build method

@override String build(String a, String b)

Builds the tape of characters to interpolate to and from.

Implementation

@override
String build(String a, String b) {
  final tape = super.build(a, b);
  final maxDistance = this.distance;
  final int length = tape.characters.length;
  final int maxIndex = length - 1;

  if (a == b) {
    if (repeatCharacters) {
      return a * (maxDistance + 2);
    } else {
      return a;
    }
  }
  if (length <= 2) {
    final int halfDist = maxDistance ~/ 2;
    return a * (halfDist + 1) + b * (halfDist + 1);
  }

  final StringBuffer newKit = StringBuffer();

  int distance = maxDistance;
  bool fromStart = true;
  while (distance > 0) {
    final progress = maxDistance - distance;
    if (fromStart) {
      final int start = min(progress, maxIndex - 1);
      newKit.write(tape.characters.elementAt(start + 1));
      // if (newKit.length >= maxDistance + 2) break;
    } else {
      final int end = max(maxIndex - progress, 1);
      newKit.write(tape.characters.elementAt(end - 1));
      // if (newKit.length >= maxDistance + 2) break;
    }
    distance--;
    fromStart = !fromStart;
  }
  return a + newKit.toString() + b;
}