From c235e4ec6532ff91b4220f044dd69a5365a5c12d Mon Sep 17 00:00:00 2001
From: Nilstrieb <48135649+Nilstrieb@users.noreply.github.com>
Date: Sun, 15 Jan 2023 15:36:54 +0100
Subject: [PATCH] port to java

---
 .../bbw/m411/connect4/Connect4ArenaMain.java  |  4 +-
 .../ch/bbw/m411/connect4/PerfectPlayer.java   | 76 +++++++++++++++++++
 .../java/ch/bbw/m411/connect4/RustPlayer.java | 23 +++++-
 3 files changed, 97 insertions(+), 6 deletions(-)
 create mode 100644 minmax-java/src/main/java/ch/bbw/m411/connect4/PerfectPlayer.java

diff --git a/minmax-java/src/main/java/ch/bbw/m411/connect4/Connect4ArenaMain.java b/minmax-java/src/main/java/ch/bbw/m411/connect4/Connect4ArenaMain.java
index 087f7e3..0411b7c 100644
--- a/minmax-java/src/main/java/ch/bbw/m411/connect4/Connect4ArenaMain.java
+++ b/minmax-java/src/main/java/ch/bbw/m411/connect4/Connect4ArenaMain.java
@@ -17,7 +17,7 @@ public class Connect4ArenaMain {
     static final int NOMOVE = -1;
 
     public static void main(String[] args) {
-        new Connect4ArenaMain().play(new RustPlayer(), new GreedyPlayer());
+        new Connect4ArenaMain().play(new HumanPlayer(), new PerfectPlayer());
     }
 
     static String toDebugString(Stone[] board) {
@@ -66,7 +66,7 @@ public class Connect4ArenaMain {
         return null; // null implies a draw
     }
 
-    boolean isWinning(Stone[] board, Stone forColor) {
+    public static boolean isWinning(Stone[] board, Stone forColor) {
         return RustPlayer.isWinning(board, forColor);
     }
 
diff --git a/minmax-java/src/main/java/ch/bbw/m411/connect4/PerfectPlayer.java b/minmax-java/src/main/java/ch/bbw/m411/connect4/PerfectPlayer.java
new file mode 100644
index 0000000..79ca215
--- /dev/null
+++ b/minmax-java/src/main/java/ch/bbw/m411/connect4/PerfectPlayer.java
@@ -0,0 +1,76 @@
+package ch.bbw.m411.connect4;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class PerfectPlayer extends Connect4ArenaMain.DefaultPlayer {
+    private static final int MAX_DEPTH = 8;
+    private static final int WON = 1000;
+    private static final int LOST = -1000;
+
+    private int bestMove = -1;
+
+    private List<Integer> possibleMoves() {
+        var moves = new ArrayList<Integer>();
+        // for all columns
+        for (int i = 0; i < 7; i++) {
+            // walk up
+            for (int j = 0; j < 4; j++) {
+                var position = i + (j * 7);
+                if (board[position] == null) {
+                    moves.add(position);
+                    break;
+                }
+            }
+
+        }
+        return moves;
+    }
+
+    private int minmax(Connect4ArenaMain.Stone maximizingPlayer, int alpha, int beta, int depth) {
+        if (depth >= MAX_DEPTH) {
+            // FIXME rate
+            return 0;
+        }
+
+        if (Connect4ArenaMain.isWinning(board, maximizingPlayer)) {
+            return WON;
+        }
+
+        if (Connect4ArenaMain.isWinning(board, maximizingPlayer.opponent())) {
+            return LOST;
+        }
+
+        var moves = possibleMoves();
+        if (moves.isEmpty()) {
+            return 0;
+        }
+
+        var maxValue = alpha;
+        for (var move : moves) {
+            board[move] = maximizingPlayer;
+            var value = -minmax(maximizingPlayer.opponent(), -beta, -maxValue, depth + 1);
+            board[move] = null;
+
+            if (value > maxValue) {
+                maxValue = value;
+                if (depth == 0) {
+                    bestMove = move;
+                }
+
+                if (maxValue >= beta) {
+                    break;
+                }
+            }
+        }
+
+        return maxValue;
+    }
+
+    @Override
+    protected int play() {
+        bestMove = -1;
+        minmax(myColor, LOST, WON, 0);
+        return this.bestMove;
+    }
+}
diff --git a/minmax-java/src/main/java/ch/bbw/m411/connect4/RustPlayer.java b/minmax-java/src/main/java/ch/bbw/m411/connect4/RustPlayer.java
index a5f978d..e91c043 100644
--- a/minmax-java/src/main/java/ch/bbw/m411/connect4/RustPlayer.java
+++ b/minmax-java/src/main/java/ch/bbw/m411/connect4/RustPlayer.java
@@ -1,14 +1,28 @@
 package ch.bbw.m411.connect4;
 
+import java.io.File;
+import java.io.IOException;
+
 public class RustPlayer extends Connect4ArenaMain.DefaultPlayer {
     private static native int rustPlay(byte player, byte[] board);
+
     private static native int rustBoardWinner(byte[] board);
 
     static {
-        // This actually loads the shared object that we'll be creating.
-        // The actual location of the .so or .dll may differ based on your
-        // platform.
-        System.loadLibrary("minmax_wrapper");
+        if (System.getProperty("os.name").toLowerCase().contains("windows")) {
+            var path = "target/release/" + System.mapLibraryName("minmax_wrapper");
+
+            try {
+                System.load(new File(path).getCanonicalPath());
+            } catch (IOException e) {
+                throw new RuntimeException(e);
+            }
+        } else {
+            // This actually loads the shared object that we 'll be creating.
+            // The actual location of the .so or .dll may differ based on your
+            // platform.
+            System.loadLibrary("minmax_wrapper");
+        }
     }
 
     static byte[] encodeBoard(Connect4ArenaMain.Stone[] board) {
@@ -29,6 +43,7 @@ public class RustPlayer extends Connect4ArenaMain.DefaultPlayer {
     }
 
     public static boolean isWinning(Connect4ArenaMain.Stone[] board, Connect4ArenaMain.Stone forColor) {
+
         byte[] boardBuf = RustPlayer.encodeBoard(board);
         byte expectedPlayer = switch (forColor) {
             case BLUE -> 1;