POP3 (RFC 1939) & MIME (RFC 2045) Compliant Client

/*
Copyright (c) 2007, Robert Wallstrm, smithimage.com
All rights reserved.
 
Redistribution and use in source and binary forms, with or without modification, 
are permitted provided that the following conditions are met:
	
	* Redistributions of source code must retain the above copyright notice, 
		this list of conditions and the following disclaimer. 
	* Redistributions in binary form must reproduce the above copyright notice, 
		this list of conditions and the following disclaimer in the documentation and/or 
		other materials provided with the distribution. 
	* Neither the name of the SMITHIMAGE nor the names of its contributors may be used to 
		endorse or promote products derived from this software 
		without specific prior written permission. 

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR 
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY 
AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR 
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DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
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*/

using System;
using System.Collections.Generic;
using System.Text;

namespace Popper
{
    /// <summary>
    /// This is the DP-state representation of the RFC 1939 Authorization state.
    /// </summary>
    public class AuthorizationState:POPState
    {
        private static AuthorizationState s_State = null;

        /// <summary>
        /// Returns teh singleton instance of this state.
        /// </summary>
        /// <returns>A Authorization state.</returns>
        public static AuthorizationState GetInstance()
        {
            if (s_State == null)
                s_State = new AuthorizationState();
            return s_State;
        }

        /// <summary>
        /// Issues a command on the context.
        /// </summary>
        /// <param name="command">The command to issue.</param>
        /// <param name="context">The context onto which the command shall be issued.</param>
        /// <returns>True if the command was issued successfully.</returns>
        public override bool IssueCommand(Popper.RFC1939.POPCommand command, POPClient context)
        {
            if (IsLegalCommand(command))
            {
                if (command is RFC1939.ConnectCommand)
                {
                    if (command.Execute())
                    {
                        context.LoggCommand(command);                        
                        context.CurrentState = TransactionState.GetInstance();
                        return true;
                    }
                    context.LoggCommand(command);
                }
                else if (command is RFC1939.UserCommand)
                {
                    if (command.Execute())
                    {
                        context.LoggCommand(command);
                        return true; // user also need to supply pass, before we change state.
                    }
                    context.LoggCommand(command);
                }
                else if (command is RFC1939.PassCommand)
                {
                    if (command.Execute())
                    {
                        context.LoggCommand(command);
                        context.CurrentState = TransactionState.GetInstance();
                        return true;
                    }
                    context.LoggCommand(command);
                }
                else if (command is RFC1939.QuitCommand)
                {
                    if (command.Execute())
                    {
                        context.LoggCommand(command);
                        context.CurrentState = DisconnectedState.GetInstane();
                        return true;
                    }
                    context.LoggCommand(command);
                }
            }
            return false;
        }

        /// <summary>
        /// Determines if this command legaly can be issued in this state.
        /// </summary>
        /// <param name="command">The command to evaluate.</param>
        /// <returns>Tru if command can legaly be issued.</returns>
        public override bool IsLegalCommand(Popper.RFC1939.POPCommand command)
        {
            if (command is RFC1939.DeleteCommand)
                return false;
            if (command is RFC1939.ListCommand)
                return false;
            if (command is RFC1939.NoopCommand)
                return false;            
            if (command is RFC1939.ResetCommand)
                return false;
            if (command is RFC1939.RetriveCommand)
                return false;
            if (command is RFC1939.StatCommand)
                return false;
            if (command is RFC1939.TopCommand)
                return false;
            if (command is RFC1939.UIDLCommand)
                return false;

            return true;
        }

        /// <summary>
        /// Returns a string representation of this state.
        /// </summary>
        /// <returns>The string 'AUTHORIZATION'</returns>
        public override string ToString()
        {
            return "AUTHORIZATION";
        }
    }
}