/// Grid shape and per-cell channel assignments.
///
/// Cell numbering is 1..N in row-major order. A cell may be unassigned
/// (channel = null), in which case it renders as empty.
class GridConfig {
  GridConfig({
    required this.rows,
    required this.cols,
    List<int?>? cellChannels,
  }) : cellChannels =
            cellChannels ?? List<int?>.filled(rows * cols, null);

  int rows;
  int cols;
  /// Length = rows * cols. Element is the proto channel index (1..16) or null.
  List<int?> cellChannels;

  int get cellCount => rows * cols;

  /// 1-based cell number → channel, or null if unassigned.
  int? channelForCell(int cellNumber) {
    if (cellNumber < 1 || cellNumber > cellCount) return null;
    return cellChannels[cellNumber - 1];
  }

  /// Set the channel assigned to a 1-based cell. If [channel] is already
  /// assigned to a different cell, that cell is cleared (auto-swap).
  void assign(int cellNumber, int? channel) {
    if (cellNumber < 1 || cellNumber > cellCount) return;
    if (channel != null) {
      for (var i = 0; i < cellChannels.length; i++) {
        if (cellChannels[i] == channel) cellChannels[i] = null;
      }
    }
    cellChannels[cellNumber - 1] = channel;
  }

  /// Resize the grid. Channel assignments to cells beyond the new range
  /// are dropped.
  void resize(int newRows, int newCols) {
    final newCells = List<int?>.filled(newRows * newCols, null);
    final keep = newCells.length < cellChannels.length
        ? newCells.length
        : cellChannels.length;
    for (var i = 0; i < keep; i++) {
      newCells[i] = cellChannels[i];
    }
    rows = newRows;
    cols = newCols;
    cellChannels = newCells;
  }

  /// Auto-assign: fill cells with the lowest-numbered enabled channels.
  void autoAssign(List<int> enabledChannels) {
    cellChannels = List<int?>.filled(cellCount, null);
    final n = enabledChannels.length < cellCount
        ? enabledChannels.length
        : cellCount;
    for (var i = 0; i < n; i++) {
      cellChannels[i] = enabledChannels[i];
    }
  }

  Map<String, dynamic> toJson() => {
        'rows': rows,
        'cols': cols,
        'cellChannels': cellChannels,
      };

  static GridConfig fromJson(Map<String, dynamic> j) => GridConfig(
        rows: j['rows'] as int,
        cols: j['cols'] as int,
        cellChannels: (j['cellChannels'] as List)
            .map((e) => e as int?)
            .toList(),
      );
}