From c6e0d83d70a6fa8b659f35a9cbf9d0bbc72034ae Mon Sep 17 00:00:00 2001
From: Tobias Krause <tobias.krause@informatik.hs-fulda.de>
Date: Mon, 31 Jan 2022 16:17:51 +0100
Subject: [PATCH] tictactoe: hard AI prevents opponents win in row

---
 src/main/java/de/tims/tictactoe/ai/AIHard.java  | 17 ++++++++++++-----
 .../java/de/tims/tictactoe/ai/AIHardTest.java   | 11 +++++++++++
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/src/main/java/de/tims/tictactoe/ai/AIHard.java b/src/main/java/de/tims/tictactoe/ai/AIHard.java
index 3e802c2..a821485 100644
--- a/src/main/java/de/tims/tictactoe/ai/AIHard.java
+++ b/src/main/java/de/tims/tictactoe/ai/AIHard.java
@@ -5,6 +5,7 @@ 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 char PLAYER_CHAR = 'x';
 	private static final int BOARD_SIZE = 3;
 	
 	private GameLogic gl;
@@ -18,16 +19,22 @@ public class AIHard implements TicTacToeAI {
 
 	@Override
 	public void calculateNextMove() {
-		boolean emptyBoard = true;
+		int charsOfOpponent = 0;
 		char[][] board = gl.getBoard();
 		
-		for (char[] row : board) {
-			for (char field : row) {
-				emptyBoard &= field == EMPTY_CHAR;
+		for (int i = 0; i < BOARD_SIZE; i++) {
+			charsOfOpponent = countCharsInRow(i, PLAYER_CHAR);
+			if (charsOfOpponent == BOARD_SIZE - 1) {
+				for (int j = 0; j < BOARD_SIZE; j++) {
+					if (board[i][j] == EMPTY_CHAR) {
+						gl.setField(i, j, AI_CHAR);
+						return;
+					}
+				}
 			}
 		}
 		
-		if (emptyBoard || board[1][1] == EMPTY_CHAR) {			
+		if (board[1][1] == EMPTY_CHAR) {			
 			gl.setField(1, 1, AI_CHAR);
 		} else {
 			boolean emptyEdgeFound = false;
diff --git a/src/test/java/de/tims/tictactoe/ai/AIHardTest.java b/src/test/java/de/tims/tictactoe/ai/AIHardTest.java
index 72934b6..e99dbf9 100644
--- a/src/test/java/de/tims/tictactoe/ai/AIHardTest.java
+++ b/src/test/java/de/tims/tictactoe/ai/AIHardTest.java
@@ -66,6 +66,17 @@ class AIHardTest {
 		verify(gl, times(1)).setField(0, 2, realChar);
 	}
 	
+	@Test
+	void preventOpponentsWinInRow() {
+		char realChar = 'o';
+		doReturn(new char[][] { {'o', '-', '-'}, {'x', '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) {