/*
 * Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *   * Redistributions of source code must retain the above copyright notice,
 *     this list of conditions and the following disclaimer.
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *   * Neither the name of Redis nor the names of its contributors may be used
 *     to endorse or promote products derived from this software without
 *     specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS 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 COPYRIGHT OWNER 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.
 */

#include "redis.h"

/*-----------------------------------------------------------------------------
 * Set Commands
 *----------------------------------------------------------------------------*/

void sunionDiffGenericCommand(redisClient *c, robj **setkeys, int setnum, 
                              robj *dstkey, int op);

/* Factory method to return a set that *can* hold "value". When the object has
 * an integer-encodable value, an intset will be returned. Otherwise a regular
 * hash table. */
robj *setTypeCreate(robj *value) {
    if (isObjectRepresentableAsLongLong(value,NULL) == REDIS_OK)
        return createIntsetObject();
    return createSetObject();
}

int setTypeAdd(robj *subject, robj *value) {
    long long llval;
    if (subject->encoding == REDIS_ENCODING_HT) {
        if (dictAdd(subject->ptr,value,NULL) == DICT_OK) {
            incrRefCount(value);
            return 1;
        }
    } else if (subject->encoding == REDIS_ENCODING_INTSET) {
        if (isObjectRepresentableAsLongLong(value,&llval) == REDIS_OK) {
            uint8_t success = 0;
            subject->ptr = intsetAdd(subject->ptr,llval,&success);
            if (success) {
                /* Convert to regular set when the intset contains
                 * too many entries. */
                if (intsetLen(subject->ptr) > server.set_max_intset_entries)
                    setTypeConvert(subject,REDIS_ENCODING_HT);
                return 1;
            }
        } else {
            /* Failed to get integer from object, convert to regular set. */
            setTypeConvert(subject,REDIS_ENCODING_HT);

            /* The set *was* an intset and this value is not integer
             * encodable, so dictAdd should always work. */
            redisAssertWithInfo(NULL,value,
                                dictAdd(subject->ptr,value,NULL) == DICT_OK);
            incrRefCount(value);
            return 1;
        }
    } else {
        redisPanic("Unknown set encoding");
    }
    return 0;
}

int setTypeRemove(robj *setobj, robj *value) {
    long long llval;
    if (setobj->encoding == REDIS_ENCODING_HT) {
        if (dictDelete(setobj->ptr,value) == DICT_OK) {
            if (htNeedsResize(setobj->ptr)) dictResize(setobj->ptr);
            return 1;
        }
    } else if (setobj->encoding == REDIS_ENCODING_INTSET) {
        if (isObjectRepresentableAsLongLong(value,&llval) == REDIS_OK) {
            int success;
            setobj->ptr = intsetRemove(setobj->ptr,llval,&success);
            if (success) return 1;
        }
    } else {
        redisPanic("Unknown set encoding");
    }
    return 0;
}

int setTypeIsMember(robj *subject, robj *value) {
    long long llval;
    if (subject->encoding == REDIS_ENCODING_HT) {
        return dictFind((dict*)subject->ptr,value) != NULL;
    } else if (subject->encoding == REDIS_ENCODING_INTSET) {
        if (isObjectRepresentableAsLongLong(value,&llval) == REDIS_OK) {
            return intsetFind((intset*)subject->ptr,llval);
        }
    } else {
        redisPanic("Unknown set encoding");
    }
    return 0;
}

setTypeIterator *setTypeInitIterator(robj *subject) {
    setTypeIterator *si = zmalloc(sizeof(setTypeIterator));
    si->subject = subject;
    si->encoding = subject->encoding;
    if (si->encoding == REDIS_ENCODING_HT) {
        si->di = dictGetIterator(subject->ptr);
    } else if (si->encoding == REDIS_ENCODING_INTSET) {
        si->ii = 0;
    } else {
        redisPanic("Unknown set encoding");
    }
    return si;
}

void setTypeReleaseIterator(setTypeIterator *si) {
    if (si->encoding == REDIS_ENCODING_HT)
        dictReleaseIterator(si->di);
    zfree(si);
}

/* Move to the next entry in the set. Returns the object at the current
 * position.
 *
 * Since set elements can be internally be stored as redis objects or
 * simple arrays of integers, setTypeNext returns the encoding of the
 * set object you are iterating, and will populate the appropriate pointer
 * (eobj) or (llobj) accordingly.
 *
 * When there are no longer elements -1 is returned.
 * Returned objects ref count is not incremented, so this function is
 * copy on write friendly. */
int setTypeNext(setTypeIterator *si, robj **objele, int64_t *llele) {
    if (si->encoding == REDIS_ENCODING_HT) {
        dictEntry *de = dictNext(si->di);
        if (de == NULL) return -1;
        *objele = dictGetKey(de);
    } else if (si->encoding == REDIS_ENCODING_INTSET) {
        if (!intsetGet(si->subject->ptr,si->ii++,llele))
            return -1;
    }
    return si->encoding;
}

/* The not copy on write friendly version but easy to use version
 * of setTypeNext() is setTypeNextObject(), returning new objects
 * or incrementing the ref count of returned objects. So if you don't
 * retain a pointer to this object you should call decrRefCount() against it.
 *
 * This function is the way to go for write operations where COW is not
 * an issue as the result will be anyway of incrementing the ref count. */
robj *setTypeNextObject(setTypeIterator *si) {
    int64_t intele;
    robj *objele;
    int encoding;

    encoding = setTypeNext(si,&objele,&intele);
    switch(encoding) {
        case -1:    return NULL;
        case REDIS_ENCODING_INTSET:
            return createStringObjectFromLongLong(intele);
        case REDIS_ENCODING_HT:
            incrRefCount(objele);
            return objele;
        default:
            redisPanic("Unsupported encoding");
    }
    return NULL; /* just to suppress warnings */
}

/* Return random element from a non empty set.
 * The returned element can be a int64_t value if the set is encoded
 * as an "intset" blob of integers, or a redis object if the set
 * is a regular set.
 *
 * The caller provides both pointers to be populated with the right
 * object. The return value of the function is the object->encoding
 * field of the object and is used by the caller to check if the
 * int64_t pointer or the redis object pointer was populated.
 *
 * When an object is returned (the set was a real set) the ref count
 * of the object is not incremented so this function can be considered
 * copy on write friendly. */
int setTypeRandomElement(robj *setobj, robj **objele, int64_t *llele) {
    if (setobj->encoding == REDIS_ENCODING_HT) {
        dictEntry *de = dictGetRandomKey(setobj->ptr);
        *objele = dictGetKey(de);
    } else if (setobj->encoding == REDIS_ENCODING_INTSET) {
        *llele = intsetRandom(setobj->ptr);
    } else {
        redisPanic("Unknown set encoding");
    }
    return setobj->encoding;
}

/* Return a number of random elements from a non empty set.
 * 
 * This is a version of setTypeRandomElement() that is modified in order to
 * return multiple entries, using dictGetRandomKeys() and intsetRandomMembers().
 *
 * The elements are stored into 'aux_set' which should be of a set type.
 *
 * The function returns the number of items stored into 'aux_set', that may
 * be less than 'count' if the hash table has less than 'count' elements
 * inside.
 *
 * Note that this function is not suitable when you need a good distribution
 * of the returned items, but only when you need to "sample" a given number
 * of continuous elements to run some kind of algorithm or to produce
 * statistics. However the function is much faster than setTypeRandomElement()
 * at producing N elements, and the elements are guaranteed to be non
 * repeating. 
 */
unsigned long setTypeRandomElements(robj *set, unsigned long count, robj *aux_set) {
    unsigned long set_size;
    unsigned long elements_to_return = count;
    unsigned long elements_copied = 0;
    unsigned long current_element = 0;

    /* Like all setType* functions, we assume good behavior on part of the caller,
     * so no extra parameter checks are made. */

    /* If the number of elements in the the set is less than the count 
       requested, just return all of them. */
    set_size = setTypeSize(set);
    if (set_size < count) {
        elements_to_return = set_size;
    }

    /* TODO: It is definitely faster adding items to the set by directly handling the Dict
       or intset inside it, avoiding the constant encoding checks inside setTypeAdd(). 
       However, We don't want to touch the set internals in non setType* functions.
       So, we just call setTypeAdd() multiple times, but this isn't an optimial
       solution. 
       Another option would be to create a bulk-add function: setTypeAddBulk(). */
    if (set->encoding == REDIS_ENCODING_HT) {
        /* Allocate result array */
        dictEntry **random_elements = 
            zmalloc(sizeof(dictEntry*) * elements_to_return);

        /* Get the random elements */
        elements_copied = 
            dictGetRandomKeys(set->ptr, random_elements, elements_to_return);
        redisAssert(elements_copied == elements_to_return);

        /* Put them into the set */
        for (current_element = 0;
             current_element < elements_copied;
             current_element++) {

            /* We get the key and duplicate it, as we know it is a string */
            setTypeAdd(aux_set, 
                dupStringObject(dictGetKey(random_elements[current_element])));
        }

        zfree(random_elements);

    } else if (set->encoding == REDIS_ENCODING_INTSET) {
        /* Allocate result array */
        int64_t *random_elements = zmalloc(sizeof(int64_t) * elements_to_return);

        elements_copied = 
            intsetRandomMembers((intset*) set->ptr, 
                                random_elements, 
                                elements_to_return);

        redisAssert(elements_copied == elements_to_return);

        /* Put them into the set */
        for (current_element = 0;
             current_element < elements_copied;
             current_element++) {

            /* Put the values in the set */
            setTypeAdd(aux_set, 
                       createStringObjectFromLongLong(
                            random_elements[current_element]));
        }

        zfree(random_elements);
    } else {
        redisPanic("Unknown set encoding");
    }

    /* We have a set with random elements. Return the actual elements in 
       the aux_set. */
    return elements_copied;
}

unsigned long setTypeSize(robj *subject) {
    if (subject->encoding == REDIS_ENCODING_HT) {
        return dictSize((dict*)subject->ptr);
    } else if (subject->encoding == REDIS_ENCODING_INTSET) {
        return intsetLen((intset*)subject->ptr);
    } else {
        redisPanic("Unknown set encoding");
    }
}

/* Convert the set to specified encoding. The resulting dict (when converting
 * to a hash table) is presized to hold the number of elements in the original
 * set. */
void setTypeConvert(robj *setobj, int enc) {
    setTypeIterator *si;
    redisAssertWithInfo(NULL,setobj,setobj->type == REDIS_SET &&
                             setobj->encoding == REDIS_ENCODING_INTSET);

    if (enc == REDIS_ENCODING_HT) {
        int64_t intele;
        dict *d = dictCreate(&setDictType,NULL);
        robj *element;

        /* Presize the dict to avoid rehashing */
        dictExpand(d,intsetLen(setobj->ptr));

        /* To add the elements we extract integers and create redis objects */
        si = setTypeInitIterator(setobj);
        while (setTypeNext(si,NULL,&intele) != -1) {
            element = createStringObjectFromLongLong(intele);
            redisAssertWithInfo(NULL,element,
                                dictAdd(d,element,NULL) == DICT_OK);
        }
        setTypeReleaseIterator(si);

        setobj->encoding = REDIS_ENCODING_HT;
        zfree(setobj->ptr);
        setobj->ptr = d;
    } else {
        redisPanic("Unsupported set conversion");
    }
}

void saddCommand(redisClient *c) {
    robj *set;
    int j, added = 0;

    set = lookupKeyWrite(c->db,c->argv[1]);
    if (set == NULL) {
        set = setTypeCreate(c->argv[2]);
        dbAdd(c->db,c->argv[1],set);
    } else {
        if (set->type != REDIS_SET) {
            addReply(c,shared.wrongtypeerr);
            return;
        }
    }

    for (j = 2; j < c->argc; j++) {
        c->argv[j] = tryObjectEncoding(c->argv[j]);
        if (setTypeAdd(set,c->argv[j])) added++;
    }
    if (added) {
        signalModifiedKey(c->db,c->argv[1]);
        notifyKeyspaceEvent(REDIS_NOTIFY_SET,"sadd",c->argv[1],c->db->id);
    }
    server.dirty += added;
    addReplyLongLong(c,added);
}

void sremCommand(redisClient *c) {
    robj *set;
    int j, deleted = 0, keyremoved = 0;

    if ((set = lookupKeyWriteOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,set,REDIS_SET)) return;

    for (j = 2; j < c->argc; j++) {
        if (setTypeRemove(set,c->argv[j])) {
            deleted++;
            if (setTypeSize(set) == 0) {
                dbDelete(c->db,c->argv[1]);
                keyremoved = 1;
                break;
            }
        }
    }
    if (deleted) {
        signalModifiedKey(c->db,c->argv[1]);
        notifyKeyspaceEvent(REDIS_NOTIFY_SET,"srem",c->argv[1],c->db->id);
        if (keyremoved)
            notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[1],
                                c->db->id);
        server.dirty += deleted;
    }
    addReplyLongLong(c,deleted);
}

void smoveCommand(redisClient *c) {
    robj *srcset, *dstset, *ele;
    srcset = lookupKeyWrite(c->db,c->argv[1]);
    dstset = lookupKeyWrite(c->db,c->argv[2]);
    ele = c->argv[3] = tryObjectEncoding(c->argv[3]);

    /* If the source key does not exist return 0 */
    if (srcset == NULL) {
        addReply(c,shared.czero);
        return;
    }

    /* If the source key has the wrong type, or the destination key
     * is set and has the wrong type, return with an error. */
    if (checkType(c,srcset,REDIS_SET) ||
        (dstset && checkType(c,dstset,REDIS_SET))) return;

    /* If srcset and dstset are equal, SMOVE is a no-op */
    if (srcset == dstset) {
        addReply(c,shared.cone);
        return;
    }

    /* If the element cannot be removed from the src set, return 0. */
    if (!setTypeRemove(srcset,ele)) {
        addReply(c,shared.czero);
        return;
    }
    notifyKeyspaceEvent(REDIS_NOTIFY_SET,"srem",c->argv[1],c->db->id);

    /* Remove the src set from the database when empty */
    if (setTypeSize(srcset) == 0) {
        dbDelete(c->db,c->argv[1]);
        notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[1],c->db->id);
    }
    signalModifiedKey(c->db,c->argv[1]);
    signalModifiedKey(c->db,c->argv[2]);
    server.dirty++;

    /* Create the destination set when it doesn't exist */
    if (!dstset) {
        dstset = setTypeCreate(ele);
        dbAdd(c->db,c->argv[2],dstset);
    }

    /* An extra key has changed when ele was successfully added to dstset */
    if (setTypeAdd(dstset,ele)) {
        server.dirty++;
        notifyKeyspaceEvent(REDIS_NOTIFY_SET,"sadd",c->argv[2],c->db->id);
    }
    addReply(c,shared.cone);
}

void sismemberCommand(redisClient *c) {
    robj *set;

    if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,set,REDIS_SET)) return;

    c->argv[2] = tryObjectEncoding(c->argv[2]);
    if (setTypeIsMember(set,c->argv[2]))
        addReply(c,shared.cone);
    else
        addReply(c,shared.czero);
}

void scardCommand(redisClient *c) {
    robj *o;

    if ((o = lookupKeyReadOrReply(c,c->argv[1],shared.czero)) == NULL ||
        checkType(c,o,REDIS_SET)) return;

    addReplyLongLong(c,setTypeSize(o));
}

/* handle the "SPOP key <count>" variant. The normal version of the
 * command is handled by the spopCommand() function itself. */

void spopWithCountCommand(redisClient *c) {
    long l;
    unsigned long count, size;
    unsigned long elements_returned;
    robj *set, *aux, *aux_set;
    int64_t llele;

    /* Get the count argument */
    if (getLongFromObjectOrReply(c,c->argv[2],&l,NULL) != REDIS_OK) return;
    if (l >= 0) {
        count = (unsigned) l;
    } else {
        addReply(c,shared.outofrangeerr);
        return;
    }

    /* Make sure a key with the name inputted exists, and that it's type is 
       indeed a set. Otherwise, return nil */
    if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.emptymultibulk))
        == NULL || checkType(c,set,REDIS_SET)) return;

    /* If count is zero, serve an empty multibulk ASAP to avoid special 
       cases later. */
    if (count == 0) {
        addReply(c,shared.emptymultibulk);
        return;
    }

    /* Get the size of the set. It is always > 0, as empty sets get
       deleted.  */
    size = setTypeSize(set);

    /* Generate an SPOP keyspace notification */
    notifyKeyspaceEvent(REDIS_NOTIFY_SET,"spop",c->argv[1],c->db->id);

    /* CASE 1:
     * The number of requested elements is greater than or equal to 
     * the number of elements inside the set: simply return the whole set. */
    if (count >= size) {

        /* We just return the entire set */ 
        sunionDiffGenericCommand(c,c->argv+1,1,NULL,REDIS_OP_UNION);

        /* Delete the set as it is now empty */
        dbDelete(c->db,c->argv[1]);
        notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[1],c->db->id);

        /* Replicate/AOF this command as an SREM operation */
        aux = createStringObject("DEL",3);
        rewriteClientCommandVector(c,2,aux,c->argv[1]);
        decrRefCount(aux);

        return;
    }

    /* CASE 2:
     * The number of requested elements is less than the number
     * of elements inside the set. */

    /* We need an auxiliary set. Optimistically, we create a set using an 
       Intset internally. */
    aux = createStringObjectFromLongLong(0);
    aux_set = setTypeCreate(aux);
    decrRefCount(aux);

    /* Get the count requested of random elements from the set into our 
       auxiliary set. */
    elements_returned = setTypeRandomElements(set, count, aux_set);
    redisAssert(elements_returned == count);

    {
        setTypeIterator *si;
        robj *objele;
        int element_encoding;

        addReplyMultiBulkLen(c, elements_returned);

        /* Replicate/AOF this command as an SREM operation */
        aux = createStringObject("SREM",4);

        si = setTypeInitIterator(aux_set);
        while ((element_encoding = setTypeNext(si, &objele, &llele)) != -1) {
            if (element_encoding == REDIS_ENCODING_HT) {

                addReplyBulk(c, objele);

                /* Replicate/AOF this command as an SREM commands */
                rewriteClientCommandVector(c, 3, aux, c->argv[1], objele);
                setTypeRemove(set, objele);
            }
            else if (element_encoding == REDIS_ENCODING_INTSET) {
                /* TODO: setTypeRemove() forces us to convert all of the ints 
                         to string... isn't there a nicer way to do this? */
                objele = createStringObjectFromLongLong(llele);
                addReplyBulk(c, objele);

                /* Replicate/AOF this command as an SREM commands */
                rewriteClientCommandVector(c, 3, aux, c->argv[1], objele);
                setTypeRemove(set, objele);

                /* We created it, we kill it. */
                decrRefCount(objele);
            }
            else {
                redisPanic("Unknown set encoding");
            }
        }
        setTypeReleaseIterator(si);

        decrRefCount(aux);
    }

    /* Free the auxiliary set - we need it no more. */
    freeSetObject(aux_set);
}

void spopCommand(redisClient *c) {
    robj *set, *ele, *aux;
    int64_t llele;
    int encoding;

    if (c->argc == 3) {
        spopWithCountCommand(c);
        return;
    } else if (c->argc > 3) {
        addReply(c,shared.syntaxerr);
        return;
    }

    /* Make sure a key with the name inputted exists, and that it's type is 
       indeed a set */
    if ((set = lookupKeyWriteOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||
        checkType(c,set,REDIS_SET)) return;

    /* Get a random element from the set */
    encoding = setTypeRandomElement(set,&ele,&llele);

    /* Remove the element from the set */
    if (encoding == REDIS_ENCODING_INTSET) {
        ele = createStringObjectFromLongLong(llele);
        set->ptr = intsetRemove(set->ptr,llele,NULL);
    } else {
        incrRefCount(ele);
        setTypeRemove(set,ele);
    }

    notifyKeyspaceEvent(REDIS_NOTIFY_SET,"spop",c->argv[1],c->db->id);

    /* Replicate/AOF this command as an SREM operation */
    aux = createStringObject("SREM",4);
    rewriteClientCommandVector(c,3,aux,c->argv[1],ele);
    decrRefCount(ele);
    decrRefCount(aux);

    /* Add the element to the reply */
    addReplyBulk(c,ele);

    /* Delete the set if it's empty */
    if (setTypeSize(set) == 0) {
        dbDelete(c->db,c->argv[1]);
        notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",c->argv[1],c->db->id);
    }

    /* Set has been modified */
    signalModifiedKey(c->db,c->argv[1]);
    server.dirty++;
}

/* handle the "SRANDMEMBER key <count>" variant. The normal version of the
 * command is handled by the srandmemberCommand() function itself. */

/* How many times bigger should be the set compared to the requested size
 * for us to don't use the "remove elements" strategy? Read later in the
 * implementation for more info. */
#define SRANDMEMBER_SUB_STRATEGY_MUL 3

void srandmemberWithCountCommand(redisClient *c) {
    long l;
    unsigned long count, size;
    int uniq = 1;
    robj *set, *ele;
    int64_t llele;
    int encoding;

    dict *d;

    if (getLongFromObjectOrReply(c,c->argv[2],&l,NULL) != REDIS_OK) return;
    if (l >= 0) {
        count = (unsigned) l;
    } else {
        /* A negative count means: return the same elements multiple times
         * (i.e. don't remove the extracted element after every extraction). */
        count = -l;
        uniq = 0;
    }

    if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.emptymultibulk))
        == NULL || checkType(c,set,REDIS_SET)) return;
    size = setTypeSize(set);

    /* If count is zero, serve it ASAP to avoid special cases later. */
    if (count == 0) {
        addReply(c,shared.emptymultibulk);
        return;
    }

    /* CASE 1: The count was negative, so the extraction method is just:
     * "return N random elements" sampling the whole set every time.
     * This case is trivial and can be served without auxiliary data
     * structures. */
    if (!uniq) {
        addReplyMultiBulkLen(c,count);
        while(count--) {
            encoding = setTypeRandomElement(set,&ele,&llele);
            if (encoding == REDIS_ENCODING_INTSET) {
                addReplyBulkLongLong(c,llele);
            } else {
                addReplyBulk(c,ele);
            }
        }
        return;
    }

    /* CASE 2:
     * The number of requested elements is greater than the number of
     * elements inside the set: simply return the whole set. */
    if (count >= size) {
        sunionDiffGenericCommand(c,c->argv+1,1,NULL,REDIS_OP_UNION);
        return;
    }

    /* For CASE 3 and CASE 4 we need an auxiliary dictionary. */
    d = dictCreate(&setDictType,NULL);

    /* CASE 3:
     * The number of elements inside the set is not greater than
     * SRANDMEMBER_SUB_STRATEGY_MUL times the number of requested elements.
     * In this case we create a set from scratch with all the elements, and
     * subtract random elements to reach the requested number of elements.
     *
     * This is done because if the number of requsted elements is just
     * a bit less than the number of elements in the set, the natural approach
     * used into CASE 3 is highly inefficient. */
    if (count*SRANDMEMBER_SUB_STRATEGY_MUL > size) {
        setTypeIterator *si;

        /* Add all the elements into the temporary dictionary. */
        si = setTypeInitIterator(set);
        while((encoding = setTypeNext(si,&ele,&llele)) != -1) {
            int retval = DICT_ERR;

            if (encoding == REDIS_ENCODING_INTSET) {
                retval = dictAdd(d,createStringObjectFromLongLong(llele),NULL);
            } else {
                retval = dictAdd(d,dupStringObject(ele),NULL);
            }
            redisAssert(retval == DICT_OK);
        }
        setTypeReleaseIterator(si);
        redisAssert(dictSize(d) == size);

        /* Remove random elements to reach the right count. */
        while(size > count) {
            dictEntry *de;

            de = dictGetRandomKey(d);
            dictDelete(d,dictGetKey(de));
            size--;
        }
    }

    /* CASE 4: We have a big set compared to the requested number of elements.
     * In this case we can simply get random elements from the set and add
     * to the temporary set, trying to eventually get enough unique elements
     * to reach the specified count. */
    else {
        unsigned long added = 0;

        while(added < count) {
            encoding = setTypeRandomElement(set,&ele,&llele);
            if (encoding == REDIS_ENCODING_INTSET) {
                ele = createStringObjectFromLongLong(llele);
            } else {
                ele = dupStringObject(ele);
            }
            /* Try to add the object to the dictionary. If it already exists
             * free it, otherwise increment the number of objects we have
             * in the result dictionary. */
            if (dictAdd(d,ele,NULL) == DICT_OK)
                added++;
            else
                decrRefCount(ele);
        }
    }

    /* CASE 3 & 4: send the result to the user. */
    {
        dictIterator *di;
        dictEntry *de;

        addReplyMultiBulkLen(c,count);
        di = dictGetIterator(d);
        while((de = dictNext(di)) != NULL)
            addReplyBulk(c,dictGetKey(de));
        dictReleaseIterator(di);
        dictRelease(d);
    }
}

void srandmemberCommand(redisClient *c) {
    robj *set, *ele;
    int64_t llele;
    int encoding;

    if (c->argc == 3) {
        srandmemberWithCountCommand(c);
        return;
    } else if (c->argc > 3) {
        addReply(c,shared.syntaxerr);
        return;
    }

    if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.nullbulk)) == NULL ||
        checkType(c,set,REDIS_SET)) return;

    encoding = setTypeRandomElement(set,&ele,&llele);
    if (encoding == REDIS_ENCODING_INTSET) {
        addReplyBulkLongLong(c,llele);
    } else {
        addReplyBulk(c,ele);
    }
}

int qsortCompareSetsByCardinality(const void *s1, const void *s2) {
    return setTypeSize(*(robj**)s1)-setTypeSize(*(robj**)s2);
}

/* This is used by SDIFF and in this case we can receive NULL that should
 * be handled as empty sets. */
int qsortCompareSetsByRevCardinality(const void *s1, const void *s2) {
    robj *o1 = *(robj**)s1, *o2 = *(robj**)s2;

    return  (o2 ? setTypeSize(o2) : 0) - (o1 ? setTypeSize(o1) : 0);
}

void sinterGenericCommand(redisClient *c, robj **setkeys, 
                          unsigned long setnum, robj *dstkey) {
    robj **sets = zmalloc(sizeof(robj*)*setnum);
    setTypeIterator *si;
    robj *eleobj, *dstset = NULL;
    int64_t intobj;
    void *replylen = NULL;
    unsigned long j, cardinality = 0;
    int encoding;

    for (j = 0; j < setnum; j++) {
        robj *setobj = dstkey ?
            lookupKeyWrite(c->db,setkeys[j]) :
            lookupKeyRead(c->db,setkeys[j]);
        if (!setobj) {
            zfree(sets);
            if (dstkey) {
                if (dbDelete(c->db,dstkey)) {
                    signalModifiedKey(c->db,dstkey);
                    server.dirty++;
                }
                addReply(c,shared.czero);
            } else {
                addReply(c,shared.emptymultibulk);
            }
            return;
        }
        if (checkType(c,setobj,REDIS_SET)) {
            zfree(sets);
            return;
        }
        sets[j] = setobj;
    }
    /* Sort sets from the smallest to largest, this will improve our
     * algorithm's performance */
    qsort(sets,setnum,sizeof(robj*),qsortCompareSetsByCardinality);

    /* The first thing we should output is the total number of elements...
     * since this is a multi-bulk write, but at this stage we don't know
     * the intersection set size, so we use a trick, append an empty object
     * to the output list and save the pointer to later modify it with the
     * right length */
    if (!dstkey) {
        replylen = addDeferredMultiBulkLength(c);
    } else {
        /* If we have a target key where to store the resulting set
         * create this key with an empty set inside */
        dstset = createIntsetObject();
    }

    /* Iterate all the elements of the first (smallest) set, and test
     * the element against all the other sets, if at least one set does
     * not include the element it is discarded */
    si = setTypeInitIterator(sets[0]);
    while((encoding = setTypeNext(si,&eleobj,&intobj)) != -1) {
        for (j = 1; j < setnum; j++) {
            if (sets[j] == sets[0]) continue;
            if (encoding == REDIS_ENCODING_INTSET) {
                /* intset with intset is simple... and fast */
                if (sets[j]->encoding == REDIS_ENCODING_INTSET &&
                    !intsetFind((intset*)sets[j]->ptr,intobj))
                {
                    break;
                /* in order to compare an integer with an object we
                 * have to use the generic function, creating an object
                 * for this */
                } else if (sets[j]->encoding == REDIS_ENCODING_HT) {
                    eleobj = createStringObjectFromLongLong(intobj);
                    if (!setTypeIsMember(sets[j],eleobj)) {
                        decrRefCount(eleobj);
                        break;
                    }
                    decrRefCount(eleobj);
                }
            } else if (encoding == REDIS_ENCODING_HT) {
                /* Optimization... if the source object is integer
                 * encoded AND the target set is an intset, we can get
                 * a much faster path. */
                if (eleobj->encoding == REDIS_ENCODING_INT &&
                    sets[j]->encoding == REDIS_ENCODING_INTSET &&
                    !intsetFind((intset*)sets[j]->ptr,(long)eleobj->ptr))
                {
                    break;
                /* else... object to object check is easy as we use the
                 * type agnostic API here. */
                } else if (!setTypeIsMember(sets[j],eleobj)) {
                    break;
                }
            }
        }

        /* Only take action when all sets contain the member */
        if (j == setnum) {
            if (!dstkey) {
                if (encoding == REDIS_ENCODING_HT)
                    addReplyBulk(c,eleobj);
                else
                    addReplyBulkLongLong(c,intobj);
                cardinality++;
            } else {
                if (encoding == REDIS_ENCODING_INTSET) {
                    eleobj = createStringObjectFromLongLong(intobj);
                    setTypeAdd(dstset,eleobj);
                    decrRefCount(eleobj);
                } else {
                    setTypeAdd(dstset,eleobj);
                }
            }
        }
    }
    setTypeReleaseIterator(si);

    if (dstkey) {
        /* Store the resulting set into the target, if the intersection
         * is not an empty set. */
        int deleted = dbDelete(c->db,dstkey);
        if (setTypeSize(dstset) > 0) {
            dbAdd(c->db,dstkey,dstset);
            addReplyLongLong(c,setTypeSize(dstset));
            notifyKeyspaceEvent(REDIS_NOTIFY_SET,"sinterstore",
                dstkey,c->db->id);
        } else {
            decrRefCount(dstset);
            addReply(c,shared.czero);
            if (deleted)
                notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",
                    dstkey,c->db->id);
        }
        signalModifiedKey(c->db,dstkey);
        server.dirty++;
    } else {
        setDeferredMultiBulkLength(c,replylen,cardinality);
    }
    zfree(sets);
}

void sinterCommand(redisClient *c) {
    sinterGenericCommand(c,c->argv+1,c->argc-1,NULL);
}

void sinterstoreCommand(redisClient *c) {
    sinterGenericCommand(c,c->argv+2,c->argc-2,c->argv[1]);
}

#define REDIS_OP_UNION 0
#define REDIS_OP_DIFF 1
#define REDIS_OP_INTER 2

void sunionDiffGenericCommand(redisClient *c, robj **setkeys, int setnum, 
                              robj *dstkey, int op) {
    robj **sets = zmalloc(sizeof(robj*)*setnum);
    setTypeIterator *si;
    robj *ele, *dstset = NULL;
    int j, cardinality = 0;
    int diff_algo = 1;

    for (j = 0; j < setnum; j++) {
        robj *setobj = dstkey ?
            lookupKeyWrite(c->db,setkeys[j]) :
            lookupKeyRead(c->db,setkeys[j]);
        if (!setobj) {
            sets[j] = NULL;
            continue;
        }
        if (checkType(c,setobj,REDIS_SET)) {
            zfree(sets);
            return;
        }
        sets[j] = setobj;
    }

    /* Select what DIFF algorithm to use.
     *
     * Algorithm 1 is O(N*M) where N is the size of the element first set
     * and M the total number of sets.
     *
     * Algorithm 2 is O(N) where N is the total number of elements in all
     * the sets.
     *
     * We compute what is the best bet with the current input here. */
    if (op == REDIS_OP_DIFF && sets[0]) {
        long long algo_one_work = 0, algo_two_work = 0;

        for (j = 0; j < setnum; j++) {
            if (sets[j] == NULL) continue;

            algo_one_work += setTypeSize(sets[0]);
            algo_two_work += setTypeSize(sets[j]);
        }

        /* Algorithm 1 has better constant times and performs less operations
         * if there are elements in common. Give it some advantage. */
        algo_one_work /= 2;
        diff_algo = (algo_one_work <= algo_two_work) ? 1 : 2;

        if (diff_algo == 1 && setnum > 1) {
            /* With algorithm 1 it is better to order the sets to subtract
             * by decreasing size, so that we are more likely to find
             * duplicated elements ASAP. */
            qsort(sets+1,setnum-1,sizeof(robj*),
                qsortCompareSetsByRevCardinality);
        }
    }

    /* We need a temp set object to store our union. If the dstkey
     * is not NULL (that is, we are inside an SUNIONSTORE operation) then
     * this set object will be the resulting object to set into the target key*/
    dstset = createIntsetObject();

    if (op == REDIS_OP_UNION) {
        /* Union is trivial, just add every element of every set to the
         * temporary set. */
        for (j = 0; j < setnum; j++) {
            if (!sets[j]) continue; /* non existing keys are like empty sets */

            si = setTypeInitIterator(sets[j]);
            while((ele = setTypeNextObject(si)) != NULL) {
                if (setTypeAdd(dstset,ele)) cardinality++;
                decrRefCount(ele);
            }
            setTypeReleaseIterator(si);
        }
    } else if (op == REDIS_OP_DIFF && sets[0] && diff_algo == 1) {
        /* DIFF Algorithm 1:
         *
         * We perform the diff by iterating all the elements of the first set,
         * and only adding it to the target set if the element does not exist
         * into all the other sets.
         *
         * This way we perform at max N*M operations, where N is the size of
         * the first set, and M the number of sets. */
        si = setTypeInitIterator(sets[0]);
        while((ele = setTypeNextObject(si)) != NULL) {
            for (j = 1; j < setnum; j++) {
                if (!sets[j]) continue; /* no key is an empty set. */
                if (sets[j] == sets[0]) break; /* same set! */
                if (setTypeIsMember(sets[j],ele)) break;
            }
            if (j == setnum) {
                /* There is no other set with this element. Add it. */
                setTypeAdd(dstset,ele);
                cardinality++;
            }
            decrRefCount(ele);
        }
        setTypeReleaseIterator(si);
    } else if (op == REDIS_OP_DIFF && sets[0] && diff_algo == 2) {
        /* DIFF Algorithm 2:
         *
         * Add all the elements of the first set to the auxiliary set.
         * Then remove all the elements of all the next sets from it.
         *
         * This is O(N) where N is the sum of all the elements in every
         * set. */
        for (j = 0; j < setnum; j++) {
            if (!sets[j]) continue; /* non existing keys are like empty sets */

            si = setTypeInitIterator(sets[j]);
            while((ele = setTypeNextObject(si)) != NULL) {
                if (j == 0) {
                    if (setTypeAdd(dstset,ele)) cardinality++;
                } else {
                    if (setTypeRemove(dstset,ele)) cardinality--;
                }
                decrRefCount(ele);
            }
            setTypeReleaseIterator(si);

            /* Exit if result set is empty as any additional removal
             * of elements will have no effect. */
            if (cardinality == 0) break;
        }
    }

    /* Output the content of the resulting set, if not in STORE mode */
    if (!dstkey) {
        addReplyMultiBulkLen(c,cardinality);
        si = setTypeInitIterator(dstset);
        while((ele = setTypeNextObject(si)) != NULL) {
            addReplyBulk(c,ele);
            decrRefCount(ele);
        }
        setTypeReleaseIterator(si);
        decrRefCount(dstset);
    } else {
        /* If we have a target key where to store the resulting set
         * create this key with the result set inside */
        int deleted = dbDelete(c->db,dstkey);
        if (setTypeSize(dstset) > 0) {
            dbAdd(c->db,dstkey,dstset);
            addReplyLongLong(c,setTypeSize(dstset));
            notifyKeyspaceEvent(REDIS_NOTIFY_SET,
                op == REDIS_OP_UNION ? "sunionstore" : "sdiffstore",
                dstkey,c->db->id);
        } else {
            decrRefCount(dstset);
            addReply(c,shared.czero);
            if (deleted)
                notifyKeyspaceEvent(REDIS_NOTIFY_GENERIC,"del",
                    dstkey,c->db->id);
        }
        signalModifiedKey(c->db,dstkey);
        server.dirty++;
    }
    zfree(sets);
}

void sunionCommand(redisClient *c) {
    sunionDiffGenericCommand(c,c->argv+1,c->argc-1,NULL,REDIS_OP_UNION);
}

void sunionstoreCommand(redisClient *c) {
    sunionDiffGenericCommand(c,c->argv+2,c->argc-2,c->argv[1],REDIS_OP_UNION);
}

void sdiffCommand(redisClient *c) {
    sunionDiffGenericCommand(c,c->argv+1,c->argc-1,NULL,REDIS_OP_DIFF);
}

void sdiffstoreCommand(redisClient *c) {
    sunionDiffGenericCommand(c,c->argv+2,c->argc-2,c->argv[1],REDIS_OP_DIFF);
}

void sscanCommand(redisClient *c) {
    robj *set;
    unsigned long cursor;

    if (parseScanCursorOrReply(c,c->argv[2],&cursor) == REDIS_ERR) return;
    if ((set = lookupKeyReadOrReply(c,c->argv[1],shared.emptyscan)) == NULL ||
        checkType(c,set,REDIS_SET)) return;
    scanGenericCommand(c,set,cursor);
}