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

namespace SpriteCompiler.Helpers
{
    public static class EnumerableExtensions
    {
        public static IEnumerable<Tuple<T, T>> Pairs<T>(this IEnumerable<T> source)
        {
            return source.Zip(source.Skip(1), (x, y) => Tuple.Create(x, y));
        }

        public static IEnumerable<IGrouping<T, T>> GroupAdjacent<T>(this IEnumerable<T> source, Func<T, T, bool> comparer)
        {
            return GroupAdjacent(source, x => x, comparer);
        }

        public static IEnumerable<IGrouping<TKey, TSource>> GroupAdjacent<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
        {
            return GroupAdjacent(source, keySelector, (a, b) => a.Equals(b));
        }

        public static IEnumerable<IGrouping<TKey, TSource>> GroupAdjacent<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, Func<TKey, TKey, bool> comparer)
        {
            TKey last = default(TKey);
            bool haveLast = false;
            List<TSource> list = new List<TSource>();
            foreach (TSource s in source)
            {
                TKey k = keySelector(s);
                if (haveLast)
                {
                    if (!comparer(last, k))
                    {
                        yield return new GroupOfAdjacent<TSource, TKey>(list, last);
                        list = new List<TSource>();
                        list.Add(s);
                        last = k;
                    }
                    else
                    {
                        list.Add(s);
                        last = k;
                    }
                }
                else
                {
                    list.Add(s);
                    last = k;
                    haveLast = true;
                }
            }
            if (haveLast)
            {
                yield return new GroupOfAdjacent<TSource, TKey>(list, last);
            }
        }
    }

    public class GroupOfAdjacent<TSource, TKey> : IEnumerable<TSource>, IGrouping<TKey, TSource>
    {
        public TKey Key { get; set; }
        private List<TSource> GroupList { get; set; }

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return ((System.Collections.Generic.IEnumerable<TSource>)this).GetEnumerator();
        }

        System.Collections.Generic.IEnumerator<TSource> System.Collections.Generic.IEnumerable<TSource>.GetEnumerator()
        {
            foreach (var s in GroupList)
                yield return s;
        }

        public GroupOfAdjacent(List<TSource> source, TKey key)
        {
            GroupList = source;
            Key = key;
        }
    }
}