moves.contains( &(pos("d4"), pos("f2"), None) ));
-        assert!(moves.contains( &(pos("d4"), pos("g1")) ));
+        assert!(moves.contains( &(pos("d4"), pos("g1"), None) ));
         // Going bottom-left.
-        assert!(moves.contains( &(pos("d4"), pos("c3")) ));
+        assert!(moves.contains( &(pos("d4"), pos("c3"), None) ));
-        assert!(moves.contains( &(pos("d4"), pos("b2")) ));
+        assert!(moves.contains( &(pos("d4"), pos("b2"), None) ));
-        assert!(moves.contains( &(pos("d4"), pos("a1")) ));
+        assert!(moves.contains( &(pos("d4"), pos("a1"), None) ));
         // Going top-left.
-        assert!(moves.contains( &(pos("d4"), pos("c5")) ));
+        assert!(moves.contains( &(pos("d4"), pos("c5"), None) ));
-        assert!(moves.contains( &(pos("d4"), pos("b6")) ));
+        assert!(moves.contains( &(pos("d4"), pos("b6"), None) ));
-        assert!(moves.contains( &(pos("d4"), pos("a7")) ));
+        assert!(moves.contains( &(pos("d4"), pos("a7"), None) ));
 
         // When blocking sight to one square with friendly piece, lose 2 moves.
         set_square(&mut b, &pos("b2"), SQ_WH_P);
@@ -375,7 +397,7 @@ mod tests {
         set_square(&mut b, &pos("d6"), SQ_BL_R);
         assert!(is_attacked(&b, &pos("d4")));
         // Move the rook on another file, no more attack.
-        apply_into(&mut b, &(pos("d6"), pos("e6")));
+        apply_into(&mut b, &(pos("d6"), pos("e6"), None));
         assert!(!is_attacked(&b, &pos("d4")));
     }
 }