prep method

@override Future<List<I>> prep(Map<String, dynamic> shared)

Prepares the batch of items for processing.

This method retrieves the list of items from the node's parameters. It expects a parameter named "items" which should be a List<I>.

Throws an ArgumentError if the "items" parameter is not provided or is of the wrong type.

Implementation

@override
/// Prepares the batch of items for processing.
///
/// This method retrieves the list of items from the node's parameters. It
/// expects a parameter named "items" which should be a `List<I>`.
///
/// Throws an [ArgumentError] if the "items" parameter is not provided or is
/// of the wrong type.
Future<List<I>> prep(Map<String, dynamic> shared) async {
  final items = params['items'] ?? shared['items'];

  if (items == null) {
    throw ArgumentError('The "items" parameter must be provided.');
  }

  if (items is List<I>) {
    return items;
  }

  if (items is List) {
    if (items.every((item) => item is I)) {
      return items.cast<I>();
    } else {
      throw ArgumentError(
        'The "items" parameter must be a List where all elements are of '
        'type $I.',
      );
    }
  }

  throw ArgumentError(
    'The "items" parameter must be a List, but got ${items.runtimeType}.',
  );
}