AppsheetEpplus/FormulaParsing/Excel/Functions/RefAndLookup/ArrayLookupNavigator.cs

using System.Linq;

namespace AppsheetEpplus;

public class ArrayLookupNavigator : LookupNavigator {
  private readonly FunctionArgument[] _arrayData;
  private int _index;
  private object _currentValue;

  public ArrayLookupNavigator(
      LookupDirection direction,
      LookupArguments arguments,
      ParsingContext parsingContext)
      : base(direction, arguments, parsingContext) {
    Require.That(arguments).Named("arguments").IsNotNull();
    Require.That(arguments.DataArray).Named("arguments.DataArray").IsNotNull();
    _arrayData = arguments.DataArray.ToArray();
    Initialize();
  }

  private void Initialize() {
    if (Arguments.LookupIndex >= _arrayData.Length) {
      throw new ExcelErrorValueException(eErrorType.Ref);
    }
    SetCurrentValue();
  }

  public override int Index => _index;

  private void SetCurrentValue() {
    _currentValue = _arrayData[_index];
  }

  private bool HasNext() {
    if (Direction == LookupDirection.Vertical) {
      return _index < (_arrayData.Length - 1);
    }
    return false;
  }

  public override bool MoveNext() {
    if (!HasNext()) {
      return false;
    }
    if (Direction == LookupDirection.Vertical) {
      _index++;
    }
    SetCurrentValue();
    return true;
  }

  public override object CurrentValue => _arrayData[_index].Value;

  public override object GetLookupValue() {
    return _arrayData[_index].Value;
  }
}