From b471aaf109057de9b16fbfd93d026f9a716eaca2 Mon Sep 17 00:00:00 2001
From: stefiosif <si.iosifidis@gmail.com>
Date: Wed, 29 May 2024 20:39:38 +0300
Subject: [PATCH] Make from_fen return Result<Board, FenError>

---
 src/fen.rs  | 58 +++++++++++++++++++++++++++++++----------------------
 src/game.rs |  5 +++--
 2 files changed, 37 insertions(+), 26 deletions(-)

diff --git a/src/fen.rs b/src/fen.rs
index b2d1237..f8d345b 100644
--- a/src/fen.rs
+++ b/src/fen.rs
@@ -2,39 +2,39 @@ use crate::board::{Board, Color, Kind, Piece};
 use crate::game::{Game, State};
 use String as FenError;
 
-pub fn from_fen(fen: &str) -> Game {
-    let mut board = Board::empty_board();
+pub fn from_fen(fen: &str) -> Result<Game, FenError> {
     let fen_parts: Vec<_> = fen.split_whitespace().collect();
 
-    piece_placement(fen_parts[0], &mut board);
+    let board = piece_placement(fen_parts[0])?;
 
-    let side_to_move = side_to_move(fen_parts[1]);
+    let side_to_move = side_to_move(fen_parts[1])?;
 
-    let castling_ability = castling_ability(fen_parts[2]);
+    let castling_ability = castling_ability(fen_parts[2])?;
 
-    let en_passant_target_square: Result<u8, FenError> = en_passant_target_square(fen_parts[3]);
+    let en_passant_target_square = en_passant_target_square(fen_parts[3])?;
 
-    let halfmove_clock = halfmove_clock(fen_parts[4]);
+    let halfmove_clock = halfmove_clock(fen_parts[4])?;
 
-    let fullmove_counter = fullmove_counter(fen_parts[5]);
+    let fullmove_counter = fullmove_counter(fen_parts[5])?;
 
-    Game {
+    Ok(Game {
         board,
         state: State::load_state(
-            side_to_move.unwrap(),
-            castling_ability.unwrap(),
-            en_passant_target_square.unwrap(),
-            halfmove_clock.unwrap(),
-            fullmove_counter.unwrap(),
+            side_to_move,
+            castling_ability,
+            en_passant_target_square,
+            halfmove_clock,
+            fullmove_counter,
         ),
-    }
+    })
 }
 
-fn piece_placement(pieces: &str, board: &mut Board) {
+fn piece_placement(pieces: &str) -> Result<Board, FenError> {
+    let mut board = Board::empty_board();
     let (mut file, mut rank): (u8, u8) = (0, 7);
 
     for c in pieces.chars() {
-        let square: u8 = rank * 8 + file;
+        let square = rank * 8 + file;
         let color = if c.is_ascii_lowercase() {
             Color::Black
         } else {
@@ -57,13 +57,18 @@ fn piece_placement(pieces: &str, board: &mut Board) {
                 rank %= n.to_digit(10).unwrap_or(0) as u8;
                 None
             }
-            _ => None,
+            _ => {
+                return Err(FenError::from(
+                    "Error while parsing board piece state from FEN",
+                ))
+            }
         } {
             board.set_piece(Piece::new(1 << square, kind, color));
         };
 
         file += 1;
     }
+    Ok(board)
 }
 
 fn side_to_move(side: &str) -> Result<Color, FenError> {
@@ -152,20 +157,25 @@ fn fullmove_counter(fullmove: &str) -> Result<u8, FenError> {
 mod tests {
     use super::*;
 
-    const FEN_EXAMPLE: [&str; 4] = [
+    const FEN_EXAMPLE: [&str; 5] = [
         "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1",
         "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1",
         "rnbqkbnr/pp1ppppp/8/2p5/4P3/8/PPPP1PPP/RNBQKBNR w KQkq c6 0 2",
         "rnbqkbnr/pp1ppppp/8/2p5/4P3/5N2/PPPP1PPP/RNBQKB1R b KQkq - 1 2 ",
+        "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR x KQkq - 0 1",
     ];
 
     #[test]
-    fn test_sqrt() -> Result<(), String> {
-        let game = from_fen(FEN_EXAMPLE[3]);
-        println!("{}\n{}", game.board, game.state);
-
-        assert_eq!(from_fen(FEN_EXAMPLE[0]), Game::new());
+    fn test_from_fen() -> Result<(), String> {
+        let new_game = from_fen(FEN_EXAMPLE[0])?;
+        assert_eq!(new_game, Game::new());
 
         Ok(())
     }
+
+    #[test]
+    #[should_panic]
+    fn test_fen_error() -> () {
+        from_fen(FEN_EXAMPLE[4]).unwrap();
+    }
 }
diff --git a/src/game.rs b/src/game.rs
index a2e1f32..9ecf425 100644
--- a/src/game.rs
+++ b/src/game.rs
@@ -2,6 +2,7 @@ use crate::{
     board::{Board, Color},
     fen::from_fen,
 };
+use String as FenError;
 
 #[derive(Debug, PartialEq)]
 pub struct Game {
@@ -17,7 +18,7 @@ impl Game {
         }
     }
 
-    pub fn new_from_fen(fen: &str) -> Game {
+    pub fn new_from_fen(fen: &str) -> Result<Game, FenError> {
         from_fen(fen)
     }
 
@@ -75,7 +76,7 @@ impl fmt::Display for State {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         writeln!(f,
             "side_to_move: {:?}\ncastling_ability: {:b}\nen_passant_target_square: {:b}\nhalfmove_clock: {}\nfullmove_counter: {}\n",
-            self.side_to_move, self.castling_ability, 1u64 << self.en_passant_target_square, self.halfmove_clock, self.fullmove_counter)
+            self.side_to_move, self.castling_ability, 1_u64 << self.en_passant_target_square, self.halfmove_clock, self.fullmove_counter)
     }
 }