#define _GNU_SOURCE

#include "mangle.h"
#include "raw_replacements.h"
#include "config.h"

#ifdef KERNEL_SPACE
#include <linux/printk.h>
#include <linux/ip.h>

#define printf pr_info
#define perror pr_err
#define lgerror(msg, ret) (pr_err(msg ": %d\n", ret))
#else 
#include <stdio.h>
#include <libnetfilter_queue/libnetfilter_queue_ipv4.h>
#include <libnetfilter_queue/libnetfilter_queue_tcp.h>

typedef uint8_t __u8;
typedef uint32_t __u32;
typedef uint16_t __u16;

#define lgerror(msg, ret) __extension__ ({errno = -ret; perror(msg);})
#endif

void tcp4_set_checksum(struct tcphdr *tcph, struct iphdr *iph) 
{
#ifdef KERNEL_SPACE
	uint32_t tcp_packet_len = ntohs(iph->tot_len) - (iph->ihl << 2);
	tcph->check = 0;
	tcph->check = csum_tcpudp_magic(
		iph->saddr, iph->daddr, tcp_packet_len,
		IPPROTO_TCP, 
		csum_partial(tcph, tcp_packet_len, 0));
#else
	nfq_tcp_compute_checksum_ipv4(tcph, iph);
#endif
}

void ip4_set_checksum(struct iphdr *iph) 
{
#ifdef KERNEL_SPACE
	iph->check = 0;
	iph->check = ip_fast_csum(iph, iph->ihl);
#else
	nfq_ip_set_checksum(iph);
#endif
}


int ip4_payload_split(__u8 *pkt, __u32 buflen,
		       struct iphdr **iph, __u32 *iph_len, 
		       __u8 **payload, __u32 *plen) {
	if (pkt == NULL || buflen < sizeof(struct iphdr)) {
		return -EINVAL;
	}

	struct iphdr *hdr = (struct iphdr *)pkt;
	if (hdr->version != IPVERSION) return -EINVAL;

	__u32 hdr_len = hdr->ihl * 4;
	__u32 pktlen = ntohs(hdr->tot_len);
	if (buflen < pktlen || hdr_len > pktlen) return -EINVAL;

	if (iph) 
		*iph = hdr;
	if (iph_len)
		*iph_len = hdr_len;
	if (payload)
		*payload = pkt + hdr_len;
	if (plen)
		*plen = pktlen - hdr_len;

	return 0;
}

int tcp4_payload_split(__u8 *pkt, __u32 buflen,
		       struct iphdr **iph, __u32 *iph_len,
		       struct tcphdr **tcph, __u32 *tcph_len,
		       __u8 **payload, __u32 *plen) {
	struct iphdr *hdr;
	__u32 hdr_len;
	struct tcphdr *thdr;
	__u32 thdr_len;
	
	__u8 *tcph_pl;
	__u32 tcph_plen;

	if (ip4_payload_split(pkt, buflen, &hdr, &hdr_len, 
			&tcph_pl, &tcph_plen)){
		return -EINVAL;
	}


	if (
		hdr->protocol != IPPROTO_TCP || 
		tcph_plen < sizeof(struct tcphdr)) {
		return -EINVAL;
	}


	thdr = (struct tcphdr *)(tcph_pl);
	thdr_len = thdr->doff * 4;

	if (thdr_len > tcph_plen) {
		return -EINVAL;
	}

	if (iph) *iph = hdr;
	if (iph_len) *iph_len = hdr_len;
	if (tcph) *tcph = thdr;
	if (tcph_len) *tcph_len = thdr_len;
	if (payload) *payload = tcph_pl + thdr_len;
	if (plen) *plen = tcph_plen - thdr_len;

	return 0;
}

// split packet to two ipv4 fragments.
int ip4_frag(const __u8 *pkt, __u32 buflen, __u32 payload_offset, 
			__u8 *frag1, __u32 *f1len, 
			__u8 *frag2, __u32 *f2len) {
	
	struct iphdr *hdr;
	const __u8 *payload;
	__u32 plen;
	__u32 hdr_len;
	int ret;

	if (!frag1 || !f1len || !frag2 || !f2len)
		return -EINVAL;

	if ((ret = ip4_payload_split(
		(__u8 *)pkt, buflen, 
		&hdr, &hdr_len, (__u8 **)&payload, &plen)) < 0) {
		lgerror("ipv4_frag: TCP Header extract error", ret);
		return -EINVAL;
	}

	if (plen <= payload_offset) {
		return -EINVAL;
	}

	if (payload_offset & ((1 << 3) - 1)) {
		lgerror("ipv4_frag: Payload offset MUST be a multiply of 8!", -EINVAL);

		return -EINVAL;
	}

	__u32 f1_plen = payload_offset;
	__u32 f1_dlen = f1_plen + hdr_len;

	__u32 f2_plen = plen - payload_offset;
	__u32 f2_dlen = f2_plen + hdr_len;

	if (*f1len < f1_dlen || *f2len < f2_dlen) {
		return -ENOMEM;
	}
	*f1len = f1_dlen;
	*f2len = f2_dlen;

	memcpy(frag1, hdr, hdr_len);
	memcpy(frag2, hdr, hdr_len);

	memcpy(frag1 + hdr_len, payload, f1_plen);
	memcpy(frag2 + hdr_len, payload + payload_offset, f2_plen);

	struct iphdr *f1_hdr = (void *)frag1;
	struct iphdr *f2_hdr = (void *)frag2;

	__u16 f1_frag_off = ntohs(f1_hdr->frag_off);
	__u16 f2_frag_off = ntohs(f2_hdr->frag_off);

	f1_frag_off &= IP_OFFMASK;
	f1_frag_off |= IP_MF;
	
	if ((f2_frag_off & ~IP_OFFMASK) == IP_MF) {
		f2_frag_off &= IP_OFFMASK;
		f2_frag_off |= IP_MF;
	} else {
		f2_frag_off &= IP_OFFMASK;
	}
	
	f2_frag_off += (__u16)payload_offset / 8;

	f1_hdr->frag_off = htons(f1_frag_off);
	f1_hdr->tot_len = htons(f1_dlen);

	f2_hdr->frag_off = htons(f2_frag_off);
	f2_hdr->tot_len = htons(f2_dlen);


	if (config.verbose)
		printf("Packet split in portion %u %u\n", f1_plen, f2_plen);

	ip4_set_checksum(f1_hdr);
	ip4_set_checksum(f2_hdr);

	return 0;
}

// split packet to two tcp-on-ipv4 segments.
int tcp4_frag(const __u8 *pkt, __u32 buflen, __u32 payload_offset, 
			__u8 *seg1, __u32 *s1len, 
			__u8 *seg2, __u32 *s2len) {

	struct iphdr *hdr;
	__u32 hdr_len;
	struct tcphdr *tcph;
	__u32 tcph_len;
	__u32 plen;
	const __u8 *payload;
	int ret;

	if (!seg1 || !s1len || !seg2 || !s2len)
		return -EINVAL;

	if ((ret = tcp4_payload_split((__u8 *)pkt, buflen,
				&hdr, &hdr_len,
				&tcph, &tcph_len,
				(__u8 **)&payload, &plen)) < 0) {
		lgerror("tcp4_frag: tcp4_payload_split", ret);

		return -EINVAL;
	}


	if (
		ntohs(hdr->frag_off) & IP_MF || 
		ntohs(hdr->frag_off) & IP_OFFMASK) {
		printf("tcp4_frag: frag value: %d\n",
			ntohs(hdr->frag_off));
		lgerror("tcp4_frag: ip fragmentation is set", -EINVAL);
		return -EINVAL;
	}


	if (plen <= payload_offset) {
		return -EINVAL;
	}

	__u32 s1_plen = payload_offset;
	__u32 s1_dlen = s1_plen + hdr_len + tcph_len;

	__u32 s2_plen = plen - payload_offset;
	__u32 s2_dlen = s2_plen + hdr_len + tcph_len;

	if (*s1len < s1_dlen || *s2len < s2_dlen) 
		return -ENOMEM;

	*s1len = s1_dlen;
	*s2len = s2_dlen;

	memcpy(seg1, hdr, hdr_len);
	memcpy(seg2, hdr, hdr_len);

	memcpy(seg1 + hdr_len, tcph, tcph_len);
	memcpy(seg2 + hdr_len, tcph, tcph_len);

	memcpy(seg1 + hdr_len + tcph_len, payload, s1_plen);
	memcpy(seg2 + hdr_len + tcph_len, payload + payload_offset, s2_plen);

	struct iphdr *s1_hdr = (void *)seg1;
	struct iphdr *s2_hdr = (void *)seg2;

	struct tcphdr *s1_tcph = (void *)(seg1 + hdr_len);
	struct tcphdr *s2_tcph = (void *)(seg2 + hdr_len);

	s1_hdr->tot_len = htons(s1_dlen);
	s2_hdr->tot_len = htons(s2_dlen);

	s2_tcph->seq = htonl(ntohl(s2_tcph->seq) + payload_offset);
	
	if (config.verbose)
		printf("Packet split in portion %u %u\n", s1_plen, s2_plen);

	tcp4_set_checksum(s1_tcph, s1_hdr);
	tcp4_set_checksum(s2_tcph, s2_hdr);

	return 0;
}

#define TLS_CONTENT_TYPE_HANDSHAKE 0x16
#define TLS_HANDSHAKE_TYPE_CLIENT_HELLO 0x01
#define TLS_EXTENSION_SNI 0x0000
#define TLS_EXTENSION_CLIENT_HELLO_ENCRYPTED 0xfe0d

typedef __u8 uint8_t;
typedef __u32 uint32_t;
typedef __u16 uint16_t;

/**
 * Processes tls payload of the tcp request.
 * 
 * data Payload data of TCP.
 * dlen Length of `data`.
 */
struct verdict analyze_tls_data(
	const uint8_t *data, 
	uint32_t dlen) 
{
	struct verdict vrd = {0};

	size_t i = 0;
	const uint8_t *data_end = data + dlen;

	while (i + 4 < dlen) {
		const uint8_t *msgData = data + i;

		uint8_t tls_content_type = *msgData;
		uint8_t tls_vmajor = *(msgData + 1);
		uint8_t tls_vminor = *(msgData + 2);
		uint16_t message_length = ntohs(*(uint16_t *)(msgData + 3));
		const uint8_t *message_length_ptr = msgData + 3;


		if (i + 5 + message_length > dlen) break;

		if (tls_content_type != TLS_CONTENT_TYPE_HANDSHAKE) 
			goto nextMessage;


		const uint8_t *handshakeProto = msgData + 5;

		if (handshakeProto + 1 >= data_end) break;

		uint8_t handshakeType = *handshakeProto;

		if (handshakeType != TLS_HANDSHAKE_TYPE_CLIENT_HELLO)
			goto nextMessage;

		const uint8_t *msgPtr = handshakeProto;
		msgPtr += 1; 
		const uint8_t *handshakeProto_length_ptr = msgPtr + 1;
		msgPtr += 3 + 2 + 32;

		if (msgPtr + 1 >= data_end) break;
		uint8_t sessionIdLength = *msgPtr;
		msgPtr++;
		msgPtr += sessionIdLength;

		if (msgPtr + 2 >= data_end) break;
		uint16_t ciphersLength = ntohs(*(uint16_t *)msgPtr);
		msgPtr += 2;
		msgPtr += ciphersLength;

		if (msgPtr + 1 >= data_end) break;
		uint8_t compMethodsLen = *msgPtr;
		msgPtr++;
		msgPtr += compMethodsLen;

		if (msgPtr + 2 >= data_end) break;
		uint16_t extensionsLen = ntohs(*(uint16_t *)msgPtr);
		const uint8_t *extensionsLen_ptr = msgPtr;
		msgPtr += 2;

		const uint8_t *extensionsPtr = msgPtr;
		const uint8_t *extensions_end = extensionsPtr + extensionsLen;
		if (extensions_end > data_end) break;

		while (extensionsPtr < extensions_end) {
			const uint8_t *extensionPtr = extensionsPtr;
			if (extensionPtr + 4 >= extensions_end) break;

			uint16_t extensionType = 
				ntohs(*(uint16_t *)extensionPtr);
			extensionPtr += 2;

			uint16_t extensionLen = 
				ntohs(*(uint16_t *)extensionPtr);
			const uint8_t *extensionLen_ptr = extensionPtr;
			extensionPtr += 2;


			if (extensionPtr + extensionLen > extensions_end) 
				break;

			if (extensionType != TLS_EXTENSION_SNI) 
				goto nextExtension;

			const uint8_t *sni_ext_ptr = extensionPtr;

			if (sni_ext_ptr + 2 >= extensions_end) break;
			uint16_t sni_ext_dlen = ntohs(*(uint16_t *)sni_ext_ptr);

			const uint8_t *sni_ext_dlen_ptr = sni_ext_ptr;
			sni_ext_ptr += 2;

			const uint8_t *sni_ext_end = sni_ext_ptr + sni_ext_dlen;
			if (sni_ext_end >= extensions_end) break;
			
			if (sni_ext_ptr + 3 >= sni_ext_end) break;
			uint8_t sni_type = *sni_ext_ptr++;
			uint16_t sni_len = ntohs(*(uint16_t *)sni_ext_ptr);
			sni_ext_ptr += 2;

			if (sni_ext_ptr + sni_len > sni_ext_end) break;

			char *sni_name = (char *)sni_ext_ptr;

			vrd.sni_offset = (uint8_t *)sni_name - data;
			vrd.sni_len = sni_len;

			if (config.all_domains) {
				vrd.target_sni = 1;
				goto out;
			}


			unsigned int j = 0;
			for (unsigned int i = 0; i <= config.domains_strlen; i++) {
				if (	i == config.domains_strlen	||	
					config.domains_str[i] == '\0'	||
					config.domains_str[i] == ','	|| 
					config.domains_str[i] == '\n'	) {

					unsigned int domain_len = (i - j);
					const char *sni_startp = sni_name + sni_len - domain_len;
					const char *domain_startp = config.domains_str + j;

					if (sni_len >= domain_len &&
						sni_len < 128 && 
						!strncmp(sni_startp, 
						domain_startp, 
						domain_len)) {
							vrd.target_sni = 1;
					}

					j = i + 1;
				}
			}

nextExtension:
			extensionsPtr += 2 + 2 + extensionLen;
		}
nextMessage:
		i += 5 + message_length;
	}

out:
	return vrd;
}

int gen_fake_sni(const struct iphdr *iph, const struct tcphdr *tcph, 
		 uint8_t *buf, uint32_t *buflen) {

	if (!iph || !tcph || !buf || !buflen)
		return -EINVAL;

	int ip_len = iph->ihl * 4;
	size_t data_len = sizeof(fake_sni);

	size_t dlen = data_len + ip_len;

	if (*buflen < dlen) 
		return -ENOMEM;
	*buflen = dlen;

	memcpy(buf, iph, ip_len);
	memcpy(buf + ip_len, fake_sni, data_len);
	struct iphdr *niph = (struct iphdr *)buf;

	niph->protocol = IPPROTO_TCP;
	niph->tot_len = htons(dlen);

	int ret = 0;
	struct tcphdr *ntcph = (struct tcphdr *)(buf + ip_len);

#ifdef KERNEL_SPACE
	ntcph->dest = tcph->dest;
	ntcph->source = tcph->source;
#else 
	ntcph->th_dport = tcph->th_dport;
	ntcph->th_sport = tcph->th_sport;

#if FAKE_SNI_STRATEGY == FKSN_STRAT_TTL
	ntcph->ack = tcph->ack;
	ntcph->ack_seq = tcph->ack_seq;
	niph->ttl = FAKE_SNI_TTL;
#endif 

#endif 

	ip4_set_checksum(niph);
	tcp4_set_checksum(ntcph, niph);

	return 0;
}