Get difference from C# strings.

Program.cs

using System;
using System.Collections.Generic;
using Newtonsoft.Json;

namespace WhiteBorad
{
    public class Program
    {
        private static int _ContinueStringLength = 5;
        public static Commit GetDiff(string sourceString, string targetString)
        {
            sourceString = sourceString +  "     ";
            targetString = targetString +  "     ";
            var commit = new Commit();
            int insertedFloat = 0;
            var min = Math.Min(sourceString.Length, targetString.Length);
            for (int i = 0; i < sourceString.Length && i+insertedFloat < targetString.Length; i++)
            {
                if (sourceString[i] != targetString[i + insertedFloat])
                {
                    string sourceHeader = sourceString.SafeSubstring(i, _ContinueStringLength);
                    int insertFound = targetString.IndexOf(sourceHeader, startIndex: i + insertedFloat);
                    int insertEndAt = insertFound - insertedFloat;

                    string targetHeader = targetString.SafeSubstring(i + insertedFloat, _ContinueStringLength);
                    int deleteEndAt = sourceString.IndexOf(targetHeader, i);
                    if(insertFound != -1 && deleteEndAt != -1)
                    {
                        if(insertEndAt > deleteEndAt)
                        {
                            insertFound = -1;
                        }
                    }
                    if (insertFound != -1 && insertEndAt > 0)
                    {
                        var length = insertEndAt - i;
                        var insertion = new Insertion
                        {
                            Position = i,
                            Length = length,
                            Content = targetString.Substring(i + insertedFloat, length)
                        };
                        commit.Modifications.Add(insertion);
                        insertedFloat += insertion.Length;
                    }
                    else
                    {
                        if(deleteEndAt == -1)
                        {
                            deleteEndAt = sourceString.Length - _ContinueStringLength;
                        }
                        int length = deleteEndAt - i;
                        var deletion = new Deletion
                        {
                            Position = i,
                            Length = length,
                            Content = sourceString.Substring(i, length)
                        };
                        commit.Modifications.Add(deletion);
                        insertedFloat -= length;
                        i += length;
                        //这是一行有玄学的代码
                        //我也不知道为什么，但是去掉它就跑不起来了
                        if(deleteEndAt == sourceString.Length - _ContinueStringLength)
                            i--;
                    }
                }
            }
            return commit;
        }

        public static void Test(string source, string target)
        {
            var diff = GetDiff(source, target);
            var result = diff.Apply(source);
            if (result == target)
            {
                Console.WriteLine("Passed!");
            }
            else
            {
                Console.WriteLine("Error!");
            }
        }
        static void Main(string[] args)
        {
            //Can't match
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The quick brown fox jumps oveLorem ipsum dolor sit amet");
            //Possible mistake
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The quick brown fox lazy dog jumps over the lazy dog");

            //Did not change
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The quick brown fox jumps over the lazy dog");
            //-
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The quick brown fomps over the lazy dog");
            //+
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The quick brown fox jumbbbps over the lazy dog");
            //--
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The qun fox jumps over the lazy do");
            //-+
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "Thuick brown fox jumps over the l+++++++++azy dog");
            //+-
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The quick br+++++own fox jumps ovee lazy dog");
            //++
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The quick brown fox jumps over      the      lazy dog");

            //---
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The qu brown foxmps over thy dog");
            //--+
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The qbrown fox jumov+++++++er the lazy dog");
            //-+-
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "The q brown fox j++++umps over the la");
            //-++
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "quick brown fo++x jumps over the lazy +dog");
            //+--
            Test(   "The quick brown fox jumps over the lazy dog", 
                    "++++++++The quick brown  ov lazy dog");
            //+-+
            // Test(   "The quick brown fox jumps over the lazy dog", 
            //         "The quick brown fox jumps over the lazy dog");
            // //++-
            // Test(   "The quick brown fox jumps over the lazy dog", 
            //         "The quick brown fox jumps over the lazy dog");
            // //+++
            // Test(   "The quick brown fox jumps over the lazy dog", 
            //         "The quick brown fox jumps over the lazy dog");

        }

    }
    public static class Library
    {
        public static string SafeSubstring(this string source, int position, int length)
        {
            if (source.Length >= position + length)
                return source.Substring(position, length);
            return source.Substring(position);
        }
    }
    public class Commit
    {
        public List<Modification> Modifications { get; set; } = new List<Modification>();
        public DateTime CommitTime { get; set; } = DateTime.Now;
        public string Apply(string sourceString)
        {
            int insertedLength = 0;
            var resultString = sourceString;
            foreach (var modify in Modifications)
            {
                if (modify.Type == nameof(Insertion))
                {
                    resultString = resultString.Substring(0, modify.Position + insertedLength)
                            + modify.Content
                            + resultString.Substring(modify.Position + insertedLength);
                    insertedLength += modify.Length;
                }
                else if (modify.Type == nameof(Deletion))
                {
                    resultString = resultString.Substring(0, modify.Position + insertedLength)
                                + resultString.Substring(modify.Position + modify.Length + insertedLength);
                    insertedLength -= modify.Length;
                }
            }
            return resultString;
        }
    }

    //Lorem ipsum dolor sit amet
    //Lorem ipsum the quick fox
    public abstract class Modification
    {
        public int Position { get; set; }
        public int Length { get; set; }
        public string Content { get; set; }
        public virtual string Type { get; set; } = nameof(Insertion);
    }
    public class Insertion : Modification
    {
        public override string Type { get; set; } = nameof(Insertion);
    }
    public class Deletion : Modification
    {
        public override string Type { get; set; } = nameof(Deletion);
    }
}