tictactoe: hard ai sets always in the nearest edge to opponents field

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

@@ -54,8 +54,24 @@ public class AIHard implements TicTacToeAI {
 			}
 		}
 		
-		if (board[1][1] == EMPTY_CHAR) {			
-			gl.setField(1, 1, AI_CHAR);
+		if (board[BOARD_SIZE / 2][BOARD_SIZE / 2] == EMPTY_CHAR) {			
+			gl.setField(BOARD_SIZE / 2, BOARD_SIZE / 2, AI_CHAR);
+		} else if (board[BOARD_SIZE / 2][BOARD_SIZE / 2] == AI_CHAR && (board[0][0] == AI_CHAR || board[0][BOARD_SIZE - 1] == AI_CHAR || board[BOARD_SIZE - 1][0] == AI_CHAR || board[BOARD_SIZE - 1][BOARD_SIZE - 1] == AI_CHAR)) {
+			for (int i = BOARD_SIZE - 2; i > 0; i--) {				
+				for (int j = 0; j < BOARD_SIZE; j += BOARD_SIZE - 1) {
+					for (int k = 1; k < BOARD_SIZE - 1; k++) {
+						if (countCharsInRow(j, AI_CHAR) == i && countCharsInCol(k, AI_CHAR) == i && countCharsInRow(j, EMPTY_CHAR) == BOARD_SIZE -i && countCharsInCol(k, EMPTY_CHAR) == BOARD_SIZE - i) {
+							gl.setField(j, k, AI_CHAR);
+							return;
+						}
+						
+						if (countCharsInRow(k, AI_CHAR) == i && countCharsInCol(j, AI_CHAR) == i && countCharsInRow(k, EMPTY_CHAR) == BOARD_SIZE -i && countCharsInCol(j, EMPTY_CHAR) == BOARD_SIZE - i) {
+							gl.setField(k, j, AI_CHAR);
+							return;
+						}
+					}
+				}
+			}
 		} else {
 			boolean emptyEdgeFound = false;
 			int row = -1;

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

@@ -154,6 +154,17 @@ class AIHardTest {
 		verify(gl, times(1)).setField(0, 2, realChar);
 	}
 	
+	@Test
+	void chooseFieldWhichCreatesMostOpportunitiesToWin() {
+		char realChar = 'o';
+		doReturn(new char[][] { {'-', 'x', 'o'}, {'-', 'o', '-'}, {'x', '-', '-'} }).when(gl).getBoard();
+		
+		TicTacToeAI ai = new AIHard(gl);
+		ai.calculateNextMove();
+		
+		verify(gl, times(1)).setField(1, 2, realChar);
+	}
+	
 	@ParameterizedTest
 	@MethodSource("testCasesForCountCharsInRow")
 	void countCharsInRowTest(String testName, char[][] board, int rowNum, char charToCount, int expectedResult) {