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

    private static string _allNumbersCheckRegex = @"^([0-9])+$";

    private static string _repeatedDigitsRegex = @"(\d)\1{2}";

    private static string _spaceCharacterString = " ";

​

    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()

    {

        List<string> engineList = new List<string> { "3UR3229008", "5477", "550", "55593", "5700", "5780", "6", "63136", "65578", "68616", "69325", "69935", "7785", "86111", "8831", "88620", "90015", "BIL", "BNIU", "BU", "BUK", "BUL", "INL", "JNI", "L400", "MI", "MIL", "MIT", "ML", "MNI", "MNO", "MO", "MOI", "MONE", "N", "N0NE", "N1", "n123", "N22A2", "NA", "NA18", "NA7", "NAIL", "NC", "NEL", "NENO", "NI", "nii", "NIIL", "NIKL", "NIL", "NIL,", "nile", "NILK", "NILL", "NILLL", "NILS", "NIN", "NINE", "NIOL", "NIONE", "NK", "NL", "NLI", "nll", "NNIL", "NNOE", "NO", "NOE", "NOEL", "NOEN", "NOL", "NOL.", "NOLE", "NOME", "NON", "NONE", "NONE.", "NONE4", "NONEL", "NONI", "NONL", "NONO", "NONOE", "NONR", "NOT", "NU", "NUL", "NULL", "ONE", "ONO", "ONOE", "ONOE3", "SRT8", "TB48", "V8", "X", "XX", "XXX", "XXXXX" };

        foreach (string engineNumber in engineList)

        {

            bool? isGcc = GetVehicleGccSpecOrNot(engineNumber);

            Console.WriteLine("Engine number " + engineNumber + (!isGcc.HasValue ? "Not decided" : (isGcc.Value ? " is GCC " : " is Non-Gcc")));

        }

    }

​

    public static bool? GetVehicleGccSpecOrNot(string engineNumber)

    {

        bool? isGccSpec = null;

​

        bool hasValidEngineNumber = !string.IsNullOrEmpty(engineNumber);

        bool existsInInvalidEngineNumber = false;

        if (hasValidEngineNumber)

        {

            engineNumber = engineNumber.Replace(_spaceCharacterString, string.Empty);

            existsInInvalidEngineNumber = EngineNumberExistInBlockList(engineNumber.ToLower());

​

            if (!existsInInvalidEngineNumber)

            {

                hasValidEngineNumber = ValidateEngineNumber(engineNumber);

            }

        }

        isGccSpec = hasValidEngineNumber && !existsInInvalidEngineNumber;

        if (isGccSpec == true)

            return null; // If it is GCC, in UI, we need to show dropdown

​

        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

        //It is now Configurable so we can append any special character needed

        var alphanumericRegex = _alphanumericRegex;

​

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

​

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

        {

            var onlyNumberRegex = _allNumbersCheckRegex; //All numbers

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

            if (onlyNumberMatch.Success)// All Numeric

            {

                if (engineNumber.Length < _minNumericEngineNumberLength)

                {

                    return false;

                }

​

                var repeatedRegex = _repeatedDigitsRegex; //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) //Regular Sequence

            {

                return true;

            }

            else if (arr[i - 1] == arr[i] + 1 && arr[i - 2] == arr[i] + 2) //Reversed Sequence

            {

                return true;

            }

        }

        return false;

    }

}