Basic move searcher, priority only based on depth (resulting in BFS), position base value takes into account isolated pawns, doubled pawns and bishop pairs

.gitignore

@@ -3,4 +3,6 @@
 .dart_tool/
 
 # project-specific
+bin/test_*
 builds/
+logs/

lib/classes/best_move_searcher.dart

@@ -1,7 +1,8 @@
-import 'dart:collection';
 
 import 'package:omnichess/classes/position.dart';
+import 'package:omnichess/constants/numbers.dart';
 import 'package:omnichess/constants/piece.dart';
+import 'package:omnichess/data_structures/position_tree_node.dart';
 import 'package:omnichess/functions/legal_moves.dart';
 
 class BestMoveSearcher {
@@ -9,14 +10,29 @@ class BestMoveSearcher {
   bool _isRunning = false;
   bool _isStopped = false;
 
-  Future<int> getPositionBaseValue(Position position) async {
+  static int getPositionBaseValue(Position position) {
-    if (await LegalMoves.isCheckmate(position)) {
+    if (LegalMoves.isCheckmate(position)) {
       return position.isWhiteTurn
-        ? -(1 << 63) // min int (white is checkmated)
+        ? Numbers.maxInteger
-        : ((1 << 63) - 1); // max int (black is checkmated)
+        : Numbers.minInteger;
     }
     int value = 0;
+    List<int> whitePawnFiles = List.filled(8, 0, growable: false); // isolated pawns, doubled pawns
+    List<int> blackPawnFiles = List.filled(8, 0, growable: false);
+    List<bool> whiteBishopColors = List.filled(2, false, growable: false); // bishop pairs
+    List<bool> blackBishopColors = List.filled(2, false, growable: false);
+    int row = 0;
+    int column = 0;
     for (int i = 0; i < 64; i++) {
+      final int verticalDisplacementFromCenter = 7 - 2*row;
+      final int horizontalDisplacementFromCenter = 7 - 2*column;
+      final int attackingValue = (98-(verticalDisplacementFromCenter*verticalDisplacementFromCenter + horizontalDisplacementFromCenter*horizontalDisplacementFromCenter)) >> 4;
+      if (LegalMoves.isWhiteAttacking(position, i)) {
+        value += attackingValue;
+      }
+      if (LegalMoves.isBlackAttacking(position, i)) {
+        value -= attackingValue;
+      }
       value += switch (position.board[i]) {
         Piece.whiteQueen  =>  900,
         Piece.whiteRook   =>  500,
@@ -30,40 +46,86 @@ class BestMoveSearcher {
         Piece.blackPawn   => -100,
         _                 =>    0,
       };
+      if (position.board[i] == Piece.whitePawn) {
+        whitePawnFiles[i % 8]++;
+        if (whitePawnFiles[i % 8] > 1) {
+          value -= 25;
+        }
+      }
+      if (position.board[i] == Piece.blackPawn) {
+        blackPawnFiles[i % 8]++;
+        if (blackPawnFiles[i % 8] > 1) {
+          value += 25;
+        }
+      }
+      if (position.board[i] == Piece.whiteBishop) {
+        whiteBishopColors[i%2] = true;
+      }
+      if (position.board[i] == Piece.blackBishop) {
+        blackBishopColors[i%2] = true;
+      }
+      column = (column + 1) % 8;
+      if (column == 0) {
+        row++;
+      }
+    }
+    if (whitePawnFiles[0] > 0 && whitePawnFiles[1] == 0) {
+      value -= 50;
+    }
+    if (whitePawnFiles[7] > 0 && whitePawnFiles[6] == 0) {
+      value -= 50;
+    }
+    if (blackPawnFiles[0] > 0 && blackPawnFiles[1] == 0) {
+      value += 50;
+    }
+    if (blackPawnFiles[7] > 0 && blackPawnFiles[6] == 0) {
+      value += 50;
+    }
+    for (int i = 1; i < 7; i++) {
+      if (whitePawnFiles[i-1] == 0 && whitePawnFiles[i] > 0 && whitePawnFiles[i+1] == 0) {
+        value -= 50;
+      }
+      if (blackPawnFiles[i-1] == 0 && blackPawnFiles[i] > 0 && blackPawnFiles[i+1] == 0) {
+        value += 50;
+      }
+    }
+    if (whiteBishopColors[0] && whiteBishopColors[1]){
+      value += 50;
+    }
+    if (blackBishopColors[0] && blackBishopColors[1]){
+      value -= 50;
     }
     return value;
   }
 
-  Future<String?> search(Position position) async {
+  Future<String?> search(Position position, int? moveTime) async {
     _isRunning = true;
-    (int, String, Position)? bestMove;
+    PositionTreeNode positionTree = PositionTreeNode.fromPosition(position);
-    Queue<(int, String, Position)> evaluatedMoves = Queue();
+    String bestLine = "";
-    await for (final (String, Position) move in LegalMoves.getLegalMoves(position)) {
+    int? bestValue;
-      final (int, String, Position) evaluatedMove = (await getPositionBaseValue(move.$2), move.$1, move.$2);
+    int depth = 0;
-      if (
+    final int startTime = DateTime.now().millisecondsSinceEpoch;
-        null == bestMove ||
+    int time = 0;
-        (bestMove.$1 < evaluatedMove.$1 && position.isWhiteTurn) ||
+    while (!_isStopped &&  positionTree.priority < Numbers.maxInteger) {
-        (bestMove.$1 > evaluatedMove.$1 && !position.isWhiteTurn)
+      positionTree.computeStep();
-      ) {
+      time = DateTime.now().millisecondsSinceEpoch - startTime;
-        bestMove = evaluatedMove;
+      if (null != moveTime && time >= moveTime) {
+        _isStopped = true;
+      }
+      if (positionTree.childrenByValue.isNotEmpty || bestValue != positionTree.value) {
+        final String thisBestLine = positionTree.childrenByValue.firstOrNull?.bestLine ?? "";
+        if (bestLine != thisBestLine || bestValue != positionTree.value || depth != positionTree.depth) {
+          bestLine = thisBestLine;
+          bestValue = positionTree.value;
+          depth = positionTree.depth;
+          print("info depth $depth multipv 1 nodes ${positionTree.nodeCount} time $time score cp ${(position.isWhiteTurn ? 1 : -1) * (positionTree.value)} pv $bestLine");
+        }
       }
-      evaluatedMoves.add(evaluatedMove);
       await Future.delayed(Duration.zero);
-      if (_isStopped) {
-        break;
     }
-      // TODO evaluate checkmate
-    }
-    if (evaluatedMoves.isEmpty) {
     _isRunning = false;
     _isStopped = false;
-      return null;
+    return positionTree.childrenByValue.firstOrNull?.move;
-    }
-    // TODO search
-    // IDEA implement a BFS with pruning on the ones that give suboptimal values
-    _isRunning = false;
-    _isStopped = false;
-    return bestMove?.$2;
   }
 
   Future<void> stop() async {

lib/constants/numbers.dart

@@ -0,0 +1,11 @@
+import 'package:meta/meta.dart';
+
+@immutable
+class Numbers {
+
+  Numbers._();
+
+  static const int maxInteger =  0x7FFFFFFFFFFFFFFF;
+  static const int minInteger = -0x7FFFFFFFFFFFFFFF;
+
+}

lib/data_structures/heap.dart

@@ -1,83 +0,0 @@
-class Heap<T> {
-
-  final int Function(T) getPriority;
-  List<(T, int)> _items;
-
-  Heap({
-    required this.getPriority
-  }): _items = [];
-
-  factory Heap.fromItems(
-    List<T> items,
-    {
-      required int Function(T) getPriority,
-    }
-  ) {
-    Heap<T> heap = Heap(getPriority: getPriority);
-    for (final T item in items) {
-      heap.add(item);
-    }
-    return heap;
-  }
-
-  T get first => _items.first.$1;
-
-  T? get firstOrNull => _items.firstOrNull?.$1;
-
-  int get length => _items.length;
-
-  bool get isEmpty => _items.isEmpty;
-
-  bool get isNotEmpty => _items.isNotEmpty;
-
-  void add(T item) {
-    final (T, int) heapItem = (item, getPriority(item));
-    final int thisKey = heapItem.$2;
-    int i = _items.length;
-    _items.add(heapItem);
-    while (i > 0 && _items[(i-1) ~/ 2].$2 > thisKey) {
-      _items[i] = _items[(i-1) ~/ 2];
-      i = (i-1)~/2;
-    }
-    _items[i] = heapItem;
-  }
-
-  T removeFirst() {
-    if (_items.isEmpty) {
-      throw StateError("No element");
-    }
-    final T firstItem = _items[0].$1;
-    if (_items.length < 2) {
-      _items.length--;
-      return firstItem;
-    }
-    final (T, int) itemToMove = _items.last;
-    _items[0] = itemToMove;
-    _items.length--;
-    int i = 0;
-    int leftIndex, rightIndex;
-    bool stop = false;
-    while (!stop) {
-      rightIndex = (i+1) << 1;
-      leftIndex = rightIndex-1;
-      if (leftIndex < _items.length && itemToMove.$2 > _items[leftIndex].$2) {
-        if (rightIndex < _items.length && _items[leftIndex].$2 > _items[rightIndex].$2) {
-          _items[i] = _items[rightIndex];
-          _items[rightIndex] = itemToMove;
-          i = rightIndex;
-        } else {
-          _items[i] = _items[leftIndex];
-          _items[leftIndex] = itemToMove;
-          i = leftIndex;
-        }
-      } else {
-        stop = true;
-      }
-    }
-    return firstItem;
-  }
-
-  @override
-  String toString() => _items.map(((T, int) item) => item.$1).toString();
-
-}

lib/data_structures/position_tree_node.dart

@@ -0,0 +1,96 @@
+import 'package:omnichess/classes/best_move_searcher.dart';
+import 'package:omnichess/classes/position.dart';
+import 'package:omnichess/constants/numbers.dart';
+import 'package:omnichess/data_structures/search_heap.dart';
+import 'package:omnichess/functions/legal_moves.dart';
+
+class PositionTreeNode {
+
+  int priority;
+  int value;
+  int nodeCount;
+  int depth;
+  final String move;
+  final Position position;
+  final Iterable<(String, Position)> legalMoves;
+  SearchHeap<String, PositionTreeNode> children;
+  SearchHeap<String, PositionTreeNode> childrenByValue;
+
+  String get bestLine {
+    final String? childBestLine = childrenByValue.firstOrNull?.bestLine;
+    return "$move${null == childBestLine ? "" : " $childBestLine"}";
+  }
+
+  PositionTreeNode({
+    required this.priority,
+    required this.value,
+    required this.move,
+    required this.position,
+    required this.legalMoves,
+    required this.children,
+    required this.childrenByValue,
+  }):
+    nodeCount = 0,
+    depth = 0;
+
+  factory PositionTreeNode.fromPosition(Position position, [ String move = "" ]) {
+    final int value = BestMoveSearcher.getPositionBaseValue(position);
+    final Iterable<(String, Position)> legalMoves = LegalMoves.getLegalMoves(position);
+    return PositionTreeNode(
+      priority: getPositionBasePriority(position, value, legalMoves, 0),
+      value: value,
+      move: move,
+      position: position,
+      legalMoves: legalMoves,
+      children: SearchHeap<String, PositionTreeNode>(
+        getKey: (PositionTreeNode node) => node.move,
+        getPriority: (PositionTreeNode node) => node.priority,
+      ),
+      childrenByValue: SearchHeap<String, PositionTreeNode>(
+        getKey: (PositionTreeNode node) => node.move,
+        getPriority: position.isWhiteTurn
+          ? (PositionTreeNode node) => -node.value
+          : (PositionTreeNode node) => node.value,
+      ),
+    );
+  }
+
+  void computeStep() {
+    if (legalMoves.isEmpty) {
+      return;
+    }
+    if (children.isEmpty) {
+      _computeChildren();
+      return;
+    }
+    final PositionTreeNode firstChild = children.first;
+    final int initialFirstChildNodeCount = firstChild.nodeCount;
+    firstChild.computeStep();
+    children.updateElement(firstChild.move);
+    childrenByValue.updateElement(firstChild.move);
+    nodeCount += firstChild.nodeCount - initialFirstChildNodeCount;
+    if (firstChild.depth + 1 > depth) {
+      depth = firstChild.depth + 1;
+    }
+    priority = (children.first.priority == Numbers.maxInteger) ? children.first.priority : children.first.priority + 1;
+    value = childrenByValue.first.value;
+  }
+
+  void _computeChildren() {
+    for (final (String, Position) move in legalMoves) {
+      final PositionTreeNode positionTreeNode = PositionTreeNode.fromPosition(move.$2, move.$1);
+      children.add(positionTreeNode);
+      childrenByValue.add(positionTreeNode);
+    }
+    nodeCount = legalMoves.length;
+    priority = (children.first.priority == Numbers.maxInteger) ? children.first.priority : children.first.priority + 1;
+    depth = 1;
+    value = childrenByValue.first.value;
+  }
+
+  static int getPositionBasePriority(Position position, int value, Iterable<(String, Position)> legalMoves, int depth) =>
+    legalMoves.isEmpty
+      ? Numbers.maxInteger
+      : 0;
+
+}

lib/data_structures/search_heap.dart

@@ -0,0 +1,135 @@
+class SearchHeap<K, T> {
+
+  final K Function(T) getKey;
+  final int Function(T) getPriority;
+  List<(T, K, int)> _items;
+  Map<K, int> _positionByKey;
+
+  SearchHeap({
+    required this.getKey,
+    required this.getPriority,
+  }):
+    _items = [],
+    _positionByKey = {};
+
+  factory SearchHeap.fromItems(
+    List<T> items,
+    {
+      required K Function(T) getKey,
+      required int Function(T) getPriority,
+    }
+  ) {
+    SearchHeap<K, T> heap = SearchHeap(getKey: getKey, getPriority: getPriority);
+    for (final T item in items) {
+      heap.add(item);
+    }
+    return heap;
+  }
+
+  T get first => _items.first.$1;
+
+  T? get firstOrNull => _items.firstOrNull?.$1;
+
+  int get length => _items.length;
+
+  bool get isEmpty => _items.isEmpty;
+
+  bool get isNotEmpty => _items.isNotEmpty;
+
+  void add(T item) {
+    final (T, K, int) heapItem = (item, getKey(item), getPriority(item));
+    final int thisKey = heapItem.$3;
+    int i = _items.length;
+    _items.add(heapItem);
+    while (i > 0 && _items[(i-1) >> 1].$3 > thisKey) {
+      _items[i] = _items[(i-1) >> 1];
+      _positionByKey[_items[i].$2] = i;
+      i = (i-1) >> 1;
+    }
+    _items[i] = heapItem;
+    _positionByKey[heapItem.$2] = i;
+  }
+
+  T removeFirst() {
+    if (_items.isEmpty) {
+      throw StateError("No element");
+    }
+    final T firstItem = _items[0].$1;
+    _positionByKey.remove(_items[0].$2);
+    if (_items.length < 2) {
+      _items.length--;
+      return firstItem;
+    }
+    final (T, K, int) itemToMove = _items.last;
+    _items.length--;
+    int i = 0;
+    int leftIndex, rightIndex;
+    bool stop = false;
+    while (!stop) {
+      rightIndex = (i+1) << 1;
+      leftIndex = rightIndex-1;
+      if (leftIndex < _items.length && itemToMove.$3 > _items[leftIndex].$3) {
+        if (rightIndex < _items.length && _items[leftIndex].$3 > _items[rightIndex].$3) {
+          _items[i] = _items[rightIndex];
+          _positionByKey[_items[i].$2] = i;
+          i = rightIndex;
+        } else {
+          _items[i] = _items[leftIndex];
+          _positionByKey[_items[i].$2] = i;
+          i = leftIndex;
+        }
+      } else if (rightIndex < _items.length && _items[leftIndex].$3 > _items[rightIndex].$3) {
+        _items[i] = _items[rightIndex];
+        _positionByKey[_items[i].$2] = i;
+        i = rightIndex;
+      } else {
+        stop = true;
+      }
+    }
+    _items[i] = itemToMove;
+    _positionByKey[itemToMove.$2] = i;
+    return firstItem;
+  }
+
+  void updateElement(K key) {
+    int i = _positionByKey[key]!;
+    final (T, K, int) item = (_items[i].$1, _items[i].$2, getPriority(_items[i].$1));
+    bool dontBubbleDown = false;
+    while (i > 0 && _items[(i-1) >> 1].$3 > item.$3) {
+      dontBubbleDown = true;
+      _items[i] = _items[(i-1) >> 1];
+      _positionByKey[_items[i].$2] = i;
+      i = (i-1) >> 1;
+    }
+    int leftIndex, rightIndex;
+    while (!dontBubbleDown) {
+      rightIndex = (i+1) << 1;
+      leftIndex = rightIndex-1;
+      if (leftIndex < _items.length && item.$3 > _items[leftIndex].$3) {
+        if (rightIndex < _items.length && _items[leftIndex].$3 > _items[rightIndex].$3) {
+          _items[i] = _items[rightIndex];
+          _positionByKey[_items[i].$2] = i;
+          i = rightIndex;
+        } else {
+          _items[i] = _items[leftIndex];
+          _positionByKey[_items[i].$2] = i;
+          i = leftIndex;
+        }
+      } else if (rightIndex < _items.length && _items[leftIndex].$3 > _items[rightIndex].$3) {
+        _items[i] = _items[rightIndex];
+        _positionByKey[_items[i].$2] = i;
+        i = rightIndex;
+      } else {
+        dontBubbleDown = true;
+      }
+    }
+    _items[i] = item;
+    _positionByKey[item.$2] = i;
+  }
+
+  @override
+  String toString() => _items.map(((T, K, int) item) => item.$1).toString();
+
+  List<T> get debugItems => _items.map(((T, K, int) item) => item.$1).toList();
+
+}

lib/functions/_partials/legal_moves_black.dart

@@ -4,9 +4,9 @@ class _LegalMovesBlack {
 
   _LegalMovesBlack._();
 
-  static Stream<(String, Position)> _getLegalMoves(Position position) => _getValidOrCheckedMoves(position).where(((String, Position) move) => !_isBlackChecked(move.$2));
+  static Iterable<(String, Position)> _getLegalMoves(Position position) => _getValidOrCheckedMoves(position).where(((String, Position) move) => !_isBlackChecked(move.$2));
 
-  static Stream<(String, Position)> _getValidOrCheckedMoves(Position position) async* {
+  static Iterable<(String, Position)> _getValidOrCheckedMoves(Position position) sync* {
     for (int i = 0; i < 64; i++) {
       switch (position.board[i]) {
         case Piece.emptySquare:
@@ -40,7 +40,7 @@ class _LegalMovesBlack {
     }
   }
 
-  static Stream<(String, Position)> _getBlackPawnMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getBlackPawnMoves(Position position, int i) sync* {
     int j = i+8;
     if (Piece.emptySquare == position.board[j]) { // pawn forward
       if (i > 47) {
@@ -87,7 +87,7 @@ class _LegalMovesBlack {
     }
   }
 
-  static Stream<(String, Position)> _getBlackKnightMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getBlackKnightMoves(Position position, int i) sync* {
     final bool canGoUp2 = i > 15;
     final bool canGoUp1 = i > 7;
     final bool canGoDown1 = i < 56;
@@ -131,7 +131,7 @@ class _LegalMovesBlack {
     }
   }
 
-  static Stream<(String, Position)> _getBlackBishopMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getBlackBishopMoves(Position position, int i) sync* {
     final int column = i % 8;
     // up left
     bool hasEncounteredPiece = false;
@@ -198,7 +198,7 @@ class _LegalMovesBlack {
       j+=9;
     }
   }
-  static Stream<(String, Position)> _getBlackRookMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getBlackRookMoves(Position position, int i) sync* {
     final int column = i % 8;
     // up
     bool hasEncounteredPiece = false;
@@ -262,7 +262,7 @@ class _LegalMovesBlack {
     }
   }
 
-  static Stream<(String, Position)> _getBlackKingMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getBlackKingMoves(Position position, int i) sync* {
     int j = i-8;
     if (j >= 0 && !Piece.isBlack(position.board[j])) {
       yield ("${Position.squareIndexToString(i)}${Position.squareIndexToString(j)}", Position.from(position)..playMoveIndices(i, j));
@@ -352,7 +352,7 @@ class _LegalMovesBlack {
   }
   
   static bool _isWhitePawnAttacking(Position position, int square) {
-    if (square < 8) {
+    if (square > 47) {
       return false;
     }
     final int column = square % 8;
@@ -480,7 +480,7 @@ class _LegalMovesBlack {
     // up
     bool hasEncounteredPiece = false;
     int j = square-8;
-    while (!hasEncounteredPiece && j > 0) {
+    while (!hasEncounteredPiece && j >= 0) {
       final int piece = position.board[j];
       if (Piece.emptySquare != piece) {
         hasEncounteredPiece = true;
@@ -507,7 +507,7 @@ class _LegalMovesBlack {
     hasEncounteredPiece = false;
     j = square - 1;
     int k = column - 1;
-    while (!hasEncounteredPiece && k > 0) {
+    while (!hasEncounteredPiece && k >= 0) {
       final int piece = position.board[j];
       if (Piece.emptySquare != piece) {
         hasEncounteredPiece = true;

lib/functions/_partials/legal_moves_white.dart

@@ -4,9 +4,9 @@ class _LegalMovesWhite {
 
   _LegalMovesWhite._();
 
-  static Stream<(String, Position)> _getLegalMoves(Position position) => _getValidOrCheckedMoves(position).where(((String, Position) move) => !_isWhiteChecked(move.$2));
+  static Iterable<(String, Position)> _getLegalMoves(Position position) => _getValidOrCheckedMoves(position).where(((String, Position) move) => !_isWhiteChecked(move.$2));
 
-  static Stream<(String, Position)> _getValidOrCheckedMoves(Position position) async* {
+  static Iterable<(String, Position)> _getValidOrCheckedMoves(Position position) sync* {
     for (int i = 0; i < 64; i++) {
       switch (position.board[i]) {
         case Piece.emptySquare:
@@ -40,7 +40,7 @@ class _LegalMovesWhite {
     }
   }
 
-  static Stream<(String, Position)> _getWhitePawnMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getWhitePawnMoves(Position position, int i) sync* {
     int j = i-8;
     if (Piece.emptySquare == position.board[j]) { // pawn forward
       if (i < 16) {
@@ -87,7 +87,7 @@ class _LegalMovesWhite {
     }
   }
 
-  static Stream<(String, Position)> _getWhiteKnightMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getWhiteKnightMoves(Position position, int i) sync* {
     final bool canGoUp2 = i > 15;
     final bool canGoUp1 = i > 7;
     final bool canGoDown1 = i < 56;
@@ -131,7 +131,7 @@ class _LegalMovesWhite {
     }
   }
 
-  static Stream<(String, Position)> _getWhiteBishopMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getWhiteBishopMoves(Position position, int i) sync* {
     final int column = i % 8;
     // up left
     bool hasEncounteredPiece = false;
@@ -198,7 +198,7 @@ class _LegalMovesWhite {
       j+=9;
     }
   }
-  static Stream<(String, Position)> _getWhiteRookMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getWhiteRookMoves(Position position, int i) sync* {
     final int column = i % 8;
     // up
     bool hasEncounteredPiece = false;
@@ -262,7 +262,7 @@ class _LegalMovesWhite {
     }
   }
 
-  static Stream<(String, Position)> _getWhiteKingMoves(Position position, int i) async* {
+  static Iterable<(String, Position)> _getWhiteKingMoves(Position position, int i) sync* {
     int j = i-8;
     if (j >= 0 && !Piece.isWhite(position.board[j])) {
       yield ("${Position.squareIndexToString(i)}${Position.squareIndexToString(j)}", Position.from(position)..playMoveIndices(i, j));
@@ -352,7 +352,7 @@ class _LegalMovesWhite {
   }
   
   static bool _isBlackPawnAttacking(Position position, int square) {
-    if (square < 8) {
+    if (square < 16) {
       return false;
     }
     final int column = square % 8;
@@ -480,7 +480,7 @@ class _LegalMovesWhite {
     // up
     bool hasEncounteredPiece = false;
     int j = square-8;
-    while (!hasEncounteredPiece && j > 0) {
+    while (!hasEncounteredPiece && j >= 0) {
       final int piece = position.board[j];
       if (Piece.emptySquare != piece) {
         hasEncounteredPiece = true;
@@ -507,7 +507,7 @@ class _LegalMovesWhite {
     hasEncounteredPiece = false;
     j = square - 1;
     int k = column - 1;
-    while (!hasEncounteredPiece && k > 0) {
+    while (!hasEncounteredPiece && k >= 0) {
       final int piece = position.board[j];
       if (Piece.emptySquare != piece) {
         hasEncounteredPiece = true;

lib/functions/legal_moves.dart

@@ -8,12 +8,17 @@ part "_partials/legal_moves_white.dart";
 class LegalMoves {
   LegalMoves._();
 
-  static Stream<(String, Position)> getLegalMoves(Position position) => position.isWhiteTurn
+  static Iterable<(String, Position)> getLegalMoves(Position position) => position.isWhiteTurn
     ? _LegalMovesWhite._getLegalMoves(position)
     : _LegalMovesBlack._getLegalMoves(position);
   
-  static Future<bool> isCheckmate(Position position) async => position.isWhiteTurn
+  static bool isCheckmate(Position position) => position.isWhiteTurn
-      ? (_LegalMovesWhite._isWhiteChecked(position) && await getLegalMoves(position).isEmpty)
+    ? (_LegalMovesWhite._isWhiteChecked(position) && getLegalMoves(position).isEmpty)
-      : (_LegalMovesBlack._isBlackChecked(position) && await getLegalMoves(position).isEmpty);
+    : (_LegalMovesBlack._isBlackChecked(position) && getLegalMoves(position).isEmpty);
+
+  static bool isWhiteAttacking(Position position, int square) => _LegalMovesBlack._isWhiteAttacking(position, square);
+  static bool isBlackAttacking(Position position, int square) => _LegalMovesWhite._isBlackAttacking(position, square);
+  static bool isWhiteChecked(Position position) => _LegalMovesWhite._isWhiteChecked(position);
+  static bool isBlackChecked(Position position) => _LegalMovesBlack._isBlackChecked(position);
 
 }

lib/omnichess.dart

@@ -22,8 +22,15 @@ class Omnichess {
   }
 
   Future<void> _goCommand(Queue<String> inputComponents) async {
+    int? moveTime;
+    while (inputComponents.isNotEmpty) {
+      final String inputComponent = inputComponents.removeFirst();
+      if ("movetime" == inputComponent) {
+        moveTime = int.tryParse(inputComponents.firstOrNull ?? "");
+      }
+    }
     final Position position = Position.fromPositionCommand(positionCommand);
-    final String? bestMove = await bestMoveSearcher.search(position);
+    final String? bestMove = await bestMoveSearcher.search(position, moveTime);
     print("bestmove ${bestMove ?? "(none)"}");
   }
 
@@ -103,11 +110,26 @@ class Omnichess {
   }
 
   void loop() async {
+    final DateTime now = DateTime.now();
+    final String logName = "${now.year}"
+      "${now.month.toString().padLeft(2, "0")}"
+      "${now.day.toString().padLeft(2, "0")}"
+      "-"
+      "${now.hour.toString().padLeft(2, "0")}"
+      "${now.minute.toString().padLeft(2, "0")}"
+      "${now.second.toString().padLeft(2, "0")}"
+      "${now.millisecond.toString().padLeft(3, "0")}"
+      ".log";
+    final File log = File("logs/$logName");
+    if (!log.existsSync()) {
+      log.createSync();
+    }
     late StreamSubscription<String> inputSubscription;
     inputSubscription = stdin
       .transform(utf8.decoder)
       .transform(LineSplitter())
       .listen((String line) async {
+        log.writeAsStringSync("$line\n", mode: FileMode.append);
         final String input = line.trim();
         final bool keepGoing = await elaborate(input);
         if (!keepGoing) {