From d788e73ea5240f72d3ca64a5ce2bad5026643ebd Mon Sep 17 00:00:00 2001
From: eug-vs <eugene@eug-vs.xyz>
Date: Sat, 21 Jan 2023 03:33:55 +0300
Subject: feat: implement FEN parsing

---
 src/board.rs | 140 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 140 insertions(+)

diff --git a/src/board.rs b/src/board.rs
index c190c52..991820a 100644
--- a/src/board.rs
+++ b/src/board.rs
@@ -1,3 +1,117 @@
+use crate::bitboard::Bitboard;
+
+#[derive(Debug)]
+pub struct Board {
+    pub pieces: [Bitboard; 12],
+}
+
+
+enum PieceTypes {
+    Pawn,
+    PawnBlack,
+    Knight,
+    KnightBlack,
+    Bishop,
+    BishopBlack,
+    Rook,
+    RookBlack,
+    Queen,
+    QueenBlack,
+    King,
+    KingBlack,
+}
+
+
+const PIECE_CHARS: [&str; 12] = [
+    "♟︎", "♙",
+    "♞", "♘",
+    "♝", "♗",
+    "♜", "♖",
+    "♛", "♕",
+    "♚", "♔",
+];
+
+
+impl Board {
+    #[allow(non_snake_case)]
+    pub fn from_FEN(fen: String) -> Self {
+        let mut pieces = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+
+        let mut rank = 7;
+        let mut file = 0i32;
+
+        for character in fen.chars() {
+            let index = rank * 8 + file;
+            let position = 1 << index.clamp(0, 63);
+
+            if character.is_numeric() {
+                let digit = match character.to_digit(10) {
+                    None => todo!("What to do here?"),
+                    Some(digit) => digit,
+                };
+                if digit > 0 && digit <= 8 {
+                    file += digit as i32;
+                }
+            } else {
+                match character {
+                    'P' => pieces[PieceTypes::Pawn as usize] |= position,
+                    'N' => pieces[PieceTypes::Knight as usize] |= position,
+                    'B' => pieces[PieceTypes::Bishop as usize] |= position,
+                    'R' => pieces[PieceTypes::Rook as usize] |= position,
+                    'Q' => pieces[PieceTypes::Queen as usize] |= position,
+                    'K' => pieces[PieceTypes::King as usize] |= position,
+                    'p' => pieces[PieceTypes::PawnBlack as usize] |= position,
+                    'n' => pieces[PieceTypes::KnightBlack as usize] |= position,
+                    'b' => pieces[PieceTypes::BishopBlack as usize] |= position,
+                    'r' => pieces[PieceTypes::RookBlack as usize] |= position,
+                    'q' => pieces[PieceTypes::QueenBlack as usize] |= position,
+                    'k' => pieces[PieceTypes::KingBlack as usize] |= position,
+                    '/' => {
+                        rank -= 1;
+                        file = -1; // So it becomes 0
+                    },
+                    ' ' => { break }, // TODO: break for now, parse everything else later
+                    '-' => {}, // TODO
+                    'w' => {}, // TODO
+                    _ => todo!("Unexpected character!"),
+                }
+                file += 1;
+            }
+        }
+
+        Self { pieces }
+    }
+
+    pub fn print(&self) {
+        println!();
+        for rank in (0..8).rev() {
+            print!("{}|", rank + 1);
+            for file in 0..8 {
+                let index = rank * 8 + file;
+                let position: Bitboard = 1 << index;
+                let mut found = false;
+                for (piec_type, piece_bitboard) in self.pieces.iter().enumerate() {
+                    if (piece_bitboard & position) > 0 {
+                        found = true;
+                        print!("{} ", PIECE_CHARS[piec_type]);
+                    }
+                }
+                if !found {
+                    print!(". ");
+                }
+            }
+            println!();
+        }
+        println!("  a b c d e f g h");
+    }
+}
+
+
+enum Color {
+    White,
+    Black,
+}
+
 /// Aliases to board square indexes
 #[allow(dead_code)]
 enum Square {
@@ -14,6 +128,7 @@ enum Square {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::bitboard;
 
     #[test]
     fn test_square_enum() {
@@ -21,4 +136,29 @@ mod tests {
         assert_eq!(Square::F1 as u8, 5);
         assert_eq!(Square::H8 as u8, 63);
     }
+
+    #[test]
+    fn test_from_fen() {
+        let fen = String::from("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
+        let board = Board::from_FEN(fen);
+
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::Pawn as usize]), 8);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::Knight as usize]), 2);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::Bishop as usize]), 2);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::Rook as usize]), 2);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::Queen as usize]), 1);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::King as usize]), 1);
+
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::PawnBlack as usize]), 8);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::KnightBlack as usize]), 2);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::BishopBlack as usize]), 2);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::RookBlack as usize]), 2);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::QueenBlack as usize]), 1);
+        assert_eq!(bitboard::pop_count(board.pieces[PieceTypes::KingBlack as usize]), 1);
+
+        assert_eq!(bitboard::bitscan(board.pieces[PieceTypes::King as usize]), Square::E1 as u8);
+        assert_eq!(bitboard::bitscan(board.pieces[PieceTypes::QueenBlack as usize]), Square::D8 as u8);
+
+        board.print();
+    }
 }
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