tictactoe: hard AI prevents opponents win in diagonal

src/main/java/de/tims/tictactoe/ai/AIHard.java

@@ -21,20 +21,37 @@ public class AIHard implements TicTacToeAI {
 	public void calculateNextMove() {
 		int charsOfOpponentInRow = 0;
 		int charsOfOpponentInCol = 0;
+		int charsOfOpponentInDiag = 0;
 		char[][] board = gl.getBoard();
 		
 		for (int i = 0; i < BOARD_SIZE; i++) {
 			charsOfOpponentInRow = countCharsInRow(i, PLAYER_CHAR);
 			charsOfOpponentInCol = countCharsInCol(i, PLAYER_CHAR);
-			if (charsOfOpponentInRow == BOARD_SIZE - 1 || charsOfOpponentInCol == BOARD_SIZE - 1) {
+			if (i < 2) {
+				charsOfOpponentInDiag = countCharsInDiag(i, PLAYER_CHAR);
+			}
+			
+			if (charsOfOpponentInRow == BOARD_SIZE - 1 || charsOfOpponentInCol == BOARD_SIZE - 1 || charsOfOpponentInDiag == BOARD_SIZE - 1) {
 				for (int j = 0; j < BOARD_SIZE; j++) {
-					if (board[(charsOfOpponentInRow == BOARD_SIZE - 1) ? i : j][(charsOfOpponentInRow == BOARD_SIZE - 1) ? j : i] == EMPTY_CHAR) {
-						gl.setField((charsOfOpponentInRow == BOARD_SIZE - 1) ? i : j, (charsOfOpponentInRow == BOARD_SIZE - 1) ? j : i, AI_CHAR);
+					if (charsOfOpponentInRow == BOARD_SIZE - 1) {
+						if (board[i][j] == EMPTY_CHAR) {
+							gl.setField(i, j, AI_CHAR);
+							return;
+						}
+					} else if (charsOfOpponentInCol == BOARD_SIZE - 1) {
+						if (board[j][i] == EMPTY_CHAR) {
+							gl.setField(j, i, AI_CHAR);
+							return;
+						}
+					} else if (charsOfOpponentInDiag == BOARD_SIZE - 1) {
+						if (board[j][(i == 0) ? j : BOARD_SIZE - 1 - j] == EMPTY_CHAR) {
+							gl.setField(j, (i == 0) ? j : BOARD_SIZE - 1 - j, AI_CHAR);
 							return;
 						}
 					}
 				}
 			}
+		}
 		
 		if (board[1][1] == EMPTY_CHAR) {			
 			gl.setField(1, 1, AI_CHAR);

src/test/java/de/tims/tictactoe/ai/AIHardTest.java

@@ -88,6 +88,17 @@ class AIHardTest {
 		verify(gl, times(1)).setField(2, 1, realChar);
 	}
 
+	@Test
+	void preventOpponentsWinInDiag() {
+		char realChar = 'o';
+		doReturn(new char[][] { {'x', '-', 'o'}, {'-', 'x', '-'}, {'-', '-', '-'} }).when(gl).getBoard();
+		
+		TicTacToeAI ai = new AIHard(gl);
+		ai.calculateNextMove();
+		
+		verify(gl, times(1)).setField(2, 2, realChar);
+	}
+	
 	@ParameterizedTest
 	@MethodSource("testCasesForCountCharsInRow")
 	void countCharsInRowTest(String testName, char[][] board, int rowNum, char charToCount, int expectedResult) {