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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."); 
           
        }
    }
}

            //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
 
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);