using System;
using System.Runtime.InteropServices;
using System.Text;

namespace AddEditDeleteDataGridView
{
	/// <summary>
	/// Summary description for SQLInfoEnumerator.
	/// This class Enumerates a network for SQL Server instances and returns a list.
	/// For a given SQL Server instance a list of all available databases is returned
	/// For more information see
	/// http://msdn.microsoft.com/library/default.asp?url=/library/en-us/odbc/htm/odbcsqlbrowseconnect.asp
	/// http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dncscol/html/csharp09192002.asp
	/// 
	/// </summary>
	public class SQLInfoEnumerator
	{
		#region ODBC32 external function definitions
		[DllImport("odbc32.dll")]private static extern short SQLAllocHandle( short handleType, IntPtr inputHandle, out IntPtr outputHandlePtr );
		[DllImport("odbc32.dll")]private static extern short SQLSetEnvAttr( IntPtr environmentHandle, int attribute, IntPtr valuePtr, int stringLength );
		[DllImport("odbc32.dll")]private static extern short SQLFreeHandle( short hType, IntPtr Handle );
		[DllImport("odbc32.dll",CharSet=CharSet.Ansi)]private static extern short SQLBrowseConnect( IntPtr handleConnection, StringBuilder inConnection, short stringLength, StringBuilder outConnection, short bufferLength, out short stringLength2Ptr );
		#endregion
		#region Constants
		private const string SQL_DRIVER_STR = "DRIVER=SQL SERVER";
		private const short SQL_SUCCESS = 0;
		private const short SQL_HANDLE_ENV = 1;
		private const short SQL_HANDLE_DBC = 2;
		private const int SQL_ATTR_ODBC_VERSION = 200;
		private const int SQL_OV_ODBC3 = 3;
		private const short SQL_NEED_DATA = 99;
		private const short DEFAULT_RESULT_SIZE = 1024;
		private const string START_STR ="{";
		private const string END_STR ="}";
		#endregion
		
		/// <summary>
		/// A string to hold the selected SQL Server
		/// </summary>
		string m_SQLServer;
		/// <summary>
		/// A string to hold the username
		/// </summary>
		string m_Username;
		/// <summary>
		/// A string to hold the password
		/// </summary>
		string m_Password;
		/// <summary>
		/// Property to set the SQL Server instance
		/// </summary>
		public string SQLServer
		{
			set{m_SQLServer=value;}
		}
		/// <summary>
		/// Property to set the Username
		/// </summary>
		public string Username
		{
			set{m_Username=value;}
		}
		/// <summary>
		/// Property to set the Password
		/// </summary>
		public string Password
		{
			set{m_Password=value;}
		}
		
		/// <summary>
		/// Enumerate the SQL Servers returning a list (if any exist)
		/// </summary>
		/// <returns></returns>
		public string[] EnumerateSQLServers()
		{
			return RetrieveInformation(SQL_DRIVER_STR);
		}
		/// <summary>
		/// Enumerate the specified SQL server returning a list of databases (if any exist)
		/// </summary>
		/// <returns></returns>
		public string[] EnumerateSQLServersDatabases()
		{
			return RetrieveInformation(SQL_DRIVER_STR+";SERVER="+ m_SQLServer+";UID=" + m_Username +";PWD=" +m_Password);
		}

		/// <summary>
		/// Enumerate for SQLServer/Databases based on the passed information it the string
		/// The more information provided to SQLBrowseConnect the more granular it gets so
		/// if only DRIVER=SQL SERVER passed then a list of all SQL Servers is returned
		/// If DRIVER=SQL SERVER;Server=ServerName is passed then a list of all Databases on the
		/// servers is returned etc
		/// </summary>
		/// <param name="InputParam">A valid string to query for</param>
		/// <returns></returns>
		private string[] RetrieveInformation(string InputParam)
		{
			IntPtr m_environmentHandle=IntPtr.Zero;
			IntPtr m_connectionHandle = IntPtr.Zero;
			StringBuilder inConnection = new StringBuilder(InputParam);
			short stringLength= (short)inConnection.Length;
			StringBuilder outConnection = new StringBuilder(DEFAULT_RESULT_SIZE);
			short stringLength2Ptr= 0;
				
			try
			{	
				if (SQL_SUCCESS == SQLAllocHandle(SQL_HANDLE_ENV, m_environmentHandle, out m_environmentHandle))
				{
					if (SQL_SUCCESS == SQLSetEnvAttr(m_environmentHandle,SQL_ATTR_ODBC_VERSION,(IntPtr)SQL_OV_ODBC3,0))
					{
						if (SQL_SUCCESS == SQLAllocHandle(SQL_HANDLE_DBC, m_environmentHandle, out m_connectionHandle))
						{
							if (SQL_NEED_DATA == SQLBrowseConnect(m_connectionHandle, inConnection, stringLength, outConnection, DEFAULT_RESULT_SIZE, out stringLength2Ptr))
							{
								if (SQL_NEED_DATA != SQLBrowseConnect(m_connectionHandle, inConnection, stringLength, outConnection, DEFAULT_RESULT_SIZE, out stringLength2Ptr))
								{
									throw new ApplicationException("No Data Returned.");
								}
							}
						}	
					}
				}
			}
						
			catch (Exception ex)
			{			
				throw new ApplicationException("Cannot Locate SQL Server."+ex.Message );
			}
			finally
			{
				FreeConnection(m_connectionHandle);
				FreeConnection(m_environmentHandle);
			}
			if (outConnection.ToString()!="")
			{return ParseSQLOutConnection(outConnection.ToString());}
			else{return null;}
			
			
		}
		/// <summary>
		/// Parse an outConnection string returned from SQLBrowseConnect
		/// </summary>
		/// <param name="outConnection">string to parse</param>
		/// <returns></returns>
		private string[] ParseSQLOutConnection(string outConnection)
		{
			int m_Start = outConnection.IndexOf(START_STR) + 1;
			int m_lenString = outConnection.IndexOf(END_STR) - m_Start;            
            if ((m_Start > 0) && (m_lenString > 0))
            {
                outConnection = outConnection.Substring(m_Start, m_lenString);
            }
            else
            {
                // outConnection = string.Empty;
                outConnection = outConnection.Substring(m_Start);
            }
			return outConnection.Split(",".ToCharArray());
		}
		private void FreeConnection(IntPtr handleToFree)
		{
				if(handleToFree!= IntPtr.Zero)
						SQLFreeHandle(SQL_HANDLE_DBC,handleToFree);
		}
		
	}
}