namespace Sortable_Collection.Sorters
{
    using Contracts;
    using System;
    using System.Collections.Generic;
    using System.Threading.Tasks;

    public class AsyncMergeSorter<T> : ISorter<T> where T : IComparable<T>
    {
        public void Sort(IList<T> collection)
        {
            if (collection.Count <= 1)
            {
                return;
            }

            T[] workArray = new T[collection.Count];
            SplitMerge(collection, workArray, 0, collection.Count);
        }

        private void SplitMerge(IList<T> collection, T[] tempArray, int start, int end)
        {
            if (end - start < 2)
            {
                return;
            }

            int midd = (start + end) / 2;

            if (end - start < 15000)
            {
                SplitMerge(collection, tempArray, start, midd);
                SplitMerge(collection, tempArray, midd, end);
            }
            else
            {
                Task t1 = Task.Factory.StartNew(() => SplitMerge(collection, tempArray, start, midd));
                Task t2 = Task.Factory.StartNew(() => SplitMerge(collection, tempArray, midd, end));
                Task.WaitAll(t1, t2);
            }


            //SplitMerge(collection, tempArray, start, midd);
            //SplitMerge(collection, tempArray, midd, end);
            Merge(collection, tempArray, start, midd, end);

            CoppyArray(collection, tempArray, start, end);
        }

        private void Merge(IList<T> collection, T[] tempArray, int start, int midd, int end)
        {
            int first = start;
            int second = midd;

            for (int i = start; i < end; i++)
            {
                if (first >= midd)
                {
                    tempArray[i] = collection[second++];
                }
                else if (second >= end)
                {
                    tempArray[i] = collection[first++];
                }
                else
                {
                    if (collection[first].CompareTo(collection[second]) <= 0)
                    {
                        tempArray[i] = collection[first++];
                    }
                    else
                    {
                        tempArray[i] = collection[second++];
                    }
                }
            }
        }

        private void CoppyArray(IList<T> collection, T[] tempArray, int start, int end)
        {
            for (int i = start; i < end; i++)
            {
                collection[i] = tempArray[i];
            }
        }
    }
}