enum PaichanContextChange { firstScan, samePaichan, switchedPaichan }

class PaichanContextDecision {
  final PaichanContextChange change;
  final int? boxNoToApply;

  const PaichanContextDecision({required this.change, this.boxNoToApply});

  bool get isSwitched => change == PaichanContextChange.switchedPaichan;
}

PaichanContextDecision decideMultiCodePaichanContext({
  required String? lastPaichanNo,
  required String? currentPaichanNo,
  required String currentBoxNoText,
  required int maxBoxNo,
}) {
  final recommendedBoxNo = maxBoxNo + 1;
  if (currentPaichanNo == null || currentPaichanNo.isEmpty) {
    return const PaichanContextDecision(change: PaichanContextChange.firstScan);
  }
  if (lastPaichanNo == null || lastPaichanNo.isEmpty) {
    return PaichanContextDecision(
      change: PaichanContextChange.firstScan,
      boxNoToApply: currentBoxNoText.trim().isEmpty ? recommendedBoxNo : null,
    );
  }
  if (lastPaichanNo == currentPaichanNo) {
    return PaichanContextDecision(
      change: PaichanContextChange.samePaichan,
      boxNoToApply: currentBoxNoText.trim().isEmpty ? recommendedBoxNo : null,
    );
  }
  return PaichanContextDecision(
    change: PaichanContextChange.switchedPaichan,
    boxNoToApply: recommendedBoxNo,
  );
}