Chess: Added abilty to import PGN files

This patch allows the user to load games using PGN files. The parsing
is not complete and has a bunch of work left to be done, but it's
okay for our use case here. It can load all of the games our PGN
exporter can save. As the Chess program impoves so can the PGN parser.

Games/Chess/ChessWidget.cpp

@@ -374,6 +374,110 @@ String ChessWidget::get_fen() const
     return m_playback ? m_board_playback.to_fen() : m_board.to_fen();
 }
 
+bool ChessWidget::import_pgn(const StringView& import_path)
+{
+    auto file_or_error = Core::File::open(import_path, Core::File::OpenMode::ReadOnly);
+    if (file_or_error.is_error()) {
+        warnln("Couldn't open '{}': {}", import_path, file_or_error.error());
+        return false;
+    }
+    auto& file = *file_or_error.value();
+
+    m_board = Chess::Board();
+
+    ByteBuffer bytes = file.read_all();
+    StringView content = bytes;
+    auto lines = content.lines();
+    StringView line;
+    size_t i = 0;
+
+    // Tag Pair Section
+    // FIXME: Parse these tags when they become relevant
+    do {
+        line = lines.at(i++);
+    } while (!line.is_empty() || i >= lines.size());
+
+    // Movetext Section
+    bool skip = false;
+    bool recursive_annotation = false;
+    bool future_expansion = false;
+    Chess::Colour turn = Chess::Colour::White;
+    String movetext;
+
+    for (size_t j = i; j < lines.size(); j++)
+        movetext = String::formatted("{}{}", movetext, lines.at(i).to_string());
+
+    for (auto token : movetext.split(' ')) {
+        token = token.trim_whitespace();
+
+        // FIXME: Parse all of these tokens when we start caring about them
+        if (token.ends_with("}")) {
+            skip = false;
+            continue;
+        }
+        if (skip)
+            continue;
+        if (token.starts_with("{")) {
+            if (token.ends_with("}"))
+                continue;
+            skip = true;
+            continue;
+        }
+        if (token.ends_with(")")) {
+            recursive_annotation = false;
+            continue;
+        }
+        if (recursive_annotation)
+            continue;
+        if (token.starts_with("(")) {
+            if (token.ends_with(")"))
+                continue;
+            recursive_annotation = true;
+            continue;
+        }
+        if (token.ends_with(">")) {
+            future_expansion = false;
+            continue;
+        }
+        if (future_expansion)
+            continue;
+        if (token.starts_with("<")) {
+            if (token.ends_with(">"))
+                continue;
+            future_expansion = true;
+            continue;
+        }
+        if (token.starts_with("$"))
+            continue;
+        if (token.contains("*"))
+            break;
+        // FIXME: When we become able to set more of the game state, fix these end results
+        if (token.contains("1-0")) {
+            m_board.set_resigned(Chess::Colour::Black);
+            break;
+        }
+        if (token.contains("0-1")) {
+            m_board.set_resigned(Chess::Colour::White);
+            break;
+        }
+        if (token.contains("1/2-1/2")) {
+            break;
+        }
+        if (!token.ends_with(".")) {
+            m_board.apply_move(Chess::Move::from_algebraic(token, turn, m_board));
+            turn = Chess::opposing_colour(turn);
+        }
+    }
+
+    m_board_playback = m_board;
+    m_playback_move_number = m_board_playback.moves().size();
+    m_playback = true;
+    update();
+
+    file.close();
+    return true;
+}
+
 bool ChessWidget::export_pgn(const StringView& export_path) const
 {
     auto file_or_error = Core::File::open(export_path, Core::File::WriteOnly);