// SPDX-FileCopyrightText: 2022 Iconica
//
// SPDX-License-Identifier: BSD-3-Clause

/// Converts an index of a set size to the corresponding index of a collection
/// of another size as if they were circular.
///
/// Takes a [position] from collection Foo, a [base] from where Foo's index
/// originated and the [length] of a second collection Baa, for which the
/// correlating index is sought.
///
/// For example; We have a Carousel of 10000(simulating infinity) but only 6
/// images. We need to repeat the images to give the illusion of a never
/// ending stream. By calling [getRealIndex] with position and base we get
/// an offset. This offset modulo our length, 6, will return a number between
/// 0 and 5, which represent the image to be placed in the given position.
int getRealIndex(int position, int base, int? length) {
  var offset = position - base;
  return remainder(offset, length);
}

/// Returns the remainder of the modulo operation [input] % [source], and adjust
/// it for negative values.
int remainder(int input, int? source) {
  if (source == 0) return 0;
  var result = input % source!;
  return result < 0 ? source + result : result;
}