From 0167794346336b83aebfe7c794eeb85f2fc34b25 Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Sun, 8 Jun 2025 17:19:00 -0700
Subject: [PATCH] [perft] A small Perft program

---
 Cargo.lock        | 11 +++++++++
 Cargo.toml        |  2 +-
 perft/Cargo.toml  | 11 +++++++++
 perft/src/main.rs | 57 +++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 perft/Cargo.toml
 create mode 100644 perft/src/main.rs

diff --git a/Cargo.lock b/Cargo.lock
index e58f1e8..c6c6f1f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -295,6 +295,17 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "perft"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "chessfriend_board",
+ "chessfriend_position",
+ "clap",
+ "thiserror",
+]
+
 [[package]]
 name = "ppv-lite86"
 version = "0.2.21"
diff --git a/Cargo.toml b/Cargo.toml
index 70558c7..3b6ebee 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -4,7 +4,7 @@ members = [
     "board",
     "core",
     "explorer",
-    "moves",
+    "moves", "perft",
     "position",
 ]
 resolver = "2"
diff --git a/perft/Cargo.toml b/perft/Cargo.toml
new file mode 100644
index 0000000..193bb43
--- /dev/null
+++ b/perft/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "perft"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+anyhow = "1.0.98"
+chessfriend_board = { path = "../board" }
+chessfriend_position = { path = "../position" }
+clap = { version = "4.4.12", features = ["derive"] }
+thiserror = "2"
diff --git a/perft/src/main.rs b/perft/src/main.rs
new file mode 100644
index 0000000..e113579
--- /dev/null
+++ b/perft/src/main.rs
@@ -0,0 +1,57 @@
+use chessfriend_position::{fen::FromFenStr, GeneratedMove, Position, ValidateMove};
+use clap::Parser;
+
+#[derive(Parser, Debug)]
+#[command(name = "Perft")]
+struct Arguments {
+    depth: usize,
+
+    #[arg(long, short, value_name = "FEN")]
+    fen: Option<String>,
+}
+
+trait Perft {
+    fn perft(&mut self, depth: usize) -> u64;
+}
+
+impl Perft for Position {
+    fn perft(&mut self, depth: usize) -> u64 {
+        if depth == 0 {
+            return 1;
+        }
+
+        let mut nodes_counted: u64 = 0;
+
+        let legal_moves: Vec<GeneratedMove> = self.all_legal_moves(None).collect();
+
+        for generated_ply in legal_moves {
+            self.make_move(generated_ply.into(), ValidateMove::No)
+                .expect("unable to make generated move");
+
+            nodes_counted += self.perft(depth - 1);
+
+            self.unmake_last_move().expect("unable to unmake last move");
+        }
+
+        nodes_counted
+    }
+}
+
+fn main() -> anyhow::Result<()> {
+    let args = Arguments::parse();
+    let depth = args.depth;
+
+    println!("Searching to depth {depth}");
+
+    let mut position = if let Some(fen) = args.fen {
+        Position::from_fen_str(&fen)?
+    } else {
+        Position::starting(None)
+    };
+
+    let nodes_searched = position.perft(depth);
+
+    println!("Nodes searched: {nodes_searched}");
+
+    Ok(())
+}