From 0f5a538f0a8ba5b6e5b3a19ba40fca0a71566c11 Mon Sep 17 00:00:00 2001
From: Eryn Wells <eryn@erynwells.me>
Date: Thu, 19 Jun 2025 11:33:35 -0700
Subject: [PATCH] [explorer, perft, position] Move node count into a new
 PerftCounters struct

---
 explorer/src/main.rs  |  4 +--
 perft/src/main.rs     |  5 ++--
 position/src/perft.rs | 57 +++++++++++++++++++++++++++++++------------
 3 files changed, 47 insertions(+), 19 deletions(-)

diff --git a/explorer/src/main.rs b/explorer/src/main.rs
index 4f98a63..0acb2a1 100644
--- a/explorer/src/main.rs
+++ b/explorer/src/main.rs
@@ -350,9 +350,9 @@ fn do_perft_command(
         .ok_or(CommandHandlingError::MissingArgument("depth"))?;
 
     let mut position = state.position.clone();
-    let nodes_count = position.perft(depth);
+    let counters = position.perft(depth);
 
-    println!("nodes {nodes_count}");
+    println!("{counters}");
 
     Ok(CommandResult {
         should_continue: true,
diff --git a/perft/src/main.rs b/perft/src/main.rs
index dece54c..d1e7f77 100644
--- a/perft/src/main.rs
+++ b/perft/src/main.rs
@@ -7,6 +7,7 @@ use clap::Parser;
 #[derive(Parser, Debug)]
 #[command(name = "Perft")]
 struct Arguments {
+    #[arg(long, short, value_name = "INT")]
     depth: usize,
 
     #[arg(long, short, value_name = "FEN")]
@@ -26,9 +27,9 @@ fn main() -> anyhow::Result<()> {
     println!("fen \"{}\"", position.to_fen_str().unwrap());
     println!("depth {depth}");
 
-    let nodes_searched = position.perft(depth);
+    let counters = position.perft(depth);
 
-    println!("nodes {nodes_searched}");
+    println!("\n{counters}");
 
     Ok(())
 }
diff --git a/position/src/perft.rs b/position/src/perft.rs
index 97b3c51..3269a04 100644
--- a/position/src/perft.rs
+++ b/position/src/perft.rs
@@ -1,20 +1,29 @@
 // Eryn Wells <eryn@erynwells.me>
 
+use chessfriend_moves::Move;
+
 use crate::{GeneratedMove, Position, ValidateMove};
+use std::fmt;
+
+#[derive(Clone, Debug, Default, Eq, PartialEq)]
+pub struct PerftCounters {
+    nodes: u64,
+}
 
 impl Position {
-    pub fn perft(&mut self, depth: usize) -> u64 {
-        self.perft_recursive(depth, depth)
+    pub fn perft(&mut self, depth: usize) -> PerftCounters {
+        self.perft_recursive(0, depth)
     }
 }
 
 impl Position {
-    fn perft_recursive(&mut self, depth: usize, max_depth: usize) -> u64 {
-        if depth == 0 {
-            return 1;
-        }
+    fn perft_recursive(&mut self, depth: usize, max_depth: usize) -> PerftCounters {
+        let mut counters = PerftCounters::default();
 
-        let mut total_nodes_counted = 0u64;
+        if depth == max_depth {
+            counters.count_node();
+            return counters;
+        }
 
         let legal_moves: Vec<GeneratedMove> = self.all_legal_moves(None).collect();
 
@@ -25,21 +34,39 @@ impl Position {
                 .make_move(ply, ValidateMove::No)
                 .expect("unable to make generated move");
 
-            let nodes_counted = if has_seen_position {
-                1
+            let recursive_counters = if has_seen_position {
+                let mut counters = PerftCounters::default();
+                counters.count_node();
+                counters
             } else {
-                self.perft_recursive(depth - 1, max_depth)
+                self.perft_recursive(depth + 1, max_depth)
             };
 
-            total_nodes_counted += nodes_counted;
-
             self.unmake_last_move().expect("unable to unmake last move");
 
-            if depth == max_depth {
-                println!("  {ply} {nodes_counted}");
+            counters.fold(&recursive_counters);
+
+            if depth == 0 {
+                println!("  {ply}: {}", recursive_counters.nodes);
             }
         }
 
-        total_nodes_counted
+        counters
+    }
+}
+
+impl PerftCounters {
+    fn count_node(&mut self) {
+        self.nodes += 1;
+    }
+    fn fold(&mut self, results: &Self) {
+        self.nodes += results.nodes;
+    }
+}
+
+impl fmt::Display for PerftCounters {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        writeln!(f, "Perft Results")?;
+        write!(f, "  Nodes: {}", self.nodes)
     }
 }