/*
 * Copyright (c) 1995 Danny Gasparovski.
 *
 * Please read the file COPYRIGHT for the
 * terms and conditions of the copyright.
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

struct quehead {
    struct quehead *qh_link;
    struct quehead *qh_rlink;
};

struct Slirp {
    struct quehead if_fastq;   /* fast queue (for interactive data) */
    struct quehead if_batchq;  /* queue for non-interactive data */
    struct mbuf *next_m;    /* pointer to next mbuf to output */
    bool if_start_busy;     /* avoid if_start recursion */
};

typedef struct Slirp Slirp;

struct socket {
    int so_queued;
    int so_nqueued;
    int so_iptos;
};

#define IPTOS_LOWDELAY 1

struct mbuf {
    struct  mbuf *m_next;       /* Linked list of mbufs */
    struct  mbuf *m_prev;
    struct  mbuf *m_nextpkt;    /* Next packet in queue/record */
    struct  mbuf *m_prevpkt;    /* Flags aren't used in the output queue */
    struct  socket *m_so;
    Slirp *slirp;
    uint64_t expiration_date;
    int encap_result;
};

#define QEMU_CLOCK_REALTIME 1
static uint64_t qemu_clock_get_ns(int x)
{
    return 0;
}

static int if_encap(Slirp *slirp, struct mbuf *ifm)
{
    printf("if_encap(%p) returning %d\n", ifm, ifm->encap_result);
    return ifm->encap_result;
}

static void m_free(void *foo)
{
}

#define ifq_prev m_prev
#define ifq_next m_next
#define ifs_prev m_prevpkt
#define ifs_next m_nextpkt
#define ifq_so m_so

inline void
insque(void *a, void *b)
{
    register struct quehead *element = (struct quehead *) a;
    register struct quehead *head = (struct quehead *) b;
    element->qh_link = head->qh_link;
    head->qh_link = (struct quehead *)element;
    element->qh_rlink = (struct quehead *)head;
    ((struct quehead *)(element->qh_link))->qh_rlink
    = (struct quehead *)element;
}

inline void
remque(void *a)
{
  register struct quehead *element = (struct quehead *) a;
  ((struct quehead *)(element->qh_link))->qh_rlink = element->qh_rlink;
  ((struct quehead *)(element->qh_rlink))->qh_link = element->qh_link;
  element->qh_rlink = NULL;
}

static void
ifs_insque(struct mbuf *ifm, struct mbuf *ifmhead)
{
    ifm->ifs_next = ifmhead->ifs_next;
    ifmhead->ifs_next = ifm;
    ifm->ifs_prev = ifmhead;
    ifm->ifs_next->ifs_prev = ifm;
}

static inline void ifs_init(struct mbuf *ifm)
{
    ifm->ifs_next = ifm->ifs_prev = ifm;
}

static void
ifs_remque(struct mbuf *ifm)
{
    ifm->ifs_prev->ifs_next = ifm->ifs_next;
    ifm->ifs_next->ifs_prev = ifm->ifs_prev;
}

void
if_init(Slirp *slirp)
{
    slirp->if_fastq.qh_link = slirp->if_fastq.qh_rlink = &slirp->if_fastq;
    slirp->if_batchq.qh_link = slirp->if_batchq.qh_rlink = &slirp->if_batchq;
    slirp->next_m = (struct mbuf *) &slirp->if_batchq;
}

void if_start(Slirp *slirp);

/*
 * if_output: Queue packet into an output queue.
 * There are 2 output queue's, if_fastq and if_batchq.
 * Each output queue is a doubly linked list of double linked lists
 * of mbufs, each list belonging to one "session" (socket).  This
 * way, we can output packets fairly by sending one packet from each
 * session, instead of all the packets from one session, then all packets
 * from the next session, etc.  Packets on the if_fastq get absolute
 * priority, but if one session hogs the link, it gets "downgraded"
 * to the batchq until it runs out of packets, then it'll return
 * to the fastq (eg. if the user does an ls -alR in a telnet session,
 * it'll temporarily get downgraded to the batchq)
 */
void
if_output(struct socket *so, struct mbuf *ifm)
{
    Slirp *slirp = ifm->slirp;
    struct mbuf *ifq;
    int on_fastq = 1;

    /*
     * See if there's already a batchq list for this session.
     * This can include an interactive session, which should go on fastq,
     * but gets too greedy... hence it'll be downgraded from fastq to batchq.
     * We mustn't put this packet back on the fastq (or we'll send it out of order)
     * XXX add cache here?
     */
    for (ifq = (struct mbuf *) slirp->if_batchq.qh_rlink;
         (struct quehead *) ifq != &slirp->if_batchq;
         ifq = ifq->ifq_prev) {
        if (so == ifq->ifq_so) {
            /* A match! */
            ifm->ifq_so = so;
            ifs_insque(ifm, ifq->ifs_prev);
            goto diddit;
        }
    }

    /* No match, check which queue to put it on */
    if (so && (so->so_iptos & IPTOS_LOWDELAY)) {
        ifq = (struct mbuf *) slirp->if_fastq.qh_rlink;
        on_fastq = 1;
        /*
         * Check if this packet is a part of the last
         * packet's session
         */
        if (ifq->ifq_so == so) {
            ifm->ifq_so = so;
            ifs_insque(ifm, ifq->ifs_prev);
            goto diddit;
        }
        } else {
        ifq = (struct mbuf *) slirp->if_batchq.qh_rlink;
                /* Set next_m if the queue was empty so far */
                if ((struct quehead *) slirp->next_m == &slirp->if_batchq) {
                    slirp->next_m = ifm;
                }
        }

    /* Create a new doubly linked list for this session */
    ifm->ifq_so = so;
    ifs_init(ifm);
    insque(ifm, ifq);

diddit:
    if (so) {
        /* Update *_queued */
        so->so_queued++;
        so->so_nqueued++;
        /*
         * Check if the interactive session should be downgraded to
         * the batchq.  A session is downgraded if it has queued 6
         * packets without pausing, and at least 3 of those packets
         * have been sent over the link
         * (XXX These are arbitrary numbers, probably not optimal..)
         */
        if (on_fastq && ((so->so_nqueued >= 6) &&
                 (so->so_nqueued - so->so_queued) >= 3)) {

            /* Remove from current queue... */
            remque(ifm->ifs_next);

            /* ...And insert in the new.  That'll teach ya! */
            insque(ifm->ifs_next, &slirp->if_batchq);
        }
    }

#ifndef FULL_BOLT
    /*
     * This prevents us from malloc()ing too many mbufs
     */
    if_start(ifm->slirp);
#endif
}

/*
 * Send a packet
 * We choose a packet based on its position in the output queues;
 * If there are packets on the fastq, they are sent FIFO, before
 * everything else.  Otherwise we choose the first packet from the
 * batchq and send it.  the next packet chosen will be from the session
 * after this one, then the session after that one, and so on..  So,
 * for example, if there are 3 ftp session's fighting for bandwidth,
 * one packet will be sent from the first session, then one packet
 * from the second session, then one packet from the third, then back
 * to the first, etc. etc.
 */
void if_start(Slirp *slirp)
{
    uint64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
    bool from_batchq, next_from_batchq;
    struct mbuf *ifm, *ifm_next, *ifqt;

    if (slirp->if_start_busy) {
        return;
    }
    slirp->if_start_busy = true;

    if (slirp->if_fastq.qh_link != &slirp->if_fastq) {
        ifm_next = (struct mbuf *) slirp->if_fastq.qh_link;
        next_from_batchq = false;
    } else if ((struct quehead *) slirp->next_m != &slirp->if_batchq) {
        /* Nothing on fastq, pick up from batchq via next_m */
        ifm_next = slirp->next_m;
        next_from_batchq = true;
    } else {
        ifm_next = NULL;
    }

    printf("\nif_start loop begins\n");
    while (ifm_next) {
        ifm = ifm_next;
        printf("ifm_next=%p (session=%p), slirp->next_m=%p\n",
        ifm, ifm->m_so, slirp->next_m);
        from_batchq = next_from_batchq;

        ifm_next = ifm->ifq_next;
        if ((struct quehead *) ifm_next == &slirp->if_fastq) {
            /* No more packets in fastq, switch to batchq */
            ifm_next = slirp->next_m;
            next_from_batchq = true;
        }
        if ((struct quehead *) ifm_next == &slirp->if_batchq) {
            /* end of batchq */
            ifm_next = NULL;
        }

        /* Try to send packet unless it already expired */
        if (ifm->expiration_date >= now && !if_encap(slirp, ifm)) {
            /* Packet is delayed due to pending ARP or NDP resolution */
            continue;
        }

        if (ifm == slirp->next_m) {
            /* Set which packet to send on next iteration */
            slirp->next_m = ifm->ifq_next;
        }

        /* Remove it from the queue */
        ifqt = ifm->ifq_prev;
        remque(ifm);

        /* If there are more packets for this session, re-queue them */
        if (ifm->ifs_next != ifm) {
            struct mbuf *next = ifm->ifs_next;

            insque(next, ifqt);
            ifs_remque(ifm);

            if (!from_batchq) {
                /* Next packet in fastq is from the same session */
                ifm_next = next;
                next_from_batchq = false;
            } else if ((struct quehead *) slirp->next_m == &slirp->if_batchq) {
                /* Set next_m and ifm_next if the session packet is now the
                 * only one on batchq */
                slirp->next_m = ifm_next = next;
            }
        }

        /* Update so_queued */
        if (ifm->ifq_so && --ifm->ifq_so->so_queued == 0) {
            /* If there's no more queued, reset nqueued */
            ifm->ifq_so->so_nqueued = 0;
        }

        m_free(ifm);
    }

    slirp->if_start_busy = false;
}

int main(int argc, char **argv)
{
    Slirp s = {0};
    if_init(&s);

    struct mbuf p0 = {0};
    struct socket s0 = {0};
    struct mbuf p1 = {0};
    struct socket s1 = {0};
    struct mbuf p2 = {0};
    struct mbuf p3 = {0};

    printf("s0                        = %p\n", &s0);
    printf("s1                        = %p\n", &s1);
    printf("\n");
    printf("p0                        = %p\n", &p0);
    printf("p1                        = %p\n", &p1);
    printf("p2                        = %p\n", &p2);
    printf("p3                        = %p\n", &p3);
    printf("&slirp->if_batchq         = %p\n", &s.if_batchq);

    p0.slirp = &s;
    p0.encap_result = 0;
    if_output(&s0, &p0);

    p1.slirp = &s;
    p1.encap_result = 0;
    if_output(&s0, &p1);

    p0.encap_result = 1;
    p2.slirp = &s;
    p2.encap_result = 1;
    if_output(&s1, &p2);

    p3.slirp = &s;
    p3.encap_result = 1;
    if_output(&s0, &p3);

    printf("\nFinal results:\n");
    printf("slirp->if_batchq.qh_link  = %p\n", s.if_batchq.qh_link);
    printf("slirp->if_batchq.qh_rlink = %p\n", s.if_batchq.qh_rlink);
    printf("slirp->next_m             = %p\n", s.next_m);

    return 0;
}