using System.Collections.Generic;
using System.Threading;

namespace System.Collections.Concurrent.Partitioners
{
	internal class UserLongRangePartitioner : OrderablePartitioner<Tuple<long, long>>
	{
		private readonly long start;

		private readonly long end;

		private readonly long rangeSize;

		public UserLongRangePartitioner(long start, long end, long rangeSize)
			: base(keysOrderedInEachPartition: true, keysOrderedAcrossPartitions: true, keysNormalized: true)
		{
			this.start = start;
			this.end = end;
			this.rangeSize = rangeSize;
		}

		public override IList<IEnumerator<KeyValuePair<long, Tuple<long, long>>>> GetOrderablePartitions(int partitionCount)
		{
			if (partitionCount <= 0)
			{
				throw new ArgumentOutOfRangeException("partitionCount");
			}
			long currentIndex = 0L;
			Func<long> getNextIndex = () => Interlocked.Increment(ref currentIndex) - 1;
			IEnumerator<KeyValuePair<long, Tuple<long, long>>>[] enumerators = new IEnumerator<KeyValuePair<long, Tuple<long, long>>>[partitionCount];
			for (int i = 0; i < partitionCount; i++)
			{
				enumerators[i] = GetEnumerator(getNextIndex);
			}
			return enumerators;
		}

		private IEnumerator<KeyValuePair<long, Tuple<long, long>>> GetEnumerator(Func<long> getNextIndex)
		{
			while (true)
			{
				long index = getNextIndex();
				long sliceStart = index * rangeSize + start;
				if (sliceStart < end)
				{
					yield return new KeyValuePair<long, Tuple<long, long>>(index, Tuple.Create(sliceStart, Math.Min(end, sliceStart + rangeSize)));
					_ = sliceStart + rangeSize;
					continue;
				}
				break;
			}
		}
	}
}