SimplePartialReplicationStrategy.cs

using Nyris.Crdt.Distributed.Model;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Nyris.Crdt.Distributed.Strategies.PartialReplication
{
    public sealed class SimplePartialReplicationStrategy : IPartialReplicationStrategy
    {
        /// <inheritdoc />
        public IDictionary<TKey, IList<NodeInfo>> GetDistribution<TKey>(
            IReadOnlyDictionary<TKey, ulong> collectionSizes,
            IEnumerable<NodeInfo> nodes
        )
            where TKey : IEquatable<TKey>, IComparable<TKey>
        {
            var result = new Dictionary<TKey, IList<NodeInfo>>(collectionSizes.Count);
            var orderedNodes = nodes.OrderBy(nodeInfo => nodeInfo.Id).ToList();
            var orderedKeys = collectionSizes
                              .OrderByDescending(pair => Chunkify(pair.Value))
                              .ThenBy(pair => pair.Key)
                              .Select(pair => pair.Key)
                              .ToList();

            var count = 0;
            while (count < orderedKeys.Count)
            {
                for (var i = 0; i < orderedNodes.Count && count < orderedKeys.Count; ++i, ++count)
                {
                    result[orderedKeys[count]] = new List<NodeInfo>(2)
                    {
                        orderedNodes[i],
                        orderedNodes[i == orderedNodes.Count - 1 ? 0 : i + 1]
                    };
                }

                for (var i = orderedNodes.Count - 1; i > 0 && count < orderedKeys.Count; --i, ++count)
                {
                    result[orderedKeys[count]] = new List<NodeInfo>(2)
                    {
                        orderedNodes[i],
                        orderedNodes[i == orderedNodes.Count - 1 ? 0 : i + 1]
                    };
                }
            }

            return result;
        }

        private static ulong Chunkify(ulong size) => size switch
        {
            < 1000 => 0,
            _ => (ulong) Math.Log10(size)
        };
    }
}