C Charp固定長分割

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

namespace FieldSplitter
{
    public class FieldSplitterService
    {
        public string SplitField(string lengthString, string inputData, string splitChar)
        {
            var buf = new StringBuilder();

            List<int> lengthList = GetLengthList(lengthString);

            using (var reader = new StringReader(inputData))
            {
                string line = null;
                while((line = reader.ReadLine()) != null) {
                    buf.Append(SplitLine(lengthList, splitChar ,line));
                    buf.Append(Environment.NewLine);
                }
            }
            return buf.ToString();
        }

        private string SplitLine(List<int> lengthList, string splitChar, string line)
        {
            var buf = new StringBuilder();
            int pos = 0;
            foreach(int len in lengthList)
            {
                if (len > 0)
                {
                    int stepc = 0;
                    int diflen = 0;
                    for(int i=pos; i<line.Length; i++)
                    {
                        var c = line[i];
                        if (((int)c) <= 255)
                        {
                            diflen += 1;
                        }
                        else
                        {
                            diflen += 2;
                        }
                        buf.Append(c);
                        stepc++;
                        if (diflen >= len)
                        {
                            break;
                        }
                    }
                    pos += stepc;
                }
                buf.Append(splitChar);
            }
            if (pos < line.Length)
            {
                buf.Append(line.Substring(pos));
            }

            return buf.ToString();
        }

        private List<int> GetLengthList(string lengthList)
        {
            var strLenList = Regex.Split(lengthList, @"[^0-9]");

            var ret = strLenList
                .Where(len => Regex.IsMatch(len, @"[0-9]+"))
                .Select(len => int.Parse(len));

            return ret.ToList();
        }

    }
}