using System;

using System.Collections.Generic;

using System.Data.SqlTypes;

using Microsoft.SqlServer.Server;

using System.Text;

using System.Linq;

​

[Serializable]

[Microsoft.SqlServer.Server.SqlUserDefinedAggregate(

    Format.UserDefined,

    IsInvariantToOrder = false, // order changes the result

    IsInvariantToNulls = false,  // nulls change the result

    IsInvariantToDuplicates = false, // duplicates change the result

    MaxByteSize = -1)]

public struct Concat : IBinarySerialize, INullable

{

    private StringBuilder _accumulator;

    private string _delimiter;

    private List<string> AccumulatorList;

    private int count;

​

    public void Init()

    {

        _accumulator = new StringBuilder();

        _delimiter = string.Empty;

        this.IsNull = true;

        AccumulatorList = new List<string>();

        count = 0;

    }

​

    public void Accumulate(SqlString Value, SqlString Delimiter)

    {

        if (Delimiter.IsNull == false && Delimiter.Value.Length > 0)

        {

            _delimiter = Delimiter.Value; /// save for Merge

        }

        //

        if (Value.IsNull == false)

        {

            AccumulatorList.Add(Value.Value);

            this.IsNull = false;

        }

    }

​

    public void Merge(Concat Group)

    {

        //if (_accumulator.Length > 0 & Group._accumulator.Length > 0)

        //    _accumulator.Append(_delimiter);

        //_accumulator.Append(Group._accumulator.ToString());

​

        if (Group.AccumulatorList != null)

        {

            AccumulatorList.AddRange(Group.AccumulatorList);

        }

    }

​

    public SqlString Terminate()

    {

        //return IsNull ? SqlString.Null : new SqlString(_accumulator.ToString()); //Old logic

        //AccumulatorList.Sort()

        return IsNull ? SqlString.Null : new SqlString(string.Join(_delimiter, AccumulatorList.Distinct())); // New logic

    }

​

    void IBinarySerialize.Read(System.IO.BinaryReader r)

    {

        IsNull = r.ReadBoolean();

        _delimiter = r.ReadString();

        //_accumulator = new StringBuilder(r.ReadString());

        AccumulatorList = new List<string>();

        AccumulatorList.Add(r.ReadString().Trim());

        if (AccumulatorList.Count != 0)

            this.IsNull = false;

    }

​

    void IBinarySerialize.Write(System.IO.BinaryWriter w)

    {

        w.Write(IsNull);

        w.Write(_delimiter);

        //w.Write(_accumulator.ToString()); // old logic

        w.Write(string.Join(_delimiter, AccumulatorList.Distinct())); //new logic

    }

​

    public Boolean IsNull { get; private set; }

}