/*
             LUFA Library
     Copyright (C) Dean Camera, 2021.

  dean [at] fourwalledcubicle [dot] com
           www.lufa-lib.org
*/

/*
  Copyright 2021  Dean Camera (dean [at] fourwalledcubicle [dot] com)

  Permission to use, copy, modify, distribute, and sell this
  software and its documentation for any purpose is hereby granted
  without fee, provided that the above copyright notice appear in
  all copies and that both that the copyright notice and this
  permission notice and warranty disclaimer appear in supporting
  documentation, and that the name of the author not be used in
  advertising or publicity pertaining to distribution of the
  software without specific, written prior permission.

  The author disclaims all warranties with regard to this
  software, including all implied warranties of merchantability
  and fitness.  In no event shall the author be liable for any
  special, indirect or consequential damages or any damages
  whatsoever resulting from loss of use, data or profits, whether
  in an action of contract, negligence or other tortious action,
  arising out of or in connection with the use or performance of
  this software.
*/

/** \file
 *
 *  Dynamic Host Configuration Protocol (DHCP) packet handling routines. This protocol
 *  handles the automatic IP negotiation to the host, so that the host will use the provided
 *  IP address given to it by the device.
 */

#include "DHCP.h"

/** Processes a DHCP packet inside an Ethernet frame, and writes the appropriate response
 *  to the output Ethernet frame if the host is requesting or accepting an IP address.
 *
 *  \param[in] IPHeaderInStart      Pointer to the start of the incoming packet's IP header
 *  \param[in] DHCPHeaderInStart    Pointer to the start of the incoming packet's DHCP header
 *  \param[out] DHCPHeaderOutStart  Pointer to the start of the outgoing packet's DHCP header
 *
 *  \return The number of bytes written to the out Ethernet frame if any, NO_RESPONSE otherwise
 */
int16_t DHCP_ProcessDHCPPacket(void* IPHeaderInStart,
                               void* DHCPHeaderInStart,
                               void* DHCPHeaderOutStart)
{
	IP_Header_t*   IPHeaderIN    = (IP_Header_t*)IPHeaderInStart;
	DHCP_Header_t* DHCPHeaderIN  = (DHCP_Header_t*)DHCPHeaderInStart;
	DHCP_Header_t* DHCPHeaderOUT = (DHCP_Header_t*)DHCPHeaderOutStart;

	uint8_t* DHCPOptionsINStart  = ((uint8_t*)DHCPHeaderInStart  + sizeof(DHCP_Header_t));
	uint8_t* DHCPOptionsOUTStart = ((uint8_t*)DHCPHeaderOutStart + sizeof(DHCP_Header_t));

	DecodeDHCPHeader(DHCPHeaderInStart);

	/* Zero out the response DHCP packet, as much of it is legacy and left at 0 */
	memset(DHCPHeaderOUT, 0, sizeof(DHCP_Header_t));

	/* Fill out the response DHCP packet */
	DHCPHeaderOUT->HardwareType          = DHCPHeaderIN->HardwareType;
	DHCPHeaderOUT->Operation             = DHCP_OP_BOOTREPLY;
	DHCPHeaderOUT->HardwareAddressLength = DHCPHeaderIN->HardwareAddressLength;
	DHCPHeaderOUT->Hops                  = 0;
	DHCPHeaderOUT->TransactionID         = DHCPHeaderIN->TransactionID;
	DHCPHeaderOUT->ElapsedSeconds        = 0;
	DHCPHeaderOUT->Flags                 = DHCPHeaderIN->Flags;
	DHCPHeaderOUT->YourIP                = ClientIPAddress;
	memmove(&DHCPHeaderOUT->ClientHardwareAddress, &DHCPHeaderIN->ClientHardwareAddress, sizeof(MAC_Address_t));
	DHCPHeaderOUT->Cookie                = SwapEndian_32(DHCP_MAGIC_COOKIE);

	/* Alter the incoming IP packet header so that the corrected IP source and destinations are used - this means that
	   when the response IP header is generated, it will use the corrected addresses and not the null/broatcast addresses */
	IPHeaderIN->SourceAddress      = ClientIPAddress;
	IPHeaderIN->DestinationAddress = ServerIPAddress;

	/* Process the incoming DHCP packet options */
	while (DHCPOptionsINStart[0] != DHCP_OPTION_END)
	{
		/* Find the Message Type DHCP option, to determine the type of DHCP packet */
		if (DHCPOptionsINStart[0] == DHCP_OPTION_MESSAGETYPE)
		{
			if ((DHCPOptionsINStart[2] == DHCP_MESSAGETYPE_DISCOVER) || (DHCPOptionsINStart[2] == DHCP_MESSAGETYPE_REQUEST))
			{
				/* Fill out the response DHCP packet options for a DHCP OFFER or ACK response */

				*(DHCPOptionsOUTStart++) = DHCP_OPTION_MESSAGETYPE;
				*(DHCPOptionsOUTStart++) = 1;
				*(DHCPOptionsOUTStart++) = (DHCPOptionsINStart[2] == DHCP_MESSAGETYPE_DISCOVER) ? DHCP_MESSAGETYPE_OFFER
																								: DHCP_MESSAGETYPE_ACK;

				*(DHCPOptionsOUTStart++) = DHCP_OPTION_SUBNETMASK;
				*(DHCPOptionsOUTStart++) = sizeof(IP_Address_t);
				*(DHCPOptionsOUTStart++) = 0xFF;
				*(DHCPOptionsOUTStart++) = 0xFF;
				*(DHCPOptionsOUTStart++) = 0xFF;
				*(DHCPOptionsOUTStart++) = 0x00;

				*(DHCPOptionsOUTStart++) = DHCP_OPTION_LEASETIME;
				*(DHCPOptionsOUTStart++) = sizeof(uint32_t);
				/* Lease Time 86400s (ONE_DAY) */
				*(DHCPOptionsOUTStart++) = 0x00;
				*(DHCPOptionsOUTStart++) = 0x01;
				*(DHCPOptionsOUTStart++) = 0x51;
				*(DHCPOptionsOUTStart++) = 0x80;

				*(DHCPOptionsOUTStart++) = DHCP_OPTION_DHCPSERVER;
				*(DHCPOptionsOUTStart++) = sizeof(IP_Address_t);
				memcpy(DHCPOptionsOUTStart, &ServerIPAddress, sizeof(IP_Address_t));
				DHCPOptionsOUTStart     += sizeof(IP_Address_t);

				*(DHCPOptionsOUTStart++) = DHCP_OPTION_END;

				return (sizeof(DHCP_Header_t) + 18 + sizeof(IP_Address_t));
			}
		}

		/* Go to the next DHCP option - skip one byte if option is a padding byte, else skip the complete option's size */
		DHCPOptionsINStart += ((DHCPOptionsINStart[0] == DHCP_OPTION_PAD) ? 1 : (DHCPOptionsINStart[1] + 2));
	}

	return NO_RESPONSE;
}

