calc method

Sm2Response calc({ required int quality, required int repetitions, required int previousInterval, required double previousEaseFactor, })

Calculates the next SM-2 state for one reviewed item.

Use repetitions: 0, previousInterval: 0, and previousEaseFactor: 2.5 for a new item.

Throws ArgumentError if the input state is outside the SM-2 domain.

Implementation

Sm2Response calc({
  /// Recall quality from 0 to 5.
  required int quality,

  /// Number of successful repetitions currently stored for the item.
  required int repetitions,

  /// Last scheduled interval in days.
  required int previousInterval,

  /// Last ease factor for the item.
  required double previousEaseFactor,
}) {
  if (quality < 0 || quality > 5) {
    throw ArgumentError.value(quality, 'quality', 'must be between 0 and 5');
  }
  if (repetitions < 0) {
    throw ArgumentError.value(repetitions, 'repetitions', 'must be >= 0');
  }
  if (previousInterval < 0) {
    throw ArgumentError.value(
      previousInterval,
      'previousInterval',
      'must be >= 0',
    );
  }
  if (repetitions > 0 && previousInterval < 1) {
    throw ArgumentError.value(
      previousInterval,
      'previousInterval',
      'must be >= 1 when repetitions is greater than 0',
    );
  }
  if (!previousEaseFactor.isFinite || previousEaseFactor < 1.3) {
    throw ArgumentError.value(
      previousEaseFactor,
      'previousEaseFactor',
      'must be finite and >= 1.3',
    );
  }

  int interval;
  if (quality >= 3) {
    switch (repetitions) {
      case 0:
        interval = 1;
        break;
      case 1:
        interval = 6;
        break;
      default:
        interval = (previousInterval * previousEaseFactor).ceil();
    }

    repetitions++;
  } else {
    repetitions = 0;
    interval = 1;
  }

  double easeFactor = previousEaseFactor +
      (0.1 - (5 - quality) * (0.08 + (5 - quality) * 0.02));

  if (easeFactor < 1.3) {
    easeFactor = 1.3;
  }

  return Sm2Response(
    interval: interval,
    repetitions: repetitions,
    easeFactor: easeFactor,
  );
}