From 73b090e9b7a578083dddb0547b00fdbab6a8a834 Mon Sep 17 00:00:00 2001
From: overflowerror <mail@overflowerror.com>
Date: Sat, 6 Jan 2024 21:24:46 +0100
Subject: [PATCH] fix: Pawn can not capture forward

---
 src/Game/Pawn.php       |  6 ++++--
 tests/Game/PawnTest.php | 16 ++++++++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/Game/Pawn.php b/src/Game/Pawn.php
index 5efc752..bc83e9c 100644
--- a/src/Game/Pawn.php
+++ b/src/Game/Pawn.php
@@ -25,10 +25,12 @@ class Pawn extends Piece {
 
         $initial = new Position($file, $rank + 2 * $direction);
 
-        if (!$occupied->has($regular)) {
+        // checking for collisions in the captureable map works because there is always
+        // a pawn before the en passant square.
+        if (!$occupied->has($regular) && !$captureable->has($regular)) {
             $result->add($regular);
 
-            if (!$this->hasMoved && !$occupied->has($initial)) {
+            if (!$this->hasMoved && !$occupied->has($initial) && !$captureable->has($initial)) {
                 $result->add($initial);
             }
         }
diff --git a/tests/Game/PawnTest.php b/tests/Game/PawnTest.php
index c7d27a1..e3c2454 100644
--- a/tests/Game/PawnTest.php
+++ b/tests/Game/PawnTest.php
@@ -155,6 +155,22 @@ final class PawnTest extends TestCase {
         );
     }
 
+    public function testMoves_bug_captureForwardNotAllowed() {
+        $subject = new Pawn(
+            new Position(4, 3),
+            Side::BLACK,
+            true
+        );
+
+        $result = $subject->getMoveCandidateMap(
+            FieldBitMap::empty(),
+            new FieldBitMap([new Position(4, 2)]),
+            FieldBitMap::empty());
+        $this->assertTrue(
+            $result->isEmpty()
+        );
+    }
+
     public function testCaptureable_default() {
         $subject = new Pawn(
             new Position(3, 4),