fix: account for mobility difference

1 files changed, 18 insertions, 56 deletions

diff --git a/src/main.c b/src/main.c
index 5b28b92..404b1fd 100644
--- a/src/main.c
+++ b/src/main.c
@@ -438,60 +438,6 @@ int compute_coverage(int* board, int color) {
   return counter;
 }
 
-/*
- * Compute player pieces score depending on how
- * well they are positioned on the board
- *
- * Returns number in range(0, 112)
- */
-int compute_positioning_score(int* board, int color) {
-  int total_score = 0;
-  double center = 3.5;
-
-  for (double rank = 7; rank >= 0; rank--) {
-    for (double file = 0; file < 8; file++) {
-      int index = rank * 16 + file;
-      int piece = board[index];
-      if (piece % 2 == color) {
-        int score = 7 - (fabs(rank - center) + fabs(file - center));
-
-        int multiplier = 1;
-        switch (piece & NO_COLOR) {
-          case KNIGHT:
-            multiplier = 4;
-            break;
-          case BISHOP:
-            multiplier = 3;
-            break;
-          case PAWN:
-            multiplier = 2;
-            break;
-          case KING:
-            multiplier = -5; // Discourage king in center (encourage castle)
-            // TODO: encourage king in center after opponent has low material <= 6
-            break;
-          default:
-            multiplier = 1;
-            break;
-        }
-        total_score += score * multiplier;
-      }
-    }
-  }
-
-  return total_score;
-}
-
-/*
- * Return a total board score symbolizing advantage
- * for WHITE, meaining WHITE tries to maximize this
- * value and BLACK tries to minimize it.
- */
-int compute_score(int* board, int mobility) {
-  int material_advantage = compute_material_advantage(board, WHITE);
-  return material_advantage + mobility;
-}
-
 int list_available_moves(Move* moves, int* board, int color) {
   int moves_count = 0;
 
@@ -505,7 +451,7 @@ int list_available_moves(Move* moves, int* board, int color) {
             int index_destination = rank_destination * 16 + file_destination;
             Move move = { index, index_destination, 0 };
             if (validate_move(move, color, board) >= 0) {
-              moves[moves_count] = move;
+              if (moves) moves[moves_count] = move;
               moves_count++;
             }
           }
@@ -517,6 +463,22 @@ int list_available_moves(Move* moves, int* board, int color) {
   return moves_count;
 }
 
+/*
+ * Return a total board score symbolizing advantage
+ * for WHITE, meaining WHITE tries to maximize this
+ * value and BLACK tries to minimize it.
+ */
+int compute_score(int* board, int mobility, int mobility_color) {
+  Move dummy[MAX_AVAILABLE_MOVES];
+
+  int white_material_advantage = compute_material_advantage(board, WHITE);
+
+  int opponent_mobility = list_available_moves(NULL, board, mobility_color ^ 1);
+  int white_mobility_advantage = (mobility - opponent_mobility) * (mobility_color == WHITE ? 1 : -1);
+
+  return white_material_advantage + white_mobility_advantage;
+}
+
 int get_piece_raw_value(int piece) {
   switch (piece & NO_COLOR) {
     case KNIGHT:
@@ -576,7 +538,7 @@ Move find_best_move(int* board, int color, int depth, int alpha, int beta, int*
 
       move.value = depth < MAX_DEPTH
         ? find_best_move(board, 1 - color, depth + 1, alpha, beta, metrics).value
-        : compute_score(board, color == WHITE ? availabel_moves_count : -availabel_moves_count);
+        : compute_score(board, availabel_moves_count, color);
 
       reverse_move(move, captured_piece, board);