using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var input = "Apple (Orange & Chai) Ten";

        var result1 = GenRegexp(ref input);

        Console.WriteLine("Gen Regexp = " + result1);

        //var result2 = ProcessRegexp("A & B & C");

        //Console.WriteLine("Process Regexp = " + result2);

    }

    public static string GenRegexp(ref string keyword) {

        var regexp = "";

        var word = "";

        if (string.IsNullOrEmpty(keyword)) { return ""; }

        while (keyword.Length > 0) {

            var k = keyword.Substring(0, 1);

            switch (k) {

                case "(":

                    keyword = keyword.Substring(1);

                    word += GenRegexp(ref keyword);

                    break;

                case ")":

                    keyword = keyword.Substring(1);

                    Console.WriteLine("Word = " + word);

                    regexp = ProcessRegexp(word);

                    Console.WriteLine("Regexp = " + regexp);

                    return regexp;

                default:

                    word += k;

                    keyword = keyword.Substring(1);

                    break;

            }

        }

        return "^(" + ProcessRegexp(word) + ").*$";

    }

​

​

    public static string ProcessRegexp(string word) {

        if (string.IsNullOrEmpty(word)) { return ""; }

        var regexp = "";

        var and = word.IndexOf('&');

        if (and >= 0) {

            var words = word.Split('&');

            foreach (var w in words) {

                Console.WriteLine("Wordy = " + w);

                var r = ProcessRegexp(w.Trim());

                if (r.Trim().StartsWith("(?=", StringComparison.Ordinal)) {

                    regexp += r.Trim();

                } else {

                    regexp += "(?=.*" + r.Trim() + ")";

                }

            }

            return regexp;

        }

        var or = word.IndexOf('^');

        if (or >= 0) {

            var words = word.Split('^');

            foreach (var w in words) {

                Console.WriteLine("Words = " + w);

                var r = ProcessRegexp(w.Trim());

                if (r.Trim().StartsWith("(?=", StringComparison.Ordinal)) {

                    regexp += r.Trim() + "|";

                } else {

                    regexp += "(?=.*" + r.Trim() + ")|";

                }

                //regexp += ProcessRegexp(w.Trim()) + "|";  

            }

            regexp = regexp.TrimEnd('|');

            return regexp;

        }

        var matches = Regex.Matches(word.Trim(), "\"[^\"]*\"");

        if (matches.Count > 0) {

            foreach (Match ma in matches) {

                Console.WriteLine("Match = " + ma.Value);

                var reg = ma.Value.Substring(1, ma.Length - 2);

                regexp += "(?=.*(" + reg + "))|";

            }

            var wo = Regex.Replace(word.Trim(), "\"[^\"]*\"", "");

            regexp += ProcessRegexp(wo.Trim());

            return regexp.TrimEnd('|');

        }

        var sp = word.Trim().IndexOf(' ');

        if (sp >= 0) {

            var words = word.Trim().Split(' ');

            foreach (var w in words) {

                Console.WriteLine("Worder = " + w);

                var r = ProcessRegexp(w.Trim());

                if (r.Trim().StartsWith("(?=", StringComparison.Ordinal)) {

                    regexp += r.Trim() + "|";

                } else {

                    regexp += "(?=.*" + r.Trim() + ")" + "|";

                }

            }

            regexp = regexp.TrimEnd('|');

            return regexp;

        }

        if (word.Trim().StartsWith("(?=", StringComparison.Ordinal)) {

            return word.Trim();

        } else {

            return "(?=.*" + word.Trim() + ")";

        }

    }

}