// utils/tcp.h
// functions for handling TCP streams/segments

#include <pcap.h>

#include "structures/array.h"
#include "structures/heap.h"

#ifndef TCP_H
#define TCP_H

typedef unsigned char byte_t;

typedef enum { SERVER, CLIENT } ConnectionSource;

// struct to persistently store TCP segments
// payload field is malloced and needs to be freed
typedef struct {
    byte_t *payload;      // payload in the segment
    size_t len;           // length of the payload
    uint32_t seq;         // TCP sequence number of the segment
    uint16_t port;        // client port of connection the segment was received from
    ConnectionSource src; // segment's source
} TCPSegment;

// get TCP segment from captured packet
// params:
//      - packet - captured packet
//      - packet_data - metadata about packet
// returns:
//      TCPSegment from packet, payload is NULL if the received packet was incorrect
extern TCPSegment
get_segment_from_packet(const byte_t *packet, const struct pcap_pkthdr *packet_data);

// struct that stores all the information about stream
typedef struct {
    DynArray bytes;       // bytes in the stream
    uint32_t seq;         // TCP sequence number of the first byte in the stream
    uint16_t port;        // client port of currently analyzed connection
    ConnectionSource src; // stream's source
    Heap *pending; // min heap of segments yet to be added to stream (sorted by TCP sequence number)
} TCPStream;

#define INIT_STREAM_CAPACITY 256

// initialize new stream
// params:
//      - src - source of the stream
// returns:
//      newly created TCPStream structure with initial values
extern TCPStream new_stream(ConnectionSource src);

// cleanup memory allocations within stream
// params:
//      stream - stream to destroy
extern void destroy_stream(TCPStream stream);

// remove parsed data from the stream
// params:
//      - stream - pointer to the stream to remove a part of
//      - parsed_len - count of n first bytes of the stream that were parsed
extern void remove_parsed_data(TCPStream *stream, size_t parsed_len);

// max difference between expected TCP seq and received TCP seq to still accept it into pending
#define MAX_SEQ_OFFSET 100000

// add TCP segment to stream, pending or completely discard it
// params:
//      - stream - pointer to the current stream
//      - segment - segment to handle
// returns:
//      1 if the segment was added to the stream, 0 if it was discarded or saved to pending
extern int handle_segment(TCPStream *stream, TCPSegment segment);

#endif