using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.RegularExpressions;

public class Program

{

    private static int _minNumericEngineNumberLength = 4;

    private static int _minAlphaNumericEngineNumberLength = 5;

    private static int _minPartialMatchEngineNumberLength = 3;

    private static List<string> _emptyEngineNumberList = new List<string> {"ONOE","NULL","NONR","NONL","NONI","NONEL","NON","NOEN","NO","NLI","NILL","NIL,","NI","N1","N","MOI","0","x","silver","-","????","?????","//","NIIL","NILE","1","2","4","5","6",".","20L4","BIL","BNIU","BU","BUK","BUL","INL","JNI","L400","MI","MIL","MIT","ML","MNI","MNO","MO","MOI","MONE","N","N0NE","none","N1","n123","N22A2","NA","NA18","NA7","NEL","NENO","NI","nii","NIKL","nil","NIL,","NILK","nill","NILLL","NIN","NINE","NIOL","NIONE","NK","NL","NLI","NLL","NNIL","NNOE","NO","NOE","NOEL","NOEN","NOL","NOL.","NOLE","NOME","NON","NONE","NONE.","NONEL","NONI","NONL","NONO","NONOE","NONR","NOT","NUL","NULL","ONE","ONO","ONOE","ONOE3","SRT8","TB48","V8","X","XX","XXX","XXXX","XXXXX","XXXXXX","XXXXXXX","XXXXXXXX","XXXXXXXXX","XXXXXXXXXX","NILL"};

​

    public static void Main()

    {

        string engineNumber = "ARUN";

        Console.WriteLine("Engine number = " + engineNumber + " is GCC "+ GetVehicleGccSpecOrNot(engineNumber));

    }

    public static bool? GetVehicleGccSpecOrNot(string engineNumber)

    {

        bool? isGccSpec = null;

        bool hasValidEngineNumber = !string.IsNullOrEmpty(engineNumber);

        bool existsInInvalidEngineNumber = false;

        if (hasValidEngineNumber)

        {

            existsInInvalidEngineNumber = EngineNumberExistInBlockList(engineNumber);

​

            if (!existsInInvalidEngineNumber)

            {

                hasValidEngineNumber = ValidateEngineNumber(engineNumber);

            }

        }

        isGccSpec = hasValidEngineNumber && !existsInInvalidEngineNumber;

        return isGccSpec;

    }

    private static bool EngineNumberExistInBlockList(string engineNumber)

    {

        foreach (string blockedItem in _emptyEngineNumberList)

        {

            if (blockedItem.Length < _minPartialMatchEngineNumberLength) //If blocked item length is less than _minPartialMatchLength then we check the exact match

            {

                if (engineNumber == blockedItem)

                {

                    return true;

                }

            }

            else if (engineNumber.Contains(blockedItem))

            {

                return true;

            }

        }

        return false;

    }

    private static bool ValidateEngineNumber(string engineNumber)

    {

        //Alphanumeric and not all engine number is alphabets 

        //the only accepted special character is '-' in the regex

        var regex = @"^([a-zA-Z0-9-])*([0-9])+([a-zA-Z0-9-])*$";

​

        Match match = Regex.Match(engineNumber, regex, RegexOptions.IgnoreCase);

​

        if (!string.IsNullOrEmpty(engineNumber) && match.Success)

        {

            var onlyNumberRegex = "^([0-9])+$"; //All numbers

            Match onlyNumberMatch = Regex.Match(engineNumber, onlyNumberRegex, RegexOptions.IgnoreCase);

            if (onlyNumberMatch.Success)// All Numeric

            {

                if (engineNumber.Length < _minNumericEngineNumberLength)

                {

                    return false;

                }

​

                var repeatedRegex = @"(\d)\1{2}"; //digit repeated 3 times in the string

                Match repeatedRegexMatch = Regex.Match(engineNumber, repeatedRegex, RegexOptions.IgnoreCase);

                if (repeatedRegexMatch.Success)

                {

                    return false;

                }

                else

                {

                    //Check if it has Sequence digits

                    return !IsEngineNumberInSequence(engineNumber);

                }

            }

            else //Alphanumeric

            {

                if (engineNumber.Length < _minAlphaNumericEngineNumberLength)

                {

                    return false;

                }

                return true;

            }

        }

        return false;

​

    }

​

    //Has At Least 3 sequence digits

    private static bool IsEngineNumberInSequence(string sequence)

    {

        int[] arr = sequence.Select(character => Convert.ToInt32(character.ToString())).ToArray();

        for (int i = 2; i < arr.Length; i++)

        {

            if (arr[i - 1] == arr[i] - 1 && arr[i - 2] == arr[i] - 2)

            {

                return true;

            }

        }

        return false;

    }

}