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

namespace IStation 
{
    public static class LinqExtensions
    {
        //public static T MinBy<T, TProp>(this IEnumerable<T> source, Func<T, TProp> propSelector)
        //{
        //    return source.OrderBy(propSelector).FirstOrDefault();
        //}

        public static int FindIndexMinBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> selector)
        {
            return source.FindIndexMinBy(selector, null);
        }
        public static int FindIndexMinBy<TSource, TKey>(this IEnumerable<TSource> source,
            Func<TSource, TKey> selector, IComparer<TKey> comparer)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (selector == null) throw new ArgumentNullException("selector");
            comparer = comparer ?? Comparer<TKey>.Default;
            int min_indx = 0;
            using (var sourceIterator = source.GetEnumerator())
            {
                if (!sourceIterator.MoveNext())
                {
                    throw new InvalidOperationException("Sequence contains no elements");
                }
                var min = sourceIterator.Current;

                int indx = 0;
                var minKey = selector(min);
                while (sourceIterator.MoveNext())
                {
                    indx++;
                    var candidate = sourceIterator.Current;
                    var candidateProjected = selector(candidate);
                    if (comparer.Compare(candidateProjected, minKey) < 0)
                    {
                        min_indx = indx;
                        min = candidate;
                        minKey = candidateProjected;
                    }
                }
                return min_indx;
            }
        }
        public static TSource FindObjMinBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> selector)
        {
            return source.FindObjMinBy(selector, null);
        }

        public static TSource FindObjMinBy<TSource, TKey>(this IEnumerable<TSource> source,
            Func<TSource, TKey> selector, IComparer<TKey> comparer)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (selector == null) throw new ArgumentNullException("selector");
            comparer = comparer ?? Comparer<TKey>.Default;

            using (var sourceIterator = source.GetEnumerator())
            {
                if (!sourceIterator.MoveNext())
                {
                    throw new InvalidOperationException("Sequence contains no elements");
                }
                var min = sourceIterator.Current;
                var minKey = selector(min);
                while (sourceIterator.MoveNext())
                {
                    var candidate = sourceIterator.Current;
                    var candidateProjected = selector(candidate);
                    if (comparer.Compare(candidateProjected, minKey) < 0)
                    {
                        min = candidate;
                        minKey = candidateProjected;
                    }
                }
                return min;
            }
        }

        public static TSource FindObjMaxBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> selector)
        {
            return source.FindObjMaxBy(selector, null);
        }

        public static TSource FindObjMaxBy<TSource, TKey>(this IEnumerable<TSource> source,
            Func<TSource, TKey> selector, IComparer<TKey> comparer)
        {
            if (source == null) throw new ArgumentNullException("source");
            if (selector == null) throw new ArgumentNullException("selector");
            comparer = comparer ?? Comparer<TKey>.Default;

            using (var sourceIterator = source.GetEnumerator())
            {
                if (!sourceIterator.MoveNext())
                {
                    throw new InvalidOperationException("Sequence contains no elements");
                }
                var max = sourceIterator.Current;
                var maxKey = selector(max);
                while (sourceIterator.MoveNext())
                {
                    var candidate = sourceIterator.Current;
                    var candidateProjected = selector(candidate);
                    if (comparer.Compare(candidateProjected, maxKey) > 0)
                    {
                        max = candidate;
                        maxKey = candidateProjected;
                    }
                }
                return max;
            }
        }
    }
}