Chess: Add ability to export game as PGN file

This patch adds an option to the menubar for exporting the current
game as a PGN file. This file can then be read by other chess
programs (and ours eventually) to replay the game or analyze it.
The implementation is mostly PGN spec compliant, however the code
could use some more work. Particularly the `const_cast`s...
But it's a start. :^)

Fixup: Chess: Fixed hard-coded home path in unveil() call

Fixup: Chess: Removed castling flags from Move struct

The castling detection logic is done inside Move::to_algebraic()
now, removing the need for is_castle_short and is_castle_long flags
inside of the Move struct.

Games/Chess/ChessWidget.cpp

@@ -27,9 +27,12 @@
 #include "ChessWidget.h"
 #include "PromotionDialog.h"
 #include <AK/String.h>
+#include <LibCore/DateTime.h>
+#include <LibCore/File.h>
 #include <LibGUI/MessageBox.h>
 #include <LibGUI/Painter.h>
 #include <LibGfx/Font.h>
+#include <unistd.h>
 
 ChessWidget::ChessWidget(const StringView& set)
 {
@@ -289,6 +292,57 @@ void ChessWidget::maybe_input_engine_move()
     });
 }
 
+bool ChessWidget::export_pgn(const StringView& export_path) const
+{
+    auto file_or_error = Core::File::open(export_path, Core::File::WriteOnly);
+    if (file_or_error.is_error()) {
+        warnln("Couldn't open '{}': {}", export_path, file_or_error.error());
+        return false;
+    }
+    auto& file = *file_or_error.value();
+
+    // Tag Pair Section
+    file.write("[Event \"Casual Game\"]\n");
+    file.write("[Site \"SerenityOS Chess\"]\n");
+    file.write(String::formatted("[Date \"{}\"]\n", Core::DateTime::now().to_string("%Y.%m.%d")));
+    file.write("[Round \"1\"]\n");
+
+    String username(getlogin());
+    const String player1 = (!username.is_empty() ? username : "?");
+    const String player2 = (!m_engine.is_null() ? "SerenityOS ChessEngine" : "?");
+    file.write(String::formatted("[White \"{}\"]\n", m_side == Chess::Colour::White ? player1 : player2));
+    file.write(String::formatted("[Black \"{}\"]\n", m_side == Chess::Colour::Black ? player1 : player2));
+
+    file.write(String::formatted("[Result \"{}\"]\n", Chess::Board::result_to_points(m_board.game_result(), m_board.turn())));
+    file.write("[WhiteElo \"?\"]\n");
+    file.write("[BlackElo \"?\"]\n");
+    file.write("[Variant \"Standard\"]\n");
+    file.write("[TimeControl \"-\"]\n");
+    file.write("[Annotator \"SerenityOS Chess\"]\n");
+    file.write("\n");
+
+    // Movetext Section
+    for (size_t i = 0, move_no = 1; i < m_board.moves().size(); i += 2, move_no++) {
+        const String white = m_board.moves().at(i).to_algebraic();
+
+        if (i + 1 < m_board.moves().size()) {
+            const String black = m_board.moves().at(i + 1).to_algebraic();
+            file.write(String::formatted("{}. {} {} ", move_no, white, black));
+        } else {
+            file.write(String::formatted("{}. {} ", move_no, white));
+        }
+    }
+
+    file.write("{ ");
+    file.write(Chess::Board::result_to_string(m_board.game_result(), m_board.turn()));
+    file.write(" } ");
+    file.write(Chess::Board::result_to_points(m_board.game_result(), m_board.turn()));
+    file.write("\n");
+
+    file.close();
+    return true;
+}
+
 void ChessWidget::flip_board()
 {
     m_side = Chess::opposing_colour(m_side);
@@ -306,6 +360,6 @@ void ChessWidget::resign()
 
     set_drag_enabled(false);
     update();
-    const String msg = m_board.result_to_string(m_board.game_result());
+    const String msg = Chess::Board::result_to_string(m_board.game_result(), m_board.turn());
     GUI::MessageBox::show(window(), msg, "Game Over", GUI::MessageBox::Type::Information);
 }

Games/Chess/ChessWidget.h

@@ -48,6 +48,7 @@ public:
     virtual void mousemove_event(GUI::MouseEvent&) override;
 
     Chess::Board& board() { return m_board; };
+    const Chess::Board& board() const { return m_board; };
 
     Chess::Colour side() const { return m_side; };
     void set_side(Chess::Colour side) { m_side = side; };
@@ -61,6 +62,8 @@ public:
     void set_drag_enabled(bool e) { m_drag_enabled = e; }
     RefPtr<Gfx::Bitmap> get_piece_graphic(const Chess::Piece& piece) const;
 
+    bool export_pgn(const StringView& export_path) const;
+
     void resign();
     void flip_board();
     void reset();

Games/Chess/main.cpp

@@ -30,9 +30,11 @@
 #include <LibGUI/AboutDialog.h>
 #include <LibGUI/ActionGroup.h>
 #include <LibGUI/Application.h>
+#include <LibGUI/FilePicker.h>
 #include <LibGUI/Icon.h>
 #include <LibGUI/Menu.h>
 #include <LibGUI/MenuBar.h>
+#include <LibGUI/MessageBox.h>
 #include <LibGUI/Window.h>
 
 int main(int argc, char** argv)
@@ -65,6 +67,16 @@ int main(int argc, char** argv)
         return 1;
     }
 
+    if (unveil("/etc/passwd", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil(Core::StandardPaths::home_directory().characters(), "wcb") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
     if (unveil(nullptr, nullptr) < 0) {
         perror("unveil");
         return 1;
@@ -93,6 +105,24 @@ int main(int argc, char** argv)
     }));
     app_menu.add_separator();
 
+    app_menu.add_action(GUI::Action::create("Import PGN...", { Mod_None, Key_F6 }, [&](auto&) {
+        GUI::MessageBox::show(window, "Feature not yet available.", "TODO", GUI::MessageBox::Type::Information);
+    }));
+    app_menu.add_action(GUI::Action::create("Export PGN...", { Mod_None, Key_F7 }, [&](auto&) {
+        Optional<String> export_path = GUI::FilePicker::get_save_filepath(window, "Untitled", "pgn");
+
+        if (!export_path.has_value())
+            return;
+
+        if (!widget.export_pgn(export_path.value())) {
+            GUI::MessageBox::show(window, "Unable to export game.\n", "Error", GUI::MessageBox::Type::Error);
+            return;
+        }
+
+        dbgln("Exported PGN file to {}", export_path.value());
+    }));
+    app_menu.add_separator();
+
     app_menu.add_action(GUI::Action::create("New game", { Mod_None, Key_F2 }, [&](auto&) {
         widget.reset();
     }));

Libraries/LibChess/Chess.cpp

@@ -122,6 +122,49 @@ String Move::to_long_algebraic() const
     return builder.build();
 }
 
+String Move::to_algebraic() const
+{
+    if (piece.type == Type::King && from.file == 4) {
+        if (to.file == 2)
+            return "O-O-O";
+        if (to.file == 6)
+            return "O-O";
+    }
+
+    StringBuilder builder;
+
+    builder.append(char_for_piece(piece.type));
+
+    if (is_ambiguous) {
+        if (from.file != ambiguous.file)
+            builder.append(from.to_algebraic().substring(0, 1));
+        else if (from.rank != ambiguous.rank)
+            builder.append(from.to_algebraic().substring(1, 1));
+        else
+            builder.append(from.to_algebraic());
+    }
+
+    if (is_capture) {
+        if (piece.type == Type::Pawn)
+            builder.append(from.to_algebraic().substring(0, 1));
+        builder.append("x");
+    }
+
+    builder.append(to.to_algebraic());
+
+    if (promote_to != Type::None) {
+        builder.append("=");
+        builder.append(char_for_piece(promote_to));
+    }
+
+    if (is_mate)
+        builder.append("#");
+    else if (is_check)
+        builder.append("+");
+
+    return builder.build();
+}
+
 Board::Board()
 {
     // Fill empty spaces.
@@ -362,6 +405,7 @@ bool Board::is_legal_no_check(const Move& move, Colour colour) const
 
                 return true;
             } else if ((move.to == Square("h1") || move.to == Square("g1")) && m_white_can_castle_kingside && get_piece(Square("f1")).type == Type::None && get_piece(Square("g1")).type == Type::None) {
+
                 return true;
             }
         } else {
@@ -369,6 +413,7 @@ bool Board::is_legal_no_check(const Move& move, Colour colour) const
 
                 return true;
             } else if ((move.to == Square("h8") || move.to == Square("g8")) && m_black_can_castle_kingside && get_piece(Square("f8")).type == Type::None && get_piece(Square("g8")).type == Type::None) {
+
                 return true;
             }
         }
@@ -408,6 +453,8 @@ bool Board::apply_move(const Move& move, Colour colour)
     if (!is_legal(move, colour))
         return false;
 
+    const_cast<Move&>(move).piece = get_piece(move.from);
+
     return apply_illegal_move(move, colour);
 }
 
@@ -467,10 +514,19 @@ bool Board::apply_illegal_move(const Move& move, Colour colour)
         }
     }
 
+    if (get_piece(move.to).colour != Colour::None) {
+        const_cast<Move&>(move).is_capture = true;
+        m_moves_since_capture = 0;
+    }
+
     if (get_piece(move.from).type == Type::Pawn && ((colour == Colour::Black && move.to.rank == 0) || (colour == Colour::White && move.to.rank == 7))) {
         // Pawn Promotion
         set_piece(move.to, { colour, move.promote_to });
         set_piece(move.from, EmptyPiece);
+
+        if (in_check(m_turn))
+            const_cast<Move&>(move).is_check = true;
+
         return true;
     }
 
@@ -481,15 +537,29 @@ bool Board::apply_illegal_move(const Move& move, Colour colour)
         } else {
             set_piece({ move.to.rank + 1, move.to.file }, EmptyPiece);
         }
+        const_cast<Move&>(move).is_capture = true;
         m_moves_since_capture = 0;
     }
 
-    if (get_piece(move.to).colour != Colour::None)
-        m_moves_since_capture = 0;
+    Square::for_each([&](Square sq) {
+        // Ambiguous Move
+        if (sq != move.from && get_piece(sq).type == move.piece.type && get_piece(sq).colour == move.piece.colour) {
+            if (is_legal(Move(sq, move.to), get_piece(sq).colour)) {
+                m_moves.last().is_ambiguous = true;
+                m_moves.last().ambiguous = sq;
+
+                return IterationDecision::Break;
+            }
+        }
+        return IterationDecision::Continue;
+    });
 
     set_piece(move.to, get_piece(move.from));
     set_piece(move.from, EmptyPiece);
 
+    if (in_check(m_turn))
+        const_cast<Move&>(move).is_check = true;
+
     return true;
 }
 
@@ -577,8 +647,10 @@ Board::Result Board::game_result() const
         return Result::NotFinished;
     }
 
-    if (in_check(turn()))
+    if (in_check(turn())) {
+        const_cast<Vector<Move>&>(m_moves).last().is_mate = true;
         return Result::CheckMate;
+    }
 
     return Result::StaleMate;
 }
@@ -692,14 +764,12 @@ void Board::set_resigned(Chess::Colour c)
     m_resigned = c;
 }
 
-String Board::result_to_string(Result r) const
+String Board::result_to_string(Result result, Colour turn)
 {
-    switch (r) {
+    switch (result) {
     case Result::CheckMate:
-        if (m_turn == Chess::Colour::White)
-            return "Black wins by Checkmate";
-        else
-            return "White wins by Checkmate";
+        ASSERT(turn != Chess::Colour::None);
+        return turn == Chess::Colour::White ? "Black wins by Checkmate" : "White wins by Checkmate";
     case Result::WhiteResign:
         return "Black wins by Resignation";
     case Result::BlackResign:
@@ -723,4 +793,33 @@ String Board::result_to_string(Result r) const
     }
 }
 
+String Board::result_to_points(Result result, Colour turn)
+{
+    switch (result) {
+    case Result::CheckMate:
+        ASSERT(turn != Chess::Colour::None);
+        return turn == Chess::Colour::White ? "0-1" : "1-0";
+    case Result::WhiteResign:
+        return "0-1";
+    case Result::BlackResign:
+        return "1-0";
+    case Result::StaleMate:
+        return "1/2-1/2";
+    case Chess::Board::Result::FiftyMoveRule:
+        return "1/2-1/2";
+    case Chess::Board::Result::SeventyFiveMoveRule:
+        return "1/2-1/2";
+    case Chess::Board::Result::ThreeFoldRepetition:
+        return "1/2-1/2";
+    case Chess::Board::Result::FiveFoldRepetition:
+        return "1/2-1/2";
+    case Chess::Board::Result::InsufficientMaterial:
+        return "1/2-1/2";
+    case Chess::Board::Result::NotFinished:
+        return "*";
+    default:
+        ASSERT_NOT_REACHED();
+    }
+}
+
 }

Libraries/LibChess/Chess.h

@@ -105,6 +105,12 @@ struct Move {
     Square from;
     Square to;
     Type promote_to;
+    Piece piece;
+    bool is_check = false;
+    bool is_mate = false;
+    bool is_capture = false;
+    bool is_ambiguous = false;
+    Square ambiguous { 50, 50 };
     Move(const StringView& algebraic);
     Move(const Square& from, const Square& to, const Type& promote_to = Type::None)
         : from(from)
@@ -115,6 +121,7 @@ struct Move {
     bool operator==(const Move& other) const { return from == other.from && to == other.to && promote_to == other.promote_to; }
 
     String to_long_algebraic() const;
+    String to_algebraic() const;
 };
 
 class Board {
@@ -145,7 +152,8 @@ public:
         NotFinished,
     };
 
-    String result_to_string(Result) const;
+    static String result_to_string(Result, Colour turn);
+    static String result_to_points(Result, Colour turn);
 
     template<typename Callback>
     void generate_moves(Callback callback, Colour colour = Colour::None) const;