//
// Created by epagris on 2023.01.16..
//

#include <memory.h>
#include <stdbool.h>
#include "tcp_window.h"
#include "etherlib/dynmem.h"

TcpWindow *tcpw_create(uint32_t size) {
    uint32_t allocSize = sizeof(TcpWindow) + size; // calculate full allocation size
    TcpWindow * tcpw = (TcpWindow *) dynmem_alloc(allocSize); // allocate data block at the end
    tcpw->mp = mp_init(tcpw->data, size); // initialize memory pool

    return tcpw;
}

#define TCP_WINDOW_MAX_WINSIZE_PADDING (16) // keep-out zone, this way allocated blocks will not block registry table growth TODO: not the best solution

uint32_t tcpw_get_max_window_size(TcpWindow * tcpw) {
    return mp_largest_free_block_size(tcpw->mp) - sizeof(TcpWindowSegment) - TCP_WINDOW_MAX_WINSIZE_PADDING;
}

TcpWindowSegment * tcpw_store_segment(TcpWindow * tcpw, const uint8_t * data, uint32_t size, uint32_t seqNum) {
    TcpWindowSegment * seg = (TcpWindowSegment *) mp_alloc(tcpw->mp, sizeof(TcpWindowSegment) + size);
    if (seg == NULL) { // could not store...
        return NULL;
    }

    // store segment descriptor
    seg->size = size;
    seg->seqNum = seqNum;

    // store segment
    memcpy(seg->data, data, size);

    // chain-in into linked list of segments
    if (tcpw->firstSeg == NULL) {
        tcpw->firstSeg = tcpw->lastSeg = seg;
    } else {
        tcpw->lastSeg->next = seg;
    }

    mp_report(tcpw->mp);

    return seg;
}

bool tcpw_acknowledge(TcpWindow * tcpw, uint32_t ackNum) {
    if (tcpw->firstSeg == NULL) { // cannot acknowledge if there's nothing to acknowledge
        return false;
    }
    uint32_t segAckNum = tcpw->firstSeg->seqNum + tcpw->firstSeg->size;
    if (segAckNum == ackNum) { // if the acknowledgement number is correct
        TcpWindowSegment * oldFirst = tcpw->firstSeg; // replace first
        TcpWindowSegment * newFirst = oldFirst->next;
        tcpw->firstSeg = newFirst;
        if (newFirst == NULL) { // if the list is empty, also clear pointer to last segment
            tcpw->lastSeg = NULL;
        }
        mp_free(tcpw->mp, (uint8_t *) oldFirst); // release old first segment

        mp_report(tcpw->mp);

        return true;
    } else {
        return false;
    }
}