using System;using System.Diagnostics;

​

namespace GetBetweenStrings_Blog

{

    public static class Extensions 

    {

        /// <summary>

        /// Get a substring between two anchor strings, maximal span

        /// </summary>

        /// <param name="s">source string</param>

        /// <param name="from">search from end of this string</param>

        /// <param name="to">to beginning of this string, searching backwards, from end to start of s</param>

        /// <returns>a substring between from and to, maximal span</returns>

        public static string GetFirstStringBetweenStringsCleanup(this string s, string from, string to)

        {

            if (string.IsNullOrEmpty(s) || string.IsNullOrEmpty(from) || string.IsNullOrEmpty(to)) return string.Empty;

            int idxFrom = s.IndexOf(from);

            int idxStart = idxFrom + from.Length; //we filter "not found" -1, never get neg number here

​

            if (idxFrom == -1 || idxStart >= s.Length - 1)

                return string.Empty;

            int idxEnd = s.LastIndexOf(to);

            if (idxEnd == -1 || idxEnd <= idxStart) 

                return string.Empty;

            return s.Substring(idxStart, idxEnd - idxStart);

​

        }

​

        //4:00AM coding journey, testing conditions you may or may not need, buiding from scatch

        /// <summary>

        /// Get a substring between two anchor strings, maximal span

        /// </summary>

        /// <param name="s">source string</param>

        /// <param name="from">search from end of this string</param>

        /// <param name="to">to beginning of this string, searching backwards, from end to start of s</param>

        /// <returns>a substring between from and to, maximal span</returns>

        public static string GetFirstStringBetweenStrings(this string s, string from, string to)

        {

            Console.Write("args from {0} to {1} = ", from, to); //debug

​

            //edge case

            if (string.IsNullOrEmpty(s) || string.IsNullOrEmpty(from) || string.IsNullOrEmpty(to)) return string.Empty;

            //if (from.Length >= s.Length || to.Length >= s.Length) return string.Empty; //redundant rule take care of below

            int idxFrom = s.IndexOf(from);

            int idxStart = idxFrom + from.Length; //we filter "not found" -1, never race condtn

​

            if (idxFrom == -1)       

                return string.Empty;

            else if (idxStart >= s.Length - 1) //for testing combine to 1 line, we combining a idx with a length, and w/ lengths we normally subtract 1 

            //else if (idxStart >= s.Length) //for testing combine to 1 line, we combining a idx with a length, and w/ lengths we normally subtract 1 

            {

                Console.WriteLine("r1. idxStart={0} >= (s.Length - 1)={1}", idxStart, s.Length - 1);

                //Console.WriteLine("r1. idxStart={0} >= s.Length={1}",  idxStart, s.Length);

                return string.Empty; 

            }

​

​

            int idxEnd = s.LastIndexOf(to); 

            //int idxEnd = s.LastIndexOf(to, idxStart); //produces unexpected results 1 when to="a" and idxStart=1 when from="a", we expect last last index of string "aaaa" which is 4-1=3

​

            //if (idxEnd == -1 || idxEnd > s.Length - 1 || idxStart >= idxEnd) //intially in-correction

            if (idxEnd == -1 )

                return string.Empty;

            //else if (idxEnd > s.Length - 1) //we can rule this out because if not found -1

            ////else if (idxEnd > s.Length)

            //{

            //    Console.WriteLine("r2. idxEnd={0} > (s.Length - 1)={1}", idxEnd, s.Length - 1);

            //    //Console.WriteLine("r2. idxEnd={0} > s.Length={1}", idxEnd, s.Length);

            //    return string.Empty;

            //}

            else if (idxEnd <= idxStart)

            {

                Console.WriteLine("r3. idxEnd={0} <= idxStart={1}", idxEnd, idxStart);

                return string.Empty;

            }

            return s.Substring(idxStart, idxEnd - idxStart);

        }

​

​

    }

    public class Program

    {

        public static void Main(string[] args)

        {

            string test = "abcd";

            Console.WriteLine(test);

            Console.WriteLine("=================");

​

            Console.WriteLine(test.GetFirstStringBetweenStrings(null, null));

            Console.WriteLine(test.GetFirstStringBetweenStrings("", ""));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, test));

            Console.WriteLine(test.GetFirstStringBetweenStrings("", test));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test,""));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "d"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "e"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("e", "e"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("abc", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("abc", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("abc", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("abc", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("a","abc"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("b", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("c", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("d", "abc"));

​

            Console.WriteLine(); 

            test = "abcdabcd";

            Console.WriteLine(test);

            Console.WriteLine("=================");

​

            Console.WriteLine(test.GetFirstStringBetweenStrings(null, null));

            Console.WriteLine(test.GetFirstStringBetweenStrings("", ""));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, test));

            Console.WriteLine(test.GetFirstStringBetweenStrings("", test));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, ""));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "d"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "e"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("e", "e"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("ab", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("abc", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("abc", "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("abc", "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("abc", "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, "b"));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, "c"));

            Console.WriteLine(test.GetFirstStringBetweenStrings(test, "d"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("b", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("c", "abc"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("d", "abc"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("abc", "d")); //pass

​

​

            Console.WriteLine();

            test = "aaaa";

            Console.WriteLine(test);

            Console.WriteLine("=================");

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("aa", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("aaa", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("aaaa", "a"));

​

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "a"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "aa"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "aaa"));

            Console.WriteLine(test.GetFirstStringBetweenStrings("a", "aaaa"));

​

            Console.WriteLine();

            test = "aaaaaaaaaaaaaaaaaaaaaaaaaaaabbbb";

            Console.WriteLine(test);

            Console.WriteLine("=================");

            Console.WriteLine(test.GetFirstStringBetweenStrings("bbbb", "aaaa"));

            string result = string.Empty; 

            Stopwatch sw = new Stopwatch();

            sw.Start();

            result = test.GetFirstStringBetweenStringsCleanup("aaaaaaa", "bb");

            sw.Stop();

            Console.WriteLine(result);

            Console.WriteLine(" in " + sw.ElapsedTicks + " ticks."); 

        }

    }

}