Functional Programming - 12. Inferno III

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


namespace CSharpAdvanced
{

    class Program
    {
        static void Main(string[] args)
        {
            var gems = Console.ReadLine()
                .Split()
                .Select(int.Parse)
                .ToList();

            var filters = new Dictionary<string, Func<List<int>, List<int>>>();

            string input;
            while ((input = Console.ReadLine()) != "Forge")
            {
                var line = input.Split(";");
                var command = line[0];
                var filterType = line[1];
                var parameter = int.Parse(line[2]);

                string dictKey = $"{filterType} {parameter}";

                if (command == "Exclude")
                {
                    filters[dictKey] = CreateFunction(filterType, parameter);
                }

                else if (command == "Reverse")
                {
                    filters.Remove(dictKey);
                }
            }

            List<int> filtered = GetFiltered(gems, filters);

            gems = gems.Where(gem => !filtered.Contains(gem)).ToList();

            Console.WriteLine(string.Join(" ", gems));
        }

        private static List<int> GetFiltered(List<int> gems, Dictionary<string, Func<List<int>, List<int>>> filters)
        {
            var filtered = new List<int>();

            foreach (var filter in filters)
            {
                filtered.AddRange(filter.Value(gems));
            }

            return filtered;
        }

        private static Func<List<int>, List<int>> CreateFunction(string filterType, int parameter)
        {
            switch (filterType)
            {
                case "Sum Left":
                    return gems => gems.Where(gem =>
                    {
                        int index = gems.IndexOf(gem);
                        int leftGem = index > 0 ? gems[index - 1] : 0;
                        return gem + leftGem == parameter;
                    }).ToList();

                case "Sum Right":
                    return gems => gems.Where(gem =>
                    {
                        int index = gems.IndexOf(gem);
                        int rightGem = index < gems.Count - 1 ? gems[index + 1] : 0 ;
                        return gem + rightGem == parameter;
                    }).ToList();

                case "Sum Left Right":
                    return gems => gems.Where(gem =>
                    {
                        int index = gems.IndexOf(gem);
                        int leftGem = index > 0 ? gems[index - 1] : 0;
                        int rightGem = index < gems.Count - 1 ? gems[index + 1] : 0;
                        return gem + leftGem + rightGem == parameter;
                    }).ToList();

                default:
                    throw new ArgumentException();
            }
        }
    }
}