declaratrions-automatization/DeclarationAutomatization/Services/Sheet3ExpandService.cs

using System.Collections.Generic;
using DeclarationAutomatization.Models;

namespace DeclarationAutomatization.Services;

public class Sheet3ExpandService
{
    // Разворачивает позиции Листа2 по рег. номерам.
    // Один товар с N рег. номерами → N строк в Листе3 (с тем же п/п).
    public List<Sheet3Row> Expand(IEnumerable<DeclarationItem> items)
    {
        var result = new List<Sheet3Row>();

        foreach (var item in items)
        {
            if (item.RegEntries.Count == 0)
            {
                result.Add(new Sheet3Row
                {
                    SequentialNumber = item.SequentialNumber,
                    TnVed = item.TnVed,
                    RegNumber = "",
                    RegDate = "",
                });
            }
            else
            {
                foreach (var entry in item.RegEntries)
                {
                    result.Add(new Sheet3Row
                    {
                        SequentialNumber = item.SequentialNumber,
                        TnVed = item.TnVed,
                        RegNumber = entry.Number,
                        RegDate = entry.Date,
                    });
                }
            }
        }

        return result;
    }
}