feat: add checkmate

1 files changed, 37 insertions, 25 deletions

diff --git a/src/main.c b/src/main.c
index b446fd6..2b7275f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -120,6 +120,9 @@ Move input_move() {
 };
 
 int validate_move(Move move, int color, int* board) {
+  // Null move means player is checkmated
+  if (move.origin == -100 && move.destination == -100) return INFINITY;
+
   if ((move.origin & 0x88) || (move.destination & 0x88)) return -1;
 
   int piece = board[move.origin];
@@ -543,34 +546,37 @@ void sort_moves(Move* moves, int moves_count, int* board) {
 Move find_best_move(int* board, int color, int depth, int alpha, int beta, int* metrics) {
   int is_maximizer = (color == 0);
 
-  Move best_move;
-  best_move.value = is_maximizer ? -INFINITY : INFINITY;
+  Move best_move = { -100, -100, 0 };
+  best_move.value = is_maximizer ? -100 * INFINITY / (depth + 1) : 100 * INFINITY / (depth + 1);
 
-  Move available_moves[MAX_AVAILABLE_MOVES];
-  int availabel_moves_count = list_available_moves(available_moves, board, color);
-  sort_moves(available_moves, availabel_moves_count, board);
+  // You only have available moves if your king hasn't been taken
+  if (compute_material_advantage(board, color) > -INFINITY / 2) {
+    Move available_moves[MAX_AVAILABLE_MOVES];
+    int availabel_moves_count = list_available_moves(available_moves, board, color);
+    sort_moves(available_moves, availabel_moves_count, board);
 
-  for (int i = 0; i < availabel_moves_count; i++) {
-    *metrics += 1;
-    Move move = available_moves[i];
+    for (int i = 0; i < availabel_moves_count; i++) {
+      *metrics += 1;
+      Move move = available_moves[i];
 
-    int captured_piece = apply_move(move, board);
+      int captured_piece = apply_move(move, board);
 
-    move.value = depth < MAX_DEPTH
-      ? find_best_move(board, 1 - color, depth + 1, alpha, beta, metrics).value
-      : compute_score(board);
+      move.value = depth < MAX_DEPTH
+        ? find_best_move(board, 1 - color, depth + 1, alpha, beta, metrics).value
+        : compute_score(board);
 
-    reverse_move(move, captured_piece, board);
+      reverse_move(move, captured_piece, board);
 
-    if (is_maximizer) {
-      if (move.value > best_move.value) best_move = move;
-      alpha = MAX(best_move.value, alpha);
-    } else {
-      if (move.value < best_move.value) best_move = move;
-      beta = MIN(best_move.value, beta);
-    }
+      if (is_maximizer) {
+        if (move.value > best_move.value) best_move = move;
+        alpha = MAX(best_move.value, alpha);
+      } else {
+        if (move.value < best_move.value) best_move = move;
+        beta = MIN(best_move.value, beta);
+      }
 
-    if (beta <= alpha) break;
+      if (beta <= alpha) break;
+    }
   }
 
   return best_move;
@@ -598,19 +604,25 @@ int main() {
       start = clock();
       move = find_best_move(board, color, 0, -INFINITY, +INFINITY, &metrics);
       end = clock();
-      char move_in_notation[] = "xy XY";
-      index_to_notation(move.origin, move_in_notation);
-      index_to_notation(move.destination, move_in_notation + 3);
       printf("[%i positions analyzed in %f seconds]\n", metrics, (double)(end - start) / CLOCKS_PER_SEC);
-      printf("Best move for black is %s with score %i in #%i moves\n", move_in_notation, move.value, MAX_DEPTH);
     }
 
     int error = validate_move(move, color, board);
     if (error < 0) {
       printf("Invalid move: %s!\n", VALIDATION_ERRORS[-1 - error]);
+    } else if (error == INFINITY) {
+      printf("Checkmate, %s is victorious!\n", COLORS[1 - color]);
+      break;
     } else {
       apply_move(move, board);
+
       print_board(board);
+
+      char move_in_notation[] = "xy XY";
+      index_to_notation(move.origin, move_in_notation);
+      index_to_notation(move.destination, move_in_notation + 3);
+      printf("%s: %s with score %i in #%i moves\n", COLORS[color], move_in_notation, move.value, MAX_DEPTH);
+
       color ^= 1;
     }
   }