WheresMyMoney/WheresMyMoney.Maui.Core/PlannedPayment.cs

namespace WheresMyMoney.Maui.Core;

public enum ReoccurenceType
{
    Days,
    Weeks,
    Months,
    Years,
    EveryLastDayOfMonth
}

public record PlannedPayment(
    int Id,
    decimal Amount,
    string Name,
    DateTime DateStart,
    DateTime? DateEnd,
    bool IsSubscription,
    int? Reoccurences,
    ReoccurenceType? ReoccurenceType)
{
    public List<PlannedPayment> ExpandSubscription(DateTime startDate, DateTime endDate)
    {
        var expandedPayments = new List<PlannedPayment>();

        if (!IsSubscription || Reoccurences is null || Reoccurences < 1 || ReoccurenceType is null)
            return DateStart >= startDate && DateStart <= endDate ? [this] : [];

        var occurrence = DateStart;

        while (occurrence <= endDate && (DateEnd == null || occurrence <= DateEnd))
        {
            if (occurrence >= startDate)
            {
                expandedPayments.Add(new PlannedPayment(
                    0, // New ID not assigned
                    Amount,
                    Name,
                    occurrence,
                    null,
                    false,
                    null,
                    null
                ));
            }

            occurrence = GetNextOccurence(occurrence, Reoccurences.Value, ReoccurenceType.Value);
        }

        return expandedPayments;

        DateTime GetNextOccurence(DateTime dateStart, int reoccurences, ReoccurenceType reoccurenceType)
        {
            switch (reoccurenceType)
            {
                case Core.ReoccurenceType.Days:
                    return dateStart.AddDays(reoccurences);
                case Core.ReoccurenceType.Weeks:
                    return dateStart.AddDays(reoccurences * 7);
                    break;
                case Core.ReoccurenceType.Months:
                    return dateStart.AddMonths(reoccurences);
                    break;
                case Core.ReoccurenceType.Years:
                    return dateStart.AddYears(reoccurences);
                    break;
                case Core.ReoccurenceType.EveryLastDayOfMonth:
                    var result = new DateTime(startDate.Year, startDate.Month,
                        DateTime.DaysInMonth(dateStart.Year, dateStart.Month));
                    if (result.Date != dateStart.Date) return result;
                    result = result.AddDays(1);
                    return new DateTime(result.Year, result.Month, DateTime.DaysInMonth(result.Year, result.Month));
                default:
                    throw new ArgumentOutOfRangeException(nameof(reoccurenceType), reoccurenceType, null);
            }
        }
    }
}