Feature/en passant (#727)

* Refactored the en passant logic * Refactored enPassantSq() * Refactored enPassantSq() * Refactored enPassant() * Implemented enPassantReset() * Refactored enPassantReset() as enPassantPawn() * Renamed enPassant as xEnPassantSq * Renamed enPassantSq() as xEnPassantSq() * Renamed enPassantPawn() as xEnPassantPawn() * Documented Chess\Variant\Classical\P * Updated Chess\Variant\AbstractPiece
chesslablab · Jan 28, 2025 · c7de8e5 · c7de8e5
1 parent 8aeb246
commit c7de8e5
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Showing 5 changed files with 64 additions and 42 deletions.
diff --git a/src/Variant/AbstractBoard.php b/src/Variant/AbstractBoard.php
@@ -199,7 +199,7 @@ protected function lanToPseudoPgn(string $color, string $lan): string
                     } else {
                         $promo = '';
                     }
-                    if ($x || $a->enPassant() === $sqs[1]) {
+                    if ($x || $a->xEnPassantSq === $sqs[1]) {
                         return "{$a->file()}x{$sqs[1]}{$promo}";
                     } else {
                         return "{$sqs[1]}{$promo}";

diff --git a/src/Variant/AbstractPiece.php b/src/Variant/AbstractPiece.php
@@ -5,6 +5,7 @@
 use Chess\Variant\RType;
 use Chess\Variant\Classical\B;
 use Chess\Variant\Classical\N;
+use Chess\Variant\Classical\P;
 use Chess\Variant\Classical\Q;
 use Chess\Variant\Classical\R;
 use Chess\Variant\Classical\PGN\Castle;
@@ -341,6 +342,7 @@ public function isKingLeftInCheck(): bool
      */
     public function move(): bool
     {
+        $this->enPassant();
         $this->capture();
         $this->board->detach($this->board->pieceBySq($this->sq));
         $class = VariantType::getClass($this->board->variant, $this->id);
@@ -358,6 +360,22 @@ public function move(): bool
         return true;
     }
 
+    /**
+     * Set the en passant capture square.
+     */
+    public function enPassant(): void
+    {
+        if ($this->id === Piece::P) { 
+            if (abs($this->rank() - (int) substr($this->move['to'], 1)) === 2) {
+                $this->xEnPassantSq($this->move['to']);
+            } elseif ($pawn = $this->xEnPassantPawn()) {
+                $pawn->xEnPassantSq = '';
+            }
+        } elseif ($pawn = $this->xEnPassantPawn()) {
+            $pawn->xEnPassantSq = '';
+        }
+    }
+
     /**
      * Piece promotion.
      */
@@ -440,6 +458,22 @@ public function updateCastle(): AbstractPiece
         return $this;
     }
 
+    /**
+     * Returns the en passant capture pawn.
+     *
+     * @return null|\Chess\Variant\Classical\P
+     */
+    public function xEnPassantPawn(): ?P
+    {
+        foreach ($this->board->pieces($this->oppColor()) as $piece) {
+            if ($piece->id === Piece::P && $piece->xEnPassantSq) {
+                return $piece;
+            }
+        }
+
+        return null;
+    }
+
     /**
      * Adds a new element to the history array.
      */

diff --git a/src/Variant/Classical/FEN/StrToBoard.php b/src/Variant/Classical/FEN/StrToBoard.php
@@ -64,7 +64,7 @@ protected function enPassant(AbstractBoard $board): AbstractBoard
             foreach ($board->pieces($this->fields[1]) as $piece) {
                 if ($piece->id === Piece::P) {
                     if (in_array($this->fields[3], $piece->xSqs)) {
-                        $piece->enPassant = $this->fields[3];
+                        $piece->xEnPassantSq = $this->fields[3];
                     }
                 }
             }

diff --git a/src/Variant/Classical/P.php b/src/Variant/Classical/P.php
@@ -17,11 +17,11 @@ class P extends AbstractPiece
     public array $xSqs;
 
     /**
-     * En passant square.
+     * En passant capture square.
      *
      * @var string
      */
-    public string $enPassant = '';
+    public string $xEnPassantSq = '';
 
     /**
      * @param string $color
@@ -85,7 +85,7 @@ public function moveSqs(): array
                 $sqs[] = $sq;
             }
         }
-        $sqs[] = $this->enPassant();
+        $sqs[] = $this->xEnPassantSq;
 
         return array_filter(array_unique($sqs));
     }
@@ -107,6 +107,23 @@ public function defendedSqs(): array
         return $sqs;
     }
 
+    /**
+     * Set the en passant capture square.
+     */
+    public function xEnPassantSq(string $sq): void
+    {
+        foreach ($this->board->pieces($this->oppColor()) as $piece) {
+            if ($piece->id === Piece::P) {
+                $rank = (int) substr($sq, 1);
+                $rank = $this->color === Color::W ? $rank - 1 : $rank + 1;
+                $xEnPassantSq = $sq[0] . $rank;
+                if (in_array($xEnPassantSq, $piece->xSqs)) {
+                    $piece->xEnPassantSq = $xEnPassantSq;
+                }
+            }
+        }
+    }
+
     /**
      * Returns the start rank.
      *
@@ -151,41 +168,6 @@ public function promoRank(Square $square): int
         return 1;
     }
 
-    /**
-     * Returns the en passant square.
-     *
-     * @return string
-     */
-    public function enPassant(): string
-    {
-        if ($end = end($this->board->history)) {
-            if ($end['color'] === $this->oppColor()) {
-                $enPassant = explode(' ', $end['fen'])[3];
-                if (in_array($enPassant, $this->xSqs)) {
-                    $this->enPassant = $enPassant;
-                }
-            }
-        }
-
-        return $this->enPassant;
-    }
-
-    /**
-     * Returns the en passant pawn.
-     *
-     * @return null|\Chess\Variant\AbstractPiece
-     */
-    public function enPassantPawn(): ?AbstractPiece
-    {
-        if ($this->enPassant) {
-            $rank = (int) substr($this->enPassant, 1);
-            $this->color === Color::W ? $rank-- : $rank++;
-            return $this->board->pieceBySq($this->enPassant[0] . $rank);
-        }
-
-        return null;
-    }
-
     /**
      * Returns true if the pawn is promoted.
      *
@@ -203,7 +185,13 @@ public function isPromoted(Square $square): bool
     public function capture(): void
     {
         if (str_contains($this->move['case'], 'x')) {
-            if ($piece = $this->enPassantPawn() ?? $this->board->pieceBySq($this->move['to'])) {
+            if ($this->xEnPassantSq) { 
+                $rank = (int) substr($this->xEnPassantSq, 1);
+                $rank = $this->color === Color::W ? $rank - 1 : $rank + 1;
+                if ($piece = $this->board->pieceBySq($this->xEnPassantSq[0] . $rank)) {
+                    $this->board->detach($piece);
+                }
+            } elseif ($piece = $this->board->pieceBySq($this->move['to'])) {
                 $this->board->detach($piece);
             }
         }

diff --git a/tests/unit/Variant/Classical/BoardTest.php b/tests/unit/Variant/Classical/BoardTest.php
@@ -1525,7 +1525,7 @@ public function play_a_sequence_of_moves_w_exf6()
         $this->assertTrue($board->play('b', 'f5'));
         $pawn_e5 = $board->pieceBySq('e5');
         $pawn_e5->moveSqs(); // this creates the en passant property
-        $this->assertSame('f6', $pawn_e5->enPassant);
+        $this->assertSame('f6', $pawn_e5->xEnPassantSq);
         $this->assertTrue($board->play('w', 'exf6'));
     }