using System;

namespace ConsoleApp1
{
    public class StringIndex
    {
        private const int NOT_FOUND = -1;
        private string _where;
        private string _what;
        private int _index;

        public StringIndex(string where, string what, int index = NOT_FOUND)
        {
            _index = index;
            _where = where;
            _what = what;
        }

        private int Validate(string name, int value)
        {
            if (value < 0) throw new Exception($"[{value}] cannot be negative!");
            return value;
        }

        public bool Found
        {
            get
            {
                return _index != NOT_FOUND;
            }
        }

        public string What
        {
            get
            {
                if (_index == NOT_FOUND) return string.Empty;
                return _where.Substring(_index, _what.Length);
            }
        }

        public string Before()
        {
            if (_index == NOT_FOUND) return string.Empty;
            return _where.Substring(0, _index);
        }

        public string After()
        {
            if (_index == NOT_FOUND) return string.Empty;
            var start = _what.Length + _index;
            if (start >= _where.Length) return string.Empty;
            return _where.Substring(start);
        }

        public string TakeBackward(int count, int skip = 0)
        {
            count = Validate("count", count);
            skip = Validate("skip", skip);
            if (count == 0 || _index == NOT_FOUND) return string.Empty;
            var start = _index - count - skip;
            if (start < 0) start = 0;
            count = _index - start - skip;
            if (count <= 0) return string.Empty;
            if (start + count >= _where.Length) count = _where.Length - start;
            return _where.Substring(start, count);
        }

        public string TakeForward(int count, int skip = 0)
        {
            count = Validate("count", count);
            skip = Validate("skip", skip);
            if (count == 0 || _index == NOT_FOUND) return string.Empty;
            var start = _index + _what.Length + skip;
            if (start >= _where.Length) return string.Empty;
            if (start + count >= _where.Length) count = _where.Length - start;
            return _where.Substring(start, count);
        }

        public static implicit operator bool(StringIndex obj) => obj.Found;
    }

    public class StringFinder
    {
        public static StringIndex Find(string where, string what, bool caseInsensitive = false)
        {
            if (string.IsNullOrEmpty(where) || string.IsNullOrEmpty(what)) return new StringIndex(string.Empty, string.Empty);
            int index;

            if (caseInsensitive)
            {
                index = where.IndexOf(what, StringComparison.CurrentCultureIgnoreCase);
            }
            else
            {
                index = where.IndexOf(what);
            }

            if (index == -1) return new StringIndex(where, what);
            return new StringIndex(where, what, index);
        }

        public static StringIndex Between(string where, string left, string right, bool caseInsensitive = false)
        {
            var first = Find(where, left, caseInsensitive);
            if (!first.Found) return first;

            var second = Find(first.After(), right, caseInsensitive);
            if (!second.Found) return first;

            return Find(where, left + second.Before() + right, caseInsensitive);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var txt = "The brown fox jumped over the lazy dog";
            var found = StringFinder.Find(txt, "FOX", caseInsensitive: true);

            if (found)
            {
                Console.WriteLine("->" + found.Before() + "<-");
                Console.WriteLine("->" + found.After() + "<-");
                Console.WriteLine("->" + found.TakeBackward(count: 5, skip: 1) + "<-");
                Console.WriteLine("->" + found.TakeForward(count: 6, skip: 1) + "<-");
                Console.WriteLine("->" + found.What + "<-");
            }
            else
            {
                Console.WriteLine("Not found!");
            }

            found = StringFinder.Between(txt, "brown", "jumped");
            Console.WriteLine("->" + found.Before() + "<-");
            Console.WriteLine("->" + found.After() + "<-");
            Console.WriteLine("->" + found.What + "<-");
        }
    }
}