// This file is part of SNMP#NET.
// 
// SNMP#NET is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
// 
// SNMP#NET is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
// 
// You should have received a copy of the GNU General Public License
// along with SNMP#NET.  If not, see <http://www.gnu.org/licenses/>.
// 

using System;
using System.Net;
using System.Net.Sockets;
using System.Diagnostics;

namespace SnmpSharpNet
{
	/// <summary>
	/// Callback used to pass result of an async SNMP operation back to the caller.
	/// </summary>
	/// <param name="result">Result code of the operation.</param>
	/// <param name="packet">SNMP packet received</param>
	public delegate void SnmpAsyncResponse(AsyncRequestResult result, SnmpPacket packet);


	/// <summary>Transport class for IPv4 using UDP</summary>
	/// <remarks>
	/// InternetProtocol version 4 User Datagram Protocol (IP/UDP) transport protocol
	/// implementation for use with SNMP versions 1, 2 and 3.
	/// </remarks>
	public class UdpTarget: UdpTransport, IDisposable
	{
		/// <summary>
		/// SNMP request target host IP address
		/// </summary>
		protected IPAddress _address;
		/// <summary>
		/// Maximum number of retries. Value of 0 (zero) will result in a single request without
		/// retries.
		/// </summary>
		protected int _retry;
		/// <summary>
		/// SNMP target UDP port number
		/// </summary>
		protected int _port;
		/// <summary>
		/// SNMP request timeout value in milliseconds
		/// </summary>
		protected int _timeout;
		/// <summary>
		/// Get/Set Udp agent IP address
		/// </summary>
		public System.Net.IPAddress Address
		{
			get { return _address; }
			set { 
				_address = value;
				if (_address.AddressFamily == AddressFamily.InterNetworkV6 && !base.IsIPv6)
					base.initSocket(true);
				else if (_address.AddressFamily == AddressFamily.InterNetwork && base.IsIPv6)
					base.initSocket(false);
			}
		}
		/// <summary>
		/// Get/Set Udp agent port number
		/// </summary>
		public int Port
		{
			get { return _port; }
			set { _port = value; }
		}
		/// <summary>
		/// Get/Set Udp agent timeout value in milliseconds
		/// </summary>
		public int Timeout
		{
			get { return _timeout; }
			set { _timeout = value; }
		}
		/// <summary>
		/// Get/Set Udp agent maximum retry value. Value of 0 (zero) will result in a single request
		/// being sent without further retry attempts.
		/// </summary>
		public int Retry
		{
			get { return _retry; }
			set { _retry = value; }
		}
		/// <summary>
		/// Constructor.
		/// </summary>
		/// <param name="peer">SNMP peer IP address</param>
		/// <param name="port">SNMP peer UDP port number</param>
		/// <param name="timeout">SNMP peer timeout in milliseconds</param>
		/// <param name="retry">SNMP peer maximum retires setting. Value of 0 will result in a single request with no retries.</param>
		public UdpTarget(IPAddress peer, int port, int timeout, int retry)
			: base(peer.AddressFamily == AddressFamily.InterNetworkV6)
		{
			_address = peer;
			_port = port;
			_timeout = timeout;
			_retry = retry;
		}
		/// <summary>
		/// Constructor
		/// </summary>
		/// <remarks>
		/// Initializes the class with defaults for timeout (2000ms = 2 seconds), retry (two) and agent UDP port
		/// number (161).
		/// </remarks>
		/// <param name="peer">Agent IP address</param>
		public UdpTarget(IPAddress peer)
			: base(peer.AddressFamily == AddressFamily.InterNetworkV6)
		{
			_address = peer;
			_port = 161;
			_timeout = 2000;
			_retry = 2;
		}
		
		/// <summary>Make SNMP Request</summary>
		/// <remarks>
		/// Make SNMP request. With this method you can make blocked SNMP version 1, 2 and 3 requests of type GET,
		/// GET-NEXT, GET-BULK, SET and REPORT (request types have to compatible with the SNMP protocol version you
		/// are using).
		/// 
		/// This method will pass through any exceptions thrown by parsing classes/methods so see individual packet
		/// classes, ASN.1 type classes, authentication, privacy, etc. classes for exceptions thrown.
		/// </remarks>
		/// <param name="pdu">Pdu class (do not pass ScopedPdu)</param>
		/// <param name="agentParameters">Security information for the request. Use <see cref="AgentParameters"/>
		/// for SNMP versions 1 and 2 requests. Use <see cref="SecureAgentParameters"/> for SNMP version 3
		/// requests.</param>
		/// <returns>Appropriate SNMP packet class for the reply received (<see cref="SnmpV1Packet"/>, 
		/// <see cref="SnmpV2Packet"/>, or <see cref="SnmpV3Packet"/>. Null value if there was an error
		/// with the request.</returns>
		/// <exception cref="SnmpAuthenticationException">Thrown on SNMPv3 requests when authentication password
		/// is not specified on authNoPriv or authPriv requests in SecureAgentParameters or if incoming packet 
		/// authentication check failed.
		/// 
		/// With SNMP ver1 and ver2c, authentication check fails when invalid community name is parsed in the reply.</exception>
		/// <exception cref="SnmpPrivacyException">Thrown on SNMPv3 requests when privacy password is not
		/// specified in SecureAgentParameters on authPriv requests.</exception>
		/// <exception cref="SnmpException">Thrown in following cases:
		/// 
		/// * IAgentParameters.Valid() returned false. SnmpException.ErrorCode is set to SnmpException.InvalidIAgentParameters
		/// * No data received on request. SnmpException.ErrorCode is set to SnmpException.NoDataReceived
		/// * Invalid RequestId in reply. SnmpException.ErrorCode is set to SnmpException.InvalidRequestId
		/// </exception>
		public SnmpPacket Request(Pdu pdu, IAgentParameters agentParameters)
		{
			byte[] outPacket;
			if (agentParameters.Version == SnmpVersion.Ver3)
			{
				SecureAgentParameters secparams = (SecureAgentParameters)agentParameters;
				if (secparams.Authentication != AuthenticationDigests.None && secparams.AuthenticationSecret.Length <= 0)
					throw new SnmpAuthenticationException("Authentication password not specified.");
				if (secparams.Privacy != PrivacyProtocols.None && secparams.PrivacySecret.Length <= 0)
					throw new SnmpPrivacyException("Privacy password not specified.");
				_noSourceCheck = false; // this option is not valid for SNMP v3 requests
				ScopedPdu outPdu = new ScopedPdu(pdu);
				SnmpV3Packet packet = new SnmpV3Packet(outPdu);
				secparams.InitializePacket(packet);
				if (secparams.HasCachedKeys)
					outPacket = packet.encode(secparams.AuthenticationKey, secparams.PrivacyKey);
				else
					outPacket = packet.encode();
			}
            else if (agentParameters.Version == SnmpVersion.Ver1)
			{
				AgentParameters param = (AgentParameters)agentParameters;
				if (!param.Valid())
					throw new SnmpException(SnmpException.InvalidIAgentParameters,"Invalid AgentParameters. Unable to process request.");
				SnmpV1Packet packet = new SnmpV1Packet();
				packet.Pdu.Set(pdu);
				packet.Community.Set(param.Community);
				outPacket = packet.encode();
				_noSourceCheck = param.DisableReplySourceCheck;
			}
            else if (agentParameters.Version == SnmpVersion.Ver2)
			{
				AgentParameters param = (AgentParameters)agentParameters;
				if (!param.Valid())
					throw new SnmpException(SnmpException.InvalidIAgentParameters, "Invalid AgentParameters. Unable to process request.");
				SnmpV2Packet packet = new SnmpV2Packet();
				packet.Pdu.Set(pdu);
				packet.Community.Set(param.Community);
				_noSourceCheck = param.DisableReplySourceCheck;
				outPacket = packet.encode();
			}
			else
			{
				throw new SnmpInvalidVersionException("Unsupported SNMP version.");
			}

			byte[] inBuffer = base.Request(_address, _port, outPacket, outPacket.Length, _timeout, _retry);

			if (inBuffer == null || inBuffer.Length <= 0)
			{
				throw new SnmpException(SnmpException.NoDataReceived, "No data received on request.");
			}
			// verify packet
			if (agentParameters.Version == SnmpVersion.Ver1)
			{
				SnmpV1Packet packet = new SnmpV1Packet();
				AgentParameters param = (AgentParameters)agentParameters;
				packet.decode(inBuffer, inBuffer.Length);
				if (packet.Community != param.Community)
				{
					// invalid community name received. Ignore the rest of the packet
					throw new SnmpAuthenticationException("Invalid community name in reply.");
				}
				if (packet.Pdu.RequestId != pdu.RequestId)
				{
					// invalid request id. unmatched response ignored
					throw new SnmpException(SnmpException.InvalidRequestId, "Invalid request id in reply.");
				}
				return packet;
			}
			else if (agentParameters.Version == SnmpVersion.Ver2)
			{
				SnmpV2Packet packet = new SnmpV2Packet();
				AgentParameters param = (AgentParameters)agentParameters;
				packet.decode(inBuffer, inBuffer.Length);
				if (packet.Community != param.Community)
				{
					// invalid community name received. Ignore the rest of the packet
					throw new SnmpAuthenticationException("Invalid community name in reply.");
				}
				if (packet.Pdu.RequestId != pdu.RequestId)
				{
					// invalid request id. unmatched response ignored
					throw new SnmpException(SnmpException.InvalidRequestId, "Invalid request id in reply.");
				}
				return packet;
			}
			else if (agentParameters.Version == SnmpVersion.Ver3)
			{
				SnmpV3Packet packet = new SnmpV3Packet();
				SecureAgentParameters secparams = (SecureAgentParameters)agentParameters;
				secparams.InitializePacket(packet);
				if (secparams.HasCachedKeys)
					packet.decode(inBuffer, inBuffer.Length, secparams.AuthenticationKey, secparams.PrivacyKey);
				else
					packet.decode(inBuffer, inBuffer.Length);
				// first check if packet is a discovery response and process it
				if (packet.Pdu.Type == PduType.Report && packet.Pdu.VbCount > 0 && packet.Pdu.VbList[0].Oid.Equals(SnmpConstants.usmStatsUnknownEngineIDs))
				{
					secparams.UpdateDiscoveryValues(packet);
					return packet;
				}
				else
				{
					if (!secparams.ValidateIncomingPacket(packet))
					{
						return null;
					}
					else
					{
						secparams.UpdateDiscoveryValues(packet); // update time, etc. values
						return packet;
					}
				}
			}
			return null;
		}

		/// <summary>
		/// Internal event to send result of the async request to.
		/// </summary>
		protected event SnmpAsyncResponse _response;
		/// <summary>
		/// Internal storage of the agent parameters information passed to the async request member function.
		/// </summary>
		protected IAgentParameters _agentParameters;

		/// <summary>
		/// Make SNMP request. With this method you can make blocked SNMP version 1, 2 and 3 requests of type GET,
		/// GET-NEXT, GET-BULK, SET and REPORT (request types have to compatible with the SNMP protocol version you
		/// are using).
		/// 
		/// This method will pass through any exceptions thrown by parsing classes/methods so see individual packet
		/// classes, ASN.1 type classes, authentication, privacy, etc. classes for exceptions thrown.
		/// </summary>
		/// <param name="pdu">Pdu class (do not pass ScopedPdu)</param>
		/// <param name="agentParameters">Security information for the request. Use <see cref="AgentParameters"/>
		/// for SNMP versions 1 and 2 requests. Use <see cref="SecureAgentParameters"/> for SNMP version 3
		/// requests.</param>
		/// <param name="responseCallback">Callback that receives the result of the async operation.</param>
		/// <returns>True if async request was successfully initiated, otherwise false.</returns>
		public bool RequestAsync(Pdu pdu, IAgentParameters agentParameters, SnmpAsyncResponse responseCallback)
		{
			if (IsBusy)
			{
				return false; // class is busy
			}
			_response = null;
			_response += responseCallback;
			_agentParameters = agentParameters;
			byte[] outPacket;
			if (agentParameters.Version == SnmpVersion.Ver3)
			{
				SecureAgentParameters secparams = (SecureAgentParameters)agentParameters;
				if (secparams.Authentication != AuthenticationDigests.None && secparams.AuthenticationSecret.Length <= 0)
				{
					// _response(AsyncRequestResult.AuthenticationError, null);
					return false;
				}
				if (secparams.Privacy != PrivacyProtocols.None && secparams.PrivacySecret.Length <= 0)
				{
					// _response(AsyncRequestResult.PrivacyError, null);
					return false;
				}
				_noSourceCheck = false; // this option is not valid for SNMP v3 requests
				ScopedPdu outPdu = new ScopedPdu(pdu);
				outPdu.ContextEngineId.Set(secparams.EngineId);
				outPdu.ContextName.Set(secparams.ContextName);
				SnmpV3Packet packet = new SnmpV3Packet(outPdu);
				secparams.InitializePacket(packet);
				try
				{
					if (secparams.HasCachedKeys)
						outPacket = packet.encode(secparams.AuthenticationKey, secparams.PrivacyKey);
					else
						outPacket = packet.encode();
				}
				catch( Exception ex )
				{
					ex.GetType();
					_response(AsyncRequestResult.EncodeError, packet);
					return false;
				}
			}
			else if (agentParameters.Version == (int)SnmpVersion.Ver1)
			{
				AgentParameters param = (AgentParameters)agentParameters;
				_noSourceCheck = param.DisableReplySourceCheck;
				SnmpV1Packet packet = new SnmpV1Packet();
				packet.Pdu.Set(pdu);
				packet.Community.Set(param.Community);
				try 
				{
					outPacket = packet.encode();
				}
				catch( Exception ex)
				{
					ex.GetType();
					_response(AsyncRequestResult.EncodeError, packet);
					return false;
				}
			}
			else if (agentParameters.Version == SnmpVersion.Ver2)
			{
				AgentParameters param = (AgentParameters)agentParameters;
				_noSourceCheck = param.DisableReplySourceCheck;
				SnmpV2Packet packet = new SnmpV2Packet();
				packet.Pdu.Set(pdu);
				packet.Community.Set(param.Community);
				try
				{
					outPacket = packet.encode();
				}
				catch( Exception ex )
				{
					ex.GetType();
					_response(AsyncRequestResult.EncodeError, packet);
					return false;
				}
			}
			else
			{
				throw new SnmpInvalidVersionException("Unsupported SNMP version.");
			}

			if( ! base.RequestAsync(_address, _port, outPacket, outPacket.Length, _timeout, _retry, new SnmpAsyncCallback(AsyncResponse) ) ) {
				return false;
			}
			return true;
		}
		/// <summary>
		/// Perform SNMP version 3 discovery operation. This is the first operation that needs to be
		/// performed on a newly accessed agent to retrieve agentId, agentBoots and agentTime values, critical
		/// for further authentication and privacy operations.
		/// </summary>
		/// <param name="param"><see cref="SecureAgentParameters"/> class instance that will be updated
		/// with discovered agent values. This class with be reset to its defaults prior to agent
		/// discovered values so do not store any critical information in it prior to calling the
		/// discovery method</param>
		/// <returns>True if discovery operation was a success, otherwise false</returns>
		public bool Discovery(SecureAgentParameters param)
		{
			param.Reset();
			param.SecurityName.Set("");
			param.Reportable = true;
			Pdu pdu = new Pdu(); // just leave everything at default.
			SnmpV3Packet inpkt = (SnmpV3Packet)Request(pdu, param);
			if (inpkt != null)
			{
				if (inpkt.USM.EngineBoots == 0 && inpkt.USM.EngineTime == 0)
				{
					inpkt = (SnmpV3Packet)Request(pdu, param);
					if (inpkt != null)
						return true;
				} else
					return true;
			}
			return false;
		}
		/// <summary>
		/// Make an async discovery request for protocol version 3.
		/// </summary>
		/// <param name="param">Agent parameters</param>
		/// <param name="callback">Callback method</param>
		/// <returns>True if operation was correctly initiated, otherwise false.</returns>
		public bool DiscoveryAsync(SecureAgentParameters param, SnmpAsyncResponse callback)
		{
			Pdu p = new Pdu();
			return RequestAsync(p, param, callback);
		}
		internal void AsyncResponse(AsyncRequestResult result, IPEndPoint peer, byte[] buffer, int buflen)
		{
			if (result != AsyncRequestResult.NoError)
			{
				_response(result, null);
			}
			else
			{
				if (buffer == null || buffer.Length <= 0 || buflen <= 0)
				{
					_response(AsyncRequestResult.NoDataReceived, null);
					return;
				}
				// verify packet
				if (_agentParameters.Version == (int)SnmpVersion.Ver1)
				{
					SnmpV1Packet packet = new SnmpV1Packet();
					try
					{
						packet.decode(buffer, buflen);
					}
					catch(Exception ex)
					{
						ex.GetType();
						// Console.WriteLine("Exception while decoding SNMP packet: " + ex.ToString());
						_response(AsyncRequestResult.DecodeError, packet);
						return;
					}
					_response(AsyncRequestResult.NoError, packet);
					return;
				}
				else if (_agentParameters.Version == SnmpVersion.Ver2)
				{
					SnmpV2Packet packet = new SnmpV2Packet();
					try
					{
						packet.decode(buffer, buflen);
					}
					catch (Exception ex)
					{
						ex.GetType();
						// Console.WriteLine("Exception while decoding SNMP packet: " + ex.ToString());
						// MutableByte b = new MutableByte(buffer, buflen);
						// Console.WriteLine("Buffer length {0}", buflen);
						// SnmpConstants.DumpHex(b);
						_response(AsyncRequestResult.DecodeError, packet);
						return;
					}

					_response(AsyncRequestResult.NoError, packet);
				}
				else if (_agentParameters.Version == SnmpVersion.Ver3)
				{
					SnmpV3Packet packet = new SnmpV3Packet();
					SecureAgentParameters secparams = (SecureAgentParameters)_agentParameters;
					secparams.InitializePacket(packet);
					try {
						if (secparams.HasCachedKeys)
							packet.decode(buffer, buflen, secparams.AuthenticationKey, secparams.PrivacyKey);
						else
							packet.decode(buffer, buflen);
					}
					catch
					{
						_response(AsyncRequestResult.DecodeError, packet);
						return;
					}
					if (!secparams.ValidateIncomingPacket(packet))
					{
						_response(AsyncRequestResult.AuthenticationError, packet);
					}
					else
					{
						secparams.UpdateDiscoveryValues(packet); // update time, etc. values
						if (packet.USM.EngineId.Length > 0 && packet.USM.EngineBoots == 0 && packet.USM.EngineTime == 0)
						{
							Pdu p = new Pdu();
							RequestAsync(p, _agentParameters, _response);
						}
						else
							_response(AsyncRequestResult.NoError, packet);
				}
				}
			}
		}
	}
}