/*
 * Copyright 1990 William Pugh 
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * Permission to include in quagga provide on March 31, 2016
 */

/*
 * Skip List impementation based on code from William Pugh.
 * ftp://ftp.cs.umd.edu/pub/skipLists/
 * 
 * Skip Lists are a probabilistic alternative to balanced trees, as
 * described in the June 1990 issue of CACM and were invented by 
 * William Pugh in 1987. 
 * 
 * This file contains source code to implement a dictionary using 
 * skip lists and a test driver to test the routines.
 * 
 * A couple of comments about this implementation:
 *   The routine randomLevel has been hard-coded to generate random
 *   levels using p=0.25. It can be easily changed.
 *   
 *   The insertion routine has been implemented so as to use the
 *   dirty hack described in the CACM paper: if a random level is
 *   generated that is more than the current maximum level, the
 *   current maximum level plus one is used instead.
 * 
 *   Levels start at zero and go up to MaxLevel (which is equal to
 * 	(MaxNumberOfLevels-1).
 * 
 * The run-time flag SKIPLIST_FLAG_ALLOW_DUPLICATES determines whether or
 * not duplicates are allowed for a given list. If set, duplicates are
 * allowed and act in a FIFO manner. If not set, an insertion of a value
 * already in the list updates the previously existing binding.
 * 
 * BitsInRandom is defined to be the number of bits returned by a call to
 * random(). For most all machines with 32-bit integers, this is 31 bits
 * as currently set. 
 */


#include <zebra.h>

#include "memory.h"
#include "log.h"
#include "vty.h"
#include "skiplist.h"

DEFINE_MTYPE_STATIC(LIB, SKIP_LIST,      "Skip List")
DEFINE_MTYPE_STATIC(LIB, SKIP_LIST_NODE, "Skip Node")

#define BitsInRandom 31

#define MaxNumberOfLevels 16
#define MaxLevel (MaxNumberOfLevels-1)
#define newNodeOfLevel(l) XCALLOC(MTYPE_SKIP_LIST_NODE, sizeof(struct skiplistnode)+(l)*sizeof(struct skiplistnode *))

static int randomsLeft;
static int randomBits;
static struct skiplist *skiplist_last_created;	/* debugging hack */

#if 1
#define CHECKLAST(sl) do {\
    if ((sl)->header->forward[0] && !(sl)->last) assert(0);	\
    if (!(sl)->header->forward[0] && (sl)->last) assert(0);	\
} while (0)
#else
#define CHECKLAST(sl)
#endif


static int
randomLevel()
{
    register int level = 0;
    register int b;

    do {
	if (randomsLeft <= 0) {
	    randomBits = random();
	    randomsLeft = BitsInRandom/2;
	}
	b = randomBits&3;
	randomBits>>=2;
	--randomsLeft;

	if (!b) {
	    level++;
	    if (level >= MaxLevel)
		return MaxLevel;
	}
    } while (!b);

    return level;
}

static int
default_cmp(void *key1, void *key2)
{
    if (key1 < key2)
	return -1;
    if (key1 > key2)
	return 1;
    return 0;
}

unsigned int
skiplist_count(struct skiplist *l)
{
    return l->count;
}

struct skiplist *
skiplist_new(
    int	flags,
    int (*cmp) (void *key1, void *key2),
    void (*del) (void *val))
{
    struct skiplist *new;

    new = XCALLOC (MTYPE_SKIP_LIST, sizeof (struct skiplist));
    assert(new);

    new->level = 0;
    new->count = 0;
    new->header = newNodeOfLevel(MaxNumberOfLevels);
    new->stats = newNodeOfLevel(MaxNumberOfLevels);

    new->flags = flags;
    if (cmp)
	new->cmp = cmp;
    else
	new->cmp = default_cmp;

    if (del)
	new->del = del;

    skiplist_last_created = new;	/* debug */

    return new;
}

void
skiplist_free(struct skiplist *l)
{
    register struct skiplistnode *p, *q;

    p = l->header;

    do {
	q = p->forward[0];
	if (l->del && p != l->header)
	    (*l->del)(p->value);
	XFREE(MTYPE_SKIP_LIST_NODE, p);
	p = q;
    } while (p);

    XFREE(MTYPE_SKIP_LIST_NODE, l->stats);
    XFREE(MTYPE_SKIP_LIST, l);
}


int
skiplist_insert(
    register struct skiplist	*l,
    register void		*key,
    register void		*value)
{
    register int			k;
    struct skiplistnode			*update[MaxNumberOfLevels];
    register struct skiplistnode	*p, *q;

    CHECKLAST(l);

/* DEBUG */
    if (!key) {
	zlog_err("%s: key is 0, value is %p", __func__, value);
    }

    p = l->header;
    k = l->level;
    do {
	while (q = p->forward[k], q && (*l->cmp)(q->key, key) < 0) p = q;
	update[k] = p;
    } while (--k >= 0);

    if (!(l->flags & SKIPLIST_FLAG_ALLOW_DUPLICATES) &&
	q && ((*l->cmp)(q->key, key) == 0)) {

	    return -1;
    }

    k = randomLevel();
    if (k>l->level) {
	k = ++l->level;
	update[k] = l->header;
    }

    q = newNodeOfLevel(k);
    q->key = key;
    q->value = value;
#if SKIPLIST_0TIMER_DEBUG
    q->flags = SKIPLIST_NODE_FLAG_INSERTED;	/* debug */
#endif

    ++(l->stats->forward[k]);
#if SKIPLIST_DEBUG
    zlog_debug("%s: incremented stats @%p:%d, now %ld", __func__, l, k,
	l->stats->forward[k] - (struct skiplistnode *)NULL);
#endif

    do {
	p = update[k];
	q->forward[k] = p->forward[k];
	p->forward[k] = q;
    } while(--k>=0);

    /*
     * If this is the last item in the list, update the "last" pointer
     */
    if (!q->forward[0]) {
	l->last = q;
    }

    ++(l->count);

    CHECKLAST(l);

    return 0;
}

int
skiplist_delete(
    register struct skiplist	*l,
    register void		*key,
    register void		*value)	/* used only if duplicates allowed */
{
    register int		k,m;
    struct skiplistnode		*update[MaxNumberOfLevels];
    register struct skiplistnode *p, *q;

    CHECKLAST(l);

    /* to make debugging easier */
    for (k = 0; k < MaxNumberOfLevels; ++k)
	update[k] = NULL;

    p = l->header;
    k = m = l->level;
    do {
	while (q = p->forward[k], q && (*l->cmp)(q->key, key) < 0) p = q;
	update[k] = p;
    } while(--k>=0);

    if (l->flags & SKIPLIST_FLAG_ALLOW_DUPLICATES) {
	while (q && ((*l->cmp)(q->key, key) == 0) && (q->value != value)) {
	    int i;
	    for (i = 0; i <= l->level; ++i) {
		if (update[i]->forward[i] == q)
		    update[i] = q;
	    }
	    q = q->forward[0];
	}
    }

    if (q && (*l->cmp)(q->key, key) == 0) {
	if (!(l->flags & SKIPLIST_FLAG_ALLOW_DUPLICATES) ||
	    (q->value == value)) {

	    /*
	     * found node to delete
	     */
#if SKIPLIST_0TIMER_DEBUG
	    q->flags &= ~SKIPLIST_NODE_FLAG_INSERTED;
#endif
	    /*
	     * If we are deleting the last element of the list,
	     * update the list's "last" pointer.
	     */
	    if (l->last == q) {
		if (update[0] == l->header)
		    l->last = NULL;
		else
		    l->last = update[0];
	    }

	    for(k=0; k<=m && (p=update[k])->forward[k] == q; k++) {
		p->forward[k] = q->forward[k];
	    }
	    --(l->stats->forward[k-1]);
#if SKIPLIST_DEBUG
	    zlog_debug("%s: decremented stats @%p:%d, now %ld",
		__func__, l, k-1,
		l->stats->forward[k-1] - (struct skiplistnode *)NULL);
#endif
	    if (l->del)
		(*l->del)(q->value);
	    XFREE(MTYPE_SKIP_LIST_NODE, q);
	    while( l->header->forward[m] == NULL && m > 0 )
		 m--;
	    l->level = m;
	    CHECKLAST(l);
	    --(l->count);
	    return 0;
	}
    }

    CHECKLAST(l);
    return -1;
}

/*
 * Obtain first value matching "key". Unless SKIPLIST_FLAG_ALLOW_DUPLICATES
 * is set, this will also be the only value matching "key".
 *
 * Also set a cursor for use with skiplist_next_value.
 */
int
skiplist_first_value(
    register struct skiplist	*l,			/* in */
    register void		*key,			/* in */
    void			**valuePointer,		/* out */
    void			**cursor)		/* out */
{
    register int k;
    register struct skiplistnode *p, *q;

    p = l->header;
    k = l->level;

    do {
	while (q = p->forward[k], q && (*l->cmp)(q->key, key) < 0)
	    p = q;

    } while (--k >= 0);

    if (!q || (*l->cmp)(q->key, key))
	return -1;

    if (valuePointer)
	*valuePointer = q->value;

    if (cursor)
	*cursor = q;

    return 0;
}

int
skiplist_search(
    register struct skiplist	*l,
    register void		*key,
    void			**valuePointer)
{
    return skiplist_first_value(l, key, valuePointer, NULL);
}


/*
 * Caller supplies key and value of an existing item in the list.
 * Function returns the value of the next list item that has the
 * same key (useful when SKIPLIST_FLAG_ALLOW_DUPLICATES is set).
 *
 * Returns 0 on success. If the caller-supplied key and value
 * do not correspond to a list element, or if they specify the
 * last element with the given key, -1 is returned.
 */
int
skiplist_next_value(
    register struct skiplist	*l,			/* in */
    register void		*key,			/* in */
    void			**valuePointer,		/* in/out */
    void			**cursor)		/* in/out */
{
    register int		k,m;
    register struct skiplistnode *p, *q;

    CHECKLAST(l);

    if (!(l->flags & SKIPLIST_FLAG_ALLOW_DUPLICATES)) {
	return -1;
    }

    if (!cursor || !*cursor) {
	p = l->header;
	k = m = l->level;

	/*
	 * Find matching key
	 */
	do {
	    while (q = p->forward[k], q && (*l->cmp)(q->key, key) < 0)
		p = q;
	} while(--k>=0);

	/* 
	 * Find matching value
	 */
	while (q && ((*l->cmp)(q->key, key) == 0) && (q->value != *valuePointer)) {
	    q = q->forward[0];
	}

	if (!q || ((*l->cmp)(q->key, key) != 0) || (q->value != *valuePointer)) {
	    /*
	     * No matching value
	     */
	    CHECKLAST(l);
	    return -1;
	}
    } else {
	q = (struct skiplistnode *)*cursor;
    }

    /*
     * Advance cursor
     */
    q = q->forward[0];

    /*
     * If we reached end-of-list or if the key is no longer the same,
     * then return error
     */
    if (!q || ((*l->cmp)(q->key, key) != 0))
	return -1;

    *valuePointer = q->value;
    if (cursor)
	*cursor = q;
    CHECKLAST(l);
    return 0;
}

int
skiplist_first(
    register struct skiplist	 *l,
    void			**keyPointer,
    void			**valuePointer)
{
    register struct skiplistnode *p;

    CHECKLAST(l);
    p = l->header->forward[0];
    if (!p)
	return -1;

    if (keyPointer)
	*keyPointer = p->key;

    if (valuePointer)
	*valuePointer = p->value;

    CHECKLAST(l);

    return 0;
}

int
skiplist_last(
    register struct skiplist	 *l,
    void			**keyPointer,
    void			**valuePointer)
{
    CHECKLAST(l);
    if (l->last) {
	if (keyPointer)
	    *keyPointer = l->last->key;
	if (valuePointer)
	    *valuePointer = l->last->value;
	return 0;
    }
    return -1;
}

/*
 * true = empty
 */
int
skiplist_empty(
    register struct skiplist	 *l)
{
    CHECKLAST(l);
    if (l->last)
	return 0;
    return 1;
}

/* 
 * Use this to walk the list. Caller sets *cursor to NULL to obtain
 * first element. Return value of 0 indicates valid cursor/element
 * returned, otherwise NULL cursor arg or EOL.
 */
int
skiplist_next(
    register struct skiplist	 *l,			/* in */
    void			**keyPointer,		/* out */
    void			**valuePointer,		/* out */
    void			**cursor)		/* in/out */
{
    struct skiplistnode *p;

    if (!cursor)
	return -1;

    CHECKLAST(l);

    if (!*cursor) {
	p = l->header->forward[0];
    } else {
	p = *cursor;
	p = p->forward[0];
    }
    *cursor = p;

    if (!p)
	return -1;

    if (keyPointer)
	*keyPointer = p->key;

    if (valuePointer)
	*valuePointer = p->value;

    CHECKLAST(l);

    return 0;
}

int
skiplist_delete_first(
    register struct skiplist	 *l)
{
    register int		k;
    register struct skiplistnode *p, *q;
    int nodelevel = 0;

    CHECKLAST(l);

    p = l->header;
    q = l->header->forward[0];

    if (!q)
	return -1;

    for (k = l->level; k >= 0; --k) {
	if (p->forward[k] == q) {
	    p->forward[k] = q->forward[k];
	    if ((k == l->level) && (p->forward[k] == NULL) && (l->level > 0))
		--(l->level);
	    if (!nodelevel)
		nodelevel = k;
	}
    }

#if SKIPLIST_0TIMER_DEBUG
    q->flags &= ~SKIPLIST_NODE_FLAG_INSERTED;
#endif
    /*
     * If we are deleting the last element of the list,
     * update the list's "last" pointer.
     */
    if (l->last == q) {
	l->last = NULL;
    }

    --(l->stats->forward[nodelevel]);
#if SKIPLIST_DEBUG
    zlog_debug("%s: decremented stats @%p:%d, now %ld", __func__, l, nodelevel,
	l->stats->forward[nodelevel] - (struct skiplistnode *)NULL);
#endif

    if (l->del)
	(*l->del)(q->value);

    XFREE(MTYPE_SKIP_LIST_NODE, q);

    CHECKLAST(l);

    --(l->count);

    return 0;
}

void
skiplist_debug(struct vty *vty, struct skiplist *l)
{
    int i;

    if (!l)
	l = skiplist_last_created;
    vty_out (vty, "Skiplist %p has max level %d\n", l, l->level);
    for (i = l->level; i >= 0; --i)
	vty_out (vty, "  @%d: %ld\n",
	    i,(long)((l->stats->forward[i]) - (struct skiplistnode *)NULL));
}

static void *
scramble(int i)
{
    uintptr_t	result;

    result = (i & 0xff) << 24;
    result |= (i >> 8);

    return (void *)result;
}

#define sampleSize 65536
void
skiplist_test(struct vty *vty) {
    struct skiplist *l;
    register int i,k;
    void *keys[sampleSize];
    void *v;

    zlog_debug("%s: entry", __func__);

    l= skiplist_new(SKIPLIST_FLAG_ALLOW_DUPLICATES, NULL, NULL);

    zlog_debug("%s: skiplist_new returned %p", __func__, l);

    for (i=0; i < 4; i++) {

	for (k=0; k < sampleSize; k++) {
	    if (!(k%1000)) {
		zlog_debug("%s: (%d:%d)", __func__, i, k);
	    }
	    //keys[k] = (void *)random();
	    keys[k] = (void *)scramble(k);
	    if (skiplist_insert(l, keys[k], keys[k]))
		zlog_debug("error in insert #%d,#%d",i,k);
	}

	zlog_debug("%s: inserts done", __func__);

        for (k=0; k < sampleSize; k++) {

	    if (!(k % 1000))
		zlog_debug("[%d:%d]", i, k);
	    if (skiplist_search(l, keys[k], &v))
		zlog_debug("error in search #%d,#%d",i,k);

	    if (v != keys[k])
		zlog_debug("search returned wrong value");
	}



        for (k=0; k < sampleSize; k++) {

	    if (!(k % 1000))
		zlog_debug("<%d:%d>", i, k);
	    if (skiplist_delete(l, keys[k], keys[k]))
		zlog_debug("error in delete");
	    keys[k] = (void *)scramble(k ^ 0xf0f0f0f0);
	    if (skiplist_insert(l, keys[k], keys[k]))
		zlog_debug("error in insert #%d,#%d",i,k);
	}

        for (k=0; k < sampleSize; k++) {

	    if (!(k % 1000))
		zlog_debug("{%d:%d}", i, k);
	    if (skiplist_delete_first(l))
		zlog_debug("error in delete_first");
	}
    }

    skiplist_free(l);
}