Create README.yaml

README.yaml

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+---
+viewer_config:
+  custom_view_config:
+    - name: fen
+      type: text
+      column: fen
+      formatter: |
+        def formatter(row):
+            import struct
+            data = row['fen']
+            if not data or len(data) < 8:
+                return "Invalid FEN data"
+            
+            # Piece mappings
+            nib_to_piece_map = {
+                0: 'K', 1: 'Q', 2: 'R', 3: 'B', 4: 'N', 5: 'P',
+                6: 'k', 7: 'q', 8: 'r', 9: 'b', 10: 'n', 11: 'p'
+            }
+            NIB_EMPTY = 12
+            
+            # Read flags
+            flags = data[0]
+            is_crazyhouse = bool(flags & 4)
+            active_player = 'b' if (flags & 1) else 'w'
+            
+            # Calculate metadata size and board end
+            meta_size = 6 + (13 if is_crazyhouse else 0)
+            board_end = len(data) - meta_size
+            
+            # Unpack board nibbles
+            nibs = []
+            for i in range(1, board_end):
+                nibs.append((data[i] >> 4) & 0xF)
+                nibs.append(data[i] & 0xF)
+            
+            # Decode board
+            board_chars = []
+            sq = 0
+            i = 0
+            while i < len(nibs) and sq < 64:
+                if nibs[i] == NIB_EMPTY and i + 1 < len(nibs):
+                    cnt = nibs[i + 1] + 1
+                    board_chars.extend([' '] * cnt)
+                    sq += cnt
+                    i += 2
+                elif nibs[i] < 12:
+                    board_chars.append(nib_to_piece_map[nibs[i]])
+                    sq += 1
+                    i += 1
+                elif nibs[i] == 0xF:
+                    break
+                else:
+                    i += 1
+            
+            # Convert board to FEN notation (8 ranks)
+            fen_ranks = []
+            for rank in range(8):
+                rank_str = ""
+                empty_count = 0
+                for file in range(8):
+                    idx = rank * 8 + file
+                    if idx < len(board_chars):
+                        piece = board_chars[idx]
+                        if piece == ' ':
+                            empty_count += 1
+                        else:
+                            if empty_count > 0:
+                                rank_str += str(empty_count)
+                                empty_count = 0
+                            rank_str += piece
+                if empty_count > 0:
+                    rank_str += str(empty_count)
+                fen_ranks.append(rank_str)
+            
+            board_fen = '/'.join(fen_ranks)
+            
+            # Read metadata
+            m = board_end
+            castlings_bits = (data[m], data[m + 1])
+            enpassant = data[m + 2]
+            halfmove = data[m + 3]
+            fullmove = data[m + 4] | (data[m + 5] << 8)
+            
+            # Build FEN string (simplified, without full castling/enpassant parsing)
+            fen_str = f"{board_fen} {active_player} - - {halfmove} {fullmove}"
+            
+            return fen_str