using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DTS.Common.Utilities
{
    public class EnumDropDown<T> : System.Windows.Forms.ComboBox where T : struct, IComparable
    {
        /// <summary>
        /// This is the class which actually holds the entrys in the list
        /// </summary>
        public class EnumListEntry : IComparable<EnumListEntry>
        {
            public T Value { get; set; }

            public override string ToString()
            {
                var decoder = new DescriptionAttributeCoder<T>();
                return decoder.DecodeAttributeValue(Value);
            }

            public EnumListEntry(T val)
            {
                Value = val;
            }

            public int CompareTo(EnumListEntry other)
            {
                return Value.CompareTo(other.Value);
            }

            public override bool Equals(object obj)
            {
                if (obj == null || GetType() != obj.GetType())
                    return false;
                var ele = (EnumListEntry)obj;
                return Value.Equals(ele.Value);
            }

            public override int GetHashCode()
            {
                return Value.GetHashCode();
            }
        }

        public delegate bool Filter(T enumEntry);

        protected Filter _EnumFilter;
        public Filter EnumFilter
        {
            set
            {
                _EnumFilter = value;
                PopulateList();
            }
        }

        public EnumDropDown(Filter defaultFilter)
            : base()
        {
            _EnumFilter = defaultFilter;
            PopulateList();
        }

        public void PopulateList()
        {
            var values = Enum.GetValues(typeof(T));
            var entryList = new List<EnumListEntry>();
            foreach (T i in values)
            {
                if (_EnumFilter == null || _EnumFilter(i))
                {
                    entryList.Add(new EnumListEntry(i));
                }
            }
            Items.Clear();
            Items.AddRange(entryList.ToArray());
        }

        /// <summary>
        /// Get or Set the selection as an EnumListEntry (can be null).
        /// </summary>
        public EnumListEntry SelectedEntry
        {
            get => (EnumListEntry)SelectedItem;

            set => SelectedItem = value;
        }

        /// <summary>
        /// Get or Set the selection as the enum itself (can NOT be null)!
        /// </summary>
        public T? SelectedEnum
        {
            get => SelectedEntry?.Value;

            set => SelectedEntry = value == null ? null : new EnumListEntry((T)value);
        }
    }
}