using System;
using System.Collections;
using System.Globalization;
using Avalonia.Data.Converters;

namespace XSDVisualiser.Desktop.Converters
{
    /// <summary>
    /// Returns true if the bound value is a collection with at least one item. Supports IEnumerable and ICollection.
    /// Optional parameter "Invert" to invert the boolean result.
    /// </summary>
    public sealed class CollectionHasItemsConverter : IValueConverter
    {
        public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
        {
            var hasItems = false;
            switch (value)
            {
                case ICollection coll:
                    hasItems = coll.Count > 0;
                    break;
                case IEnumerable enumerable:
                {
                    var enumerator = enumerable.GetEnumerator();
                    hasItems = enumerator.MoveNext();
                    break;
                }
            }

            var invert = parameter is string s && s.Equals("Invert", StringComparison.OrdinalIgnoreCase);
            return invert ? !hasItems : hasItems;
        }

        public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
            => throw new NotSupportedException();
    }
}