Minor UI improvement

src/board/board.rs

@@ -1,6 +1,5 @@
 use std::fmt::Display;
-
-use termion::color;
+use termion::color::{self, Color};
 
 use super::{PlayerAction, TreeElement};
 use crate::util::{Player, Symb};
@@ -49,18 +48,30 @@ enum Token {
 #[derive(Clone)]
 pub struct Board {
 	board: [Option<(Symb, Player)>; 11],
+
+	/// Number of Nones in `board`
 	free_spots: usize,
+
+	/// Index of the last board index that was changed
+	last_placed: Option<usize>,
 }
 
 impl Display for Board {
 	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
 		// Print board
-		for i in &self.board {
-			match i {
+		for (i, o) in self.board.iter().enumerate() {
+			match o {
 				Some((symb, player)) => write!(
 					f,
 					"{}{}{}",
-					color::Fg(player.color()),
+					// If index matches last placed, draw symbol in red.
+					// If last_placed is None, this check will always fail
+					// since self.board.len is always greater than i.
+					if self.last_placed.unwrap_or(self.board.len()) == i {
+						color::Fg(&color::Red as &dyn Color)
+					} else {
+						color::Fg(player.color())
+					},
 					symb,
 					color::Fg(color::Reset)
 				)?,
@@ -78,6 +89,7 @@ impl Board {
 		Self {
 			free_spots: 11,
 			board: Default::default(),
+			last_placed: None,
 		}
 	}
 
@@ -174,6 +186,7 @@ impl Board {
 
 		self.board[action.pos] = Some((action.symb, player));
 		self.free_spots -= 1;
+		self.last_placed = Some(action.pos);
 		true
 	}
 
@@ -333,6 +346,10 @@ impl Board {
 			}
 		}
 
-		Some(Self { board, free_spots })
+		Some(Self {
+			board,
+			free_spots,
+			last_placed: None,
+		})
 	}
 }