From 1c0053f6681e4825fa4f5f63031b1ba82678e947 Mon Sep 17 00:00:00 2001
From: eug-vs <eugene@eug-vs.xyz>
Date: Mon, 23 Jan 2023 09:10:20 +0300
Subject: test: implement perft

---
 src/board.rs | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

(limited to 'src/board.rs')

diff --git a/src/board.rs b/src/board.rs
index 24bdefa..88b87a9 100644
--- a/src/board.rs
+++ b/src/board.rs
@@ -118,6 +118,10 @@ impl Board {
         occupancy
     }
 
+    pub fn color_to_move(&self) -> Color {
+        Color::from((self.ply % 2) as u8)
+    }
+
     pub fn print(&self) {
         println!();
         for rank in (0..8).rev() {
@@ -158,6 +162,7 @@ impl Board {
                         };
                     }
 
+                    // Make sure no blocking piece is standing in front of the pawn
                     let able_to_double_push_mask = match color {
                         Color::White => empty >> 8,
                         Color::Black => empty << 8,
@@ -281,6 +286,38 @@ impl Board {
 
         self.ply -= 1;
     }
+
+    fn perft(&mut self, depth: u8, print: bool) -> u64 {
+        if depth == 0 {
+            return 1 // This a leaf, exactly one node
+        }
+        let color = self.color_to_move();
+
+        let moves = self.generate_moves(color);
+
+        if print {
+            println!("Running perft for depth {}. Color to move is {:?}\n{} moves available", depth, color, moves.len());
+            println!("{} moves available", moves.len());
+        }
+
+        let mut total = 0;
+
+        for mov in moves {
+            let captured_piece = self.make_move(mov);
+            if print {
+                println!("{:?}", mov);
+                self.print();
+            }
+            total += self.perft(depth - 1, print);
+            self.unmake_move(mov, captured_piece);
+        }
+
+        if print {
+            println!("Found {} nodes in this subtree (depth {})", total, depth);
+        }
+
+        total
+    }
 }
 
 
@@ -406,4 +443,15 @@ mod tests {
 
         assert_eq!(board, initial_board, "Board state after unmake_move should be the same as before make_move");
     }
+
+    #[test]
+    fn test_perft() {
+        let fen = String::from(DEFAULT_FEN);
+        let mut board = Board::from_FEN(fen);
+
+        assert_eq!(board.perft(0, false), 1);
+        assert_eq!(board.perft(1, false), 20);
+        assert_eq!(board.perft(2, false), 400);
+        // TODO: assert_eq!(board.perft(3, false), 8902);
+    }
 }
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