SortOrderCalculator.cs

using System;
using System.Collections.Generic;
using LinkDotNet.Blog.Domain;

namespace LinkDotNet.Blog.Web.Features.Services;

public sealed class SortOrderCalculator : ISortOrderCalculator
{
    public int GetSortOrder(ProfileInformationEntry target, IEnumerable<ProfileInformationEntry> all)
    {
        ArgumentNullException.ThrowIfNull(target);

        var linkedEntries = new LinkedList<ProfileInformationEntry>(all);
        var targetNode = linkedEntries.Find(target);
        var next = targetNode!.Next;

        if (next is null)
        {
            var prev = targetNode.Previous;
            return (target.SortOrder + prev!.Value.SortOrder) / 2;
        }

        return (target.SortOrder + next.Value.SortOrder) / 2;
    }
}