/**************************************************************************************
 This script relates to the following SQL Server Central forum thread:
 Simple CLR request ( http://www.sqlservercentral.com/Forums/Topic1795321-3412-1.aspx )
 
 Written by: Solomon Rutzky
 On: 2016-06-26
 
 This script is located at:   http://pastebin.com/Rd4G7T3B
***************************************************************************************/

using System; // Array, Object
using System.Collections; // IEnumerable
using System.Data.SqlTypes; // SqlChars, SqlInt32
using Microsoft.SqlServer.Server; // SqlFacet

public class NGrams
{
    [Microsoft.SqlServer.Server.SqlFunction(FillRowMethodName = "NGramSolomon_FillRow",
                                            TableDefinition = "Position INT, Token NVARCHAR(4000)")]
    public static IEnumerable NGramSolomon([SqlFacet(MaxSize = 4000)] SqlChars InputString, SqlInt32 TokenSize)
    {
        if (InputString.IsNull || TokenSize.IsNull)
        {
            yield break;
        }

        int _Take = TokenSize.Value;
        int _Limit = ((int)InputString.Length - _Take);

        if (_Take < 1 || _Limit < 0)
        {
            yield break;
        }

        ResultRow _Result = new ResultRow();

        char[] _Chars = InputString.Value;
        char[] _Temp = new char[_Take];

        for (int _Index = 0; _Index <= _Limit; _Index++)
        {
            Array.Copy(_Chars, _Index, _Temp, 0, _Take);

            _Result.Position = (_Index + 1);
            _Result.Token = new SqlChars(_Temp);

            yield return _Result;
        }
    }

    public class ResultRow
    {
        public int Position;
        public SqlChars Token;
    }

    public static void NGramSolomon_FillRow(Object obj, out SqlInt32 position, out SqlChars token)
    {
        ResultRow _Item = (ResultRow)obj;
        position = new SqlInt32(_Item.Position);
        token = _Item.Token;
    }
}