add back functionality

src/agent.rs

@@ -3,11 +3,18 @@ use rand::prelude::*;
 use std::io;
 use std::io::prelude::*;
 
+#[derive(Debug, Clone, Copy)]
+pub enum AgentMove {
+    CoordPair(CoordPair),
+    Back,
+    Skip,
+}
+
 #[allow(dead_code)]
 // implements `Send` so we can use it in a multithreaded `EloArena`
 pub trait Agent: Send {
     /// Returns the move of an [`Agent`]
-    fn next_move(&mut self, board: &Board) -> Option<CoordPair>;
+    fn next_move(&mut self, board: &Board) -> AgentMove;
     /// Returns the name of the [`Agent`]
     fn name(&self) -> &'static str;
     /// Returns the color the [`Agent`] is playing
@@ -28,16 +35,23 @@ impl ManualAgent {
 
 #[allow(dead_code)]
 impl Agent for ManualAgent {
-    fn next_move(&mut self, board: &Board) -> Option<CoordPair> {
+    fn next_move(&mut self, board: &Board) -> AgentMove {
         let stdin = io::stdin();
         let mut input = String::new();
-        println!("Your turn! ('Skip' to skip)");
+        println!("Your turn! ('Skip' to skip 'back' to go back a move)");
         loop {
             input.clear();
-            stdin.lock().read_line(&mut input).ok()?;
+            if stdin.lock().read_line(&mut input).is_err() {
+                return AgentMove::Skip;
+            };
+
             if input.to_lowercase().trim() == "skip" {
                 // skips move
-                return None;
+                return AgentMove::Skip;
+            }
+            if input.to_lowercase().trim() == "back" {
+                // skips move
+                return AgentMove::Back;
             }
 
             let got = input
@@ -53,7 +67,7 @@ impl Agent for ManualAgent {
                     println!("Invalid move! Try again.");
                     continue;
                 }
-                return Some(got.into());
+                return AgentMove::CoordPair(got.into());
             }
         }
     }
@@ -74,8 +88,11 @@ pub struct RandomAgent {
 
 #[allow(dead_code)]
 impl Agent for RandomAgent {
-    fn next_move(&mut self, board: &Board) -> Option<CoordPair> {
-        board.possible_moves(self.color).choose(&mut rand::rng())
+    fn next_move(&mut self, board: &Board) -> AgentMove {
+        match board.possible_moves(self.color).choose(&mut rand::rng()) {
+            Some(x) => AgentMove::CoordPair(x),
+            None => AgentMove::Skip,
+        }
     }
 
     fn name(&self) -> &'static str {