testing/QueryParser.cs

using System.Collections.Generic;
using System.IO;
using System.Linq;
namespace TestConsoleApp
{
    public class QueryParser
    {

        public List<string> Parse()
        {
            var totalQuery = File.ReadAllText(@"D:\testquery.txt");
            return _Parse(totalQuery);

        }
        List<string> _Parse(string actualQuery)
        {
            string columnString = GetColumnString(actualQuery);
            List<string> resultColumnlist = new List<string>();
            var commaSeperatedArray = columnString.Split(',');

            for (int i = 0; i < commaSeperatedArray.Length; i++)
            {
                var column = commaSeperatedArray[i];
                if (IsPredefinedFunction(column))
                {
                    if (!IsPerfectPredefinedFunction(column))
                    {
                        column = MakeItPerfect(ref i, commaSeperatedArray, commaSeperatedArray[i]);
                    }
                    resultColumnlist.Add(column);
                }
                else
                {
                    resultColumnlist.Add(column);
                }
            }
            return resultColumnlist;
        }

        string GetColumnString(string actualQuery)
        {
            actualQuery = actualQuery.Replace(System.Environment.NewLine, " ");
            var fromidex = actualQuery.ToLower().LastIndexOf("from ");
            var splitted = actualQuery.Substring(0, fromidex);
            splitted = splitted.TrimStart().Remove(0, "select".Length);
            return splitted;
        }
        bool IsPredefinedFunction(string name)
        {
            var _name = name.ToLower();
            bool result = false;
            foreach (var function in PredefinedFunctions())
            {
                if (_name.Contains(function.ToLower()))
                {
                    result = true;
                    break;
                }
            }
            return result;
        }
        string[] PredefinedFunctions()
        {
            return new string[] {
            "coalesce","concat","select","min","max","count"
            };
        }
        bool IsPerfectPredefinedFunction(string name)
        {
            var opencount = name.Count(c => c == '(');
            var closecount = name.Count(c => c == ')');
            return opencount == closecount;
        }
        string MakeItPerfect(ref int index, string[] colArray, string columnName)
        {
            index = index + 1;
            var column = columnName + "," + colArray[index];
            if (!IsPerfectPredefinedFunction(column))
            {
                column = MakeItPerfect(ref index, colArray, column);
            }

            return column;
        }

       
    }
}