tictactoe: hard AI sets edge in second move

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

@@ -26,7 +26,7 @@ public class AIEasy implements TicTacToeAI {
 		do {
 			row = rand.nextInt(boardSize);
 			col = rand.nextInt(boardSize);
-		} while (board[row][col] != '-');
+		} while (board[row][col] != EMPTY_CHAR);
 			
 		gl.setField(row, col, AI_CHAR);
 	}

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

@@ -5,11 +5,12 @@ import de.tims.tictactoe.GameLogic;
 public class AIHard implements TicTacToeAI {
 	private static final char AI_CHAR = 'o';
 	private static final char EMPTY_CHAR = '-';
+	private static final int BOARD_SIZE = 3;
 	
 	private GameLogic gl;
 	
 	public AIHard(GameLogic gl) throws IllegalArgumentException {
-		if (gl.getBoard().length != 3) {
+		if (gl.getBoard().length != BOARD_SIZE) {
 			throw new IllegalArgumentException("Hard AI only supports 3x3 boards!");
 		}
 		this.gl = gl;
@@ -19,15 +20,39 @@ public class AIHard implements TicTacToeAI {
 	public void calculateNextMove() {
 		boolean emptyBoard = true;
 		char[][] board = gl.getBoard();
+		
 		for (char[] row : board) {
 			for (char field : row) {
 				emptyBoard &= field == EMPTY_CHAR;
 			}
 		}
+		
 		if (emptyBoard || board[1][1] == EMPTY_CHAR) {			
 			gl.setField(1, 1, AI_CHAR);
 		} else {
-			gl.setField(0, 0, AI_CHAR);
+			boolean emptyEdgeFound = false;
+			int row = 0;
+			int col = 0;
+			
+			for (int i = 0; i < BOARD_SIZE; i = i + BOARD_SIZE - 1) {
+				for (int j = 0; j < BOARD_SIZE; j = j + BOARD_SIZE - 1) {
+					row = i;
+					col = j;
+					
+					if (board[i][j] == EMPTY_CHAR) {
+						row = i;
+						col = j;
+						emptyEdgeFound = true;
+						break;
+					}
+				}
+				
+				if (emptyEdgeFound) {
+					break;
+				}
+			}
+			
+			gl.setField(row, col, AI_CHAR);
 		}
 	}
 }

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

@@ -49,4 +49,15 @@ class AIHardTest {
 		verify(gl, times(1)).setField(1, 1, realChar);
 	}
 	
+	@Test
+	void setEdgeFieldInSecondMove() {
+		char realChar = 'o';
+		doReturn(new char[][] { {'x', '-', '-'}, {'-', 'o', '-'}, {'-', '-', '-'} }).when(gl).getBoard();
+		
+		TicTacToeAI ai = new AIHard(gl);
+		ai.calculateNextMove();
+		
+		verify(gl, times(1)).setField(0, 2, realChar);
+	}
+
 }