namespace POP3Client
{
    using System.IO ;
    using System.Net;
    using System.Net.Sockets ;
    //Please note that all code is copyright 2002 by William J Dean
    public class POP3client
    {
        public enum connect_state {disc,AUTHORIZATION,TRANSACTION,UPDATE};

        public string user;
        public string pwd;
        public string pop;
        public bool error;
        public connect_state state=connect_state.disc ;

        //borrowed from Agus Kurniawan's article:"Retrieve Mail From a POP3 Server Using C#"  at http://www.codeproject.com/csharp/popapp.asp 
        private TcpClient Server;
        private NetworkStream NetStrm;
        private StreamReader  RdStrm;
        private string Data;
        private byte[] szData;
        private string CRLF = "\r\n";    

        public POP3client()
        {
            //nothing to do..just create to object    
        }

        public POP3client(string pop_server,string user_name,string password)
        {
            //put the specied server (pop_server), user (user_name) and password (password)
            //into the appropriate properties.
            pop=pop_server;
            user=user_name;
            pwd=password;
        }

        #region Utility Methods, some public, some private
        public string connect (string pop_server)
        {
            pop=pop_server;    //put the specified server into the pop property
            return(connect()); //call the connect method
        }
        public string connect()
        {
            //Initialize to the pop server.  This code snipped "borrowed"
            //with some modifications...
            //from the article "Retrieve Mail From a POP3 Server Using C#" at
            //www.codeproject.com by Agus Kurniawan
            //http://www.codeproject.com/csharp/popapp.asp

            // create server with port 110
            Server = new TcpClient(pop,110);                                
        
            try
            {
                // initialization
                NetStrm = Server.GetStream();
                RdStrm= new StreamReader(Server.GetStream());

                //The pop session is now in the AUTHORIZATION state
                state=connect_state.AUTHORIZATION ;
                return(RdStrm.ReadLine ());
            }            
            catch(InvalidOperationException err)
            {
                return("Error: "+err.ToString());
            }

        }
        private string disconnect ()
        {
            string temp="disconnected successfully.";
            if(state !=connect_state.disc)
            {

                //close connection
                NetStrm.Close();
                RdStrm.Close();
                state=connect_state.disc ;
            }
            else
            {
                temp="Not Connected.";
            }
            return(temp);
        }

        private void issue_command(string command)
        {
            //send the command to the pop server.  This code snipped "borrowed"
            //with some modifications...
            //from the article "Retrieve Mail From a POP3 Server Using C#" at
            //www.codeproject.com by Agus Kurniawan
            //http://www.codeproject.com/csharp/popapp.asp
            Data= command + CRLF;
            szData = System.Text.Encoding.ASCII.GetBytes(Data.ToCharArray());
            NetStrm.Write(szData,0,szData.Length);

        }
        private string read_single_line_response()
        {
            //read the response of the pop server.  This code snipped "borrowed"
            //with some modifications...
            //from the article "Retrieve Mail From a POP3 Server Using C#" at
            //www.codeproject.com by Agus Kurniawan
            //http://www.codeproject.com/csharp/popapp.asp
            string temp;
            try
            {
                temp = RdStrm.ReadLine();
                was_pop_error(temp);                
                return(temp);
            }
            catch(InvalidOperationException err)
            {
                return("Error in read_single_line_response(): " + err.ToString ()) ;
            }

        }
        private string read_multi_line_response()
        {
            //read the response of the pop server.  This code snipped "borrowed"
            //with some modifications...
            //from the article "Retrieve Mail From a POP3 Server Using C#" at
            //www.codeproject.com by Agus Kurniawan
            //http://www.codeproject.com/csharp/popapp.asp
            string temp="";
            string szTemp;

            try
            {
                szTemp = RdStrm.ReadLine();
                was_pop_error(szTemp);                
                if(!error) 
                {
                
                    while(szTemp!=".")
                    {
                        temp += szTemp+CRLF;
                        szTemp = RdStrm.ReadLine();
                    }
                }
                else
                {
                    temp=szTemp;
                }
                return(temp);
            }
            catch(InvalidOperationException err)
            {
                return("Error in read_multi_line_response(): " + err.ToString ());
            }
        }
        private void was_pop_error(string response)
        {
            //detect if the pop server that issued the response believes that
            //an error has occured.

            if(response.StartsWith ("-"))
            {
                //if the first character of the response is "-" then the 
                //pop server has encountered an error executing the last 
                //command send by the client
                error=true;
            }
            else
            {
                //success
                error=false;
            }
        }
        #endregion
        #region POP commands
        public string DELE(int msg_number)
        {
            string temp;
            
            if (state != connect_state.TRANSACTION )
            {
                //DELE is only valid when the pop session is in the TRANSACTION STATE
                temp="Connection state not = TRANSACTION";
            }
            else
            {
                issue_command("DELE " + msg_number.ToString ());
                temp=read_single_line_response();            
            }
            return(temp);
        }

        public string LIST()
        {
            string temp="";
            if (state != connect_state.TRANSACTION )
            {
                //the pop command LIST is only valid in the TRANSACTION state
                temp="Connection state not = TRANSACTION";
            }
            else
            {
                issue_command ("LIST");
                temp=read_multi_line_response();
            }
            return(temp);            
        }

        public string LIST(int msg_number)
        {
            string temp="";

            if (state != connect_state.TRANSACTION )
            {
                //the pop command LIST is only valid in the TRANSACTION state
                temp="Connection state not = TRANSACTION";
            }
            else
            {
                issue_command ("LIST " + msg_number.ToString ());
                temp=read_single_line_response();  //when the message number is supplied, expect a single line response
            }
            return(temp);

        }

        public string NOOP()
        {
            string temp;
            if (state != connect_state.TRANSACTION )
            {
                //the pop command NOOP is only valid in the TRANSACTION state
                temp="Connection state not = TRANSACTION";
            }
            else
            {
                issue_command ("NOOP");
                temp=read_single_line_response();

            }
            return(temp);

        }
        public string PASS()
        {
            string temp;
            if (state != connect_state.AUTHORIZATION) 
            {
                //the pop command PASS is only valid in the AUTHORIZATION state
                temp="Connection state not = AUTHORIZATION";
            }
            else
            {
                if (pwd !=null)
                {
                    issue_command ("PASS " + pwd);
                    temp=read_single_line_response();

                    if (!error)
                    {
                        //transition to the Transaction state
                        state=connect_state.TRANSACTION;
                    }
                }
                else
                {
                    temp="No Password set.";
                }
            }
            return(temp);
        }
        public string PASS(string password)
        {
            pwd=password;   //put the supplied password into the appropriate property
            return(PASS()); //call PASS() with no arguement
        }

        public string QUIT()
        {
            //QUIT is valid in all pop states

            string temp;
            if (state !=connect_state.disc)
            {
                issue_command ("QUIT");
                temp=read_single_line_response();
                temp += CRLF + disconnect();
    
            }
            else
            {
                temp="Not Connected.";
            }
            return(temp);

        }
        public string RETR (int msg)
        {
            string temp="";
            if (state != connect_state.TRANSACTION )
            {
                //the pop command RETR is only valid in the TRANSACTION state
                temp="Connection state not = TRANSACTION";
            }
            else
            {
                // retrieve mail with number mail parameter
                issue_command ("RETR "+ msg.ToString ());
                temp=read_multi_line_response();
            }
            return(temp);

        }

        public string RSET()
        {
            string temp;
            if (state != connect_state.TRANSACTION )
            {
                //the pop command STAT is only valid in the TRANSACTION state
                temp="Connection state not = TRANSACTION";
            }
            else
            {
                issue_command("RSET");
                temp=read_single_line_response();
            }
            return(temp);

        }

        public string STAT()
        {
            string temp;
            if (state==connect_state.TRANSACTION)
            {
                issue_command("STAT");
                temp=read_single_line_response();

                return(temp);
            }
            else

            {
                //the pop command STAT is only valid in the TRANSACTION state
                return ("Connection state not = TRANSACTION");
            }
        }        

        public string USER()
        {
            string temp;
            if (state != connect_state.AUTHORIZATION) 
            {
                //the pop command USER is only valid in the AUTHORIZATION state
                temp="Connection state not = AUTHORIZATION";
            }
            else
            {
                if (user !=null)
                {   
                    issue_command("USER "+ user);
                    temp=read_single_line_response();
                }
                else
                {   //no user has been specified
                    temp="No User specified.";
                }
            }
            return(temp);
        }

        public string USER(string user_name)
        {
            user=user_name;  //put the user name in the appropriate propertity
            return(USER());  //call USER with no arguements
        }
        #endregion
    }

}